Method for calculating thrust gain of whole machine with medium bypass ratio based on mixed boundary

Abstract

The invention discloses a method for calculating thrust gain of a whole machine with a medium bypass ratio based on a mixing boundary. The method comprises the following steps: identifying the mixing boundary of inner and outer culvert air flows from a mixer to an outlet of a spray pipe through three-dimensional simulation; dividing a nozzle outlet flow field based on the mixing boundary, and dividing the nozzle outlet flow field into N areas according to the characteristics of the average temperature of the areas and the temperature in the areas; the mass flow and the temperature of the N areas are obtained respectively, and the engine outlet mixed exhaust thrust Fi is calculated; and calculating the thrust gain according to the mass flow of the N areas, the test and the total thrust of the engine outlet. According to the technical scheme, the thrust calculation accuracy of the medium-bypass-ratio hybrid exhaust engine under the condition of non-uniformity of an outlet flow field can be effectively improved in combination with the influence of thrust at different temperatures.

Description

Technical Field

[0001] The present invention relates to the field of aircraft engine performance analysis, and in particular to a method for calculating the thrust gain of a medium bypass ratio whole engine based on a mixed boundary. Background Art

[0002] A medium bypass ratio turbofan engine is an engine with a moderate ratio between the outer bypass and the inner bypass. Generally speaking, its bypass ratio is between 1 and 3, at which time the flow rate of the engine's outer bypass channel is greater than the flow rate of the inner channel. Compared with a small bypass ratio engine, this design of a medium bypass ratio engine can maintain considerable thrust at a lower fuel consumption rate. For a medium bypass ratio engine with mixed exhaust, the inner and outer bypass airflows are mixed after the mixer, so that the inner and outer bypass airflows tend to be relatively uniform in temperature, pressure, and velocity, and then discharged from the nozzle. Different mixing degrees, that is, different degrees of flow field uniformity, will result in different thrust gains. Figure 4 A schematic diagram of the change of different dimensionless axial lengths under different mixer mixing degrees and thrust gains is provided. Generally, as the mixing degree increases, the flow field becomes more uniform and the thrust gain increases.

[0003] In the research on the performance of the whole machine, the thrust gain of the whole machine is often calculated by the temperature, pressure and speed after the inner and outer fluids are mixed by mass, that is, the thrust gain of the whole machine is calculated by the airflow state after complete mixing under the ideal state. In fact, it is impossible for the engine mixer outlet to achieve a complete mixing state, that is, the flow field still has a large distribution difference, and the flow field cannot be calculated according to the unique mixing temperature T i Especially for medium bypass ratio engines, if a single speed and temperature are used to represent the flow field characteristics to calculate the thrust gain, there will be deviations in the thrust gain calculation. Summary of the invention

[0004] To solve the above problems, the present application provides a method for calculating the thrust gain of a medium bypass ratio aircraft based on a hybrid boundary, comprising the following steps:

[0005] Identify the mixing boundary of the inner and outer flow from the mixer to the nozzle outlet through three-dimensional simulation;

[0006] Based on the mixing boundary, the nozzle outlet flow field is divided, and according to the characteristics of the average temperature of the region and the temperature in the region, the nozzle outlet flow field is divided into N regions;

[0007] The mass flow rate and temperature of the N regions are obtained respectively, and the mixed exhaust thrust F at the engine outlet is calculated. i ;

[0008] The thrust gain is calculated according to the mass flow rates of the N regions, the test, and the total thrust at the engine outlet.

[0009] The mixing boundary is identified through the total temperature distribution cloud map after the aerodynamic parameters of the internal and external inlet of the afterburner at the typical state point are known. Generally, at least one mixing boundary can be identified; when the number of the mixing boundaries is 1, the nozzle outlet flow field is divided into 2 areas.

[0010] Furthermore, the characteristics of the average temperature of the region and the temperature within the region are: the deviation between the average temperature of the region and the temperature within the region is less than a specified threshold.

[0011] Furthermore, the method for calculating the thrust gain is: Among them, W1 and W2 are the mass flow rates of each region after being divided by the mixing boundary, T1 and T2 are the temperatures of each region after being divided by the mixing boundary, and F i To generate the total thrust at the engine outlet, F6, F 16 They are inner and outer thrust, T6, T 16 are the total temperatures of the inner and outer airflows, respectively.

[0012] Among them, the mass flow rate and temperature of N areas are obtained through three-dimensional simulation.

[0013] Engine outlet total thrust F i The calculation method is: calculate the thrust of the N regions respectively, and add them up to generate the total thrust F at the engine outlet i .

[0014] The present invention aims at the problem of uneven distribution of outlet flow field of mixed exhaust engine with medium bypass ratio, and proposes an optimization scheme. Through simulation tools, the afterburner with nozzle is taken as the object, based on the mixing boundary after the mixer, the boundary is processed and simulated as the aerodynamic balance interface, the nozzle outlet field is divided into several parts, and the mixed exhaust is assumed to be exhausted separately, and the thrust gain is calculated. Through this method, since the influence of thrust at different temperatures is taken into account, the accuracy of thrust calculation of mixed exhaust engine with medium bypass ratio under the condition of uneven outlet flow field can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a step diagram of a method for calculating the thrust gain of a medium bypass ratio machine according to an embodiment of the present invention;

[0016] Figure 2 It is a schematic diagram of the inner and outer mixing boundaries of the afterburner and the adjustable nozzle component provided in an embodiment of the present invention;

[0017] Figure 3 is a schematic diagram of engine outlet temperature distribution according to an embodiment of the present invention;

[0018] Figure 4This is a schematic diagram of the relationship between the mixing degree and thrust gain of different mixers as a function of L / D. DETAILED DESCRIPTION

[0019] For medium bypass ratio turbofan engines, the thrust gain of the whole engine is usually calculated by taking the temperature, pressure, velocity and other parameters of the inner and outer bypass fluids after mass average mixing. Taking the ground design point as an example, assuming that the tail nozzle pressure ratio is constant, the thrust gain δ F The calculation method is:

[0020] Among them, F i is the mixed exhaust thrust, W6, W 16 are the inner and outer mass flow rates, T i is the average temperature after mixing, F6, F 16 are the inner and outer duct thrusts respectively, T6 and T16 are the total temperatures of the inner and outer duct airflow respectively.

[0021] On this basis, the present invention optimizes the problem that it is impossible to achieve complete mixing at the outlet of the engine mixer: the area is divided according to the temperature distribution at the outlet of the engine mixer, the mixed exhaust thrust is converted into a separate exhaust thrust form through the mixing boundary (i.e., the imaginary boundary), and the separate exhaust thrusts are superimposed to solve the total exhaust thrust, and the thrust gain is calculated on this basis.

[0022] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings.

[0023] Figure 1 The present invention provides a method for calculating the thrust gain of a medium bypass ratio aircraft based on a hybrid boundary, including:

[0024] Step S100: identifying the mixing boundary of the inner and outer airflows from the mixer to the nozzle outlet through three-dimensional simulation;

[0025] In this step, a three-dimensional simulation is first performed on the afterburner and the adjustable nozzle, such as Figure 2 As shown, the aerodynamic parameters of the internal and external inlets of the afterburner combustion chamber at a typical state point are known, and the mixing boundary from the mixer to the nozzle outlet is identified and determined through the total temperature distribution cloud diagram.

[0026] In general, multiple mixing boundaries can be identified, and there should be at least one mixing boundary. When determining the number and location of mixing boundaries, it is required to control the average temperature of the areas on both sides of the mixing boundary. The temperature in the two sides (T xi ) deviation is as small as possible, that is, the temperature standard deviation of the area divided by the mixing boundary is as small as possible.

[0027] Step S110: dividing the nozzle outlet flow field based on the mixing boundary; when dividing the nozzle outlet flow field, the nozzle outlet flow field is divided into N regions according to the average temperature of the region and the characteristics of the temperature in the region;

[0028] According to the requirements for determining the number and position of mixing boundaries, the characteristics of the average temperature of the region and the temperature within the region are determined: that is, the average temperature of the region and the standard deviation of the temperature within the region are as small as possible, for example, less than a specified threshold. Generally, the threshold can be defined as 10 (in K), that is, the temperature standard deviation is less than or equal to 10 Kelvin temperature.

[0029] When the number of mixing boundaries is 1, the nozzle outlet flow field is divided into two regions. Figure 3 As shown, the nozzle outlet flow field is divided into two parts, and the two parts are obtained by three-dimensional simulation with the mixing boundary as the boundary.

[0030] Step S120: Obtain the mass flow and temperature of the N regions respectively, and calculate the engine outlet mixed exhaust thrust F i ;

[0031] In this step, the mass flow rate and average temperature (averaged by mass) of N regions divided by the mixing boundary are obtained through three-dimensional simulation.

[0032] When calculating thrust, the nozzle outlet is divided according to the mixing boundary, and the mixed exhaust thrust is converted into the form of separate exhaust thrust, and the solution is accumulated, that is, the thrust of N regions is calculated separately. For example, according to 1 mixing boundary, the thrust of two regions is calculated separately, and the total thrust F at the engine outlet is accumulated. i .

[0033] Step S130: Calculate the thrust gain according to the mass flow rate, temperature, and total thrust at the engine outlet of the N regions.

[0034] The method to calculate thrust gain is: Among them, W1 and W2 are the mass flow rates of each region after being divided by the mixing boundary, T1 and T2 are the temperatures of each region after being divided by the mixing boundary, and F i To generate the total thrust at the engine outlet, F6, F 16 They are inner and outer thrust, T6, T 16 are the total temperatures of the inner and outer airflows, respectively.

[0035] In the present invention, an optimization scheme is proposed for the problem of uneven distribution of outlet flow field of mixed exhaust engine with medium bypass ratio. Through simulation tools, an afterburner with a nozzle is taken as the object, based on the mixing boundary after the mixer, the boundary treatment is simulated as an aerodynamic balance interface, the nozzle outlet field is divided into several parts, and the mixed exhaust is assumed to be exhausted separately to calculate the thrust gain. Through this method, since the influence of thrust at different temperatures is taken into account, the accuracy of thrust calculation of mixed exhaust engine with medium bypass ratio under the condition of uneven outlet flow field can be effectively improved.

[0036] The above disclosures are only several specific embodiments of the present invention; however, the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for calculating the thrust gain of a medium bypass ratio aircraft based on a mixed boundary, characterized in that: The following steps are involved: Identify the mixing boundary of the inner and outer flow from the mixer to the nozzle outlet through three-dimensional simulation; Based on the mixing boundary, the nozzle outlet flow field is divided, and according to the characteristics of the average temperature of the region and the temperature in the region, the nozzle outlet flow field is divided into N regions; The mass flow rate and temperature of the N regions are obtained respectively, and the mixed exhaust thrust F at the engine outlet is calculated. i ; The thrust gain is calculated according to the mass flow rates of the N regions, the test, and the total thrust at the engine outlet.

2. The method according to claim 1, characterized in that: The mixing boundary is identified through the total temperature distribution cloud map after the aerodynamic parameters of the internal and external inlets of the afterburner combustion chamber at a typical state point are known.

3. The method according to claim 1, characterized in that The characteristics of the average temperature of the region and the temperature within the region are: the deviation between the average temperature of the region and the temperature within the region is less than a specified threshold.

4. The method according to claim 1, characterized in that: At least one mixing boundary can be identified; when the number of the mixing boundary is 1, the nozzle outlet flow field is divided into two regions.

5. The method according to claim 4, characterized in that The method for calculating the thrust gain is: Among them, W1 and W2 are the mass flow rates of each region after being divided by the mixing boundary, T1 and T2 are the temperatures of each region after being divided by the mixing boundary, and F i To generate the total thrust at the engine outlet, F6, F 16 They are inner and outer thrust, T6, T 16 are the total temperatures of the inner and outer airflows, respectively.

6. The method according to claim 1, characterized in that The mass flow rate and temperature of the N regions are obtained through three-dimensional simulation.

7. The method according to claim 1, characterized in that Engine outlet total thrust F i The calculation method is: calculate the thrust of the N regions respectively, and add them up to generate the total thrust F at the engine outlet i .

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