A method for quickly selecting the fin spacing of a heat exchanger under the condition of limited total pressure of intake air

Abstract

The present application relates to the technical field of aircraft thermal management and heat exchange equipment design, and discloses a heat exchanger fin spacing rapid selection method under the condition of limited total pressure of inlet air, which first establishes a parameterized numerical calculation domain, identifies a first characteristic spacing scheme with the minimum structure mass satisfying a target heat exchange amount and a second characteristic spacing scheme with the minimum inlet air aerodynamic resistance, then calculates the structure mass difference of unit heat exchange amount of the two schemes, converts the structure mass difference into an equivalent induced resistance threshold value by using the optimal lift-drag ratio of the aircraft, simultaneously, constructs a full-flow passage net aerodynamic benefit index by combining the inlet air aerodynamic resistance benefit and the exhaust thrust recovery gain, and finally compares the net aerodynamic benefit index with the equivalent induced resistance threshold value: if the benefit is greater than the threshold value, the second characteristic spacing is determined as the target, otherwise, the first characteristic spacing is determined as the target. The present application comprehensively considers the structure weight increase cost and the full-flow passage momentum benefit, and realizes the optimization of the comprehensive aerodynamic performance of the aircraft.

Description

Technical Field

[0001] This invention relates to the field of aircraft thermal management and heat exchange equipment design technology, specifically a method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure. Background Technology

[0002] During cruise, high-speed aircraft face increasingly stringent heat dissipation requirements for their power systems and avionics. Heat exchangers utilizing ram air as a cooling source are core components of thermal management systems, and their performance directly impacts the aircraft's survivability and range. Under conditions of limited total intake pressure, heat exchanger design must not only meet thermal load requirements but also strictly control the aerodynamic drag it imposes on the aircraft platform. Fin spacing, a key geometric parameter affecting heat exchanger compactness and flow resistance characteristics, directly influences the overall aircraft's energy efficiency.

[0003] Existing methods for selecting heat exchanger fin spacing primarily rely on empirical correlations or computational fluid dynamics simulations. The design process typically involves parametrically scanning different fin spacings under given constraints on the windward area and core volume to calculate the heat transfer coefficient and flow channel pressure loss for each scheme. Selection is generally based on directly choosing the scheme with the minimum pressure loss or the lightest structural weight, provided that the heat transfer capacity meets design specifications. Some advanced methods employ multi-objective optimization algorithms to find the Pareto optimal solution between pressure loss and structural mass.

[0004] While existing technologies can screen fin schemes that meet basic heat dissipation requirements to some extent, they still have some shortcomings: Current methods typically treat the flow channel drag characteristics and structural mass characteristics of heat exchangers as two independent evaluation dimensions, lacking a unified physical dimension to correlate and compare them. Specifically, when a sparser fin spacing is used to reduce flow channel pressure drop, the heat exchanger volume usually needs to be increased to compensate for the heat transfer area, inevitably leading to an increase in structural mass. Existing technologies cannot accurately quantify the additional induced drag cost caused by this structural weight increase at the aircraft level, making it difficult for designers to determine whether the aerodynamic benefits of flow channel drag reduction are sufficient to cover the energy costs of the increased weight. Furthermore, traditional flow drag assessments often only focus on the pressure loss of airflow through the heat exchanger core, ignoring the thrust recovery effect generated when high-speed airflow expands after absorbing heat and is discharged through the exhaust nozzle. This fails to comprehensively reflect the actual contribution of the heat exchanger's momentum change across the entire flow channel to the aircraft's propulsion system, easily leading to a final selection that is not the optimal solution for overall aerodynamic performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a rapid selection method for heat exchanger fin spacing under conditions of limited total intake pressure. This method solves the problem that existing selection methods fail to comprehensively consider the flight-induced drag cost caused by structural weight gain and the momentum conversion benefits of the entire flow channel, resulting in low aerodynamic performance matching between the heat exchanger and the aircraft platform.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure, comprising the following steps:

[0007] The flight operating parameters and thermal parameters of the heat source side are obtained, a numerical calculation domain including parameterized fin structure is established, and the parameters are set as the fluid inlet and outlet boundary conditions of the calculation domain.

[0008] Perform parameterized scanning of fin spacing within the numerical computation domain to identify the structural mass minimum scheme that satisfies the design target heat exchange, define it as the first characteristic spacing scheme, and identify the scheme with the minimum intake aerodynamic resistance, define it as the second characteristic spacing scheme.

[0009] Calculate the structural mass difference per unit heat exchange of the second characteristic spacing scheme relative to the first characteristic spacing scheme, and convert the structural mass difference into an equivalent induced drag threshold based on the optimal lift-to-drag ratio of the aircraft in cruise mode.

[0010] Calculate the gain in intake aerodynamic resistance and exhaust thrust recovery per unit heat exchange of the second characteristic spacing scheme relative to the first characteristic spacing scheme, and superimpose them to construct a net aerodynamic gain index.

[0011] The net aerodynamic benefit index is compared with the equivalent induced drag threshold: if the net aerodynamic benefit index is greater than the equivalent induced drag threshold, the spacing corresponding to the second characteristic spacing scheme is determined to be the target fin spacing; otherwise, the spacing corresponding to the first characteristic spacing scheme is determined to be the target fin spacing.

[0012] Preferably, before establishing the numerical calculation domain containing the parameterized fin structure, the acquisition of flight condition parameters specifically includes: determining the flight speed, ambient static pressure, and ambient temperature of the aircraft during cruise; for the condition of limited total intake pressure, introducing the total intake pressure recovery coefficient, and combining the flight Mach number and ambient static pressure to calculate the available total pressure and total temperature of the cold side inlet of the heat exchanger as the pressure inlet boundary condition of the fluid dynamics simulation model.

[0013] Preferably, identifying the structural mass-minimum scheme and the intake aerodynamic resistance-minimum scheme that meet the design target heat exchange rate specifically includes:

[0014] A performance database for different fin spacings is generated, and feasible schemes with calculated heat exchange values ​​not lower than the design target heat exchange are selected. Among the feasible schemes, the scheme with the smallest total structural mass of the heat exchanger core is selected as the first characteristic spacing scheme.

[0015] In the performance database, the sum of the pressure difference resistance and friction resistance of the fluid flowing through the heat exchanger is calculated by integration, and the one with the smallest intake aerodynamic resistance value is selected as the second characteristic spacing scheme.

[0016] Preferably, before calculating the structural mass difference, intake aerodynamic drag gain, and exhaust thrust recovery gain, a normalization parameter extraction step is also included:

[0017] For the first and second feature spacing schemes, the ratio of their total structural mass to total heat exchange is calculated respectively to obtain the structural mass of the first unit heat exchange and the structural mass of the second unit heat exchange.

[0018] Calculate the ratio of intake aerodynamic resistance to total heat exchange to obtain the intake aerodynamic resistance per unit heat exchange and the intake aerodynamic resistance per unit heat exchange.

[0019] Preferably, the calculation of the difference in unit heat exchange structural mass between the second feature spacing scheme and the first feature spacing scheme specifically involves subtracting the first unit heat exchange structural mass from the second unit heat exchange structural mass.

[0020] The calculation of the gain from the intake aerodynamic resistance per unit of heat exchange is specifically done by subtracting the intake aerodynamic resistance per unit of heat exchange from the intake aerodynamic resistance per unit of heat exchange.

[0021] Preferably, the specific execution logic for converting the structural mass difference into an equivalent induced drag threshold is as follows:

[0022] Based on the principle of force balance in the steady cruise state of an aircraft, the structural mass difference per unit heat exchange is multiplied by the gravitational acceleration to convert it into a gravity term. Then, this gravity term is divided by the aircraft's optimal lift-to-drag ratio to obtain the additional aerodynamic drag value that needs to be overcome to maintain the weight corresponding to the structural mass difference. This value is then set as the equivalent induced drag threshold.

[0023] Preferably, the calculation of the exhaust thrust recovery gain requires first obtaining the exhaust thrust per unit heat exchange, and the calculation process of the exhaust thrust per unit heat exchange includes:

[0024] On the cold-side outlet boundary section of the numerical computation domain, the mass-weighted average algorithm is used to extract the average velocity of the cold air outlet and read the mass flow rate of the cold air.

[0025] Based on the fluid momentum theorem, the product of the mass flow rate of the cold airflow and the velocity difference is calculated, where the velocity difference is the difference between the average velocity at the cold airflow outlet and the flight speed.

[0026] Divide the product by the corresponding total heat exchange to obtain the exhaust thrust per unit heat exchange for the scheme.

[0027] Preferably, the calculation of exhaust thrust recovery gain specifically involves subtracting the exhaust thrust per unit heat exchange of the first characteristic spacing scheme from the exhaust thrust per unit heat exchange of the second characteristic spacing scheme.

[0028] The aforementioned net aerodynamic benefit index is specifically constructed by algebraically summing the inlet aerodynamic resistance benefit per unit heat exchange and the exhaust thrust recovery gain, thereby quantifying the total aerodynamic value of the heat exchanger's full-channel momentum synergistic optimization.

[0029] Preferably, the comparison and determination step specifically follows the whole-channel momentum coordination criterion:

[0030] When the net aerodynamic benefit index is strictly greater than the equivalent induced drag threshold, it is determined that the intake drag reduction and exhaust thrust enhancement benefits obtained through flow channel optimization are sufficient to cover the flight drag cost caused by the increase in structural mass. A positive collaborative selection decision is executed, and the second characteristic spacing scheme is output.

[0031] When the net aerodynamic benefit index is less than or equal to the equivalent induced drag threshold, it is determined that the aerodynamic benefit is insufficient to offset the quality penalty, a negative collaborative selection decision is executed, and the first feature spacing scheme is output.

[0032] Preferably, the steps of establishing a numerical computational domain including a parameterized fin structure and setting the parameters as the fluid inlet and outlet boundary conditions of the computational domain specifically include:

[0033] A parametric geometric model is constructed using periodic elements of the heat exchanger fin flow channel as the numerical computation domain;

[0034] For the cold-side fluid domain of the numerical calculation domain, the inlet boundary is set as a pressure inlet, and the input values ​​are the available total pressure and total temperature. The outlet boundary is set as a pressure outlet, and the input value is the ambient static pressure.

[0035] For the hot-side fluid domain of the numerical computation domain, the inlet boundary is set as the mass flow rate inlet, and the input values ​​are the mass flow rate of the hot-side fluid and the inlet temperature of the hot-side fluid.

[0036] This invention provides a method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure. It has the following beneficial effects:

[0037] 1. This invention, by introducing the optimal lift-to-drag ratio parameter for the aircraft, converts the structural mass increment caused by the adjustment of the heat exchanger fin spacing into an equivalent induced drag that the aircraft must overcome to maintain cruise flight, based on the principle of force balance. This approach eliminates the difference in physical dimensions between structural weight and aerodynamic drag, providing a unified calculation benchmark for comprehensive trade-offs across physical fields, and avoiding design deviations that solely pursue low flow resistance while ignoring the cost of increased structural weight.

[0038] 2. This invention constructs a full-flow-channel aerodynamic evaluation system that includes an exhaust thrust recovery mechanism. Based on the fluid momentum theorem, this method, while calculating the aerodynamic drag gain at the inlet, quantifies the exhaust thrust gain generated after the fluid's heat absorption and expansion using the cold air outlet velocity and mass flow rate parameters. By incorporating the exhaust thrust recovery gain into the aerodynamic gain index, it can more comprehensively reflect the actual momentum contribution of the heat exchanger flow channel design to the aircraft propulsion system under conditions of limited total inlet pressure.

[0039] 3. This invention provides a positive selection decision logic based on overall aircraft energy efficiency. By establishing a comparison criterion between the net aerodynamic benefit index and the equivalent induced drag threshold, this invention can directly determine whether the aerodynamic benefits of the low flow resistance scheme are sufficient to cover the flight drag cost caused by its increased volume and mass. This method ensures that the finally determined fin spacing scheme can minimize the overall flight drag at the aircraft platform level while meeting heat dissipation requirements, guaranteeing the optimal match between the heat exchanger subsystem and the overall performance of the aircraft. Attached Figure Description

[0040] Figure 1 This is the main flowchart of the method for rapid selection of heat exchanger fin spacing under the condition of limited total inlet pressure based on the synergistic correction of momentum across the entire flow channel, according to the present invention.

[0041] Figure 2 This is a flowchart illustrating the specific implementation of the present invention for determining design operating parameters and numerical calculation boundaries.

[0042] Figure 3 This is a flowchart illustrating the specific implementation of the present invention for identifying the optimal thermal-to-weight ratio characteristic scheme and the minimum aerodynamic drag characteristic scheme, and extracting the flow field parameters of the entire flow channel;

[0043] Figure 4 This is a flowchart illustrating the specific implementation of the calculation of differences in the underlying physical parameters of the present invention.

[0044] Figure 5 This is a flowchart illustrating the specific implementation of the present invention regarding the equivalent induced drag threshold caused by structural quality.

[0045] Figure 6 This is a flowchart illustrating the specific implementation of the present invention for calculating the exhaust thrust recovery gain;

[0046] Figure 7 This is a flowchart illustrating the specific implementation of the present invention for constructing a full-channel momentum synergy criterion and executing selection decisions;

[0047] Figure 8 The graph shows the variation trend of the mass of unit heat exchange and aerodynamic resistance of the heat exchanger of the present invention with the fin spacing. Detailed Implementation

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] See attached document Figure 1 , Figure 1 This is a main flowchart of a rapid selection method for heat exchanger fin spacing under inlet total pressure-limited conditions based on full-channel momentum collaborative correction, according to an embodiment of the present invention. The present invention provides a rapid selection method for heat exchanger fin spacing under inlet total pressure-limited conditions, comprising the following steps:

[0050] S1. First, flight operating parameters, thermal parameters of the heat source side, and aerodynamic performance parameters of the aircraft platform are obtained to establish the numerical calculation input boundary. Specifically, the flight speed and ambient static pressure are determined based on the aircraft's cruise state, and the available total pressure on the cold side is calculated by combining the total pressure recovery coefficient of the inlet. At the same time, the mass flow rate of the hot-side fluid, the inlet temperature, and the design target heat transfer are determined, and the optimal lift-to-drag ratio parameters of the aircraft are obtained. On this basis, a numerical calculation domain containing parameterized fin structures is constructed, and the parameters determined above are set as the boundary conditions of the fluid inlet and outlet of the calculation domain, providing a physical model basis for subsequent simulation calculations.

[0051] S2. After establishing the computational domain, a parametric scan is performed to identify the optimal heat-to-weight ratio (TGR) characteristic scheme and extract normalized indices. Within the numerical computational domain, a parametric scan of the fin spacing is performed. First, feasible schemes that meet the design target heat transfer are selected. Among these feasible schemes, the scheme with the minimum structural mass is identified, and its corresponding fin spacing is defined as the first characteristic spacing. Then, the total structural mass, inlet aerodynamic drag, and exhaust flow field momentum parameters under this spacing are extracted to calculate the structural mass per unit heat transfer and the inlet aerodynamic drag per unit heat transfer, which serve as the basis for subsequent comparisons.

[0052] S3. Based on the scan results of the same batch, the scheme with the minimum aerodynamic drag characteristic was identified, and the normalized index was extracted. The trend of the intake aerodynamic drag with the fin spacing was further analyzed, and the scheme with the minimum intake aerodynamic drag was identified. The corresponding fin spacing was defined as the second characteristic spacing. Similarly, the total structural mass, intake aerodynamic drag and exhaust flow field momentum parameters under this spacing were extracted, and the second unit heat exchange structural mass and the second unit heat exchange intake aerodynamic drag were calculated as the optimization objects for subsequent comparison.

[0053] S4. After completing the feature scheme identification, calculate the differences in basic physical parameters. For the selected second feature spacing scheme and the first feature spacing scheme, calculate the difference in normalized parameters. Specifically, calculate the difference in structural mass per unit heat exchange of the second feature spacing scheme relative to the first feature spacing scheme, quantifying the structural cost; at the same time, calculate the gain in air intake aerodynamic resistance per unit heat exchange, quantifying the direct aerodynamic benefit at the intake end.

[0054] S5. To achieve a unified dimension of comparison, an equivalent induced drag threshold caused by structural mass is constructed. Based on the principle of force balance in the cruise state of an aircraft, the structural mass difference per unit heat exchange obtained in step S4 is converted into an equivalent induced drag threshold using the optimal lift-to-drag ratio. This threshold represents the lower limit of the additional drag that the aircraft needs to overcome to maintain flight with this added mass.

[0055] S6. Based on the intake resistance, the exhaust thrust recovery gain is further calculated. Based on the fluid momentum theorem, the exhaust thrust per unit heat exchange of the two schemes is calculated using the extracted cold air mass flow rate and the average cold air outlet velocity. By calculating the difference between the two, the exhaust thrust recovery gain of the second characteristic spacing scheme relative to the first characteristic spacing scheme is determined.

[0056] S7. Integrating the aerodynamic changes at both the intake and exhaust ends, a momentum coordination criterion for the entire flow path is constructed. The intake aerodynamic resistance gain per unit heat exchange in step S4 and the exhaust thrust recovery gain in step S6 are superimposed to construct a net aerodynamic benefit index that reflects the overall aerodynamic performance benefit of the entire machine.

[0057] S8. Finally, perform a collaborative comparison and determine the target fin spacing. The net aerodynamic benefit index obtained in step S7 is logically compared with the equivalent induced drag threshold determined in step S5: if the net aerodynamic benefit index is greater than the equivalent induced drag threshold, it indicates that the aerodynamic benefit covers the weight cost, and the second characteristic spacing is determined to be the target fin spacing; if the net aerodynamic benefit index is less than or equal to the equivalent induced drag threshold, it indicates that the aerodynamic benefit is insufficient to offset the weight cost, and the first characteristic spacing is determined to be the target fin spacing.

[0058] Please see the appendix Figure 2 , Figure 2This is a flowchart illustrating the specific implementation of determining design operating parameters and numerical calculation boundaries in an embodiment of the present invention. In a preferred embodiment of the present invention, the specific implementation process of determining design operating parameters and numerical calculation boundaries includes the following sub-steps:

[0059] S110, Obtain flight operating parameters. Determine the aircraft cruise state parameters for which the heat exchanger selection and design are based, including flight speed, ambient static pressure corresponding to flight altitude, and ambient temperature. For operating conditions with limited total inlet pressure, it is necessary to determine the available total pressure and total temperature at the cold-side inlet of the heat exchanger. For ramjet inlet, the available total pressure is calculated based on the isentropic flow relationship in gas dynamics. The calculation needs to incorporate the inlet total pressure recovery coefficient, which characterizes the inlet duct's ability to maintain total pressure. This coefficient, combined with the flight Mach number and ambient static pressure, determines the inlet energy boundary of the cold-side fluid.

[0060] S120: Obtain the thermal parameters on the heat source side. Determine the physical properties and flow state of the fluid to be cooled, including the hot-side fluid mass flow rate, hot-side fluid inlet temperature, and hot-side fluid operating pressure. Simultaneously, set the design target heat transfer capacity of the heat exchanger, or set the target outlet temperature that the hot-side fluid must reach. These parameters together constitute the calculation boundary conditions of the hot-side fluid domain of the heat exchanger, used to subsequently determine whether different fin spacing schemes meet the heat dissipation requirements.

[0061] S130: Obtain the aerodynamic performance parameters of the aircraft platform. Determine the optimal lift-to-drag ratio for the aircraft during cruise. This parameter reflects the overall aerodynamic efficiency of the aircraft platform, i.e., the drag cost associated with generating a unit of lift. For conventional fixed-wing aircraft, this value is typically obtained through wind tunnel test data or a full-aircraft aerodynamic simulation database, and is a key conversion factor for subsequently converting structural mass into equivalent induced drag.

[0062] S140, Establish the boundary of the numerical computation domain. The parameters obtained in steps S110 and S120 are set as boundary conditions for the fluid dynamics simulation model or heat transfer calculation model. To achieve rapid calculations under different fin spacings, a parametric geometric model containing the fin structure is constructed, or periodic elements of the fin flow channel are selected as the computation domain. For the cold air fluid domain, the inlet boundary is set as a pressure inlet, with the input values ​​being the previously calculated available total pressure and total temperature; the outlet boundary is set as a pressure outlet, with the input value being the ambient static pressure. For the hot-side fluid domain, the inlet boundary is set as a mass flow rate inlet, with the input values ​​being the hot-side fluid mass flow rate and inlet temperature. By using a parametric or periodic element model, the mesh can be quickly updated and solved for continuously changing fin spacings, ensuring that the calculation results accurately reflect the physical response under actual flight conditions. The mesh generation, turbulence model selection, and solver settings involved in the numerical calculations can be conventionally configured by those skilled in the art based on fluid characteristics; these are well-known techniques in the field and will not be elaborated upon here.

[0063] Please see the appendix Figure 3 , Figure 3 This is a flowchart illustrating the specific implementation of identifying the optimal thermal-to-weight ratio characteristic scheme and the minimum aerodynamic drag characteristic scheme and extracting the flow field parameters of the entire flow channel in an embodiment of the present invention. In a preferred embodiment of the present invention, the specific implementation process of identifying the optimal thermal-to-weight ratio characteristic scheme and the minimum aerodynamic drag characteristic scheme and extracting the flow field parameters of the entire flow channel includes the following sub-steps:

[0064] S210 executes parametric scan calculation of fin spacing. Under the established boundary conditions of the numerical computation domain, the fin spacing is set as an independent variable, and discretization sampling or continuous parametric scanning is performed within the allowable geometric dimensions of the engineering project. For each set fin spacing value, a fluid dynamics simulation model is used to solve the problem until the flow field residuals converge, thereby obtaining a series of steady-state flow field distribution results for the heat exchanger under different fin spacings. This process is automatically completed by the parametric scan function, generating a performance database containing multiple sets of design points.

[0065] S220, Identify the optimal heat-to-weight ratio characteristic scheme. Analyze the generated performance database and filter out all feasible fin spacing schemes where the calculated heat transfer value is not lower than the design target heat transfer value, or the hot-side fluid outlet temperature is not higher than the target outlet temperature. Among the selected feasible schemes, identify the scheme with the minimum overall structural mass of the heat exchanger core, and define the fin spacing corresponding to this scheme as the first characteristic spacing. This scheme represents the design point with the lowest structural mass cost while meeting thermal management requirements.

[0066] S230 identifies the minimum aerodynamic drag characteristic scheme. Using the same performance database, the variation trend of inlet aerodynamic drag with fin spacing is analyzed. Inlet aerodynamic drag is obtained by integrating the sum of pressure differential drag and frictional drag generated by the fluid flowing through the heat exchanger. The scheme that minimizes the inlet aerodynamic drag is identified, and the fin spacing corresponding to this scheme is defined as the second characteristic spacing. This scheme represents the design point where the inlet momentum loss is minimized when the airflow passes through the heat exchanger.

[0067] S240, calculate and extract normalized basic parameters. For the schemes corresponding to the first and second characteristic spacings, process the simulation results data separately. Calculate the ratio of the total structural mass to the total heat exchange of the scheme with the first characteristic spacing to obtain the structural mass per unit heat exchange; calculate the ratio of its inlet aerodynamic drag to the total heat exchange to obtain the inlet aerodynamic drag per unit heat exchange. Similarly, calculate the structural mass per unit heat exchange and the inlet aerodynamic drag per unit heat exchange for the scheme with the second characteristic spacing. Through the above ratio calculations, the comparison error caused by small differences in absolute heat exchange between different schemes is eliminated, and the evaluation benchmark is unified.

[0068] S250, Extracting Outlet Momentum Flux Parameters. For the two characteristic schemes mentioned above, data is extracted from the cold-side outlet boundary section of the simulation model. Due to the non-uniformity of the heat exchanger outlet velocity distribution, a mass-weighted averaging algorithm is used to extract the average velocity of the cold airflow at the outlet section, while simultaneously reading the mass flow rate of the cold airflow passing through this section. The outlet velocity and flow rate data obtained in this step are the physical basis for subsequent calculations of exhaust thrust recovery gain and the realization of momentum-coordinated correction. Directly extracting this momentum state data from the outlet boundary of the simulated flow field accurately reflects the true exhaust kinetic energy of the airflow after absorbing heat and expanding, providing necessary input for subsequent thrust compensation calculations.

[0069] Please see the appendix Figure 4 , Figure 4 This is a flowchart illustrating the specific implementation of calculating the differences in basic physical parameters in an embodiment of the present invention. In a preferred embodiment of the present invention, the specific implementation process for calculating the differences in basic physical parameters includes the following sub-steps:

[0070] S410, Calculate the structural mass difference per unit heat exchange. Using the normalized parameters extracted in the previous steps, calculate the increase in structural mass of the scheme corresponding to the second characteristic spacing relative to the scheme corresponding to the first characteristic spacing. This step aims to quantify the structural mass cost required to reduce flow channel resistance by using a looser fin arrangement. The calculation formula is as follows:

[0071] ;

[0072] In the formula, Differences in structural mass per unit heat exchanger; The second unit of heat exchange structure mass; The first unit heat exchange structural mass is denoted as S. Physically, because the scheme corresponding to the second characteristic spacing has higher flow channel permeability to reduce flow resistance, the heat exchange surface area per unit volume is reduced. To achieve the same total heat exchange as the scheme with the first characteristic spacing, the core volume of the heat exchanger must be increased. Therefore, the structural mass of the second unit heat exchange is usually greater than that of the first unit heat exchange. The calculated mass difference is usually a positive value, which is defined as a mass penalty in the selection process.

[0073] S420, Calculate the intake aerodynamic drag benefit per unit heat exchange. Using the normalized parameters extracted in the previous steps, calculate the reduction in intake aerodynamic drag of the scheme corresponding to the second characteristic spacing compared to the scheme corresponding to the first characteristic spacing. This step aims to quantify the direct aerodynamic benefit of the low flow resistance design scheme in reducing momentum loss at the intake end. The calculation formula is as follows:

[0074] ;

[0075] In the formula, Benefits from airflow aerodynamic resistance per unit heat exchange; The aerodynamic resistance of the intake air is the first unit of heat exchange. The inlet aerodynamic resistance is the second unit of heat exchange. Since the first characteristic spacing scheme is a compact high-resistance scheme, its inlet aerodynamic resistance is usually greater than that of the second characteristic spacing scheme. Therefore, the calculated difference is a positive value, which represents the reduction in resistance loss when the airflow passes through the heat exchanger.

[0076] Please see the appendix Figure 5 This is a flowchart illustrating the specific implementation of constructing the equivalent induced drag threshold caused by structural mass in an embodiment of the present invention. In a preferred embodiment of the present invention, the specific implementation process of constructing the equivalent induced drag threshold caused by structural mass includes the following sub-steps:

[0077] S510 establishes the conversion relationship between structural mass and flight aerodynamic drag. Based on the force balance principle of an aircraft in steady cruise, it clarifies the numerical mapping logic between the increase in structural mass of the heat exchanger subsystem and the drag that the aircraft needs to overcome. In cruise, the lift generated by the aircraft wings must be balanced with gravity. The increase in structural mass requires adjustment of the wing angle of attack to increase lift output, which in turn leads to an increase in flight drag. This step maps the mass parameters in the structural dimension to drag parameters in the aerodynamic dimension, providing a unified quantitative benchmark for comparing schemes with different physical properties.

[0078] S520, Calculate the equivalent induced drag threshold. Based on the structural mass difference per unit heat exchange obtained in the previous steps, it is converted using the aircraft's optimal lift-to-drag ratio parameters. The mass dimension is converted to a mechanical dimension using gravitational acceleration, and then divided by the lift-to-drag ratio efficiency coefficient to obtain the equivalent induced drag required to maintain this mass increment. The calculation formula is as follows:

[0079] ;

[0080] In the formula, The equivalent induced drag threshold has the physical meaning of: the additional aerodynamic drag that the aircraft propulsion system must overcome in optimal cruise conditions in order to carry the structural mass added by the scheme corresponding to the second characteristic spacing relative to the scheme corresponding to the first characteristic spacing. It is the acceleration due to gravity; Differences in structural mass per unit heat exchanger; This represents the optimal lift-to-drag ratio for the aircraft.

[0081] S530 establishes the drag cost benchmark for selection. The calculated equivalent induced drag threshold is set as the drag cost benchmark for evaluating the feasibility of the scheme corresponding to the second characteristic spacing. If the net aerodynamic benefits calculated subsequently cannot cover this drag threshold, it indicates that the design approach of increasing structural mass in exchange for low flow resistance cannot achieve positive benefits in terms of overall system energy efficiency. This step completes the one-way value conversion from structural parameters to aerodynamic performance parameters.

[0082] Please see the appendix Figure 6 , Figure 6 This is a flowchart illustrating the specific implementation of calculating the exhaust thrust recovery gain in an embodiment of the present invention. In a preferred embodiment of the present invention, the specific implementation process of calculating the exhaust thrust recovery gain includes the following sub-steps:

[0083] S610, Construct an exhaust thrust calculation model. Based on the fluid momentum theorem, the heat exchanger flow channel is considered as a thrust-generating unit. According to the pressure outlet boundary conditions set in the previous steps, it is assumed that the gas flow discharged from the cold side of the heat exchanger has fully expanded to the ambient static pressure. At this time, the thrust generated by the fluid is mainly contributed by the momentum change, and the static pressure difference thrust term at the outlet section is ignored. This step uses the total pressure potential energy generated by the ram air intake and the volume expansion effect after absorbing heat to calculate the momentum change rate of the exhaust fluid relative to the free flow, thereby determining the net thrust or net drag component contributed by the heat exchanger as part of the propulsion system under different flow resistance characteristics.

[0084] S620, calculate the exhaust thrust per unit heat exchange for the first characteristic spacing scheme. Based on the extracted cold air mass flow rate and average cold air outlet velocity corresponding to the first characteristic spacing, and combined with flight operating parameters, calculate the exhaust thrust generated by this scheme under unit heat exchange. The calculation formula is as follows:

[0085] ;

[0086] In the formula, The first unit of heat exchanged is the exhaust thrust. This parameter characterizes the gain or loss of exhaust momentum per unit of heat exchanged in the optimal heat-to-weight ratio scheme. The mass flow rate of the cold airflow corresponding to the first characteristic spacing; The average velocity of the cold air outlet corresponding to the first characteristic distance; This refers to the cruising speed of the aircraft. This represents the total heat transfer corresponding to the first characteristic spacing. When the outlet velocity is less than the flight speed, this value represents momentum drag; when the outlet velocity is greater than the flight speed, this value represents net thrust.

[0087] S630, calculate the exhaust thrust per unit heat exchange for the second characteristic spacing scheme. Using the same physical model as the previous steps, for the second characteristic spacing scheme...

[0088] The flow field parameters corresponding to the distance between the nodes are calculated. The calculation formula is as follows:

[0089] ;

[0090] In the formula, The second unit of heat exchange exhaust thrust; The mass flow rate of the cold airflow corresponding to the second characteristic spacing; The average velocity of the cold air outlet corresponding to the second characteristic spacing; This represents the total heat transfer corresponding to the second characteristic spacing. Physically, the scheme with the second characteristic spacing has lower flow resistance, resulting in less total pressure loss of the airflow as it flows through the heat exchanger core. This allows for higher total pressure at the outlet for expansion acceleration. Therefore, the average outlet velocity of the cold airflow in this scheme is typically higher than that in the scheme with the first characteristic spacing, leading to a larger algebraically calculated exhaust thrust per unit heat transfer.

[0091] S640, calculate the exhaust thrust recovery gain. Compare the exhaust thrust performance of the second characteristic spacing scheme with that of the first characteristic spacing scheme to quantify the momentum gain due to flow channel optimization. The calculation formula is as follows:

[0092] ;

[0093] In the formula, This refers to the exhaust thrust recovery gain. This metric reflects the additional thrust compensation obtained at the exhaust end by a low-flow-resistance design compared to a high-compact design under the same heat exchange task. This gain value stems from the more efficient conversion of fluid pressure potential energy into kinetic energy and is a key parameter for evaluating the momentum synergy between the heat exchanger and the aircraft propulsion system.

[0094] Please see the appendix Figure 7 , Figure 7 This is a flowchart illustrating the specific implementation of constructing a full-channel momentum collaborative criterion and executing selection decisions in an embodiment of the present invention. In a preferred embodiment of the present invention, the specific implementation process of constructing a full-channel momentum collaborative criterion and executing selection decisions includes the following sub-steps:

[0095] S710, Construct the net aerodynamic benefit index. Based on the momentum conservation analysis of the entire flow channel, the aerodynamic benefits at the inlet and exhaust ends brought about by the improvement of the heat exchanger flow channel are superimposed to synthesize a comprehensive index that can characterize the total improvement in the overall aerodynamic performance of the machine. Specifically, the inlet aerodynamic resistance benefit per unit heat exchange calculated in step S420 is added to the exhaust thrust recovery gain calculated in step S640. The calculation formula is as follows:

[0096] ;

[0097] In the formula, This is a net aerodynamic benefit indicator; The gain in intake aerodynamic resistance per unit heat exchange represents the reduction in momentum loss on the intake side. The exhaust thrust recovery gain represents the increase in momentum thrust on the exhaust side. This step achieves a unified quantification of the aerodynamic value of the entire flow path of the heat exchanger, no longer viewing inlet resistance or exhaust thrust in isolation, but rather considering it as a complete momentum conversion process.

[0098] S720, Construct a momentum synergy criterion for the entire flow path. Establish a inequality between aerodynamic gains and structural costs to evaluate whether the structural mass cost incurred to improve aerodynamic performance has a positive overall energy efficiency benefit. Compare the net aerodynamic gain index with the equivalent induced drag threshold calculated in step S520. The criterion formula is as follows:

[0099] ;

[0100] Right now:

[0101] ;

[0102] In the formula, This is a net aerodynamic benefit indicator; This is the equivalent induced drag threshold. The physical meaning of this criterion is that the optimization scheme is only positive at the overall aircraft level when the net aerodynamic gains (including drag reduction and thrust increase) obtained through flow channel optimization are numerically significantly greater than the additional flight drag that the aircraft must overcome due to the increased heat exchanger volume and structural mass. This criterion constitutes the core decision-making logic of momentum-coordinated design.

[0103] S810 executes a positive collaborative selection decision. If the aforementioned full-flow-channel momentum collaboration criterion holds, i.e., the net aerodynamic benefit index is greater than the equivalent induced drag threshold, then the scheme corresponding to the second characteristic spacing is determined to be the preferred scheme. At this time, although the physical mass of the heat exchanger subsystem increases, the thrust compensation and drag reduction brought about by its excellent flow-channel aerodynamic characteristics are sufficient to cover the negative impact of the weight, with a surplus. Therefore, the second characteristic spacing is output as the final heat exchanger fin spacing design value, and the detailed structural design is carried out using the geometric parameters corresponding to this scheme.

[0104] S820 executes a negative collaborative selection decision. If the above-mentioned full-channel momentum collaborative criterion is not met, i.e., the net aerodynamic benefit index is less than or equal to the equivalent induced drag threshold, then the aerodynamic benefit of the scheme corresponding to the second characteristic spacing is determined to be insufficient to offset its mass penalty. At this time, the system should revert to a design logic primarily focused on reducing structural mass. The scheme corresponding to the first characteristic spacing is determined to be the preferred scheme, and the first characteristic spacing is output as the final heat exchanger fin spacing design value. This step ensures that under operating conditions where aerodynamic benefits are not significant (such as low-speed cruise or low heat load conditions), the design scheme can automatically converge to the optimal thermogravimetric ratio scheme with the highest structural efficiency, avoiding blindly pursuing low flow resistance and resulting in excessive overall dead weight.

[0105] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure, characterized in that, Includes the following steps: The flight operating parameters and thermal parameters of the heat source side are obtained, a numerical calculation domain including parameterized fin structure is established, and the parameters are set as the fluid inlet and outlet boundary conditions of the calculation domain. Perform parameterized scanning of fin spacing within the numerical computation domain to identify the structural mass minimum scheme that satisfies the design target heat exchange, define it as the first characteristic spacing scheme, and identify the scheme with the minimum intake aerodynamic resistance, define it as the second characteristic spacing scheme. Calculate the structural mass difference per unit heat exchange of the second characteristic spacing scheme relative to the first characteristic spacing scheme, and convert the structural mass difference into an equivalent induced drag threshold based on the optimal lift-to-drag ratio of the aircraft in cruise mode. Calculate the gain in intake aerodynamic resistance and exhaust thrust recovery per unit heat exchange of the second characteristic spacing scheme relative to the first characteristic spacing scheme, and superimpose them to construct a net aerodynamic gain index. The net aerodynamic benefit index is compared with the equivalent induced drag threshold: if the net aerodynamic benefit index is greater than the equivalent induced drag threshold, the spacing corresponding to the second characteristic spacing scheme is determined to be the target fin spacing; otherwise, the spacing corresponding to the first characteristic spacing scheme is determined to be the target fin spacing.

2. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 1, characterized in that, Before establishing the numerical calculation domain containing the parameterized fin structure, the acquisition of flight condition parameters specifically includes: determining the flight speed, ambient static pressure, and ambient temperature of the aircraft during cruise; for the condition of limited total intake pressure, introducing the total intake pressure recovery coefficient, and combining the flight Mach number and ambient static pressure to calculate the available total pressure and total temperature of the cold side inlet of the heat exchanger as the pressure inlet boundary condition of the fluid dynamics simulation model.

3. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 1, characterized in that, The identification of the structural mass-minimum scheme and the intake aerodynamic resistance-minimum scheme that meet the design target heat exchange target specifically includes: A performance database for different fin spacings is generated, and feasible schemes with calculated heat exchange values ​​not lower than the design target heat exchange are selected. Among the feasible schemes, the scheme with the smallest total structural mass of the heat exchanger core is selected as the first characteristic spacing scheme. In the performance database, the sum of the pressure difference resistance and friction resistance of the fluid flowing through the heat exchanger is calculated by integration, and the one with the smallest intake aerodynamic resistance value is selected as the second characteristic spacing scheme.

4. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 1, characterized in that, Before calculating the structural mass difference, intake aerodynamic drag gain, and exhaust thrust recovery gain, a normalization parameter extraction step is also included: For the first and second feature spacing schemes, the ratio of their total structural mass to total heat exchange is calculated respectively to obtain the structural mass of the first unit heat exchange and the structural mass of the second unit heat exchange. Calculate the ratio of intake aerodynamic resistance to total heat exchange to obtain the intake aerodynamic resistance per unit heat exchange and the intake aerodynamic resistance per unit heat exchange.

5. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 4, characterized in that, The calculation of the difference in unit heat exchange structural mass between the second characteristic spacing scheme and the first characteristic spacing scheme specifically involves subtracting the unit heat exchange structural mass of the first unit heat exchange scheme from the second unit heat exchange structural mass. The calculation of the gain from the intake aerodynamic resistance per unit of heat exchange is specifically done by subtracting the intake aerodynamic resistance per unit of heat exchange from the intake aerodynamic resistance per unit of heat exchange.

6. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 5, characterized in that, The specific execution logic for converting the structural mass difference into an equivalent induced drag threshold is as follows: Based on the principle of force balance in the steady cruise state of an aircraft, the structural mass difference per unit heat exchange is multiplied by the gravitational acceleration to convert it into a gravity term. Then, this gravity term is divided by the aircraft's optimal lift-to-drag ratio to obtain the additional aerodynamic drag value that needs to be overcome to maintain the weight corresponding to the structural mass difference. This value is then set as the equivalent induced drag threshold.

7. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 1, characterized in that, The calculation of the exhaust thrust recovery gain requires first obtaining the exhaust thrust per unit heat exchange. The calculation process for the exhaust thrust per unit heat exchange includes: On the cold-side outlet boundary section of the numerical computation domain, the mass-weighted average algorithm is used to extract the average velocity of the cold air outlet and read the mass flow rate of the cold air. Based on the fluid momentum theorem, the product of the mass flow rate of the cold airflow and the velocity difference is calculated, where the velocity difference is the difference between the average velocity at the cold airflow outlet and the flight speed. Divide the product by the corresponding total heat exchange to obtain the exhaust thrust per unit heat exchange for the scheme.

8. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 7, characterized in that, The calculation of exhaust thrust recovery gain specifically involves subtracting the exhaust thrust per unit heat exchange of the first characteristic spacing scheme from the exhaust thrust per unit heat exchange of the second characteristic spacing scheme. The aforementioned net aerodynamic benefit index is specifically constructed by algebraically summing the inlet aerodynamic resistance benefit per unit heat exchange and the exhaust thrust recovery gain, thereby quantifying the total aerodynamic value of the heat exchanger's full-flow-channel momentum synergistic optimization.

9. The method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 1, characterized in that, The comparison and determination steps specifically follow the full-channel momentum coordination criterion: When the net aerodynamic benefit index is strictly greater than the equivalent induced drag threshold, it is determined that the intake drag reduction and exhaust thrust enhancement benefits obtained through flow channel optimization are sufficient to cover the flight drag cost caused by the increase in structural mass. A positive collaborative selection decision is executed, and the second characteristic spacing scheme is output. When the net aerodynamic benefit index is less than or equal to the equivalent induced drag threshold, it is determined that the aerodynamic benefit is insufficient to offset the quality penalty, a negative collaborative selection decision is executed, and the first feature spacing scheme is output.

10. A method for rapid selection of heat exchanger fin spacing under conditions of limited total intake pressure as described in claim 1, characterized in that, The steps for establishing a numerical computational domain containing parameterized fin structures and setting the parameters as fluid inlet and outlet boundary conditions of the computational domain include: A parametric geometric model is constructed using periodic elements of the heat exchanger fin flow channel as the numerical computation domain; For the cold-side fluid domain of the numerical calculation domain, the inlet boundary is set as a pressure inlet, and the input values ​​are the available total pressure and total temperature. The outlet boundary is set as a pressure outlet, and the input value is the ambient static pressure. For the hot-side fluid domain of the numerical computation domain, the inlet boundary is set as the mass flow rate inlet, and the input values ​​are the mass flow rate of the hot-side fluid and the inlet temperature of the hot-side fluid.

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