A three-dimensional method for assessing the mixing loss of engine turbine blade film cooling

Abstract

This invention discloses a three-dimensional method for evaluating the mixing loss of engine turbine blades in film cooling, aiming to improve the accuracy of calculating and evaluating mixing losses in film cooling, and considering the influence of secondary flow on the relative motion and interaction between the mainstream and jet streams. The method includes: first, establishing a three-dimensional flow model to calculate the velocity components of the mainstream gas and the jet cooler; second, establishing momentum and energy equations for the mixing process based on the laws of conservation of momentum and energy; then, calculating the mixing loss based on the principle of entropy increase; and finally, analyzing the entropy increase caused by mixing to obtain the final form of the entropy increase in the mainstream gas and the jet cooler, thereby evaluating the film cooling effect of the turbine blades. This invention, by establishing a three-dimensional flow model to simulate the momentum exchange between the mainstream gas and the jet cooler, can more accurately determine the mixing loss at various locations on the blade, especially at the film cooling holes near the endwall, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine turbine blade cooling technology and relates to a method for evaluating the mixing loss of air film cooling of engine turbine blades. Specifically, it involves using a full three-dimensional mixing loss evaluation method to evaluate, analyze and calculate the mixing loss generated during the air film cooling process of aero-engine turbine blades, and can more accurately determine the mixing loss at various locations of the turbine blade, especially at the air film holes near the end wall. Background Technology

[0002] Film cooling technology is an effective method that uses high-pressure cold gas to form a protective film on the surface of turbine blades, thereby reducing blade temperature and ensuring blade performance and structural integrity. With the continuous increase in turbine inlet temperature (TIT) of aero-engines, film cooling technology is becoming increasingly common, but it also brings some significant problems. One of these is that the amount of cold gas used for turbine cooling has gradually reached 15% or even 20%, leading to a rapid increase in mixing losses in the main jet. Mixing losses refer to the total pressure drop and entropy increase caused by the mixing of the film outflow and the main jet, which reduces turbine efficiency and performance. Therefore, while developing and analyzing the effectiveness of film cooling, loss analysis and control are also essential.

[0003] Existing aerodynamic loss analyses based on film cooling systems suggest that the main cooling loss is due to the mixing of the film outflow and the mainstream. Furthermore, by considering the entropy increase angle and the flow state of the main jet, the mixing loss can be isolated from the total loss in the entire flow channel for separate evaluation. Results show that a larger compounding angle results in better longitudinal distribution of the cooled air and higher cooling efficiency; a smaller angle between the mainstream and the jet leads to lower aerodynamic losses.

[0004] However, existing methods for assessing mixing losses based on entropy increase originate from the Flat Plate Film Cooling Model (FPSM). When applied to turbine blade cascades, these methods fail to consider the changes in the mainstream flow caused by secondary flow. The FPSM model is a simplified film cooling problem that assumes both the mainstream and the jet are homogeneous, irrotational, and inviscid, neglecting factors such as blade curvature and endwall boundary layers. These assumptions are invalid in actual turbine blade cascades due to complex three-dimensional flow phenomena such as secondary flow, wakes, and shock waves. Secondary flow refers to the flow perpendicular to the mainstream direction generated within the channel due to factors such as blade curvature, pressure gradient, and endwall boundary layers, altering the pressure, velocity, and temperature distributions within the channel. Secondary flows of varying intensities and directions can not only change the outflow direction of the film but also alter the flow state of the local mainstream, with these changes becoming more pronounced at high speeds. In other words, current calculation methods for assessing mixing losses in film cooling are mainly based on simplified models. When considering local flow characteristics and blade surface temperature distribution, existing methods cannot fully capture the changes in flow field structure and the effects of secondary flows caused by blade geometry under real operating conditions. This results in limited accuracy in assessing mixing losses in film cooling in practical applications, failing to meet the needs of high-precision design and optimization.

[0005] Therefore, when assessing and controlling film cooling mixing losses, the influence of secondary flow on the relative motion and interaction between the main flow and the jet must be considered. How to more accurately determine mixing losses at various blade locations, especially near the endwall film cooling orifices, and develop more refined, comprehensive, and universally applicable methods for assessing and calculating film cooling mixing losses, is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] (I) Purpose of the Invention

[0007] To address the aforementioned deficiencies and shortcomings of existing technologies, and to improve the accuracy of calculating and evaluating mixing losses in film cooling, while fully considering the influence of secondary flow on the relative motion and interaction between the mainstream and the jet, this invention proposes a three-dimensional method for evaluating mixing losses in film cooling of engine turbine blades. By incorporating changes in the local mainstream flow conditions into the loss assessment, this method assumes that the mixing process is jointly completed by the three-dimensional flowing cold gas jet and the equally three-dimensional mainstream. Furthermore, it considers the flow changes caused by secondary flow in both the mainstream and the jet cold gas. Both processes, as well as the mixing process itself, are analyzed in a three-dimensional environment, making the calculation results more consistent with actual conditions. This method can more accurately determine mixing losses at various locations on the blade, especially near the endwall film cooling pores, and has broad application prospects.

[0008] (II) Technical Solution

[0009] To achieve the objective of this invention, the present invention adopts the following technical solution:

[0010] A three-dimensional method for evaluating the mixing loss of engine turbine blade film cooling is characterized by comprising at least the following implementation steps:

[0011] SS1. Establish a full three-dimensional flow model to simulate the momentum exchange between the mainstream gas and the jet cooler during the film cooling process of turbine blades, where the mainstream velocity v g The components v in three mutually orthogonal spatial directions gx v gy v gz and the velocity v of the jet cooling air c The corresponding components v in three mutually orthogonal spatial directions cx v cy v cz All were considered, and the mainstream speed v g With the velocity v of the jet of cold air c The corresponding components together determine the mixing rate v after blending. m The corresponding components v in three mutually orthogonal spatial directions xm v ym v zm ;

[0012] SS2. Based on the law of conservation of momentum and the velocity components of the mainstream gas and the jet cooling gas, calculate the mixing velocity v after mixing the mainstream gas and the jet cooling gas using the following formula. m and its components v xm v ym v zm Size:

[0013]

[0014]

[0015]

[0016]

[0017] Where, m g and m c Let x, y, and z represent the mass flow rates of the mainstream gas and the jet cooler gas involved in the mixing, respectively. Subscripts x, y, and z represent three mutually orthogonal directions in space. Subscript g represents the mainstream parameters before mixing, subscript c represents the jet cooler gas parameters before mixing, and subscript m represents the parameters after mixing. α cLet β be the jet angle of the jet cooling gas and be defined as the angle between the component of the jet cooling gas in the xoy plane and the x-axis. c Let κ be the composite angle of the jet cooling gas and defined as the angle between the jet cooling gas and its components in the xoy plane. c The spatial angle of the jet cooling gas is defined as the angle between the jet cooling gas itself and the x-axis of the coordinate system.

[0018] SS3. Based on the mass flow rate, velocity, temperature, and enthalpy of the mainstream gas and the jet cooling gas involved in the mixing, and according to the law of conservation of energy, establish the energy equation that follows the mixing process:

[0019]

[0020] Among them, h g and h c T represents the enthalpy values ​​of the mainstream gas and the jet cooler gas involved in the mixing, respectively. g and T c T represents the temperatures of the mainstream gas and the jet cooler gas involved in the mixing, respectively. m This indicates the mixing temperature after the mainstream gas and the jet of cold gas are mixed.

[0021] SS4. Based on the energy equation established in step SS3, and according to the entropy increase principle formula... Calculate the mixing loss ΔΣ between the mainstream gas and the jet cooling gas. mix ,in:

[0022]

[0023] In the formula, δs, δh, and δp represent the entropy increase, enthalpy increase, and pressure change, respectively; ρ is the density; T is the temperature; p is the local pressure; and c pg c pc T represents the isobaric specific heat of the mainstream gas and the jet of cold air. m This refers to the mixing temperature;

[0024] SS5. The mixing loss ΔΣ between the mainstream gas and the jet cooling gas established in step SS4. mix The calculation formula is used to analyze the entropy increase ΔΣ caused by non-uniform mixing. mix,KE ′ and the entropy increase ΔΣ due to non-isothermal mixing mix,Q ′, and the information about the mixing rate v obtained in step SS2 m The expression is introduced into the calculation to obtain the final form of the entropy increase ΔΣ of the mixing of the mainstream gas and the jet cooling gas. mix The entropy increase effect of the mixing process is calculated to evaluate the effectiveness of film cooling for engine turbine blades.

[0025]

[0026]

[0027] ΔΣ′ mix =ΔΣ′ mix,Q +ΔΣ′ mix,KE

[0028] In the formula, γ g R g Ma g , and represent the specific heat ratio, gas constant, and Mach number of the mainstream gas, respectively.

[0029] Preferably, in step SS1 above, in order to more accurately simulate the film cooling effect of turbine blades, a turbulence model including eddy currents should be considered when establishing a full three-dimensional flow model. The turbulence model adopts a modified k-ωSST (Shear Stress Transport) turbulence model to better capture the near-wall flow characteristics and achieve the mainstream velocity v. g and jet cooling air velocity v c Accurate calculations under turbulent conditions, and consequently the mixing velocity v m To conduct more detailed simulations.

[0030] Preferably, in step SS2 above, the mixing rate v after the mainstream gas and the jet cooling gas are mixed is calculated. m and its components v xm v ym v zm When calculating the mixing velocity, the influence of the pressure difference between the mainstream gas and the jet cooling gas is further considered to improve the accuracy and practicality of the calculation. The pressure difference will cause changes in the mass flow rate ratio and momentum flow rate ratio between the mainstream gas and the jet cooling gas, thus affecting the calculated mixing velocity. After considering the influence of the pressure difference, the mixing velocity v is expressed by the following formula. m and its components v xm v ym v zm Size:

[0031]

[0032]

[0033]

[0034]

[0035] In the formula, Δp is the pressure difference between the mainstream gas and the jet of cold gas, p g The pressure of the mainstream gas.

[0036] Preferably, in step SS2 above, the mixing rate v after the mainstream gas and the jet cooling gas are mixed is calculated. m and its components v xm v ym v zm When considering the magnitude of the mixing velocity, the effects of turbulent and viscous dissipation between the mainstream gas and the jet cooling gas are further taken into account. After considering the effects of turbulent and viscous dissipation, the mixing velocity v is expressed by the following formula. m and its components v xm v ym v zm Size:

[0037]

[0038]

[0039]

[0040]

[0041] In the formula, ε is the turbulent dissipation rate, τ is the viscous stress tensor, and ρ is the fluid density.

[0042] Preferably, in step SS3 above, the mass flow rate m of the mainstream gas participating in the mixing is... g This is not the total mass flow rate of the mainstream gas within the flow channel, but rather the mass flow rate of the mainstream gas that participates in mixing with the jet cooling gas within the mixing layer. The mixing layer is obtained based on mixing layer theory, and the mass flow rate m of the mainstream gas participating in mixing within the mixing layer is... g The value is typically 0.05-0.3 times the mainstream total mass flow rate.

[0043] Preferably, in step SS4 above, the mixing loss ΔΣ between the mainstream gas and the jet cooling gas is calculated. mix Furthermore, the effects of turbulent and viscous dissipation between the mainstream gas and the jet cooling gas were also considered. After considering the effects of turbulent and viscous dissipation, the mixing loss ΔΣ is expressed by the following formula. mix :

[0044]

[0045] In the formula, ε t ε v These are the energy losses caused by turbulent dissipation and viscous dissipation between the mainstream gas and the jet of cold gas, respectively.

[0046] Preferably, in step SS5 above, considering that as the outlet Mach number increases, the mainstream velocity near the suction surface increases while the temperature decreases, under high-speed operating conditions, the temperature at the interface between the cold gas near the jet outlet and the mainstream is selected as the mixing temperature T.m This will more accurately reflect the entropy increase caused by the absorption of heat by the cold air, thereby improving the accuracy of assessing mixing losses under high-speed operating conditions.

[0047] Furthermore, the mixing temperature T m The temperature distribution at the outlet section is used to determine T. Specifically, the difference between the highest and lowest temperatures at the outlet section is multiplied by a fixed coefficient (e.g., 0.3), and then the lowest temperature is added to obtain the calculated T. m This represents the average temperature of the outlet section. By considering the temperature gradient of the outlet section when determining the blending temperature, it not only reflects the temperature difference between the highest and lowest temperatures, but also comprehensively considers the temperature distribution of the entire outlet section through averaging. This makes the selection of the blending temperature more consistent with the actual flow conditions and improves the accuracy of blending loss assessment.

[0048] Preferably, in step SS5 above, a calculation is performed for each air film pore based on the different local mainstream parameters at each air film pore, and the two entropy increases ΔΣ at each air film pore are calculated. mix,KE ′、ΔΣ mix,Q Summing these values ​​yields the total entropy increase ΔΣ. mix If a straight-leaf cascade model is used, the calculation process for symmetrical film air holes can be omitted.

[0049] Preferably, after step SS5 above, the following implementation steps are further included:

[0050] SS6. Based on the entropy increase ΔΣ of mixing mix Based on the size and evaluation results, the parameters for film cooling of the engine turbine blades are optimized, including but not limited to the cooling gas velocity v. c , jet angle α c Composite angle β c , spatial angle κ c Air conditioning temperature T c ;

[0051] SS7. Repeat steps SS1 to SS6 above until the mixing entropy increases by ΔΣ. mix The preset minimum value or the preset allowable range is reached.

[0052] Furthermore, in step SS6 above, the parameter optimization design uses a genetic algorithm or a particle swarm optimization algorithm for searching, in order to improve the efficiency and globality of the optimization search.

[0053] (III) Technical Effects

[0054] Compared with the prior art, the three-dimensional mixing loss assessment method for air film cooling of engine turbine blades of the present invention has the following beneficial and significant technical effects:

[0055] (1) The three-dimensional mixing loss assessment method for engine turbine blade film cooling of the present invention incorporates the changes in the local mainstream flow conditions into the loss assessment, assuming that the mixing process is jointly completed by the three-dimensional flowing cold gas jet and the equally three-dimensional mainstream flow. The method also considers the flow changes caused by secondary flow in both the mainstream and the jet cold gas. Both the mainstream and the mixing process are analyzed in a three-dimensional environment, making the calculation results more consistent with reality. Compared with the simplified or two-dimensional models commonly used in the prior art, the present invention can better reflect the relative motion and interaction between the mainstream gas and the jet cold gas in three spatial directions, thereby improving the accuracy and reliability of the mixing loss assessment method.

[0056] (2) This invention establishes a comprehensive and complete method for evaluating mixing losses by introducing parameters such as the mainstream Mach number, jet angle, recombination angle, and spatial angle. These parameters can fully consider the changes in physical quantities such as velocity, temperature, pressure, and density between the mainstream gas and the jet cooling gas under different operating conditions. Compared with the simplified processing methods in the prior art, this invention can more realistically simulate the energy conversion and loss during the mixing process, thereby more effectively evaluating the quality of the gas film cooling effect. Furthermore, most of the parameters involved in the calculation are simple to obtain, and the method is easy to implement in both numerical simulation and actual experiments, without consuming additional computing resources.

[0057] (3) The calculation method of this invention simplifies the entropy increase process of film cooling to the mixing of two airflows in space. It can be applied to flat plate cooling models and various turbine blade models, and is suitable for calculating and analyzing the mixing loss of film cooling at various locations on the blade. Compared with traditional methods that are only applicable to specific locations or specific models, this invention can more broadly cover various situations that may occur during the film cooling process of turbine blades, and has strong adaptability and flexibility. Attached Figure Description

[0058] Figure 1 The diagram shows the implementation flow of the three-dimensional mixing loss assessment method for air film cooling of engine turbine blades according to the present invention.

[0059] Figure 2 The diagram shows the overall structure of a turbine blade with film cooling holes.

[0060] Figure 3 The image shown is a top view of a turbine blade with film cooling holes.

[0061] Figure 4 The image shows a side view (suction surface) of a turbine blade with film cooling holes.

[0062] Figure 5 The diagram shows a three-dimensional mixing angle at a local air film pore.

[0063] Figure 6 The diagram shows the three-dimensional mixing velocity components at a local air film pore.

[0064] Explanation of reference numerals in the attached figures:

[0065] 1-Air film inlet

[0066] 2-Air film outlet

[0067] 3-Blade suction surface

[0068] 4-Leaf leading edge

[0069] 5-blade pressure surface

[0070] 6-blade trailing edge

[0071] V g - Mainstream speed

[0072] V gx -Main x-direction velocity

[0073] V gy -Main y-direction velocity

[0074] V gz -Main z-direction velocity

[0075] V c - Air conditioning speed

[0076] V cx - Velocity of the airflow in the x direction

[0077] V cy - Velocity of the cold air in the y direction

[0078] V cz -Z-axis velocity of the cold air

[0079] V m - Mixing speed

[0080] HG - Select the local mainstream distance from the vertical distance of the blade surface

[0081] α g - Mainstream jet angle

[0082] β g - Mainstream composite angles

[0083] k g - Mainstream spatial angles

[0084] α c - Air jet angle

[0085] β c -Complex angle of air conditioning

[0086] κc - Space angle of the air conditioner Detailed Implementation

[0087] To better understand the present invention, the following embodiments further illustrate its content. Throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The described embodiments are some, but not all, of the embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. 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. The structure and technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings, providing one embodiment of the present invention.

[0088] Example 1

[0089] like Figure 1 As shown, the three-dimensional mixing loss assessment method for engine turbine blade film cooling of the present invention includes at least the following steps when implemented:

[0090] SS1. Establish a full three-dimensional flow model to simulate the momentum exchange between the mainstream gas and the jet cooler during the film cooling process of turbine blades, where the mainstream velocity v g The components v in three mutually orthogonal spatial directions gx v gy v gz and the velocity v of the jet cooling air c The corresponding components v in three mutually orthogonal spatial directions cx v cy v cz All were considered, and the mainstream speed v g With the velocity v of the jet of cold air c The corresponding components together determine the mixing rate v after blending. m The corresponding components v in three mutually orthogonal spatial directions xm v ym v zm ;

[0091] SS2. Based on the law of conservation of momentum and the velocity components of the mainstream gas and the jet cooling gas, calculate the mixing velocity v after mixing the mainstream gas and the jet cooling gas using the following formula. m and its components v xm v ym v zm Size:

[0092]

[0093]

[0094]

[0095]

[0096] Where, m g and m c Let x, y, and z represent the mass flow rates of the mainstream gas and the jet cooler gas involved in the mixing, respectively. Subscripts x, y, and z represent three mutually orthogonal directions in space. Subscript g represents the mainstream parameters before mixing, subscript c represents the jet cooler gas parameters before mixing, and subscript m represents the parameters after mixing. α c Let β be the jet angle of the jet cooling gas and be defined as the angle between the component of the jet cooling gas in the xoy plane and the x-axis. c Let κ be the composite angle of the jet cooling gas and defined as the angle between the jet cooling gas and its components in the xoy plane. c The spatial angle of the jet cooling gas is defined as the angle between the jet cooling gas itself and the x-axis of the coordinate system.

[0097] SS3. Based on the mass flow rate, velocity, temperature, and enthalpy of the mainstream gas and the jet cooling gas involved in the mixing, and according to the law of conservation of energy, establish the energy equation that follows the mixing process:

[0098]

[0099] Among them, h g and h c T represents the enthalpy values ​​of the mainstream gas and the jet cooler gas involved in the mixing, respectively. g and T c T represents the temperatures of the mainstream gas and the jet cooler gas involved in the mixing, respectively. m This indicates the mixing temperature after the mainstream gas and the jet of cold gas are mixed.

[0100] SS4. Based on the energy equation established in step SS3, and according to the entropy increase principle formula... Calculate the mixing loss ΔΣ between the mainstream gas and the jet cooling gas. mix ,in:

[0101]

[0102] In the formula, δs, δh, and δp represent the entropy increase, enthalpy increase, and pressure change, respectively; ρ is the density; T is the temperature; p is the local pressure; and c pg c pc T represents the isobaric specific heat of the mainstream gas and the jet of cold air. m This refers to the mixing temperature;

[0103] SS5. The mixing loss ΔΣ between the mainstream gas and the jet cooling gas established in step SS4. mix The calculation formula is used to analyze the entropy increase ΔΣ caused by non-uniform mixing. mix,KE ′ and the entropy increase ΔΣ due to non-isothermal mixing mix,Q ′, and the information about the mixing rate v obtained in step SS2 m The expression is introduced into the calculation to obtain the final form of the entropy increase ΔΣ of the mixing of the mainstream gas and the jet cooling gas. mix The entropy increase effect of the mixing process is calculated to evaluate the effectiveness of film cooling for engine turbine blades.

[0104]

[0105]

[0106] ΔΣ′ mix =ΔΣ′ mix,Q +ΔΣ′ mix,KE

[0107] In the formula, γ g R g Ma g , and represent the specific heat ratio, gas constant, and Mach number of the mainstream gas, respectively.

[0108] Example 2

[0109] Based on Example 1, and while maintaining its inventive concept and main framework, this example further optimizes each step of Example 1 as a further optimized example.

[0110] In step SS1 above, to more accurately simulate the film cooling effect of turbine blades, a turbulence model including eddy currents should be considered when establishing a full three-dimensional flow model. The turbulence model uses a modified k-ωSST (Shear Stress Transport) turbulence model to better capture near-wall flow characteristics and achieve the mainstream velocity v. g and jet cooling air velocity v c Accurate calculations under turbulent conditions, and consequently the mixing velocity v m To conduct more detailed simulations.

[0111] In step SS2 above, the mixing velocity v after the mainstream gas and the jet cooling gas are mixed is calculated. m and its components v xm v ym v zmWhen calculating the mixing velocity, the influence of the pressure difference between the mainstream gas and the jet cooling gas is further considered to improve the accuracy and practicality of the calculation. The pressure difference will cause changes in the mass flow rate ratio and momentum flow rate ratio between the mainstream gas and the jet cooling gas, thus affecting the calculated mixing velocity. After considering the influence of the pressure difference, the mixing velocity v is expressed by the following formula. m and its components v xm v ym v zm Size:

[0112]

[0113]

[0114]

[0115]

[0116] In the formula, Δp is the pressure difference between the mainstream gas and the jet of cold gas, p g The pressure of the mainstream gas.

[0117] In step SS2 above, the mixing velocity v after the mainstream gas and the jet cooling gas are mixed is calculated. m and its components v xm v ym v zm When considering the magnitude of the mixing velocity, the effects of turbulent and viscous dissipation between the mainstream gas and the jet cooling gas are further taken into account. After considering the effects of turbulent and viscous dissipation, the mixing velocity v is expressed by the following formula. m and its components v xm v ym v zm Size:

[0118]

[0119]

[0120]

[0121]

[0122] In the formula, ε is the turbulent dissipation rate, τ is the viscous stress tensor, and ρ is the fluid density.

[0123] In step SS3 above, the mass flow rate m of the mainstream gas involved in the mixing gThis is not the total mass flow rate of the mainstream gas within the flow channel, but rather the mass flow rate of the mainstream gas that participates in mixing with the jet cooling gas within the mixing layer. The mixing layer is obtained based on mixing layer theory, and the mass flow rate m of the mainstream gas participating in mixing within the mixing layer is... g The value is typically 0.05-0.3 times the mainstream total mass flow rate.

[0124] In step SS4 above, the mixing loss ΔΣ between the mainstream gas and the jet cooling gas is calculated. mix Furthermore, the effects of turbulent and viscous dissipation between the mainstream gas and the jet cooling gas were also considered. After considering the effects of turbulent and viscous dissipation, the mixing loss ΔΣ is expressed by the following formula. mix :

[0125]

[0126] In the formula, ε t ε v These are the energy losses caused by turbulent dissipation and viscous dissipation between the mainstream gas and the jet of cold gas, respectively.

[0127] In step SS5 above, considering that the mainstream velocity near the suction surface increases and the temperature decreases as the exit Mach number increases, the temperature at the interface between the cold gas near the jet exit and the mainstream is selected as the mixing temperature T under high-speed conditions. m This allows for a more accurate reflection of the entropy increase caused by the absorption of heat by the cold air, thereby improving the accuracy of assessing mixing losses under high-speed operating conditions. For example, the mixing temperature T... m The temperature distribution at the outlet section is used to determine T. Specifically, the difference between the highest and lowest temperatures at the outlet section is multiplied by a fixed coefficient (e.g., 0.3), and then the lowest temperature is added to obtain the calculated T. m This represents the average temperature of the outlet section. By considering the temperature gradient of the outlet section when determining the blending temperature, it not only reflects the temperature difference between the highest and lowest temperatures, but also comprehensively considers the temperature distribution of the entire outlet section through averaging. This makes the selection of the blending temperature more consistent with the actual flow conditions and improves the accuracy of blending loss assessment.

[0128] In step SS5 above, a calculation is performed for each air film pore based on the different local mainstream parameters at each pore, and the two entropy increases ΔΣ at each air film pore are calculated. mix,KE ′、ΔΣ mix,Q Summing these values ​​yields the total entropy increase ΔΣ. mix If a straight-leaf cascade model is used, the calculation process for symmetrical film air holes can be omitted.

[0129] Following step SS5 above, the following implementation steps are also included:

[0130] SS6. Based on the entropy increase ΔΣ of mixing mix Based on the size and evaluation results, the parameters for film cooling of the engine turbine blades are optimized, including but not limited to the cooling gas velocity v. c , jet angle α c Composite angle β c , spatial angle κ c Air conditioning temperature T c ;

[0131] SS7. Repeat steps SS1 to SS6 above until the mixing entropy increases by ΔΣ. mix The preset minimum value or the preset allowable range is reached.

[0132] In step SS6 above, the parameter optimization design uses a genetic algorithm or particle swarm optimization algorithm to search for parameters, so as to improve the efficiency and globality of the optimization process.

[0133] Example 3

[0134] Based on Example 1, while maintaining its inventive concept and main framework, this example provides further illustrations of Example 1.

[0135] Due to the mainstream speed v in three dimensions g The components in all three directions are not negligible, therefore its relationship with cold air v c The mixing speed v after blending m The components v in the three directions xm v ym and v zm Both are composed of the corresponding directional components of the mainstream and the cold air velocity. Figure 2 and Figure 3 A schematic diagram of the mainstream and cold air velocity is given. In the diagram, 1 is the inlet of the film cooling vent, 2 is the outlet of the film cooling vent, 3 is the suction surface of the blade, 4 is the leading edge of the blade, 5 is the pressure surface of the blade, and 6 is the trailing edge of the blade. g As the mainstream speed, V gx As the main velocity component in the x-direction, V gy Assuming the velocity is in the mainstream y-direction, V gz As the main component of velocity in the z-direction, V c V represents the air conditioning speed. cx Let V be the velocity component of the cold air in the x-direction. cy Let V be the velocity component of the cold air in the y-direction. cz Let V be the velocity component of the cold air in the z-direction. mHG represents the mixing velocity, where HG is the vertical distance from the local mainstream to the blade surface. The mainstream and cold air component velocities can be expressed according to the law of conservation of momentum as equations (1)-(3). Including the latter equation, the subscript m represents the parameter after mixing, the subscript g represents the mainstream parameter before mixing, and the subscript c represents the cold air parameter before mixing. In the equations, the subscripts x, y, and z represent the component velocities in the corresponding directions, for example, v0. gx This represents the component of the mainstream velocity in the x-direction, and the mixing velocity is indicated by [reference needed]. Figure 4 .

[0136] Equations (1)-(3) define the angles of the cooling air, and the specific angle definitions can be found in [link to definition]. Figure 5 Jet angle α c The angle between the component of the cold air in the xoy plane and the x-axis represents the degree of displacement of the cold air in the y-direction; the composite angle β c The angle between the cold air and its component in the xoy plane represents the degree of displacement of the cold air in the spanwise direction, i.e., the z-direction; the spatial angle κ c This refers to the angle between the airflow itself and the x-axis of the coordinate system. In reality, this definition doesn't strictly depend on the coordinate system setting; it's just more convenient to use the default coordinate system in simulation calculations. For detailed local velocity components under the default coordinate system, see [link to relevant documentation]. Figure 6 .

[0137]

[0138]

[0139]

[0140] The mixing velocity v is obtained by combining the mixing velocities in the three directions. m See equation (4).

[0141]

[0142] The established energy equation for the mixing process is shown in equation (5). Combining equations (5) and (6) yields the mixing loss as shown in equation (7). Equations (5) and (6), in addition to the velocities of the main stream and the cold air, also involve the mass flow rate m, local pressure p, local density ρ, enthalpy h, and temperature T. It is worth noting that m... g It is not the total mainstream mass flow rate within the flow channel, but rather the mainstream mass flow rate within the mixing layer that is mixed with the cold air. The mixing layer is obtained based on existing mixing layer theories, and the mainstream mass flow rate within the layer is generally taken as 0.05-0.3 times the total mainstream mass flow rate.

[0143]

[0144]

[0145]

[0146] In equation (7), since it is generally believed that the mainstream temperature is the highest and the cold air temperature is the lowest, the entropy increase of the mainstream part due to non-isothermal heat transfer is negative during the mixing process, but the entropy of the entire system increases. Separate the terms containing velocity and temperature in equation (7) and substitute them into v in equation (4). m Equations (8) and (9) are obtained, namely, the entropy increase ΔΣ for non-uniform mixing. mix,KE Entropy increase ΔΣ when mixed with non-isothermal materials mix,Q The sum of the two is expressed by equation (10), ΔΣ mix ′ is the final form of entropy increase due to mixing, which is equivalent to equation (7).

[0147]

[0148]

[0149] ΔΣ mix ′=ΔΣ mix,Q ′+ΔΣ mix,KE ′ (10)

[0150] In equations (8) to (10), γ is the specific heat ratio, R is the gas constant, Ma is the Mach number, and c p This represents the specific heat at constant pressure. As the Mach number at the outlet increases, the mainstream velocity near the suction surface continuously rises, and the temperature drop along the flow direction becomes more pronounced. Under high-speed conditions, the temperature drop at the outlet cannot be ignored; therefore, the temperature near the interface between the cold air at the outlet and the mainstream is selected as the mixing temperature T. m It can more accurately measure the entropy increase caused by the absorption of heat by the cold air.

[0151] More specifically, post-processing mixing loss can be calculated based on completed CFX numerical calculation cases:

[0152] First, record the mainstream mass flow rate within the channel, using the integral of the mass flow rate at the inlet as the standard. Based on existing theories of mixed layers, the mixed portion of the mainstream mass accounts for 0.05-0.3% of the total mainstream mass, and changes in this value have little impact on loss calculation. Therefore, for the local film vent, the mainstream mass flow rate m near it is... g In practice, it can be defined as (0.2 / total number of pores) times the total mainstream mass, with the flow direction distance of 1-3 times the pore diameter upstream of the film pore, and the value taken at the vertical distance HG from the suction surface as the local mainstream velocity and temperature T near the film pore. gBased on existing research, HG can use 0.04 times the chord length. This distance is relatively close to the blade surface, but not so close that it is affected by the cooling air. The difference between using the shortest line to calculate the average value and using point values ​​for the parameter is not significant. After obtaining the mainstream parameters, the velocities in each direction can be obtained. For ease of operation, the three-dimensional components can be determined using the default coordinate system. Based on the velocities, the jet angle α of the mainstream can be determined. g Composite angle β g and spatial angle κ g The spatial angle is the angle between the velocity and the x-axis of the coordinate system.

[0153] First, record the mass flow rate (m) of the cold air inside the air film vent. c With average static temperature T c According to existing research, there is a characteristic interface within the film gas vent, namely a plane perpendicular to the vent axis and tangent to the upstream portion of the vent outlet boundary curve. This portion is taken as the region for the cold gas parameters emanating from the corresponding film gas vent. The average velocity component in this region is obtained, and thus the jet angle α of the cold gas is derived. c Composite angle β c and spatial angle κ c .

[0154] However, if the temperature is taken at the same location, considering that the mixing process essentially references the initial and final main jet parameters, the results will have a large error under high-speed conditions. Therefore, the mixing temperature T m The temperature at the mixing interface of the main jet closer to the outlet increases with the increase of flow distance. The channel vortex absorbs some cool air, and its influence on the overall flow becomes increasingly significant. The interface temperature can be defined as: (highest outlet section temperature - lowest outlet section temperature) × 0.3 + lowest outlet section temperature. The mass average of this value over the outlet section is the mixing temperature T. m .

[0155] Since the local mainstream parameters differ at each pore, the above process requires calculation at each film gas pore. If a straight-leaf cascade model is used, the calculation process for symmetrical film gas pores can be omitted. According to formulas (9)-(11), the non-uniform mixing entropy increase ΔΣ of a single film gas pore can be obtained. mix,KE Entropy increase ΔΣ when mixed with non-isothermal materials mix,Q By summing the entropy increases of the two parts of each air film pore, we can obtain the total mixing entropy increase ΔΣ. mix ′.

[0156] The objectives of this invention have been fully and effectively achieved through the above embodiments. Those skilled in the art will understand that this invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments described above. Although the invention has been described with reference to what is currently considered the most practical and preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments, and any modifications that do not depart from the functional and structural principles of the invention will be included within the scope of the claims.

Claims

1. A three-dimensional method for evaluating the mixing loss of engine turbine blade film cooling, characterized in that, The evaluation method includes at least the following implementation steps: SS1. Establish a full three-dimensional flow model to simulate the momentum exchange between the mainstream gas and the jet cooler during the film cooling process of turbine blades, where the mainstream velocity v g The components v in three mutually orthogonal spatial directions gx v gy v gz and the velocity v of the jet cooling air c The corresponding components v in three mutually orthogonal spatial directions cx v cy v cz All were considered, and the mainstream speed v g With the velocity v of the jet of cold air c The corresponding components together determine the mixing rate v after blending. m The corresponding components v in three mutually orthogonal spatial directions xm v ym v zm ; SS2. Based on the law of conservation of momentum and the velocity components of the mainstream gas and the jet cooling gas, calculate the mixing velocity v after mixing the mainstream gas and the jet cooling gas using the following formula. m and its components v xm v ym v zm Size: Where, m g and m c Let x, y, and z represent the mass flow rates of the mainstream gas and the jet cooler gas involved in the mixing, respectively. Subscripts x, y, and z represent three mutually orthogonal directions in space. Subscript g represents the mainstream parameters before mixing, subscript c represents the jet cooler gas parameters before mixing, and subscript m represents the parameters after mixing. α c Let β be the jet angle of the jet cooling gas and be defined as the angle between the component of the jet cooling gas in the xoy plane and the x-axis. c The composite angle of the jet cooling gas is defined as the angle between the jet cooling gas and its components in the xoy plane, κ. c The spatial angle of the jet cooling gas is defined as the angle between the jet cooling gas itself and the x-axis of the coordinate system. SS3. Based on the mass flow rate, velocity, temperature, and enthalpy of the mainstream gas and the jet cooling gas involved in the mixing, and according to the law of conservation of energy, establish the energy equation that follows the mixing process: Among them, h g and h c T represents the enthalpy values ​​of the mainstream gas and the jet cooler gas involved in the mixing, respectively. g and T c T represents the temperatures of the mainstream gas and the jet cooler gas involved in the mixing, respectively. m This indicates the mixing temperature after the mainstream gas and the jet of cold gas are mixed. SS4. Based on the energy equation established in step SS3, and according to the entropy increase principle formula... Calculate the mixing loss ΔΣ between the mainstream gas and the jet cooling gas. mix ,in: In the formula, δs, δh, and δp represent the entropy increase, enthalpy increase, and pressure change, respectively; ρ is the density; T is the temperature; p is the local pressure; and c pg c pc T represents the isobaric specific heat of the mainstream gas and the jet of cold air. m This refers to the mixing temperature; SS5. The mixing loss ΔΣ between the mainstream gas and the jet cooling gas established in step SS4. mix The calculation formula is used to analyze the entropy increase ΔΣ caused by non-uniform mixing. mix,KE ′ and the entropy increase ΔΣ due to non-isothermal mixing mix,Q ′, and the information about the mixing rate v obtained in step SS2 m The expression is introduced into the calculation to obtain the final form of the entropy increase ΔΣ of the mixing of the mainstream gas and the jet cooling gas. mix The entropy increase effect of the mixing process is calculated to evaluate the effectiveness of film cooling for engine turbine blades. DS′ mix =DS′ mix,Q +DS′ mix,KE In the formula, γ g R g Ma g , , represent the specific heat ratio, gas constant, and Mach number of the mainstream gas, respectively.

2. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, In step SS1 above, to more accurately simulate the film cooling effect of turbine blades, a turbulence model including eddy currents should be considered when establishing a full three-dimensional flow model. The turbulence model uses a modified k-ωSST turbulence model to better capture near-wall flow characteristics and achieve the mainstream velocity v. g and jet cooling air velocity v c Accurate calculations under turbulent conditions, and consequently the mixing velocity v m To conduct more detailed simulations.

3. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, In step SS2 above, the mixing velocity v after the mainstream gas and the jet cooling gas are mixed is calculated. m and its components v xm v ym v zm When calculating the mixing velocity, the influence of the pressure difference between the mainstream gas and the jet cooling gas is further considered to improve the accuracy and practicality of the calculation. The pressure difference will cause changes in the mass flow rate ratio and momentum flow rate ratio between the mainstream gas and the jet cooling gas, thus affecting the calculated mixing velocity. After considering the influence of the pressure difference, the mixing velocity v is expressed by the following formula. m and its components v xm v ym v zm Size: In the formula, Δp is the pressure difference between the mainstream gas and the jet of cold gas, p g The pressure of the mainstream gas.

4. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, In step SS2 above, the mixing velocity v after the mainstream gas and the jet cooling gas are mixed is calculated. m and its components v xm v ym v zm When calculating the mixing velocity, the effects of turbulent and viscous dissipation between the mainstream gas and the jet cooler are further considered. Turbulent and viscous dissipation cause the kinetic energy between the mainstream gas and the jet cooler to be converted into internal energy, thus affecting the calculated mixing velocity. After considering the effects of turbulent and viscous dissipation, the mixing velocity v is expressed by the following formula. m and its components v xm v ym v zm Size: In the formula, ε is the turbulent dissipation rate, τ is the viscous stress tensor, and ρ is the fluid density.

5. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, In step SS3 above, the mass flow rate m of the mainstream gas involved in the mixing g This is not the total mass flow rate of the mainstream gas within the flow channel, but rather the mass flow rate of the mainstream gas that participates in mixing with the jet cooling gas within the mixing layer. The mixing layer is obtained based on mixing layer theory, and the mass flow rate m of the mainstream gas participating in mixing within the mixing layer is... g The value is typically 0.05-0.3 times the mainstream total mass flow rate.

6. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, In step SS5 above, considering that the mainstream velocity near the suction surface increases and the temperature decreases as the exit Mach number increases, the temperature at the interface between the cold gas near the jet exit and the mainstream is selected as the mixing temperature T under high-speed conditions. m This will more accurately reflect the entropy increase caused by the absorption of heat by the cold air, thereby improving the accuracy of assessing mixing losses under high-speed operating conditions.

7. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 6, characterized in that, Blending temperature T m The temperature distribution at the outlet section is used to determine T. Specifically, the difference between the highest and lowest temperatures at the outlet section is multiplied by a fixed coefficient, and then the lowest temperature is added to calculate T. m This represents the average temperature of the outlet section.

8. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, In step SS5 above, a calculation is performed for each air film pore based on the different local mainstream parameters at each pore, and the entropy increase ΔΣ at each air film pore is calculated. mix,KE and entropy increase ΔΣ mix,Q Summing these values ​​yields the total entropy increase ΔΣ. mix ′.

9. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 8, characterized in that, If a straight-leaf cascade model is used, the above calculations for symmetrical film vents are omitted.

10. The method for evaluating the full three-dimensional mixing loss of engine turbine blade film cooling according to claim 1, characterized in that, Following step SS5 above, the following implementation steps are also included: SS6. Based on the entropy increase ΔΣ of mixing mix Based on the size and evaluation results, the parameters for film cooling of the engine turbine blades are optimized, including but not limited to the cooling gas velocity v. c , jet angle α c Composite angle β c , spatial angle κ c Air conditioning temperature T c ; SS7. Repeat steps SS1 to SS6 above until the mixing entropy increases by ΔΣ. mix The preset minimum value or the preset allowable range is reached.

Images