A new method for oil-cooled blade structure design

Abstract

The application discloses a new method suitable for oil-cooled blade structure design, and belongs to the field of high-temperature thermal protection of an aero-engine, and comprises the following steps: 1. numerical simulation calculation of an external flow field to obtain a blade external surface thermal environment; 2. determination of fuel physical properties, limitation of a blade external surface average temperature, a fuel outlet average temperature and a fuel and blade solid interface temperature according to a blade material, and calculation of required cooling fuel flow; 3. design of an internal cooling channel structure; 4. determination of an internal cooling structure average temperature; 5. calculation of a sandwich thickness between a blade shell and the internal cooling channel structure; 6. determination of a sandwich structure design scheme; and 7. three-dimensional numerical simulation calculation of the oil-cooled blade structure, provision of an optimized improvement scheme of the internal cooling channel structure and determination of the design scheme of the oil-cooled blade structure. The oil-cooled turbine blade structure is decoupled into a blade shell, a sandwich and an internal cooling heat conduction structure for separate design, so that the difficulty of structure design is simplified, and energy utilization is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high-temperature protection of aero-engines, and particularly relates to a new method suitable for oil-cooled blade structure design. BACKGROUND

[0002] The performance of an aero-engine is mainly improved by increasing the turbine inlet temperature, and the turbine inlet temperature is now close to 2000K, far exceeding the heat resistance limit of turbine blade materials. The turbine blade needs to withstand a huge thermal load at high temperature, in addition to the huge centrifugal load caused by high-speed rotation of the turbine blade. Therefore, it is very important to use advanced cooling technology to protect the turbine blade from heat. The traditional turbine blade uses film cooling method for cooling, using air as the cooling medium. This method needs to extract high-pressure cooling gas from the compressor part, and the amount of extracted air increases with the increase of temperature, thus increasing the demand for high-pressure cooling gas, which ultimately leads to waste of high-pressure gas. For example, for a working condition with a turbine inlet temperature of 1900K, at least about 15% of the air from the compressor needs to be extracted for turbine cooling. And with the increase of the pressure ratio of the compressor, the temperature of the available high-pressure cooling gas is also increasing, and its cooling capacity is decreasing.

[0003] Compared with air, the fuel carried by the aircraft has the following advantages: 1. High convective heat transfer coefficient, low inlet temperature, and strong heat absorption capacity. It not only can absorb heat through physical heat sink, but also can realize chemical heat sink heat absorption through cracking reaction, and has good heat absorption capacity. 2. The cooled fuel can take the absorbed heat back to the combustion chamber for reuse, improving energy utilization. However, due to the coking characteristics of fuel, the outlet temperature of the fuel is limited (≯423K), and the temperature of the fuel-solid interface is also limited (≯500K), so the heat absorption capacity of the fuel is limited. Therefore, the traditional air-cooled blade structure design method is no longer suitable for the structure design of oil-cooled blades, and thus a new method suitable for oil-cooled blade structure design is proposed.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide a new method suitable for oil-cooled blade structure design. To solve the above technical problems, the basic idea of the technical solution adopted by the present application is:

[0006] A new method suitable for oil-cooled blade structure design, comprising the following steps:

[0007] Step 1, calculate the heat environment of the outer surface of the blade according to the numerical simulation of the outer flow field, and obtain the adiabatic wall temperature t g of the outer surface of the blade, the convective heat transfer coefficient hg ;

[0008] Step 2, determining fuel property, limiting the average temperature t of the outer surface of the blade according to the blade material w1 , limiting the average temperature t1" of the fuel outlet according to the coking property of the fuel, and the temperature (500K) of the interface between the fuel and the blade solid, calculating the required cooling fuel flow m;

[0009] Step 3, designing the structure of the internal cooling channel: initially assuming the structure of the internal cooling fuel channel by designing the diameter D, the number of revolutions n and the length L of the internal cooling fuel channel, calculating the convective heat transfer coefficient in the pipe by using the empirical correlation of flow and heat transfer, calculating the heat absorption, temperature rise and pressure loss of the fuel in the cooling channel, judging whether the design of the structure of the internal cooling fuel channel is reasonable and until the design requirements are met;

[0010] Step 4, determining the average temperature t of the internal cooling structure w2 : calculating the convective heat transfer coefficient h of the internal cooling channel according to the designed structure of the internal cooling channel, the calculated required cooling fuel flow m and the average temperature t1" of the fuel outlet, making the heat Q' absorbed by the fuel cooling equal to the heat Q released by the gas on the outer surface of the blade, combining the average temperatures of the fuel inlet and outlet w2 ;

[0011] Step 5, calculating the thickness δ of the interlayer between the outer shell of the blade and the internal cooling channel structure;

[0012] Step 6, determining the design scheme of the interlayer structure: selecting different material media for filling according to the calculated thickness δ of the interlayer.

[0013] Step 7, carrying out three-dimensional numerical simulation calculation on the oil-cooled blade structure, proposing an optimization and improvement scheme of the internal cooling channel structure, and determining the final design scheme of the oil-cooled blade structure.

[0014] Further, the step 1 is specifically:

[0015] Step 11, according to the known outflow field parameters, giving boundary conditions, carrying out the first group of calculations, and obtaining the adiabatic wall temperature t of the outer surface of the blade g ; wherein the given boundary conditions include the inlet boundary condition, the outlet boundary condition and the wall boundary condition, the inlet boundary condition is the pressure and temperature inlet, the outlet boundary condition is the pressure outlet, and the wall boundary condition is the adiabatic wall;

[0016] Step 12, setting the wall boundary condition as a constant temperature boundary to carry out the second group of calculations, obtaining the heat flux density q of the outer surface of the blade, and calculating the convective heat transfer coefficient h of the outer surface of the blade according to the following formula g :

[0017]

[0018] where t w is the given blade wall temperature, t w = t g - 100.

[0019] Further, the calculation of the required cooling fuel flow m in step 2 is through the following process:

[0020] Step 21, calculate the heat Q released by the gas on the blade outer surface:

[0021] Q =∑h g A g (t g -t w1 ) (2)

[0022] where A g is the blade outer surface area;

[0023] Step 22, calculate the heat Q' absorbed by the fuel cooling:

[0024] Q' = mc p (t1" - t1') (3)

[0025] where c p is the specific heat capacity of the fuel at constant pressure, t1' is the average temperature of the fuel inlet;

[0026] Step 23, set the heat Q' absorbed by the fuel cooling equal to the heat Q released by the gas on the blade outer surface, and calculate the cooling fuel flow m as:

[0027]

[0028] Further, step 3 is specifically:

[0029] Step 31, preliminarily assume the structure of the internal cooling fuel channel by designing the diameter D, the number of revolutions n, and the length L of the channel;

[0030] Step 32, take the fuel inlet temperature t1' as the qualitative temperature, and calculate the convective heat transfer coefficient and the fuel heat absorption of the first section of the channel according to the empirical correlation of flow heat transfer;

[0031] Step 33, calculate the fuel temperature rise and the average fuel temperature from the fuel heat absorption;

[0032] Step 34, take the average fuel temperature as the qualitative temperature and perform a cyclic iteration on this step until the accurate heat absorption, temperature rise, and corresponding qualitative temperature are solved, and the fuel pressure loss in this section of the channel is solved with the qualitative temperature.

[0033] Step 35, for each section of the channel, the method of steps 32 to 35 is used to solve, and the heat absorption, temperature rise and pressure loss of the fuel are accumulated, and finally the heat absorption Q' of the fuel in the whole cooling channel is obtained;

[0034] Step 36, judge whether the internal cooling fuel channel structure design is reasonable: if the heat Q released by the gas on the outer surface of the blade is less than the heat Q' absorbed by the fuel cooling, it means that this structure meets the design requirements; otherwise, return to step 31 to redesign the structure until the design requirements are met.

[0035] Further, step 5 is specifically:

[0036] Step 51, calculate the interlayer thermal resistance R according to the obtained parameters:

[0037]

[0038] Where t w1 is the average temperature of the outer surface of the blade, t w2 is the average temperature of the internal cooling channel structure, and Q is the heat released by the gas on the outer surface of the blade.

[0039] Step 52, calculate the interlayer thickness δ according to the interlayer thermal resistance:

[0040]

[0041] Where λ is the thermal conductivity.

[0042] Further, in step 32, the flow heat transfer empirical correlation uses the existing empirical formula obtained by experiment, as follows:

[0043] For standard pipes:

[0044]

[0045] 2300≤Re≤100000

[0046] Where,

[0047] ξ=(1.82lgRe-1.64) -2 (8)

[0048] Straight pipe section:

[0049] Nu z =Nu s ·ε L (9)

[0050] Where,

[0051]

[0052] Bend section:

[0053] Nu w Nu s ·ε R (11)

[0054] In the formula,

[0055]

[0056] d i is the equivalent diameter, and R is the radius of curvature at the bend.

[0057] In the above formula, ε L is the inlet effect correction coefficient, and ε R is the bend section correction coefficient.

[0058] The average Nusselt number in the pipe is calculated as follows:

[0059]

[0060] In the formula, L w is the total length of the bend section, and L z is the total length of the straight section.

[0061] When the Reynolds number is less than 2300, i.e., the fluid is in a laminar state, according to theoretical calculation, the Nusselt number for a circular pipe is 3.66.

[0062] After the above technical solution, the present application has the following beneficial effects compared with the prior art.

[0063] The oil-cooled turbine blade structure is decoupled into a blade shell, a sandwich, and an internal cooling heat conduction structure in the present application, which are designed separately, so that the difficulty of structural design is simplified. Unlike the traditional air-cooled blade structure design, the fuel carried by the aircraft itself is used as the cooling medium, which not only effectively reduces the temperature of the turbine blade, but also reduces the waste of high-pressure cooling air. The heat absorbed by the fuel after cooling the high-temperature components can be used for combustion, thereby improving the energy utilization rate.

[0064] The specific embodiments of the present application will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0065] The drawings are part of the present application and serve to provide a further understanding of the present application. The schematic embodiments of the present application and their descriptions serve to explain the present application, but do not constitute an improper limitation on the present application. Obviously, the drawings described below are only some embodiments, and other drawings can be obtained from these drawings by those of ordinary skill in the art without creative labor. In the drawings:

[0066] Fig. 1 is a schematic diagram of a simplified structure of a blade of the present application;

[0067] Fig. 2 is a schematic diagram of a flow chart of a design scheme of the present application.

[0068] It should be noted that these drawings and written descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0069] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments will be described clearly and completely below in conjunction with the drawings of the embodiments of the present application. The following embodiments are used to illustrate the present application, but not to limit the scope of the present application.

[0070] Since the fuel has the coking property, the outlet temperature of the fuel is limited, and the temperature of the interface between the fuel and the solid is also limited. The traditional air-cooled blade structure design method is no longer applicable to the structure design of the oil-cooled blade, and therefore we propose a new method applicable to the structure design of the oil-cooled blade: a method of decoupling the oil-cooled turbine blade structure into three parts (blade shell, interlayer and internal cooling heat conduction structure) for separate design.

[0071] In conjunction with the drawings, Figs. 1-2 , the new method applicable to the structure design of the oil-cooled blade of the present application comprises the following steps:

[0072] Step 1: Numerical simulation of the external flow field to calculate the thermal environment of the outer surface of the blade.

[0073] First, a first group of calculations is performed according to the given inlet boundary conditions of pressure and temperature, the outlet boundary condition of pressure outlet and the constraint of the adiabatic wall boundary condition of the wall surface, to obtain the adiabatic wall temperature t g of the outer surface of the blade; then a second group of calculations is performed by setting the wall boundary condition as a constant temperature boundary (the blade wall temperature is given as t w , t w =t g -100), to obtain the heat flux density q of the outer surface of the blade, and the convective heat transfer coefficient h g of the outer surface of the blade is calculated according to the formula. The convective heat transfer coefficient h g of the outer surface of the blade is:

[0074]

[0075] Step 2: Determine the fuel properties, and limit the average temperature t w1The required cooling fuel flow rate m is calculated according to the coking characteristics of the fuel, the limitation of the fuel outlet average temperature t1" and the fuel and blade solid interface temperature (500K).

[0076] The heat Q released by the fuel gas on the outer surface of the blade is:

[0077] Q =∑h g A g (t g -t w1 ) (2)

[0078] Where A g is the outer surface area of the blade.

[0079] The heat Q' absorbed by the fuel cooling is:

[0080] Q' = mc p (t1" - t1') (3)

[0081] Where c p is the specific heat capacity of the fuel at constant pressure, and t1' is the fuel inlet average temperature.

[0082] Since the heat Q' absorbed by the fuel cooling is equal to the heat Q released by the fuel gas on the outer surface of the blade, the cooling fuel flow rate m can be calculated as:

[0083]

[0084] Step 3, design the internal cooling channel structure.

[0085] The structure of the internal cooling fuel channel is initially assumed by designing the diameter D, the number of revolutions n and the length L of the channel, the convective heat transfer coefficient in the tube is calculated using the flow and heat transfer empirical correlation, and the heat absorption, temperature rise and pressure loss of the fuel in the cooling channel are calculated.

[0086] The specific calculation method is: assuming that the temperature of the heat conduction plate is uniform, the fuel in the channel is equal wall temperature heat transfer, the cooling channel is discretized into straight pipe section and elbow pipe section, and the relationship between the fuel property and temperature in the channel is fitted by piecewise polynomial. First, the fuel inlet temperature t1' is taken as the qualitative temperature, the convective heat transfer coefficient of the first section channel and the fuel heat absorption are calculated according to the empirical relationship, then the fuel temperature rise and the fuel average temperature are calculated from the fuel heat absorption, then the fuel average temperature is taken as the qualitative temperature, and the above step is iterated until the accurate heat absorption, temperature rise and corresponding qualitative temperature are solved, and the fuel pressure loss in the channel is solved according to the qualitative temperature. Repeat the above process, and the heat absorption, temperature rise and pressure loss of the fuel are accumulated for each section of the channel, and finally the heat absorption Q' of the fuel in the whole cooling channel is obtained. It should be noted that: in this calculation process, due to the sharp change of fuel property with temperature, the influence of fuel property change on flow and heat transfer should be considered, and the convective heat transfer coefficient in the pipe is corrected according to the fuel temperature rise.

[0087] Determine whether the internal cooling fuel channel structure design is reasonable: if the heat Q released by the gas on the outer surface of the blade is less than the heat Q' absorbed by the fuel cooling, it is explained that the structure meets the design requirements; Otherwise, the structure needs to be redesigned until the design requirements are met.

[0088] Step 4, determine the average temperature t of the internal cooling structure w2 .

[0089] According to the designed internal cooling channel structure and the calculated required cooling fuel flow m and fuel outlet average temperature t1'', the convective heat transfer coefficient h of the internal cooling channel is calculated, the heat Q' absorbed by the fuel cooling is equal to the heat Q released by the gas on the outer surface of the blade, and the average temperature of the fuel inlet and outlet The actual temperature of the fuel and solid interface can be calculated, that is, the average temperature t of the internal cooling channel structure w2 .

[0090] Step 5, calculate the thickness δ of the interlayer between the blade shell and the internal cooling channel structure.

[0091] First, calculate the interlayer thermal resistance R according to the obtained parameters:

[0092]

[0093] Where t w1 is the average temperature of the outer surface of the blade, t w2 is the average temperature of the internal cooling channel structure, and Q is the heat released by the gas on the outer surface of the blade.

[0094] Then calculate the thickness δ of the interlayer according to the interlayer thermal resistance:

[0095]

[0096] wherein lambda is the thermal conductivity.

[0097] Step 6, determine the sandwich structure design scheme.

[0098] According to the calculated sandwich thickness delta, select different material media to fill.

[0099] Step 7, three-dimensional numerical simulation calculation is carried out on the oil-cooled blade structure, the optimization improvement scheme of the internal cooling channel structure is put forward, and finally the design scheme of the oil-cooled blade structure is determined.

[0100] The method proposes the following assumptions based on the characteristics of fuel: 1. The blade is a thin-walled part, which meets the lumped parameter assumption, and the blade surface temperature is considered uniform; 2. The internal cooling heat conduction structure has good heat dissipation performance and meets the uniform temperature assumption. For the specific structure that meets the above assumptions, decoupling design is carried out, and the blade structure is decoupled into three parts for separate design, so that the difficulty of structure design is simplified. In addition, the fuel carried by the aircraft itself is used as the cooling medium, which not only effectively reduces the temperature of the turbine blade, but also reduces the waste of high-pressure cooling air. The heat absorbed by the fuel after cooling the high-temperature part can be used for combustion, improving the energy utilization rate.

[0101] The above only describes the preferred embodiments of the present application and does not limit the present application in any form. Although the present application has been disclosed as above, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above-mentioned technical content without departing from the scope of the technical solution of the present application, and any simple modification, equivalent change and modification of the above-mentioned embodiments within the scope of the present application are still within the scope of the present application.

Claims

1. A new method suitable for oil-cooled blade structural design, characterized by, The method comprises the following steps: Step 1, calculate the heat environment of the blade outer surface according to the numerical simulation of the external flow field, and obtain the adiabatic wall temperature t of the blade outer surface g , the convective heat transfer coefficient h of the blade outer surface g ; Step 2, determine fuel properties, limit blade outer surface average temperature t according to blade material w1 Calculate required cooling fuel flow rate m according to fuel coking characteristics limit fuel outlet average temperature t1", and fuel and blade solid interface temperature Step 3, designing the internal cooling channel structure: the structure of the internal cooling fuel channel is initially assumed by designing the diameter D, the number of turns n and the length L of the internal fuel cooling channel, the heat absorption amount, the temperature rise and the pressure loss of the fuel in the cooling channel are calculated by using the flow heat empirical correlation formula to calculate the convective heat transfer coefficient in the pipe, and it is judged whether the internal cooling fuel channel structure design is reasonable and meets the design requirements; Step 4, determine the average temperature t of the internal cooling structure w2 : According to the designed internal cooling channel structure, the calculated required cooling fuel flow m and the average temperature t1" of the fuel outlet, the convective heat transfer coefficient h of the internal cooling channel is calculated, the heat Q' absorbed by the fuel cooling is equal to the heat Q released by the gas on the outer surface of the blade, combined with the average temperature of the fuel inlet and outlet The average temperature t of the internal cooling structure is calculated w2 ; Step 5, calculating the thickness δ of the interlayer between the blade shell and the internal cooling channel structure; Step 6, determining the interlayer structure design scheme: according to the calculated interlayer thickness δ, different material media are selected for filling; Step 7, carrying out three-dimensional numerical simulation calculation on the oil-cooled blade structure, proposing an optimization and improvement scheme of the internal cooling channel structure, and determining the final oil-cooled blade structure design scheme.

2. A new method suitable for oil cooled blade design according to claim 1, characterized in that: The step 1 is specifically: Step 11, according to the known external flow field parameters, the given boundary conditions are performed to obtain the first set of calculations, and the adiabatic wall temperature t of the outer surface of the blade is obtained g ; wherein the given boundary conditions include an inlet boundary condition, an outlet boundary condition, and a wall boundary condition, the inlet boundary condition is a pressure and temperature inlet, the outlet boundary condition is a pressure outlet, and the wall boundary condition is an adiabatic wall. Step 12, the wall boundary conditions are set to a constant temperature boundary for a second set of calculations to obtain the heat flux density q of the blade outer surface, and the convective heat transfer coefficient h of the blade outer surface is calculated according to the following formula g : （1） where t w is the temperature of the blade wall surface, t w= is the temperature of the blade root surface, and t g -100.

3. A new method suitable for oil cooled blade design according to claim 1, characterized in that: The calculation of the required cooling fuel flow m in the step 2 is carried out through the following process: Step 21, calculating the heat Q released by the gas on the outer surface of the blade: （2） wherein A g is the outer surface area of the blade; Step 22, calculating the heat Q' absorbed by the fuel cooling: （3） where c p is the specific heat capacity of the fuel at constant pressure, and t1' is the average temperature of the fuel at the inlet. Step 23, setting the heat Q' absorbed by the fuel cooling equal to the heat Q released by the gas on the outer surface of the blade, and calculating the cooling fuel flow m as: （4）。 4. A new method suitable for oil cooled blade design according to claim 3, characterized in that: The step 3 is specifically: Step 31, initially assuming the structure of the internal cooling fuel channel by designing the diameter D, the number of turns n and the length L of the internal fuel cooling channel; Step 32, taking the fuel inlet temperature t1' as the qualitative temperature, and calculating the convective heat transfer coefficient and the heat absorption amount of the fuel in the first section according to the flow heat empirical correlation formula; Step 33, calculating the temperature rise and the average temperature of the fuel from the heat absorption amount of the fuel; Step 34, carrying out cyclic iteration on this step by taking the average temperature of the fuel as the qualitative temperature, until the accurate heat absorption amount, temperature rise and corresponding qualitative temperature are solved, and the fuel pressure loss in the section is solved according to the qualitative temperature; Step 35, the solving method of steps 32 to 35 is used for each section, and the heat absorption amount, temperature rise and pressure loss coefficient of the fuel are accumulated, and finally the heat absorption amount Q' of the fuel in the whole cooling channel is obtained; Step 36, judging whether the internal cooling fuel channel structure design is reasonable: if the heat Q released by the gas on the outer surface of the blade is less than the heat Q' absorbed by the fuel cooling, it is indicated that the structure meets the design requirements; Otherwise, return to step 31 to redesign the structure until the design requirements are met.

5. A new method suitable for oil cooled blade design according to claim 1, characterized in that: The step 5 is specifically: Step 51, calculating the interlayer thermal resistance R according to the obtained parameters: （5） where t w1 is the average temperature of the outer surface of the blade, t w2 is the average temperature of the inner cooling channel structure, and Q is the heat released by the combustion gas at the outer surface of the blade. Step 52, calculating the interlayer thickness δ according to the interlayer thermal resistance: （6） Wherein λ is the thermal conductivity.

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