Wireless transmission wall turbulence pulsating pressure surface array measurement system based on FPGA

Abstract

The invention discloses an FPGA-based wireless transmission wall turbulence pulsating pressure surface array measurement system, which is used for a model surface pressure test in a wind tunnel test, and comprises an FPGA chip, the FPGA chip is internally provided with a control module, a synchronization module and a cache module, the control module is externally connected with the outputs of a plurality of digital sensors, and the synchronization module is connected with the cache module. The control module processes output data of a plurality of digital sensors by using an internal clock of the synchronization module and stores the output data into the cache module, and the upper computer communicates with the FPGA through the wireless transmission module; dependence on an ADC or a codec is eliminated, the pulsating pressure signal wave number frequency spectrum can be directly obtained, the problems of signal level attenuation caused by long-distance signal transmission and electromagnetic interference in a transmission path are avoided, spatial distribution characteristics of the pulsating pressure signal wave number frequency spectrum can be accurately described, the structure of a hardware acquisition system is optimized, and the cost is reduced. Therefore, the construction difficulty of the hardware test system is reduced, and meanwhile, the system has good system expandability.

Description

Technical Field

[0001] The present invention relates to the field of wind tunnel tests, and particularly to a wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA. Background Art

[0002] Wall turbulent pulsating pressure is the key excitation source for flow-induced vibration and noise problems of various military and civilian equipment. Wall turbulent pulsating pressure results from the unsteady force exerted by vortices of various scales in the turbulent boundary layer on the wall surface. On the one hand, it directly radiates noise outward, and on the other hand, it causes the wall structure to vibrate to form a secondary sound source and lead to structural fatigue. Therefore, its experimental measurement is crucial. The traditional measurement method is to directly input the wall turbulent pulsating pressure signal into the acquisition device for quantization after transmitting it over a long distance by arranging multiple sensors. There are the following deficiencies: One is that it is not easy to form an array effect. The spectral analysis of each sensor signal can only obtain the auto-power spectral density function (abbreviated as "auto-spectrum") of each measurement point, lacking spatial distribution characteristics.

[0003] Two is that the economic cost of expanding the acquisition system is high. Since the traditional measurement method accesses analog signals to the acquisition system, the traditional test method is very likely to exceed the limit capacity of the acquisition system.

[0004] Three is that long-distance transmission of analog signals affects data quality and the number of cables is huge. The traditional measurement method needs to transmit the signal to the acquisition system through extremely thin shielded long cables. Due to the relatively special use environment, the length of the long cable must be at least greater than 20m to meet the test use requirements. The long transmission distance of the extremely thin cable will cause signal level attenuation, and signals between channels are prone to crosstalk during transmission, directly affecting data quality; at the same time, if the experimental measurement object has a large size and many measurement positions, the number of measurement arrays used will increase, resulting in a sharp increase in the number of extremely long and thin cables. Therefore, the layout and volume of the cables need to be comprehensively considered during the processing of the experimental measurement object.

[0005] Four is that the construction of the hardware test system is complex. The traditional test method involves too many hardware accessories and requires certain personnel capabilities. During the hardware construction process, the probability of human misoperation increases. Based on the above factors, wireless transmission can simplify the hardware configuration of the acquisition system, optimize the acquisition process, only requires the host computer to read its ID, reducing the probability of misoperation; by applying MEMS sensors, a surface array can be formed, and through a supporting algorithm, the wave number-frequency spectrum of the complex function space characteristics can be obtained while obtaining the auto-spectrum result. Summary of the Invention

[0006] Based on the deficiencies of existing wind tunnel tests, the object of the present invention is to improve the wall turbulence pulsating pressure test ability in the fields of wind tunnels and flight tests by installing a wireless transmission wall turbulence pulsating pressure surface array measurement system based on FPGA, and using digital transmission and processing technology to obtain sensor data.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A wireless transmission wall turbulence pulsating pressure surface array measurement system based on FPGA, used for model surface pressure test in wind tunnel tests, includes an FPGA chip, in which a control module, a synchronization module and a cache module are provided. The control module is externally connected to the outputs of multiple digital sensors. The control module uses an internal clock of the synchronization module to process the output data of multiple digital sensors and store them in the cache module. The host computer communicates with the cache module through a wireless transmission module.

[0008] In the above technical solution, the digital sensor is connected to the control module of the FPGA through an 2 S interface.

[0009] In the above technical solution, the control module of the FPGA is externally connected to several connectors, each connector corresponds to the outputs of multiple digital sensors, and each connector shares a serial data clock and a word clock.

[0010] In the above technical solution, the word clock locks multiple digital sensors to the same sampling start edge through the FPGA.

[0011] In the above technical solution, several FPGA chips are included, and the several FPGA chips include a main FPGA chip and several slave FPGA chips; In each FPGA chip, a control module, a synchronization module and a cache module are provided. The control module is externally connected to the outputs of multiple digital sensors. The control module uses an internal clock of the synchronization module to process the output data of multiple digital sensors and store them in the cache module; All the FPGA chips communicate with the host computer synchronously through a wireless transmission module.

[0012] In the above technical solution, in the FPGA chip, fine phase shift is performed through a mixed-mode clock manager to synchronize the clocks of all digital sensors.

[0013] In the above technical solution, the main FPGA chip and the slave FPGA chips perform clock synchronization through the synchronization module respectively.

[0014] In the above technical solution, the data transmission between the FPGA chip and the digital sensor adopts parallel packing processing, and the packing rule is based on the arrangement order of the elements of the digital sensor array.

[0015] In the above technical solution, the FPGA chip switches the working mode of the digital sensor array by controlling the frequency on the digital sensor.

[0016] In the solution of the present invention, the pulsating pressure sensor array is designed based on a MEMS digital sensor. In order to achieve the purpose of wireless transmission, the MEMS digital sensor adopts an 2 S interface, the advantage of which is to completely eliminate the dependence on the ADC or codec and directly output digital data. At the same time, 2 as a standard digital interface, the FPGA microprocessor can directly process the received signal. The MEMS digital sensor mainly consists of three important interfaces: serial data clock, word clock, and serial data output. Among them, the word clock can lock multiple MEMS digital sensors to the same sampling frequency through the FPGA. The serial data clock and the word clock are uniformly controlled by the FPGA to ensure that the MEMS sensor is in the idle / busy state. The serial data output is that the sensor sends the responded digital signal back to the FPGA for processing.

[0017] The FPGA chip is mainly responsible for four parts. One is to receive the digital signal output by the pulsating pressure sensor array, perform packing processing, store it in the cache module, and finally send it to the wireless transmission module. The second is to control the pulsating pressure sensor array through the clock frequency. When the clock is at a low frequency, the sensor array is in the sleep state. When it is at the working frequency of the MEMS sensor, the sensor array is in the high-performance state. The third is to synchronize the signal output of all MEMS sensors. One FPGA can divide out multiple groups of interface signal lines, and at the same time, one group of interface signal lines can control multiple MEMS sensors, and the synchronous output of the sensors is maintained by dividing the edge of the fundamental frequency clock. The fourth is to synchronize the signal output of the portable wireless transmission surface pulsating pressure measurement device. When multiple such measurement devices work simultaneously, the host computer first sends a signal to the wireless transmission module, and then the synchronization module of the FPGA performs synchronization.

[0018] The wireless transmission module has three functions. One is to send the cached data in the FPGA cache module to the host computer through the wireless communication protocol. The second is to receive the control command from the host computer, and after being parsed by the FPGA, switch the working state of the pulsating pressure sensor array. The third is that when multiple measurement devices work simultaneously, the wireless module distributes the command to the FPGA through module and waits for the synchronization command.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: First, multiple MEMS digital sensors form an array effect, enabling the direct acquisition of the wavenumber frequency spectrum of the pulsating pressure signal and accurately describing its spatial distribution characteristics. Second, the MEMS digital sensor with an I 2 S interface completely eliminates the dependence on ADC or codec, saving the cost of the acquisition board in terms of hardware. Third, it avoids the signal level attenuation caused by long-distance signal transmission and electromagnetic interference problems in the transmission path. Fourth, it optimizes the structure of the hardware acquisition system, reduces the difficulty of building the hardware test system, and also has good system scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be described by way of examples with reference to the accompanying drawings, where: Figure 1 is a schematic diagram of the system architecture; Figure 2 is a schematic diagram of the measured result of the flow wavenumber-frequency spectrum obtained. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] All features disclosed in this specification, or all steps in the disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any manner.

[0022] Any feature disclosed in this specification (including any additional claims, abstract, and drawings), unless specifically stated, can be replaced by other equivalent or similar-purpose alternative features. That is, unless specifically stated, each feature is only an example of a series of equivalent or similar features.

[0023] As Figure 1 shown, the pulsating pressure sensor array in this embodiment has a total of 16 measurement units. The MEMS digital sensor selects TDK T5848, which has a standard 24-bit I 2 S interface, with 20 digital signal output bits and multiple operating modes (low-power mode, high-performance mode, sleep mode). The acoustic overload point in the high-performance operating mode can reach 133 dB SPL, and the clock frequency is 2.0 MHz to 3.7 MHz. In this embodiment, T5848 includes a serial data clock (SCK), a word clock (WS), a serial data output (SD), a working power supply (VDD), and a ground (GND). Among them, in order to achieve better performance and avoid parasitic circuits, a 0.1 μF capacitor needs to be placed between VDD and GND. The capacitor selects a ceramic type X7R capacitor and should be as close as possible to the VDD pin. VDD is externally connected to a 3.3 VDC working power supply. In addition, the SD pin is in a tri-state state when there is no driving output channel. Therefore, a 100 kΩ pull-down resistor needs to be provided at this pin to discharge the circuit when the outputs of all sensors on the bus are in a tri-state.

[0024] The FPGA mainly includes three parts: a control module, a synchronization module, and a cache module. Its core chip uses Xilinx's XCZU9EG. Each FPGA needs to be equipped with an ID name. The FPGA also needs to parse and execute the control commands from the host computer.

[0025] The control module of the FPGA is externally connected to two high-speed connectors. Each connector corresponds to 8 MEMS sensors. The 8 sensors share the serial data clock and word clock to ensure synchronous output of the 8 sensors. Since the clock frequency of T5848 can reach 3.7 MHz, the data captured by the 8 sensors will have a maximum time difference of 3.5 cycles, that is, less than 1 μs. The synchronization between the two groups of sensors can use the internal clock of the same FPGA. The serial data output of each sensor corresponds to a connection line. Therefore, the FPGA can perform parallel packaging processing on the output data of the sensors. The packaging rule is based on the arrangement order of the elements of the pulsating pressure sensor array. After packaging, the data is stored in the cache module. At the same time, the FPGA switches the working mode of the pulsating pressure sensor array by controlling the frequency on the SCK of the T5848 sensor. When SCK = 100 KHz, it is in the low-power mode. When SCK = 3.7 MHz, it is in the high-performance mode. The data acquisition of the pulsating pressure sensor array is carried out in the high-performance mode.

[0026] The cache module of the FPGA uses two Micron DDR4s with a memory size of 1 GB / PCS, for a total of 2G. The T5848 sensor operates at a clock frequency of 3.7 MHz, and its maximum sampling rate is 57.8 KHz. Then, 16 sensors generate approximately 3 MB of data per second. After excluding 10% redundancy, the cache module is sufficient to store 10 minutes of data volume, and the data in the cache module is continuously sent to the wireless transmission module.

[0027] The synchronization module of the FPGA mainly performs clock synchronization on different devices when multiple measurement devices are used simultaneously. It uses the IEEE 1588 synchronization protocol, and sets the measurement device with a smaller ID as the master device, and other ID measurement devices as slave devices. The master device publishes PTP messages at a cycle of 1 s. The slave devices receive the timestamp information and calculate the time delay and time deviation between the master and slave devices. Then, fine phase shift processing is performed through the mixed-mode clock manager MMCM in the FPGA, so that the entire system is synchronized and the phase difference between the pulsating pressure sensor arrays is reduced.

[0028] The wireless transmission module uses the ESP32 WIFI module as an external device of the FPGA to implement TCP communication between the upper computer and the FPGA. It supports 2.4GHz WI-FI. The UART communication protocol is adopted between the ESP32 WIFI module and the FPGA. Since the ESP32 WIFI module requires a stable working power supply, an external power supply is used.

[0029] The power supply module uses a lithium battery, which mainly provides working power for the FPGA, the pulsating pressure sensor array, and the wireless transmission module. It is necessary to convert the output of the lithium battery into the rated working voltage of the above-mentioned devices. The rated working voltage of the FPGA is 12VDC, the rated working voltage of the pulsating pressure sensor array is 3.3VDC, and the rated working voltage of the wireless transmission module is 3.3VDC. Therefore, a DC / DC module is used for the LM2569 buck-type power management chip, and separate power supplies are required during circuit design to avoid problems such as signal interference.

[0030] The pulsating pressure sensor array is arranged on the surface of the flat plate model. To ensure that the fluid is fully transitioned before measurement, a transition tape is installed at the front end of the surface array. During the experiment, the sampling time is set to 8s. After the sampling is completed, the line array data processing method for measuring the surface pulse pressure wave number-frequency spectrum can be used to obtain the streamwise wave number-frequency spectrum, specifically as Figure 2 shown. The left vertical coordinate in the figure is the wave number in the streamwise direction during the propagation of the turbulent boundary layer wave, and the horizontal coordinate is the angular frequency. The right horizontal coordinate is the turbulent boundary layer pulsating pressure wave number-frequency spectrum density function.

[0031] The present invention is not limited to the foregoing specific embodiments. The present invention extends to any new feature or any new combination disclosed in this specification, as well as any new method or process step or any new combination disclosed.

Claims

1. A wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA, which is used for model surface pressure testing in wind tunnel experiments, is characterized in that: It includes an FPGA chip, in which a control module, a synchronization module and a cache module are provided. The control module is externally connected to the outputs of multiple digital sensors. The control module processes the output data of the multiple digital sensors by using an internal clock of the synchronization module and stores the processed data into the cache module. The host computer communicates with the cache module through a wireless transmission module.

2. The wireless transmission wall turbulence pulsating pressure surface array measurement system based on FPGA according to claim 1, characterized in that: The digital sensor is connected to the control module of the FPGA through an I 2 S interface.

3. A wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA according to claim 2, characterized in that: The control module of the FPGA is externally connected to several connectors. Each connector corresponds to the outputs of multiple digital sensors, and each connector shares a serial data clock and a word clock.

4. A wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA according to claim 3, characterized in that: The word clock locks multiple digital sensors to the same sampling start edge through the FPGA.

5. The wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA according to claim 1, characterized in that: It includes several FPGA chips, and among the several FPGA chips, there is a main FPGA chip and several slave FPGA chips. In each FPGA chip, a control module, a synchronization module and a cache module are provided. The control module is externally connected to the outputs of multiple digital sensors. The control module processes the output data of the multiple digital sensors by using an internal clock of the synchronization module and stores the processed data into the cache module. All the FPGA chips communicate with the host computer synchronously through a wireless transmission module.

6. The wireless transmission wall turbulent pulsation pressure surface array measurement system based on FPGA according to claim 5, characterized in that: In the FPGA chip, fine phase shift is performed through a mixed-mode clock manager to synchronize the clocks of all the digital sensors.

7. A wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA according to claim 6, characterized in that: The main FPGA chip and the slave FPGA chips perform clock synchronization through the synchronization module respectively.

8. A wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA according to any one of claims 1-7, characterized in that: The data transmission between the FPGA chip and the digital sensors adopts parallel packaging processing, and the packaging rule is based on the arrangement order of the elements of the digital sensor array.

9. The wireless transmission wall turbulent pulsating pressure surface array measurement system based on FPGA according to claim 8, wherein: The FPGA chip switches the working mode of the digital sensor array by controlling the frequency on the digital sensor.

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