CN114814284B - Method and device for measuring cascade flow field by using reflectively-installed ultrasonic array - Google Patents
Method and device for measuring cascade flow field by using reflectively-installed ultrasonic array Download PDFInfo
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Abstract
本发明公开了一种反射式安装的超声阵列测量叶栅流场的方法，包括以下步骤：步骤1，在平面叶栅通道正上方布置二维超声波换能器阵列，当气体从叶栅通道中流过时，超声测量系统发射并接收超声波，并获取超声波顺、逆流状态下的渡越时间信号波形；步骤2，采用信号处理方法对渡越时间信号波形进行处理，得出超声波到达接收换能器的渡越时间，通过渡越时间重建二维速度场。其中，在平面叶栅通道内相邻两叶片的通道正上方垂直布置M×N个超声波换能器，且超声波换能器的匹配层需与叶片的上表面平齐。本发明还公开了一种反射式安装的超声阵列测量叶栅流场的装置。本测量方法及装置结构和原理简单，可实现非接触式的在线测量，且对流场不造成干扰。
The invention discloses a method for measuring the flow field of a cascade with a reflectively installed ultrasonic array, which includes the following steps: Step 1: Arrange a two-dimensional ultrasonic transducer array directly above the plane cascade channel. When the gas flows from the cascade channel, When the time passes, the ultrasonic measurement system transmits and receives ultrasonic waves, and obtains the transit time signal waveforms of the ultrasonic waves in the forward and reverse flow states; Step 2, use the signal processing method to process the transit time signal waveforms, and obtain the time when the ultrasonic waves reach the receiving transducer. Transit time, reconstruct the two-dimensional velocity field through the transit time. Among them, M×N ultrasonic transducers are arranged vertically just above the channels of two adjacent blades in the plane cascade channel, and the matching layer of the ultrasonic transducers needs to be flush with the upper surface of the blades. The invention also discloses a device for measuring the flow field of a cascade using a reflective ultrasonic array. The measurement method and device have a simple structure and principle, can realize non-contact online measurement, and do not cause interference to the flow field.
Description
Technical Field
The invention relates to the technical field of flow field measurement, in particular to a method and a device for measuring a blade grid flow field by using a reflective installed ultrasonic array.
Background
The factors influencing the cascade flow field are numerous and complex, and have geometric factors: consistency, geometric setting angle, etc., with aerodynamic factors: mach number of incoming flow, shock boundary layer disturbances, etc. The air flow in the air compressor is diffusion flow, so that flow separation is easy to occur, and stall flutter of blades is triggered or the air compressor surge is caused, so that serious accidents are caused. In the gas turbine, phenomena such as supercharging acceleration, vortex flow and the like can be generated among the multi-stage blade grids, so that the combustion efficiency in the combustion chamber of the gas turbine is influenced, and the performance of the whole gas turbine is further influenced. The key to solving these problems is to grasp the flow field distribution in the cascade. Therefore, flow field measurement techniques are the basis for understanding the performance of the cascade. The complex flow phenomenon can be known through flow field measurement, the complex physical mechanism of the flow phenomenon is explored, a new flow phenomenon is established and found for people, and a basis is provided for establishing a new concept and a new physical model.
The existing measurement modes are mainly divided into contact measurement and non-contact measurement. The contact type measurement is mainly a pressure probe and a pneumatic probe, and is characterized by low cost, high signal to noise ratio, single point measurement and large influence on a flow field. The non-contact measurement is mainly particle image velocimetry PIV (Particle Image Velocimetry), but trace particles need to be scattered in a flow field during measurement, uniformity of the trace particles cannot be guaranteed under high-speed airflow, and the trace particles collide with the wall surface of a flow channel, so that abrasion is caused.
Disclosure of Invention
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method and apparatus for measuring a cascade flow field by using a reflectively mounted ultrasonic array.
The invention provides a method for measuring a cascade flow field by a reflective ultrasonic array, which has the characteristics that the method comprises the following steps: step 1, arranging a two-dimensional ultrasonic transducer array right above a plane cascade channel, transmitting and receiving ultrasonic waves by an ultrasonic measurement system when gas flows through the cascade channel, and acquiring transit time signal waveforms of the ultrasonic waves in forward and backward flow states; and 2, processing the transit time signal waveform by adopting a signal processing method to obtain the transit time of the ultrasonic wave reaching the receiving transducer, and reconstructing a two-dimensional velocity field through the transit time. In step 1, the two-dimensional ultrasonic transducer array includes a plurality of ultrasonic transducers. And M multiplied by N ultrasonic transducers are vertically arranged right above the channels of two adjacent blades in the planar blade grid channel, and the matching layers of the ultrasonic transducers are required to be flush with the upper surfaces of the blades.
In the method for measuring the cascade flow field by the reflective installed ultrasonic array, the method can also have the following characteristics: in step 1, specific values of M and N are determined according to the piezoelectric wafer size of the ultrasonic transducer, the frequency of the ultrasonic transducer, and the size of the space between the two blades. When the two-dimensional ultrasonic transducer array is arranged perpendicular to the incoming flow direction, the ultrasonic transducer emits ultrasonic waves in the range of the sound beam angle, and the ultrasonic waves continue to propagate after being reflected by the reflecting surface at the root of the blade grid, reach the receiving transducer and are received by the receiving transducer.
In the method for measuring the cascade flow field by the reflective installed ultrasonic array, the method can also have the following characteristics: the size of the sound beam angle alpha is determined by the piezoelectric wafer size of the ultrasonic transducer and the frequency of the ultrasonic transducer:
α/2＝arcsin 1.22λ/D s ＝70λ/D s
wherein λ represents the wavelength of the ultrasonic wave, D S Representing the dimensions of the piezoelectric wafer of the ultrasonic transducer, ensuring that the two transducers at the far-end receive signals from each other when determining M and N.
In the method for measuring the cascade flow field by the reflective installed ultrasonic array, the method can also have the following characteristics: wherein, step 2 specifically includes the following steps: step 2-1, measuring the temperature of the experimental environment by using a high-precision thermometer, calculating the sound velocity c in the air at the ambient temperature according to a formula, collecting static data of (M+N) x (M+N-1) groups for a plurality of times under the working condition that the wind speed is 0, obtaining the time of the ultrasonic wave reaching the receiving transducer,
wherein T represents the ambient temperature of the experiment, T 0 ＝273.16K，c 0 =331.45 m/s, c represents the sound velocity in air corresponding to the temperature T, and the theoretical propagation time of ultrasound under static conditions is:
wherein T represents the propagation time of ultrasonic waves, L represents the propagation path of the ultrasonic waves, c represents the actual sound velocity, and the measured time average value is compared with the theoretical time to eliminate static errors; step 2-2, collecting (M+N) x (M+N-1) waveform data under the working condition of wind tunnel air supply, and obtaining the transit time of the ultrasonic wave reaching the receiving transducer; and 2-3, introducing (M+N) x (M+N-1) effective transit times into a flow field reconstruction program to obtain a two-dimensional speed field.
In the method for measuring the cascade flow field by the reflective installed ultrasonic array, the method can also have the following characteristics: the specific process of the step 2-2 is as follows: the upstream transducer a transmits a signal to be received by the downstream transducer B, while the downstream transducer B transmits a signal to be received by the upstream transducer a. Due to the influence of the flow velocity of the fluid, the transmission time of the ultrasonic wave in the forward and backward directions is different:
t up ＝L/(c+vcosθ)
t down ＝L/(c-vcosθ)
wherein t is up For the time of forward flow propagation of ultrasonic waves in the fluid, namely, the ultrasonic waves are emitted by the transducer A, and the ultrasonic waves are received by the transducer B; t is t down For the time of counter-current propagation of ultrasonic waves in the fluid, i.e. the ultrasonic waves are emitted by the transducer B, which receives the ultrasonic waves; c ultrasonic wave propagation speed; l is the distance that ultrasonic waves propagate in the flow field; θ is the included angle between the ultrasonic propagation path and the axial direction of the fluid; v is the fluid flow rate. The formula of the speed difference method can be obtained by the two formulas:
in the procedure of reconstructing the flow field, the planar cascade two-dimensional flow field is reconstructed based on the formula.
In the method for measuring the cascade flow field by the reflective installed ultrasonic array, the method can also have the following characteristics: the reconstruction process in the step 2-3 is as follows: calculating the cos theta value of the included angle between different transducers according to the distance between the transducers and the blade height of the plane blade cascade, constructing a plane grid in a measurement area between two blades, decomposing the speed value calculated by a formula into two directions of x and y, generating sound Cheng Jiaodian on different ultrasonic wave propagation paths in a blade cascade channel, calculating the speed at the intersection point of the sound paths, and finally carrying out Lagrange interpolation based on the existing speed data measured between the ultrasonic transducers to meet the measurement resolution of a flow field.
In the method for measuring the cascade flow field by the reflective installed ultrasonic array, the method can also have the following characteristics: in the step 2-3, the method for calculating the speed at the sound path intersection point is as follows: if the sound Cheng Jiaodian is formed by intersecting two sound paths, the x-direction speed of the point is obtained by adding the x-direction speeds of the two sound paths and taking the average value, and the y-direction speed is obtained by adding the y-direction speeds of the two sound paths and taking the average value. If more sound Cheng Xiangjiao is present at sound Cheng Jiaodian, then so on.
The invention provides a device for measuring a cascade flow field by a reflective ultrasonic array, which has the characteristics that: the data generating part is used for arranging a two-dimensional ultrasonic transducer array right above the plane cascade channel, and when gas flows through the cascade channel, the ultrasonic measuring system transmits and receives ultrasonic waves to acquire transit time signal waveforms of the ultrasonic waves in a forward and backward flow state; and the data acquisition processing part processes the transit time signal waveform by adopting a signal processing method to obtain the transit time of the ultrasonic wave reaching the receiving transducer, and reconstructing a two-dimensional velocity field through the transit time. Wherein, in the data generation part, the two-dimensional ultrasonic transducer array includes a plurality of ultrasonic transducers. And M multiplied by N ultrasonic transducers are vertically arranged right above the channels of two adjacent blades in the planar blade grid channel, and the matching layers of the ultrasonic transducers are required to be flush with the upper surfaces of the blades.
Effects and effects of the invention
The method for measuring the cascade flow field by the reflectively-installed ultrasonic array comprises the following specific steps: step 1, arranging a two-dimensional ultrasonic transducer array right above a plane cascade channel, transmitting and receiving ultrasonic waves by an ultrasonic measurement system when gas flows through the cascade channel, and acquiring transit time signal waveforms of the ultrasonic waves in forward and backward flow states; and 2, processing the transit time signal waveform by adopting a signal processing method to obtain the transit time of the ultrasonic wave reaching the receiving transducer, and reconstructing a two-dimensional velocity field through the transit time. In step 1, the two-dimensional ultrasonic transducer array includes a plurality of ultrasonic transducers. And M multiplied by N ultrasonic transducers are vertically arranged right above the channels of two adjacent blades in the planar blade grid channel, and the matching layers of the ultrasonic transducers are required to be flush with the upper surfaces of the blades.
Therefore, the method and the device for measuring the cascade flow field by the reflective installed ultrasonic array have simple structure and principle, can realize non-contact on-line measurement, and do not cause interference to the flow field.
Drawings
FIG. 1 is a flow chart of a method of reflectively mounted ultrasonic array measurement cascade flow field in an embodiment of the present invention;
FIG. 2 is a schematic diagram of an MxN reflective ultrasound array in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram of the principle of ultrasonic transmission and reception according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a two-dimensional flow field measurement apparatus in an embodiment of the invention;
FIG. 5 is a schematic diagram of a 2X 4 reflective ultrasound array in an embodiment of the invention;
FIG. 6 is a schematic diagram of the principle of ultrasonic moveout method in an embodiment of the invention;
FIG. 7 is a flow field reconstruction flow chart in an embodiment of the invention;
FIG. 8 is a graph showing the results of flow field reconstruction at 10m/s in an embodiment of the present invention.
Detailed Description
In order to make the technical means, creation characteristics, achievement purposes and effects achieved by the present invention easy to understand, the following embodiments specifically describe a method and apparatus for measuring a cascade flow field by using a reflectively mounted ultrasonic array in accordance with the present invention with reference to the accompanying drawings.
In this embodiment, a method of reflectively mounted ultrasonic array measurement of a cascade flow field is provided.
FIG. 1 is a flow chart of a method of reflectively mounted ultrasonic array measurement of a cascade flow field in an embodiment of the present invention.
As shown in fig. 1, the method for measuring the cascade flow field by using the reflectively-mounted ultrasonic array according to the embodiment comprises the following steps:
and S1, arranging a two-dimensional ultrasonic transducer array right above the planar cascade channels, transmitting and receiving ultrasonic waves by an ultrasonic measurement system when gas flows through the cascade channels, and acquiring transit time signal waveforms of the ultrasonic waves in forward and backward flow states.
FIG. 2 is a schematic diagram of an MxN reflective ultrasound array in accordance with an embodiment of the present invention.
As shown in FIG. 2, M×N ultrasonic transducers are vertically arranged right above channels of two adjacent blades a and b in the blade cascade to form a reflective ultrasonic array c, and the matching layer of the ultrasonic transducers needs to be flush with the upper surfaces of the blades, so that the influence of the installation of the transducers on a flow field is avoided.
The specific values of M and N are determined according to the size of the piezoelectric wafer of the transducer, the frequency of the ultrasonic transducer, the size of the space between the two blades and the like. When the ultrasonic array is arranged perpendicular to the incoming flow direction, the ultrasonic transducer emits ultrasonic waves in the range of the sound beam angle, and the ultrasonic waves continue to propagate after being reflected by the reflecting surface at the root of the blade grid, reach the receiving transducer and are received by the receiving transducer. And the size of the sound beam angle alpha is determined by the piezoelectric wafer size of the transducer and the frequency of the ultrasonic transducer:
α/2＝arcsin 1.22λ/D s ＝70λ/D s
in the above formula, λ represents the wavelength of ultrasonic wave, D S Representing the size of the piezoelectric wafer of the ultrasonic transducer. In determining M and N, it is considered that the two transducers at the far end can receive signals from each other.
Fig. 3 is a schematic diagram of the principle of ultrasonic transmission and reception in the embodiment of the invention.
As shown in FIG. 3, the industrial personal computer interface comprises a man-machine interaction interface, so that the transmitting and receiving waveform diagrams of ultrasonic signals can be intuitively displayed. The system operation process is as follows: firstly, the industrial personal computer is stimulated to generate ultrasonic signals; then, the amplitude of the signal can be manually adjusted to a reasonable size according to the waveform condition on the human-computer interaction interface; then, ultrasonic waves are transmitted into the space of the cascade channels to propagate through the inverse piezoelectric effect of the ultrasonic transducer, and signals are received by the receiving transducer through the piezoelectric effect. And finally, storing the signal data into the industrial personal computer through the acquisition card. The device system can realize that one transducer transmits signals and the other transducers receive signals, and can quickly and automatically switch the transducer to transmit next after the signal transmission and the signal reception are completed. The acquisition and preservation time for completing a complete set of (M+N) x (M+N-1) signals is relatively short, about 1s.
Fig. 4 is a schematic diagram of a two-dimensional flow field measurement apparatus in an embodiment of the invention.
Fig. 5 is a schematic diagram of a 2 x 4 reflective ultrasound array in an embodiment of the invention.
In the present embodiment, as shown in fig. 4, the two-dimensional flow field measuring device 100 takes 2×4 ultrasonic transducers as an example, and 2×4 ultrasonic transducers 20 are vertically arranged right above two adjacent blade channels in the blade grid 10, and the matching layer of the ultrasonic transducers needs to be flush with the upper surfaces of the blades, so as to avoid the influence of the installation of the transducers on the flow field, and the specific installation mode is shown in fig. 5. Waveform data is then collected under the condition of the wind tunnel 30 blowing.
And S2, processing the transit time signal waveform by using a signal processing method to obtain the transit time of the ultrasonic wave reaching the receiving transducer, and reconstructing a two-dimensional velocity field through the transit time. The method specifically comprises the following steps:
step S2-1, measuring the temperature of the experimental environment by using a high-precision thermometer, calculating the sound velocity c in the air at the environmental temperature according to a formula, collecting 7X 8 groups of static data for a plurality of times under the working condition that the wind speed is 0, obtaining the time of the ultrasonic wave reaching the receiving transducer,
wherein T represents the ambient temperature of the experiment,T 0 ＝273.16K，c 0 =331.45 m/s, c represents the sound velocity in air corresponding to the temperature T, and the theoretical propagation time of ultrasound under static conditions is:
where T represents the propagation time of the ultrasonic wave, L represents the propagation path of the ultrasonic wave, c represents the actual sound velocity, and the measured time averaged value is compared with the theoretical time to eliminate the static error.
And S2-2, collecting 7 multiplied by 8 sets of waveform data under the working condition of wind tunnel air supply, and solving the transit time of the ultrasonic wave reaching the receiving transducer.
Fig. 6 is a schematic diagram of the principle of ultrasonic moveout method in an embodiment of the invention.
As shown in fig. 6, the upstream transducer a transmits a signal to be received by the downstream transducer B, while the downstream transducer B transmits a signal to be received by the upstream transducer a. Due to the influence of the flow velocity of the fluid, the transmission time of the ultrasonic wave in the forward and backward directions is different:
t up ＝L/(c+vcosθ)
t down ＝L/(c-vcosθ)
wherein t is up For the time of forward flow propagation of ultrasonic waves in the fluid, namely, the ultrasonic waves are emitted by the transducer A, and the ultrasonic waves are received by the transducer B; t is t down For the time of counter-current propagation of ultrasonic waves in the fluid, i.e. the ultrasonic waves are emitted by the transducer B, which receives the ultrasonic waves; c ultrasonic wave propagation speed; l is the distance that ultrasonic waves propagate in the flow field; θ is the included angle between the ultrasonic propagation path and the axial direction of the fluid; v is the fluid flow rate. The formula of the speed difference method can be obtained by the two formulas:
compared with the traditional time difference method, the speed obtained by the speed difference method is independent of temperature, namely, the temperature condition inside the outflow field does not need to be measured. In the procedure of reconstructing the flow field, the planar cascade two-dimensional flow field is reconstructed based on the formula.
And S2-3, introducing (M+N) x (M+N-1) effective transit times into a flow field reconstruction program to obtain a two-dimensional speed field.
Using a time signal flow field reconstruction process: and calculating the value of the included angle cos theta between different transducers according to the distance between the transducers and the leaf height of the plane blade cascade. And constructing a plane grid in a measurement area between two blades, and decomposing a speed value calculated by using a formula into two directions of x and y. In the cascade channels, since an intersection point (called sound Cheng Jiaodian) is generated by different ultrasonic propagation paths, the manner of calculating the velocity at this point is slightly different. If the point is formed by intersecting two sound paths, the x-direction speed of the point is obtained by adding the x-direction speeds of the two sound paths and taking the average value, and the y-direction speed is obtained by adding the y-direction speeds of the two sound paths and taking the average value. If this point is made of more sound Cheng Xiangjiao, then this is the case.
Fig. 7 is a flow field reconstruction flow chart in an embodiment of the invention.
As shown in fig. 7, in this embodiment, the flow field reconstruction step is:
step S2-3-1, after basic parameters such as cos theta and L are calculated, 56 pieces of sound time data are imported into the speed in the calculated path.
And S2-3-2, finding out the sound path cross point between the transducers and judging whether the sound path cross point is in the measuring area, if so, calculating the speed at the point, and if not, rejecting the point.
And S2-3-3, interpolating and reconstructing the two-dimensional flow field by using a Lagrangian method.
The x and y direction velocity magnitudes and vector velocity magnitude and angle data for the two-dimensional flow field are shown in table 1.
Table 1 shows the flow field reconstruction result under the working condition of 10m/s, wherein the negative number is opposite to the positive direction of the coordinate axis, and the positive number is consistent with the positive direction of the coordinate axis.
TABLE 1
FIG. 8 is a graph showing the results of flow field reconstruction at 10m/s in an embodiment of the present invention.
The embodiment also provides a device for measuring the cascade flow field by the reflectively-mounted ultrasonic array.
The device for measuring the cascade flow field by the reflective ultrasonic array in the embodiment comprises:
the data generating unit acquires the transit time signal waveform in the ultrasonic forward and backward flow states by the method of step S1 in the present embodiment.
The data acquisition processing unit reconstructs a two-dimensional velocity field by using the method of step S2 in the present embodiment.
Effects and effects of the examples
The method for measuring the cascade flow field by the reflective installed ultrasonic array according to the embodiment comprises the following specific steps: step 1, arranging a two-dimensional ultrasonic transducer array right above a plane cascade channel, transmitting and receiving ultrasonic waves by an ultrasonic measurement system when gas flows through the cascade channel, and acquiring transit time signal waveforms of the ultrasonic waves in forward and backward flow states; and 2, processing the transit time signal waveform by adopting a signal processing method to obtain the transit time of the ultrasonic wave reaching the receiving transducer, and reconstructing a two-dimensional velocity field through the transit time. In step 1, the two-dimensional ultrasonic transducer array includes a plurality of ultrasonic transducers. And M multiplied by N ultrasonic transducers are vertically arranged right above the channels of two adjacent blades in the planar blade grid channel, and the matching layers of the ultrasonic transducers are required to be flush with the upper surfaces of the blades.
Therefore, the method and the device for measuring the cascade flow field by the reflectively-installed ultrasonic array are simple in structure and principle, can realize non-contact on-line measurement, and do not interfere with the flow field.
The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.
Claims (2)
1. A method for measuring a cascade flow field by a reflective installed ultrasonic array is characterized in that,
the method for measuring the cascade flow field by using the reflective ultrasonic array is carried out by using a device for measuring the cascade flow field by using the reflective ultrasonic array, and the device for measuring the cascade flow field by using the reflective ultrasonic array comprises the following steps:
the data generating part is used for arranging a two-dimensional ultrasonic transducer array right above the plane cascade channel, and when gas flows through the cascade channel, the ultrasonic measuring system transmits and receives ultrasonic waves to acquire transit time signal waveforms of the ultrasonic waves in a forward and backward flow state;
the data acquisition processing part is used for processing the transit time signal waveform by adopting a signal processing method to obtain the transit time of ultrasonic waves reaching a receiving transducer, and reconstructing a two-dimensional speed field through the transit time, wherein in the data generation part, the two-dimensional ultrasonic transducer array comprises a plurality of ultrasonic transducers, M multiplied by N ultrasonic transducers are vertically arranged right above channels of two adjacent blades in the plane blade grid channel, a matching layer of each ultrasonic transducer is required to be flush with the upper surfaces of the blades,
the method for measuring the cascade flow field by the reflectively-installed ultrasonic array comprises the following steps of:
step 1, arranging a two-dimensional ultrasonic transducer array right above a plane cascade channel, transmitting and receiving ultrasonic waves by an ultrasonic measurement system when gas flows through the cascade channel, and acquiring transit time signal waveforms of the ultrasonic waves in forward and backward flow states;
step 2, processing the transit time signal waveform by adopting a signal processing method to obtain the transit time of the ultrasonic wave reaching the receiving transducer, reconstructing a two-dimensional velocity field by the transit time,
wherein in step 1, the two-dimensional ultrasonic transducer array comprises a plurality of ultrasonic transducers,
m x N ultrasonic transducers are vertically arranged right above the channels of two adjacent blades in the planar cascade channel, the matching layer of the ultrasonic transducers is required to be flush with the upper surfaces of the blades,
in the step 1, the specific values of M and N are determined according to the size of the piezoelectric wafer of the ultrasonic transducer, the frequency of the ultrasonic transducer and the size of the space between the two blades,
when the two-dimensional ultrasonic transducer array is arranged perpendicular to the incoming flow direction, the ultrasonic transducer emits the ultrasonic wave in the range of the sound beam angle, and the ultrasonic wave continuously propagates after being reflected by the reflecting surface at the root of the blade grating, reaches the receiving transducer and is received by the receiving transducer,
the magnitude of the beam angle α is determined by the piezoelectric wafer size of the ultrasonic transducer and the ultrasonic transducer frequency together:
α/2＝arcsin1.22λ/D s ＝70λ/D s
wherein λ represents the wavelength of the ultrasonic wave, D S Representing the dimensions of the piezoelectric wafers of the ultrasonic transducers, ensuring that the two transducers furthest apart receive signals from each other when determining M and N,
the step 2 specifically comprises the following steps:
step 2-1, measuring the temperature of the experimental environment by a high-precision thermometer, calculating the sound velocity c in the air at the ambient temperature according to a formula, collecting (M+N) x (M+N-1) groups of static data for a plurality of times under the working condition that the sound velocity c is 0, obtaining the time of the ultrasonic wave reaching the receiving transducer,
wherein T represents the ambient temperature of the experiment, T 0 ＝273.16K，c 0 =331.45 m/s, c represents the sound velocity in air corresponding to the temperature T, and the theoretical propagation time of ultrasound under static conditions is:
wherein T represents the propagation time of ultrasonic waves, L represents the propagation path of the ultrasonic waves, c represents the actual sound velocity, and the measured time average value is compared with the theoretical time to eliminate static errors;
step 2-2, collecting (M+N) x (M+N-1) waveform data under the working condition of wind tunnel air supply, and obtaining the transit time of the ultrasonic wave reaching the receiving transducer;
step 2-3, introducing (M+N) x (M+N-1) effective transit times into a flow field reconstruction program to obtain the two-dimensional speed field,
the specific process of the step 2-2 is as follows:
the upstream transducer a transmits a signal to be received by the downstream transducer B, while the downstream transducer B transmits a signal to be received by the upstream transducer a,
due to the influence of the flow velocity of the fluid, the transmission time of the ultrasonic wave in the forward and backward directions is different:
t up ＝L/(c+vcosθ)
t down ＝L/(c-vcosθ)
wherein t is up For the time of forward flow propagation of ultrasonic waves in the fluid, namely, the ultrasonic waves are emitted by the transducer A, and the ultrasonic waves are received by the transducer B; t is t down For the time of counter-current propagation of ultrasonic waves in the fluid, i.e. the ultrasonic waves are emitted by the transducer B, which receives the ultrasonic waves; c ultrasonic wave propagation speed; l is the distance that ultrasonic waves propagate in the flow field; θ is the included angle between the ultrasonic propagation path and the axial direction of the fluid; v is the flow rate of the fluid,
the formula of the speed difference method can be obtained by the two formulas:
in the procedure of reconstructing the flow field, reconstructing the planar cascade two-dimensional flow field based on the formula,
the reconstruction process in the step 2-3 is as follows:
calculating the cos theta value of the included angle between different transducers according to the distance between the transducers and the blade height of the plane blade cascade, constructing a plane grid in a measurement area between two blades, decomposing the speed value calculated by a formula into two directions of x and y, generating sound Cheng Jiaodian on different ultrasonic wave propagation paths in a blade cascade channel, calculating the speed at the intersection point of the sound paths, and finally carrying out Lagrange interpolation based on the existing speed data measured between the ultrasonic transducers to meet the measurement resolution of a flow field.
2. The method for reflectively mounted ultrasonic array measurement of a cascade flow field of claim 1, wherein:
in step 2-3, the method for calculating the speed at the sound path intersection point is as follows:
if the sound Cheng Jiaodian is formed by intersecting two sound paths, the x-direction speed of the point is obtained by adding the x-direction speeds of the two sound paths and taking the average value, the y-direction speed is obtained by adding the y-direction speeds of the two sound paths and taking the average value,
if the sound Cheng Jiaodian is made up of more sound Cheng Xiangjiao, then so on.
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