A method for measuring mechanical efficiency of a low reynolds number turbine test

Abstract

The application provides a mechanical efficiency measurement method for low Reynolds number turbine test, comprising the following steps: measuring the temperature of the inner wall of the casing and the temperature of the outer wall of the casing; laying a thermal insulation layer outside the turbine casing, and measuring the temperature of the outer surface of the thermal insulation layer; operating the turbine test equipment and staying for a period of time to establish thermal equilibrium; calculating the turbine efficiency based on the outlet temperature and the turbine mechanical efficiency based on the power of the dynamometer in the design point state in the first stage turbine component aerodynamic performance test; gradually reducing the test Reynolds number, and fitting the correlation between the turbine efficiency and the turbine mechanical efficiency based on the power of the dynamometer in the first stage turbine component aerodynamic performance test; performing the second stage turbine component aerodynamic performance test, continuously reducing the test Reynolds number, and staying for a period of time to establish thermal equilibrium; calculating the turbine efficiency based on the outlet temperature in the design point state under each Reynolds number; and calculating the mechanical efficiency of the low Reynolds number turbine test.

Description

Technical Field

[0001] This invention relates to the field of aero-engine testing technology, specifically to a method for measuring the mechanical efficiency of a low Reynolds number turbine. Background Technology

[0002] The turbine is a core hot-end component in an aero-engine, operating in an environment characterized by high temperature, high pressure, and high speed, playing a crucial role in the modern aero-engine development system. To meet the needs of different aero-engines, turbine models vary significantly in size, operating parameters, and power ratings. Furthermore, turbine performance decreases with increasing flight altitude, necessitating performance tests of turbine components at different flight altitudes. These tests are conducted on turbine testing equipment. Current industry standards employ a method that alters the airflow pressure at the turbine inlet and outlet by adjusting valves upstream and downstream of the turbine under test, and controls the turbine speed by adjusting a hydraulic dynamometer. When the turbine inlet and outlet airflow parameters and turbine speed reach predetermined test conditions, the inlet and outlet airflow parameters and turbine power are collected to calculate the turbine mechanical efficiency ηP. Here, the turbine mechanical power P (unit: kW) is an indirect value obtained through calculation using measured torque M (unit: N·m) and speed n (unit: r / min) under stable operating conditions. Therefore, the accuracy of turbine torque measurement and the stability of test speed control are extremely important for evaluating turbine mechanical efficiency.

[0003] Turbine testing equipment is extremely complex and has high construction and operating costs. From an economic perspective, it is impractical to build a dedicated testing facility for each turbine under test. Therefore, conventional turbine testing equipment must undertake multiple turbine testing tasks. Consequently, the power and speed of the hydraulic dynamometers in conventional turbine testing equipment are configured at their maximum values ​​to avoid safety accidents caused by excessive torque or speed. This objective reality necessitates the simulation of test conditions when conducting low Reynolds number turbine tests using conventional turbine testing equipment. However, as the simulation altitude increases, the power of the turbine under test decreases rapidly, while the speed remains essentially constant, resulting in extremely low turbine torque. The high speed and low torque encountered in low Reynolds number turbine tests cause the turbine torque to fall near the lower limit of the torque sensor's measurement range, reducing the accuracy of torque measurement. This leads to errors in the calculated turbine mechanical power exceeding the standard allowable range, and the mechanical efficiency assessment failing to meet the basic requirements of the test.

[0004] Therefore, conventional turbine testing equipment faces the challenge of accurately obtaining the mechanical efficiency of turbines at high altitudes due to random fluctuations in speed and torque during low Reynolds number turbine tests, rendering the test data invalid. While this problem can be mitigated by constructing dedicated low Reynolds number turbine performance simulation testing equipment, the construction time is lengthy and the costs are substantial, failing to meet the timeliness and economic requirements of aero-engine development. Furthermore, the main approach to constructing dedicated testing equipment involves replacing hydraulic dynamometers with smaller-power-class instruments and torque measuring instruments with narrower ranges. This results in a very narrow operating range for such turbine testing equipment, and the efficiency evaluation methods are similar to those of conventional equipment, failing to fundamentally solve the problem of accurately evaluating the mechanical efficiency of turbines at low Reynolds number.

[0005] Among them, 10 4 ~10 6 It has a low Reynolds number. Summary of the Invention

[0006] In view of this, the present invention provides a method for measuring the mechanical efficiency of a low Reynolds number turbine test.

[0007] This invention provides the following technical solution: a method for measuring the mechanical efficiency of a low Reynolds number turbine, comprising the following steps:

[0008] Step S1: Install measuring probes at the turbine inlet and turbine outlet respectively to measure the turbine inlet total temperature, inlet total pressure, outlet total pressure and outlet total temperature; Step S2: Install temperature measuring points on the inner and outer walls of the turbine casing at the location of the turbine inlet total temperature measuring probe, respectively, to measure the inner and outer wall temperatures of the turbine casing; install temperature measuring points on the inner and outer walls of the turbine casing at the location of the turbine outlet total temperature measuring probe, respectively, to measure the inner and outer wall temperatures of the turbine casing; lay an insulation layer on the outside of the turbine casing, and install temperature measuring points on the outside of the insulation layer to measure the outer surface temperature of the insulation layer; Step S3: Run the turbine test equipment to conduct the first stage of turbine component aerodynamic performance test. After reaching a set of test states determined by the turbine inlet total temperature, inlet total pressure, speed and expansion ratio, stay for a period of time to establish thermal equilibrium so that the inner wall temperature and outer wall temperature of the casing meet the preset conditions. Step S4: Record the turbine torque, speed, flow rate, expansion ratio, working fluid specific heat capacity ratio, and working fluid constant pressure specific heat capacity data under each test condition during the first stage of turbine component aerodynamic performance test; Step S5: Calculate the turbine efficiency based on the outlet temperature and the turbine mechanical efficiency based on the dynamometer power at the design point state during the first-stage turbine component aerodynamic performance test. Step S6: Gradually reduce the test Reynolds number and complete turbine aerodynamic performance tests under no less than three test conditions; Step S7: Fit the correlation between turbine efficiency based on outlet temperature and turbine mechanical efficiency based on dynamometer power at each Reynolds number in the first stage turbine component aerodynamic performance test. Step S8: Conduct the second stage aerodynamic performance test of turbine components, continue to reduce the test Reynolds number, and after reaching the test state determined by the turbine inlet total temperature, inlet total pressure, speed and expansion ratio for each group, stay for a period of time to establish thermal equilibrium so that the inner wall temperature and outer wall temperature of the casing meet the preset conditions. Step S9: Record the turbine inlet total temperature, expansion ratio, working fluid specific heat ratio and outlet total temperature data at the design point state at each Reynolds number during the second stage turbine component aerodynamic performance test, and calculate the turbine efficiency based on the outlet temperature at the design point state at each Reynolds number. Step S10: Substitute the turbine efficiency based on the outlet temperature at the design point state at each Reynolds number in the second-stage turbine component aerodynamic performance test into the correlation established in step S7, and calculate the mechanical efficiency of the low Reynolds number turbine test.

[0009] Compared with the prior art, the beneficial effects that the at least one technical solution adopted by the present invention can achieve include at least the following: 1) This invention establishes a set of test methods that enable conventional wide-power envelope turbine test equipment to accurately evaluate the mechanical efficiency of low Reynolds number turbine tests; 2) By adding a small number of temperature measuring points and strictly controlling the test procedure, this invention can ensure that conventional wide-power envelope turbine test equipment has good safety when conducting low Reynolds number turbine aerodynamic performance tests. 3) This invention reduces the need for specialized testing equipment for low Reynolds number turbine aerodynamic performance testing, thereby saving on the cost of building such equipment. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a flowchart illustrating an embodiment of the present invention. Detailed Implementation

[0012] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0013] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0014] like Figure 1 As shown, this embodiment of the invention provides a method for testing and evaluating the mechanical efficiency of a low Reynolds number turbine, specifically including the following steps S1: Installing measuring probes at the turbine inlet and turbine outlet to measure the total inlet temperature T0, total inlet pressure P0, total outlet pressure P1, and total outlet temperature T1; Step S2: Install temperature measuring points inside and outside the casing at the locations of the turbine inlet and outlet total temperature measuring probes to measure the inner wall temperature T of the casing. n External wall surface temperature T w An insulation layer is laid on the outside of the turbine casing, and temperature measuring points are installed on the outside of the insulation layer to measure the temperature T of the outer surface of the insulation layer. out ; Step S3: Run the turbine testing equipment to conduct the first stage of turbine component aerodynamic performance testing. After reaching the test state with parameters such as the turbine inlet total temperature T0, inlet total pressure P0, speed n, and expansion ratio π, remain in this state for a period of time to establish thermal equilibrium, so that T... n T W The requirements are met. Here, the turbine expansion ratio π is the ratio of the total inlet pressure P0 to the total outlet pressure P1. ; Step S4: Record the turbine torque M, speed n, flow rate G, turbine expansion ratio π, working fluid specific heat ratio k, and working fluid isobaric specific heat capacity under various conditions during the first stage of turbine component aerodynamic performance testing. Data, etc. Step S5: Calculate the turbine efficiency η based on the outlet temperature at the design point (speed n=1.0) during the first stage aerodynamic performance test of the turbine components. r And the turbine mechanical efficiency η based on dynamometer power P ,in: , ; Step S6: Gradually reduce the test Reynolds number and complete turbine aerodynamic performance tests under no less than 3-6 test conditions, wherein the collected turbine torque M and speed n data should meet the requirements; Step S7: Fit the turbine efficiency η based on the outlet temperature to the design point state at each Reynolds number during the aerodynamic performance tests of turbine components in the first stage, considering the inlet total temperature T0 and inlet total pressure P0. Td1 And the turbine mechanical efficiency η based on dynamometer power Pd1 Relationship ; Step S8: Conduct the second stage aerodynamic performance test of the turbine components, continue to reduce the test Reynolds number, and after reaching the test state determined by parameters such as the total inlet temperature T0, total inlet pressure P0, speed n, and expansion ratio π for each turbine group, hold the test state for a period of time, allowing T0 to decrease. n T W The requirements are met; Step S9: Record the turbine inlet total temperature T0, expansion ratio π, working fluid specific heat ratio k, and outlet total temperature T1 at each Reynolds number during the second-stage turbine component aerodynamic performance test. Based on this, calculate the turbine efficiency η at each Reynolds number at the design point state based on the outlet temperature. Td2 ; Step S10: Conduct the second-stage aerodynamic performance test of the turbine components, and determine the turbine efficiency η at each Reynolds number based on the outlet temperature, representing the design point state. Td2 Substitute into the fitting formula Calculate the mechanical efficiency of a turbine test at a low Reynolds number.

[0015] In step 1, the number of turbine inlet and outlet total temperature measuring probes should be four or more, and their orientation should include the directions directly above, below, and to the left and right of the turbine. T represents the average temperature measured at all probe points on each cross-section. G i T represents the mass of gas flowing through the area of ​​a given measuring point. i G represents the temperature at a certain measuring point, and G represents the flow rate.

[0016] In step 2, the temperature T on the inner wall of the casing is measured. n and the outer wall surface temperature T w The temperature measuring points should be arranged on the metal substrate of the casing near the probe mounting base and firmly attached to the substrate surface; Furthermore, in step S2, the insulation layer applied to the outside of the turbine casing should ensure that the outer surface temperature T of the insulation layer is within the test range. out With ambient temperature T ∞ The preset temperature difference conditions that the total inlet temperature T0 and the total outlet temperature T1 should meet are as follows: , ; Preferably, in step S3, after reaching the test state determined by parameters such as the turbine inlet total temperature T0, inlet total pressure P0, rotational speed n, and expansion ratio π, the dwell time should be sufficient to ensure that after this time, T0... n T w The temperature at the current moment continuously changes slowly from the temperature at the previous moment within 1 minute, that is... , ; For T n The temperature at the previous moment, For Tn The temperature at the current moment; For T w The temperature at the previous moment, For T w The temperature at the current moment.

[0017] Furthermore, in step S3, the dwell time is no less than 8 minutes each time a new expansion ratio is reached; Preferably, in step S4, the recording frequency of the test data should be no less than 1 time / second, and the time for each acquisition should be no less than 1 minute; Preferably, in step S6, the successive reduction of the test Reynolds number should be carried out by keeping the inlet total temperature T0 basically constant while gradually reducing the inlet total pressure P0, in order to shorten the time required for the test. n T w The duration required to meet the requirements of slow change; Furthermore, in step S6, the collected turbine torque M should satisfy the following at the rotational speed n: ;in, The rotational speed at the previous moment. This represents the rotational speed at the current moment.

[0018] Preferably, in step S7, η should be arranged in descending order of Reynolds number. Td1 η Pd1 Then use a quadratic polynomial Fitting. The coefficients in this preferred embodiment are: , , .

[0019] Preferably, in step S8, the dwell time for each test state in the second-stage turbine component aerodynamic performance test should be sufficient to ensure that after that time, T n T w If the rate of temperature change between the current moment and the previous moment is slower within 1 minute, then... , ; Preferably, in step S9, the change in rotational speed n should be observed in the recorded test data to ensure that it meets the requirements. This is to confirm that the dynamometer of the equipment can effectively control the test speed, so as not to cause large fluctuations that could lead to speed control failure and safety accidents. Preferably, in step S10, η is used to calculate the mechanical efficiency of the low Reynolds number turbine test. Td2 It should satisfy 0.91 < η Td2 <0.96.

[0020] Using the above method, conventional turbine performance test benches can be used to conduct turbine aerodynamic performance tests at high and medium Reynolds numbers to establish the correlation between the test bench's thermal balance and efficiency. Thus, when the test bench enters the low Reynolds number operating range, the turbine test mechanical efficiency can be calculated using the turbine efficiency based on the outlet temperature, thereby meeting the industry's efficiency assessment conventions.

[0021] The above are merely specific embodiments of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of protection of this patent, should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical solutions, and technical solutions in this invention can be freely combined and used.

Claims

1. A method for measuring the mechanical efficiency of a low Reynolds number turbine test, characterized in that, Includes the following steps: Step S1: Install measuring probes at the turbine inlet and turbine outlet respectively to measure the turbine inlet total temperature, inlet total pressure, outlet total pressure and outlet total temperature; Step S2: Install temperature measuring points on the inner and outer walls of the turbine casing at the location of the turbine inlet total temperature measuring probe, respectively, to measure the inner and outer wall temperatures of the turbine casing; install temperature measuring points on the inner and outer walls of the turbine casing at the location of the turbine outlet total temperature measuring probe, respectively, to measure the inner and outer wall temperatures of the turbine casing; lay an insulation layer on the outside of the turbine casing, and install temperature measuring points on the outside of the insulation layer to measure the outer surface temperature of the insulation layer; Step S3: Run the turbine test equipment to conduct the first stage of turbine component aerodynamic performance test. After reaching a set of test states determined by the turbine inlet total temperature, inlet total pressure, speed and expansion ratio, stay for a period of time to establish thermal equilibrium so that the inner wall temperature and outer wall temperature of the casing meet the preset conditions. Step S4: Record the turbine torque, speed, flow rate, expansion ratio, working fluid specific heat capacity ratio, and working fluid constant pressure specific heat capacity data under each test condition during the first stage of turbine component aerodynamic performance test; Step S5: Calculate the turbine efficiency based on the outlet temperature and the turbine mechanical efficiency based on the dynamometer power at the design point state during the first-stage turbine component aerodynamic performance test. Step S6: Gradually reduce the test Reynolds number and complete turbine aerodynamic performance tests under no less than three test conditions; Step S7: Fit the correlation between turbine efficiency based on outlet temperature and turbine mechanical efficiency based on dynamometer power at each Reynolds number in the first stage turbine component aerodynamic performance test. Step S8: Conduct the second stage aerodynamic performance test of turbine components, continue to reduce the test Reynolds number, and after reaching the test state determined by the turbine inlet total temperature, inlet total pressure, speed and expansion ratio for each group, stay for a period of time to establish thermal equilibrium so that the inner wall temperature and outer wall temperature of the casing meet the preset conditions. Step S9: Record the turbine inlet total temperature, expansion ratio, working fluid specific heat ratio and outlet total temperature data at the design point state at each Reynolds number during the second stage turbine component aerodynamic performance test, and calculate the turbine efficiency based on the outlet temperature at the design point state at each Reynolds number. Step S10: Substitute the turbine efficiency based on the outlet temperature at the design point state at each Reynolds number in the second-stage turbine component aerodynamic performance test into the correlation established in step S7, and calculate the mechanical efficiency of the low Reynolds number turbine test.

2. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S1, there are no fewer than four total temperature measuring probes at both the turbine inlet and the turbine outlet, and the measuring probes are oriented in the directions of directly above the turbine, directly below the turbine, horizontally to the left, and horizontally to the right. The total temperature at the turbine inlet is the average of the temperatures measured by all probes at the turbine inlet section, and the total temperature at the outlet is the average of the temperatures measured by all probes at the turbine outlet section.

3. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S2, the temperature measuring points on the inner wall of the casing and the temperature measuring points on the outer wall of the casing are respectively arranged on the metal substrate of the casing near the corresponding probe mounting base.

4. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S2, the laying of the insulation layer should be ensured to be within the test range, and the temperature difference between the outer surface temperature of the insulation layer and the ambient temperature, the temperature difference between the outer surface temperature of the insulation layer and the total temperature of the turbine inlet, and the temperature difference between the outer surface temperature of the insulation layer and the total temperature of the outlet should all meet their respective preset temperature difference conditions.

5. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S3, the condition for establishing thermal equilibrium is that the temperature change rate of both the inner wall temperature and the outer wall temperature of the casing is lower than their respective preset thresholds within one minute.

6. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S3, the dwell time is no less than eight minutes each time a new expansion ratio corresponding to the experimental state is reached.

7. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S4, the experimental data recording frequency shall be no less than once per second, and the collection time for each data acquisition shall be no less than one minute.

8. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S6, the experimental Reynolds number is gradually reduced by keeping the total turbine inlet temperature constant while gradually reducing the total inlet pressure.

9. The method for measuring the mechanical efficiency of a low Reynolds number turbine test according to claim 1, characterized in that, In step S7, the design point states at each Reynolds number are sorted in descending order. The turbine efficiency based on the outlet temperature and the turbine mechanical efficiency based on the dynamometer power are then fitted using a quadratic polynomial to establish a correlation.

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