A method for optimizing a shock tube velocity measurement

Abstract

The application discloses a shock tube speed measurement optimization method, and belongs to the technical field of dynamic pressure. The method is realized mainly based on a speed measurement sensor screening and compensation method and a shock speed calculation and correction method. Two pressure sensors C1 and C2 are used as reference sensors, and two pressure sensors C3 and C4 are selected as selected sensors; the time difference between adjacent pressure sensors is calculated by using the difference value of corresponding sampling points, and the average speed between the two pressure sensors is calculated as the midpoint speed by using a weighting method, so that the influence of the calculation method on the shock speed measurement is reduced. The application adopts a distributed shock speed measurement method to obtain the shock speed attenuation law, uses a distributed pressure sensor to obtain the attenuation model of the shock speed propagation, corrects the shock speed, avoids the problem that the shock speed deviation is caused by the fact that the measurement point position is different from the installation position of the end face pressure sensor, and guarantees the accuracy of the shock speed at the calibrated pressure sensor.

Description

Technical Field

[0001] This invention belongs to the field of dynamic pressure generation technology, specifically relating to an optimization method for shock tube velocity measurement. Background Technology

[0002] The dynamic performance of a pressure sensor is crucial to the accuracy and reliability of dynamic pressure measurements. As a vital piece of equipment for measuring and calibrating the dynamic performance of pressure sensors, the performance of the shock tube directly impacts the calibration results. When using a shock tube for dynamic calibration of pressure sensors, shock wave theory is commonly employed. This involves calculating the shock wave step pressure amplitude using factors such as the pressure and temperature of the low-pressure chamber before membrane rupture, and the shock wave velocity. Among these factors, the shock wave velocity is a key influence on the shock wave step pressure amplitude.

[0003] Currently, shock wave velocity measurement typically employs two pressure sensors mounted on the sidewall of the shock tube. The propagation time of the shock wave between the two sensors is calculated using their response curves, and the shock wave velocity is then calculated based on the distance between the sensors. However, this method generally results in a large uncertainty in shock tube amplitude measurement, typically reaching 10% (k=2). This is because, firstly, the inherent characteristics of the pressure sensors used for measurement, such as deviations in the sensitive parts of the diaphragm, rise time, and delay characteristics, lead to inaccurate results. Secondly, the shock wave undergoes axial attenuation during propagation within the tube, and the use of two sensors to calculate the shock wave velocity does not account for this attenuation, resulting in inaccurate measurements. Thirdly, the use of a single-point calculation method, i.e., selecting a specific amplitude value to calculate the shock wave propagation time, leads to significant errors. Based on the above reasons, the shock tube velocity measurement method can be optimized in three aspects: first, select a suitable pressure sensor for velocity measurement or correct the measurement results according to the sensor performance; second, select a suitable method to calculate the shock velocity at the pressure sensor being calibrated; and third, optimize the calculation method by using a multi-point fitting method to calculate the shock velocity, avoiding the shock velocity calculation error caused by a single point. Summary of the Invention

[0004] The purpose of this invention is to provide an optimized method for shock tube velocity measurement. When calculating the shock step pressure amplitude using shock wave theory, it can reduce the shock wave velocity measurement deviation caused by differences in the manufacturing process and performance of the pressure sensor used for velocity measurement. On the other hand, it adopts a distributed velocity measurement method to obtain the shock wave velocity attenuation law, thereby correcting the shock wave velocity and avoiding shock wave velocity deviation caused by the difference between the measurement point position and the installation position of the pressure sensor being calibrated on the end face, thus improving the accuracy of shock wave velocity measurement.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] The present invention discloses a shock tube velocity measurement optimization method, which is mainly based on the velocity sensor screening and compensation method and the shock velocity calculation and correction method.

[0007] The speed sensor screening and compensation method uses two pressure sensors C1 and C2 as reference sensors, and arbitrarily selects two pressure sensors C3 and C4 as selected sensors. A shock tube test is performed to obtain the shock wave times t1 and t2 measured by the two reference pressure sensors C1 and C2 and the two selected pressure sensors C3 and C4. Keeping the positions of the two reference pressure sensors C1 and C2 unchanged, the positions of the two selected pressure sensors C3 and C4 are swapped, and a shock tube test is performed again to obtain the shock wave times t3 and t4 measured by the two reference pressure sensors C1 and C2 and the two selected pressure sensors C3 and C4 at this time. The difference between t4-t2 and t3-t1 is compared. If the difference meets a preset requirement, the two selected pressure sensors C3 and C4 are selected as the speed measurement pressure sensors. If the difference does not meet the preset requirement, the above steps are repeated by replacing the selected pressure sensors until a suitable pressure sensor is selected.

[0008] Preferably, the speed sensor selection method can also correct the shock wave velocity measured by the two selectable pressure sensors C3 and C4 based on the difference between t4-t2 and t3-t1.

[0009] Preferably, there are two reference sensor mounting holes in the axial direction of the low-pressure chamber wall of the shock tube. The line connecting the two reference sensor mounting holes is parallel to the axis. The distance between the two reference sensor mounting holes needs to be easy to measure and is not less than 200 mm. There are two optional sensor mounting holes at the axisymmetric position of the two reference sensor mounting holes.

[0010] The shock wave velocity calculation and correction method involves arranging n velocity-measuring pressure sensors distributed along the wall of the low-pressure chamber of the shock tube. The propagation time of the incident shock wave between two adjacent velocity sensors is calculated based on the time difference between the rising edges of their output curves. Furthermore, the shock wave velocity at the midpoint between the two adjacent velocity sensors is calculated based on the distance between them, resulting in the incident shock wave velocities {V1, V2, ..., V...} at n-1 locations. p ,…,V n-1 Based on the incident shock wave velocities at the n-1 locations, an incident shock wave velocity attenuation model is obtained, and the shock wave velocity at the pressure sensor under calibration is calculated based on the location of the pressure sensor under calibration, the measured shock wave velocity, and the measurement location.

[0011] As a preferred method, based on the velocity measurement sequence and the position sequence of each measurement point, the incident shock wave velocity model is calculated using the least squares fitting method: V p =aL p +b, where L p The distance between the measured point S1 and the first measurement point; considering the minimum average sum of errors between the actual measured shock wave velocity and the model output, the parameters a and b are defined as follows: The shock wave velocity at the pressure sensor under calibration is calculated based on the relative position between the pressure sensor under calibration and the first measurement point S1.

[0012] Calculate the propagation time of the incident shock wave between two adjacent velocity sensors. Preferably, the time difference between the rising edges of the p-th velocity sensor and the (p+1)-th velocity sensor is denoted as [t]. p1 ,…,t pq ,…,t pQ ] p＝1,2,…,n-1 Where Q is the number of effective sampling points on the rising edge of the speed sensor output signal, and the optimal propagation time t of the incident shock wave passing through the two adjacent speed sensors is calculated using a weighted average method. p This avoids errors caused by using single-point data to calculate shock wave propagation time.

[0013] Preferably, the optimal propagation time t p Defined as

[0014]

[0015] in,

[0016] Beneficial effects:

[0017] 1. The present invention discloses a shock tube velocity measurement optimization method, which uses relative compensation method and distributed measurement method to reduce the impact of performance differences of pressure sensor used for velocity measurement, such as diaphragm sensitive part deviation, rise time deviation, and different delay characteristics, on shock velocity measurement.

[0018] 2. The shock tube velocity measurement optimization method disclosed in this invention uses the difference between corresponding sampling points to calculate the time difference between adjacent pressure sensors, and uses a weighted method to calculate the average velocity between two pressure sensors as the midpoint velocity, thereby reducing the influence of the calculation method on the shock velocity measurement.

[0019] 3. The shock tube velocity measurement optimization method disclosed in this invention adopts a distributed shock velocity measurement method, uses a distributed pressure sensor to obtain the attenuation model of shock velocity propagation, corrects the measurement results, and ensures the accuracy of the shock velocity at the pressure sensor being calibrated. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the principle of distributed shock wave velocity measurement in this invention.

[0021] Reference numerals: 1—shock tube low-pressure chamber wall, 2—pressure sensor under calibration, 3—speed sensor sequence, S1—speed and pressure sensor 1, S2—speed and pressure sensor 2, Sp—speed and pressure sensor p, Sp+1—speed and pressure sensor p+1, Sn—speed and pressure sensor n.

[0022] Figure 2 This is a schematic diagram of the method for screening speed and pressure sensors according to the present invention, wherein: Figure 2 (a) is a diagram showing the sensor installation location in the first experiment. Figure 2 (b) is a diagram showing the sensor installation location for the secondary experiment.

[0023] Reference numerals: C1—Reference pressure sensor 1, C2—Reference pressure sensor 2, C3—Selective pressure sensor 1, C4—Selective pressure sensor 2. Detailed Implementation

[0024] The following examples, combined with appendices, illustrate this point. Figure 1 and attached Figure 2 The technical solution of the present invention will be further described in detail below.

[0025] This embodiment discloses a shock tube velocity measurement optimization method, which is based on a shock velocity calculation and correction method and a velocity sensor selection and compensation method.

[0026] The method for calculating and correcting shock wave velocity is described in the attached figure. Figure 1 As shown, it includes n speed-measuring pressure sensors s1 to sn and a multi-channel data acquisition system.

[0027] The principle of speed sensor screening and compensation method is as follows: Figure 2 As shown, it includes two reference pressure sensors and a selected pressure sensor.

[0028] This embodiment discloses a shock tube velocimetry optimization method, the specific implementation method of which is as follows:

[0029] The first step is to determine the method for calculating the shock wave velocity. The time difference between the rise times of the first and second velocity sensors is denoted as [t1,…,t]. q ,…,t Q ], where Q is the number of effective sampling points on the rising edge of the output signal of the speed sensor, and the optimal propagation time t0 of the incident shock wave through two adjacent speed sensors is calculated using the weighted average method.

[0030] The second step involves screening and performance testing of pressure sensors for speed measurement, as shown in the attached document. Figure 2 As shown, reference pressure sensors C1 and C2 and selected pressure sensors C3 and C4 are arranged according to the attached... Figure 2 (a) After installing the diaphragm, a shock tube experiment is conducted. The shock times t1 and t2 measured by C1 and C2, C3 and C4 are calculated according to the method described in the first step.

[0031] Third, keeping the installation positions and methods of reference pressure sensors C1 and C2 unchanged, interchange the positions of the selected pressure sensors C3 and C4, as shown in the attached diagram. Figure 2 As shown in (b), after installing the thick film, a shock tube experiment was conducted. The shock times t3 and t4 measured by C1 and C2, C4 and C3 were calculated according to the method described in the first step.

[0032] The fourth step is to evaluate the selected pressure sensor based on the results of the two experiments: the shock wave velocity will differ between the two experiments, i.e., the shock wave propagation time difference is t3-t1. When the shock wave propagation time changes by (t3-t1), the change in shock wave propagation time after swapping C3 and C4 is t4-t2. By comparing the relationship between (t3-t1) and (t4-t2), it is determined whether the selected pressure sensor can meet the requirements; and the shock wave propagation time is compensated based on the relationship between (t3-t1) and (t4-t2).

[0033] The fifth step involves distributing the selected n pressure sensors on the side wall of the low-pressure chamber of the shock tube. The shock wave velocity values ​​measured by the p-th and p+1-th sensors are calculated according to the method described in the first step. These values ​​are taken as the shock wave velocity Vp at the center of the installation points of the p-th and p+1-th sensors, where p = 1, 2, ... n. The shock wave velocity attenuation law is obtained based on the shock wave velocity values ​​measured at different locations.

[0034] The sixth step involves calculating the shock wave velocity Vp at the center of the installation points of the p-th and p+1-th sensors and the distance between them and the pressure sensor being calibrated, based on the shock wave velocity attenuation law. Substituting this into the shock wave theory calculation formula, the incident step pressure amplitude and the reflected step pressure amplitude are obtained.

[0035] Although this invention frequently uses terms such as reference pressure sensor C1, C2, and selected pressure sensors C3 and C4, the possibility of using other terms is not excluded. These terms are used for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention.

[0036] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A shock tube velocimetry optimization method, characterized in that: It is mainly based on the speed sensor screening and compensation method and the shock wave velocity calculation and correction method; The speed sensor screening and compensation method uses two pressure sensors C1 and C2 as reference sensors, and arbitrarily selects two pressure sensors C3 and C4 as selected sensors. A shock tube test is performed to obtain the shock wave times t1 and t2 measured by the two reference pressure sensors C1 and C2 and the two selected pressure sensors C3 and C4. Keeping the positions of the two reference pressure sensors C1 and C2 unchanged, the positions of the two selected pressure sensors C3 and C4 are swapped, and a shock tube test is performed again to obtain the shock wave times t3 and t4 measured by the two reference pressure sensors C1 and C2 and the two selected pressure sensors C3 and C4 at this time. The difference between t4-t2 and t3-t1 is compared. If the difference meets a preset requirement, the two selected pressure sensors C3 and C4 are selected as the speed measurement pressure sensors. If the difference does not meet the preset requirement, the above steps are repeated by replacing the selected pressure sensors until a suitable pressure sensor is selected. The shock wave velocity calculation and correction method involves arranging n velocity-measuring pressure sensors distributed along the wall of the low-pressure chamber of the shock tube. The propagation time of the incident shock wave between two adjacent velocity sensors is calculated based on the time difference between the rising edges of their output curves. Furthermore, the shock wave velocity at the midpoint between the two adjacent velocity sensors is calculated based on the distance between them, resulting in the incident shock wave velocities {V1, V2, ..., V...} at n-1 locations. p ,…,V n-1 Based on the incident shock wave velocities at the n-1 locations, an incident shock wave velocity attenuation model is obtained, and the shock wave velocity at the pressure sensor under calibration is calculated based on the location of the pressure sensor under calibration, the measured shock wave velocity, and the measurement location.

2. The shock tube velocimetry optimization method as described in claim 1, characterized in that: The speed sensor selection method described above can also correct the shock wave velocity measured by the two selectable pressure sensors C3 and C4 based on the difference between t4-t2 and t3-t1.

3. The shock tube velocimetry optimization method as described in claim 2, characterized in that: There are two reference sensor mounting holes along the axis of the low-pressure chamber wall of the shock tube. The line connecting the two reference sensor mounting holes is parallel to the axis. The distance between the two reference sensor mounting holes needs to be easy to measure and is not less than 200mm. There are two optional sensor mounting holes at the axisymmetric position of the two reference sensor mounting holes.

4. The shock tube velocimetry optimization method as described in claim 3, characterized in that: Based on the velocity measurement sequence and the position sequence of each measurement point, the incident shock wave velocity model is calculated using the least squares fitting method: V p =aL p +b, where L p The distance between the measured point S1 and the first measurement point; considering minimizing the average sum of errors between the actual measured shock wave velocity and the model output, the parameters a and b are defined as follows. The shock wave velocity at the pressure sensor under calibration is calculated based on the relative position between the pressure sensor under calibration and the first measurement point S1.

5. The shock tube velocimetry optimization method as described in claim 4, characterized in that: The method for calculating the propagation time of the incident shock wave between two adjacent velocity sensors is as follows: the time difference between the rising edges of the p-th velocity sensor and the (p+1)-th velocity sensor is denoted as [t]. p1 ,…,t pq ,…,t pQ ] p＝1,2,…,n-1 Where Q is the number of effective sampling points on the rising edge of the speed sensor output signal, and the optimal propagation time t of the incident shock wave passing through the two adjacent speed sensors is calculated using a weighted average method. p This avoids errors caused by using single-point data to calculate shock wave propagation time.

6. The shock tube velocimetry optimization method as described in claim 5, characterized in that: The optimal propagation time t p Defined as in,

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