A Method for Measuring the Turbulence Intensity of High-Temperature Combustion Gas Flow Inside an Engine

Abstract

The present invention discloses a method for measuring the turbulence intensity of high-temperature gas flow inside an engine. The test bench is operated at room temperature to collect the instantaneous velocity and instantaneous static pressure of the incoming flow. Based on the instantaneous velocity and instantaneous static pressure, the velocity fluctuation u′ and pressure fluctuation p′ of the incoming flow are calculated, and a correlation function of the velocity fluctuation and pressure fluctuation of the incoming flow is established. The test bench is operated at the temperature required for the test to collect the instantaneous static pressure of the incoming flow at the temperature required for the test. Based on the instantaneous static pressure, the pressure fluctuation of the incoming flow is calculated. Based on the pressure fluctuation of the incoming flow at the temperature required for the test and the correlation function, the velocity fluctuation of the incoming flow at the point to be predicted at the temperature required for the test is calculated. Finally, the turbulence intensity of the incoming flow at the temperature required for the test is calculated according to the turbulence intensity calculation formula. The measurement method of the present invention can realize the measurement of the turbulence intensity of the flow field in medium / high-temperature tests, and is particularly suitable for medium / high-temperature cascade tests and stage tests of aeroengines / gas turbines.

Description

Technical Field

[0001] The present invention belongs to the technical field of turbulence intensity measurement, and particularly relates to a method for measuring the turbulence intensity of high-temperature gas flow inside an engine. Background Art

[0002] A turbine is a main hot-end component of an aeroengine / gas turbine and bears a very high thermal load. The turbulence intensity of the incoming gas flow is one of the decisive factors affecting the thermal load and heat transfer and cooling characteristics of the turbine blades, and has a very significant impact on the performance and life of the engine. Its accurate measurement and prediction have special practical significance. However, the inlet gas temperature of the turbine of the fourth-generation gas turbine engine and the J-class gas turbine has reached over 1600 °C, and the working temperature of the blade high-temperature test system is also over 700 °C. It is very difficult to accurately measure the incoming flow turbulence intensity under the characteristic working conditions of the engine on various medium / high-temperature test benches of the engine, and this problem has not been effectively solved all the time.

[0003] Traditional measurement means mainly include a hot-wire anemometer and a particle image velocimetry (PIV). The hot-wire anemometer is an important means for calculating the turbulence intensity of the air flow under normal temperature conditions. By measuring the instantaneous value and time-average value of the air flow velocity, the pulsating velocity and turbulence intensity are calculated. However, due to the limitations of metal materials and dimensions, the operating temperature of the hot wire in the hot-wire anemometer is very difficult to exceed 150 °C, and it cannot be used for measuring the turbulence intensity of the high-temperature flow field on medium / high-temperature cascade test benches and stage test benches. The visualization flow velocity measurement technology represented by the particle image velocimetry PIV is also used for calculating the turbulence intensity under normal temperature conditions and requires an optical window. It can be seen that the prior art cannot measure the incoming flow turbulence intensity on various medium / high-temperature test benches of the engine. Summary of the Invention

[0004] Based on the above purpose, the present invention provides a method for measuring the turbulence intensity of high-temperature gas flow inside an engine, which solves the problem that the prior art cannot measure the incoming flow turbulence intensity in a medium / high-temperature test environment.

[0005] To achieve the above purpose, the present invention is implemented by adopting the following technical solutions:

[0006] A method for measuring the turbulence intensity of high-temperature gas flow inside an engine, which is used to measure the incoming flow turbulence intensity on various medium / high-temperature test benches of the engine, and specifically includes the following steps:

[0007] Step 1, operate the test bench at normal temperature, collect the instantaneous velocity and instantaneous static pressure of the incoming flow, calculate the velocity pulsation u′ and pressure pulsation p′ of the incoming flow based on the instantaneous velocity and instantaneous static pressure, and establish the correlation function r of the velocity pulsation and pressure pulsation of the incoming flow u′p′ ;

[0008] Step 2: Run the test bench at the required test temperature, collect the instantaneous static pressure of the oncoming flow at the required test temperature, and calculate the pressure pulsation of the oncoming flow based on the instantaneous static pressure. Based on the pressure pulsation of the oncoming flow at the required test temperature and the correlation function r in Step 1 u′p′ , obtain the velocity pulsation of the oncoming flow at the point to be predicted at the required test temperature through Equation (9).

[0009]

[0010] In the formula, x0, y0, and z0 respectively represent the position coordinates of the point to be predicted in the x, y, and z directions of the three-dimensional space, Δx, Δy, and Δz respectively represent the change step sizes in the x, y, and z directions; t0 represents the time coordinate of the point to be predicted; Δt is the time change step size; p′ rms (x i , y j , z k ) is the root mean square of p′(x i , y j , z k ), p′(x i , y j , z k ) represents the pressure pulsation of the oncoming flow at normal temperature; N x , N y , N z are respectively the number of pressure sampling points in the x, y, and z directions; N t is the total acquisition time; i = 1, 2, 3, …, N x ; j = 1, 2, 3, …, N y ; k = 1, 2, 3, …, N z ; l = 1, 2, 3, …, N t ;

[0011] Step 3: Calculate the turbulence intensity of the oncoming flow at the required test temperature according to the turbulence intensity calculation formula (10).

[0012]

[0013] In the formula, Tu represents the turbulence intensity, represents the average velocity of the oncoming flow at the required test temperature.

[0014] Preferably, in Step 1, it specifically includes: measuring the instantaneous velocity of the oncoming flow using a hot-wire probe, and obtaining the velocity pulsation u′ according to the instantaneous velocity;

[0015] measuring the instantaneous static pressure of the oncoming flow using a dynamic pressure sensor installed on the inner side wall of the test bench, denoising the instantaneous static pressure, and calculating the pressure pulsation p′ at the installation point of the dynamic pressure sensor.

[0016] Establish the correlation function r between the pressure pulsation and the velocity pulsation u′p′ ,

[0017]

[0018] Wherein, N x , N y , N z are the number of pressure sampling points in the x, y, and z directions respectively; N t is the total acquisition time; i = 1, 2, 3,..., N x ; j = 1, 2, 3,..., N y ; k = 1, 2, 3,..., N z ; l = 1, 2, 3,..., N t .

[0019] More preferably, the instantaneous static pressure denoising method is: use a dynamic pressure sensor installed on the outer wall surface to synchronously measure the pulsation noise, and adopt a method based on Fourier transform to remove the noise from the instantaneous static pressure of the oncoming flow.

[0020] Preferably, in step 2, the instantaneous velocity acquisition device is removed before the test bench runs at the required test temperature to avoid affecting the medium / high temperature flow field.

[0021] Preferably, the average velocity of the oncoming flow at the required temperature is measured by a pneumatic probe.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The measurement method of the present invention can realize the measurement of the turbulence intensity of the flow field in medium / high temperature tests, and is particularly suitable for medium / high temperature cascade tests and stage tests of aeroengines / gas turbines;

[0024] (2) The method of the present invention does not require inserting a probe into the flow field, and has very little influence on the flow field;

[0025] (3) The method of the present invention arranges dynamic pressure sensors on the wall surface, measures the pulsating pressure and estimates the turbulence intensity, and can avoid direct contact between the sensor and the high-temperature gas;

[0026] (4) The method of the present invention does not require opening a window on the test bench wall, and has no influence on the structural strength of the test bench. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of the test section of the test bench described in the embodiment of the present invention.

[0028] The meanings of the reference numerals in the figure: 1 - test bench, 2 - hot-wire probe, 3 - dynamic pressure sensor. Specific implementation manner

[0029] The principle of the method of the present invention is:

[0030] For Newtonian fluids, the momentum equation in the governing equations contains velocity and pressure. The differential form of the momentum equation can generally be written as:

[0031]

[0032] In the formula, ρ is the density, μ is the dynamic viscosity coefficient, f is the body force (for the flow described in the present invention, it is gravity), and 1, 2, 3 are the three coordinate directions.

[0033] The most important feature of turbulent flow is that physical quantities (such as velocity, pressure, temperature, etc.) fluctuate randomly in time and are studied by means of statistical averaging. According to Reynolds decomposition, the instantaneous value of a physical quantity in turbulence can be expressed as the sum of the time-averaged value and the fluctuating value. For velocity u and pressure p, there are:

[0034]

[0035] Among them, represents the time-averaged value of velocity, u' represents the fluctuating value of velocity, represents the time-averaged value of pressure, p' represents the fluctuating value of pressure.

[0036] And the instantaneous value of turbulent flow also satisfies the momentum equation:

[0037]

[0038] It can be seen from the above formula that in turbulent flow, there is a correlation between the instantaneous values of velocity and pressure at any moment, and this correlation has no direct relationship with temperature.

[0039] Therefore, the correlation function r of velocity fluctuation and pressure fluctuation can be established by measurement under cold conditions u′p′ . Using the data measured under cold conditions, a linear prediction of the relationship between velocity fluctuation and pressure fluctuation is made. Based on the least-squares approximation, the linear prediction coefficient A between velocity fluctuation and pressure fluctuation is calculated (A is related to r u′p′ ). Through the pressure fluctuation measured under hot conditions Using the linear prediction coefficient A between pressure fluctuation and velocity fluctuation, the velocity fluctuation under hot conditions is predicted And the turbulence intensity Tu is calculated therefrom.

[0040] In addition, the "test bench" described in the present invention refers to various engine test systems, such as blade test systems, and these systems are common various engine test systems in the current technology.

[0041] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0042] Embodiment

[0043] A method for measuring the turbulence intensity of high-temperature gas flow inside an engine disclosed in this embodiment is used to measure the incoming flow turbulence intensity in various medium / high-temperature test benches of the engine. The test bench described in this embodiment is a high-temperature experimental bench for engine blades, such as Figure 1 The structural schematic diagram of the test section of the test bench is shown. In the test bench 1, a hot-wire probe 2 and multiple dynamic pressure sensors 3 are arranged. The hot-wire probe 2 is generally arranged at the inlet part of the test section of the test bench 1, or can also be set as required. Multiple dynamic pressure sensors 3 are arranged on the inner wall of the test bench 1, and a dynamic pressure sensor 3 is also arranged on the outer side wall of the test bench 1.

[0044] The measurement method of this embodiment specifically includes the following steps:

[0045] Step 1, operate the test bench at room temperature, collect the instantaneous velocity and instantaneous static pressure of the incoming flow, calculate the velocity fluctuation u′ and pressure fluctuation p′ of the incoming flow based on the instantaneous velocity and instantaneous static pressure, and establish the correlation function r of the velocity fluctuation and pressure fluctuation of the incoming flow u′p′ , specifically:

[0046] Use a hot-wire probe to measure the instantaneous velocity of the incoming flow, and calculate the velocity fluctuation u′ according to the instantaneous velocity. Among them, the calculation of the velocity fluctuation is: subtract the average velocity within the measurement time period from the instantaneous velocity within the measurement time period, and take the average of the absolute values of these differences, which is the velocity fluctuation.

[0047] Use the dynamic pressure sensor installed on the inner side wall surface of the test bench to measure the instantaneous static pressure of the incoming flow, use the dynamic pressure sensor installed on the outer side wall surface to synchronously measure the pulsating noise, and use the method based on Fourier transform to remove the noise from the instantaneous static pressure of the incoming flow. Then calculate the pressure fluctuation p′ at the installation point of the dynamic pressure sensor according to the denoised instantaneous static pressure. Similar to the calculation idea of the velocity fluctuation, subtract the average pressure within the measurement time period from the instantaneous static pressure within the measurement time period, and take the average of the absolute values of these differences, which is the pressure fluctuation.

[0048] Establish the correlation function r of the pressure fluctuation and velocity fluctuation u′p′ ,

[0049]

[0050] where x i , y j , zk respectively represent the position coordinates of the sampling point in the x, y, and z directions of the three-dimensional space, and Δx, Δy, and Δz respectively represent the change step sizes in the x, y, and z directions; t l represents the time coordinate of the sampling point; Δt is the time change step size; N x , N y , N z are respectively the number of pressure sampling points in the x, y, and z directions; N t is the total number of acquisition times; i = 1, 2, 3, …, N x ; j = 1, 2, 3, …, N y ; k = 1, 2, 3, …, N z ; l = 1, 2, 3, …, N t .

[0051] Step 2: Run the test bench at medium / high temperature, generally above 700 °C or above 1600 °C. Since the hot-wire probe cannot be used at high temperature, it needs to be removed in advance and a pneumatic probe is installed. The dynamic pressure sensor 3 on the side wall is used to collect the instantaneous static pressure of the oncoming flow at this temperature, and the pressure pulsation of the oncoming flow is calculated based on the instantaneous static pressure Based on the pressure pulsation of the oncoming flow at the temperature required for the test and the correlation function r in Step 1 u′p′ , the oncoming flow velocity pulsation at the point to be predicted at the temperature required for the test is obtained

[0052] In the formula, x0, y0, and z0 respectively represent the position coordinates of the point to be predicted in the x, y, and z directions in the three-dimensional space, Δx, Δy, and Δz respectively represent the change step sizes in the x, y, and z directions; t0 represents the time coordinate of the point to be predicted; Δt is the time change step size.

[0053] Among them, A is the linear prediction coefficient, which gives the linear relationship between the pressure and the velocity pulsation. A is determined by the minimized prediction energy E 2 The definition of E is:[[]]

[0054]

[0055] By A can be determined, that is

[0056]

[0057]

[0058] p′ rms (x i , y j , zk ) is the root mean square of p′(x i , y j , z k ), and p′(x i , y j , z k ) represents the pressure fluctuation of the oncoming flow at the measurement point at room temperature, obtained through Step 1.

[0059] Therefore, Equation (5) can be expressed as:

[0060]

[0061] The velocity fluctuation of the oncoming flow at the point to be predicted at the temperature required for the test is obtained through Equation (9)

[0062] Then, the average velocity of the oncoming flow at the point to be predicted is measured by a pneumatic probe

[0063] Step 3: Calculate the turbulence intensity of the oncoming flow at the temperature required for the test according to the turbulence intensity calculation formula (10),

[0064]

[0065] where Tu represents the turbulence intensity, represents the average velocity of the oncoming flow at the temperature required for the test.

Claims

1. A method for measuring the turbulence intensity of high-temperature gas flow inside an engine, characterized in that, This measurement method is used to measure the incoming flow turbulence in various medium / high-temperature test benches of engines, and includes the following steps: Step 1: Operate the test bench at room temperature, collect the instantaneous velocity and static pressure of the incoming flow, calculate the velocity fluctuation u′ and pressure fluctuation p′ of the incoming flow based on the instantaneous velocity and static pressure, and establish the correlation function r of the velocity fluctuation and pressure fluctuation of the incoming flow u′p′ ; Step 2: Operate the test bench at the temperature required for the test, collect the instantaneous static pressure of the oncoming flow at the temperature required for the test, and calculate the pressure pulsation of the oncoming flow based on the instantaneous static pressure. Based on the pressure pulsation of the oncoming flow at the temperature required for the test and the correlation function r in Step 1 u′p′ , obtain the oncoming flow velocity pulsation at the point to be predicted at the temperature required for the test through Equation (9). where \(x_0\), \(y_0\), and \(z_0\) respectively represent the position coordinates of the predicted point in the x, y, and z directions of the three-dimensional space, \(\Delta x\), \(\Delta y\), and \(\Delta z\) respectively represent the change step sizes in the x, y, and z directions; \(t_0\) represents the time coordinate of the predicted point; \(\Delta t\) is the time change step size; \(p\) r ′ ms (x i ,y j ,z k ) is the root mean square of \(p'(x i ,y j ,z k ), and \(p'(x i ,y j ,z k ) represents the pressure pulsation of the oncoming flow at normal temperature; \(N x , \(N y , \(N z are respectively the number of pressure sampling points in the x, y, and z directions; \(N t is the total acquisition time; \(i = 1, 2, 3, \cdots, N x ; \(j = 1, 2, 3, \cdots, N y ; \(k = 1, 2, 3, \cdots, N z ; \(l = 1, 2, 3, \cdots, N t ; Step 3, calculate the turbulence of the incoming flow at the temperature required for the test (10) according to the turbulence calculation formula, where Tu represents the turbulence intensity, represents the average velocity of the oncoming flow at the temperature required for the test.

2. The method for measuring the turbulence intensity of high-temperature gas flow inside an engine according to claim 1, characterized in that, Specifically, in Step 1: use a hot-wire probe to measure the instantaneous velocity of the incoming flow, and obtain the velocity fluctuation u′ based on the instantaneous velocity; Use a dynamic pressure sensor installed on the inner side wall of the test bench to measure the instantaneous static pressure of the incoming flow, denoise the instantaneous static pressure, and calculate the pressure fluctuation p′ at the installation point of the dynamic pressure sensor; Establish the correlation function r between pressure pulsation and velocity pulsation u′p′ , where N x , N y , N z are the pressure sampling point numbers in the x, y, and z directions respectively; N t is the total acquisition time; i = 1, 2, 3, …, N x ; j = 1, 2, 3, …, N y ; k = 1, 2, 3, …, N z ; l = 1, 2, 3, …, N t .

3. The method for measuring the turbulence intensity of high-temperature gas flow inside an engine according to claim 2, characterized in that, The method for denoising the instantaneous static pressure is: use a dynamic pressure sensor installed on the outer side wall to synchronously measure the pulsating noise, and use a method based on Fourier transform to remove the noise from the instantaneous static pressure of the incoming flow.

4. The method for measuring the turbulence intensity of high-temperature gas flow inside an engine according to claim 1, characterized in that, In Step 2, remove the instantaneous velocity acquisition device before the test bench runs at the temperature required for the test.

5. The method for measuring the turbulence intensity of high-temperature gas flow inside an engine according to claim 1, characterized in that, The average velocity of the oncoming flow at the required temperature is obtained by measurement with a pneumatic probe.

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