A non-contact flow field measurement device and method using nitrogen droplets as tracer particles

Abstract

The application discloses a non-contact flow field measuring device and method with nitrogen droplets as tracer particles, and belongs to the technical field of flow field visualization. A Laval nozzle is used as a nitrogen droplet generating device, and the Laval nozzle is arranged in a high-speed flow section. After the nitrogen droplets flowing out of the Laval nozzle are mixed with the main flow in the high-speed flow section, the nitrogen droplets pass through an expansion section and a flow regulation section and then enter a speed measuring section. A high-speed camera is used in the speed measuring section to capture the nitrogen droplets and obtain the air flow speed. By actively regulating and controlling the operating parameters of the wind tunnel, the total temperature, the Ma number and the expansion ratio of the Laval nozzle in the wind tunnel are reasonably controlled, so that the condensation nitrogen droplets are spontaneously generated at a proper position, the condensation degree is controlled, and the disturbance of the flow field near the test model is reduced as much as possible. The application aims to solve the key problem that suitable and available tracer particles are lacked in the application of the non-contact measurement technology in a low-temperature wind tunnel, and provides a new feasible way for the application of the non-contact flow field measurement technology in a transonic low-temperature wind tunnel.

Description

Technical Field

[0001] This invention belongs to the field of flow field visualization technology, and more specifically, relates to a non-contact flow field measurement device and method using nitrogen droplets as tracer particles. Background Technology

[0002] Non-contact flow field measurement techniques indirectly reflect flow field velocity by capturing externally applied tracer particles. Under cryogenic conditions, the aggregation and clustering effect of these tracer particles needs to be considered. In existing technologies, the most commonly used tracer particles in cryogenic wind tunnel flow field tracing studies are only oil-based particles and ice particles. However, oil droplets adhere to and penetrate insulation materials, making them difficult to remove completely and affecting the internal insulation materials and components of the wind tunnel, causing permanent damage. Ice particles exhibit significantly enhanced aggregation at cryogenic temperatures, resulting in excessively large particle sizes, uneven particle distribution, and poorer flow field tracking.

[0003] It is evident that a perfect tracer particle has yet to be found for use in my country's transonic cryogenic wind tunnels under construction. The availability of tracer particles has become a key issue limiting the application of non-contact measurement techniques in cryogenic wind tunnels. Summary of the Invention

[0004] To address the shortcomings and improvement needs of existing technologies, this invention provides a non-contact flow field measurement device and method using nitrogen droplets as tracer particles. It aims to solve the key problem of the lack of suitable and available tracer particles in the application of non-contact measurement technology in cryogenic wind tunnels, and to provide a new feasible approach for the application of non-contact flow field measurement technology in transonic cryogenic wind tunnels.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a non-contact flow field measurement device using nitrogen droplets as tracer particles, comprising: a liquid nitrogen tank, a Laval nozzle, and a liquid nitrogen injection section, a bend, a high-speed flow section and a velocity measurement section connected in sequence;

[0006] The liquid nitrogen tank is connected to the liquid nitrogen injection section via a valve to provide cryogenic liquid nitrogen; the cryogenic liquid nitrogen is injected into the liquid nitrogen injection section and vaporized before entering the first bend and the high-speed flow section in sequence;

[0007] The Laval nozzle is fixed in the high-speed flow section by a bracket, and is used to spontaneously condense a portion of the nitrogen gas entering the Laval nozzle to form nitrogen droplets. The nitrogen droplets, as tracer particles, mix with the remaining nitrogen gas in the high-speed flow section at the outlet of the Laval nozzle and then enter the velocity measurement section to complete non-contact flow field measurement.

[0008] Furthermore, the Laval nozzle includes a contraction section, an expansion section, an adjusting rod, a piston, a track support, a rod connection hole, an expansion section extension housing, and a central support;

[0009] The central support is fixed to the contraction section;

[0010] The adjusting rod is divided into two sections: one section connects the central support to one end of the piston, and the other section connects the other end of the piston to the expansion section housing.

[0011] The track support is fixed to the outlet of the expansion section, and the track support has a tie rod connection hole so that the adjusting tie rod can be connected to the expansion section expansion shell. The bottom of the track support has a track so that the expansion section expansion shell can move stably.

[0012] The piston is used to push the expansion section housing along the track support until it connects with the Laval nozzle outlet.

[0013] Furthermore, the adjusting rod, piston, track support, rod connecting hole, and expansion section expansion housing are all multi-stage configurations to achieve multi-stage expansion rate adjustment of the Laval nozzle.

[0014] Furthermore, the expansion section and the expansion section expansion shell, or the multi-stage expansion section expansion shell, are sealed with polytetrafluoroethylene.

[0015] Furthermore, the non-contact flow field measurement device also includes a connected expansion section and a rectification section;

[0016] The expansion section and the rectification section are located between the high-speed flow section and the velocity measurement section, and are used to uniformly mix the nitrogen droplets and the remaining nitrogen gas.

[0017] Furthermore, the non-contact flow field measurement device also includes a heat exchanger and a fan;

[0018] The heat exchanger and the fan are used to control the inlet temperature and inlet pressure of the Laval nozzle, respectively, thereby adjusting the particle size of the nitrogen droplets generated by the Laval nozzle.

[0019] Furthermore, observation windows are provided on both the front and rear sides of the speed measuring section. One side is illuminated by a supplementary light source, and the other side is captured by a high-speed camera to capture nitrogen droplets.

[0020] Furthermore, the main body of the speed measuring section is sealed with an indium seal method between itself and the cover plate containing the observation window.

[0021] Furthermore, the Laval nozzle is made of stainless steel.

[0022] Secondly, the present invention provides a non-contact flow field measurement method using nitrogen droplets as tracer particles, comprising:

[0023] Adjust the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle according to the following formulas to ensure that the nitrogen droplet size range generated by the Laval nozzle meets the requirements:

[0024] d=aP b T c K

[0025] K = 1 + (1.8 × 10) -4 ×ε)

[0026] Where d represents the nitrogen droplet size, a, b, and c represent the fitting coefficients, P, T, and ε represent the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle, respectively, and K represents the fitting correction coefficient.

[0027] Adjust the inlet pressure and inlet temperature of the Laval nozzle according to the following formula to ensure that the nitrogen droplet density range generated by the Laval nozzle meets the requirements:

[0028] log10(N) = eP f T g

[0029] Where N represents the number of nitrogen droplets, and e, f, and g are fitting coefficients;

[0030] After determining the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle, nitrogen droplets that meet the requirements are generated based on the non-contact flow field measurement device described in the first aspect to complete the non-contact flow field measurement.

[0031] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0032] (1) The present invention sets up a Laval nozzle in the high-speed flow section, and generates nitrogen droplets through the Laval nozzle as tracer particles. Since nitrogen droplets can spontaneously condense and generate, the external equipment is technically simple, easy to operate, and inexpensive; and the spontaneously condensed nitrogen droplets will not affect the internal insulation materials and components of the wind tunnel, so it is suitable for low-temperature wind tunnels.

[0033] (2) The expansion rate of the Laval nozzle of the present invention can be adjusted according to experimental needs, thereby flexibly adjusting the range of nitrogen droplet size to adapt to different low-temperature wind tunnel test conditions.

[0034] (3) The nitrogen droplets generated by the Laval nozzle of this invention are mixed with the mainstream and then pass through the expansion section and the rectification section, resulting in uniform particle distribution and good flow field following.

[0035] (4) By fitting the relationship between nitrogen droplet size and density and the inlet pressure, inlet temperature and expansion rate of the Laval nozzle, this invention can actively regulate the wind tunnel operating parameters, reasonably control the total temperature and Mach number in the wind tunnel, and appropriately adjust the expansion rate of the Laval nozzle so that the nitrogen droplet size and density range generated by the Laval nozzle meet the requirements. At the same time, it can control the degree of droplet condensation so that the condensed droplets continue to the velocity measurement section. In the test section, the droplets evaporate, which can reduce the disturbance of the flow field near the test model. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a non-contact flow field measurement device using nitrogen droplets as tracer particles, provided in an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of a conventional Laval nozzle structure provided in an embodiment of the present invention;

[0038] Figure 3 A schematic diagram of a Laval nozzle structure with adjustable expansion rate provided in an embodiment of the present invention;

[0039] Figure 4 A schematic diagram of the adjustable expansion section of the Laval nozzle provided in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the speed measuring section structure provided in an embodiment of the present invention.

[0041] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0042] 1-Liquid nitrogen tank; 2-Safety valve; 3-Solenoid valve; 4-Liquid nitrogen injection section; 5-First bend; 6-Laval nozzle; 7-High-speed flow section; 8-Expansion section; 9-Rectifying section; 10-Velocity measurement section; 11-High-speed camera; 12-Supplemental lighting instrument; 13-Test section; 14-Nozzle section; 15-Contraction section; 16-Stabilization section; 17-Second bend; 18-Nitrogen exhaust section; 19-Third bend; 20-Heat exchanger; 21-Power section; 22 23-Fan; 24-Electric motor; 25-Four-turn; 26-Laval nozzle inlet; 27-Contraction section; 28-Expansion section; 29-Laval nozzle outlet; 30-Laval nozzle cover plate; 31-Adjusting rod; 32-Rail support; 33-Rod connection hole; 34-Expansion section extension housing; 35-Center support; 36-Velocity measuring section main body; 37-Velocity measuring section cover plate; 38-Velocity measuring section viewing window. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0045] Cryogenic wind tunnels use nitrogen as the working fluid, significantly increasing the Reynolds number by lowering the fluid temperature, increasing its density, and reducing its viscosity. Cryogenic wind tunnels have a wide adjustment range, achieving Mach numbers (Ma) of 0.15-1.3 and total temperatures of 110-323 K. In cryogenic wind tunnels, to maximize the experimental Reynolds number and reduce drive power, the total nitrogen temperature must be minimized. However, the lower the temperature, the closer the operating conditions are to the condensation limit; therefore, nitrogen condensation often occurs in cryogenic wind tunnels.

[0046] In fact, supersaturated condensation in a transonic cryogenic wind tunnel is a rapid non-equilibrium heat and mass transfer process. During the expansion and depressurization of nitrogen, the gas is restricted by the free energy barrier at the saturation point and will not condense. Instead, it continues to expand into a metastable state, which is called the supercooled (or supersaturated) stage. When the supercooled state reaches its extreme (i.e., the Wilson point), gas molecules overcome the free energy barrier and begin to condense spontaneously, entering the "rapid nucleation" stage. When the diameter of the condensation nuclei reaches a critical value, it enters the "droplet growth" stage. The droplets formed in this non-equilibrium process are uniformly distributed in the gas flow.

[0047] The number and size of droplets are determined by state parameters such as total temperature, total pressure, and supersaturation of the flow field. The latent heat released during the condensation phase transition is absorbed by the flow field, gradually reducing its supercooling. Therefore, in a transonic cryogenic wind tunnel, the microscale nucleation and droplet growth processes are coupled with the macroscale high-speed airflow, forming a complex multi-scale flow and heat / mass transfer process. Thus, nitrogen droplet condensation can be controlled based on non-equilibrium condensation theory, using nitrogen droplets as tracer particles in the wind tunnel.

[0048] Based on the above theory, this invention provides a non-contact flow field measurement device that uses nitrogen droplets as tracer particles, such as... Figure 1As shown, it includes: liquid nitrogen tank 1, Laval nozzle 6, and liquid nitrogen injection section 4, first bend 5, high-speed flow section 7, velocity measurement section 10, test section 13, nozzle section 14, contraction section 15, stabilization section 16, second bend 17, nitrogen discharge section 18, third bend 19, heat exchanger 20, power section 21, fan 22, electric motor 23, and fourth bend 24 connected in sequence.

[0049] The liquid nitrogen tank 1 is connected to the liquid nitrogen injection section 4 via a safety valve 2 and a solenoid valve 3. The liquid nitrogen tank 1 is used to provide cryogenic liquid nitrogen. The cryogenic liquid nitrogen is injected into the liquid nitrogen injection section 4 and vaporized before entering the first bend 5 and the high-speed flow section 7 in sequence.

[0050] The Laval nozzle 6 is fixed in the high-speed flow section 7 by a bracket, and is used to spontaneously condense a portion of the nitrogen gas entering the Laval nozzle 6 into nitrogen droplets; the nitrogen droplets, as tracer particles, mix with the remaining nitrogen gas in the high-speed flow section 7 at the outlet of the Laval nozzle 6 and then enter the velocity measurement section 10.

[0051] Traditional Laval nozzle structure, such as Figure 2 As shown, the Laval nozzle consists of a main body and a cover plate 29. The main body includes an inlet 25, a contraction section 26, an expansion section 27, and an outlet 28. Both the main body and the cover plate are made of stainless steel and are connected by flanges. Furthermore, the Laval nozzle is fixed to the high-speed flow section by a bracket. A portion of the high-speed flowing nitrogen gas passes through the Laval nozzle, where the gas flow accelerates and depressurizes, causing the temperature to drop and the nitrogen to begin condensing, breaking through the condensation point. Nitrogen droplets flow out of the Laval nozzle, mix with the mainstream, and flow with the mainstream, exhibiting tracer characteristics. After being uniformly mixed in the expansion section 8 and the rectification section 9, it enters the velocity measurement section 10.

[0052] In traditional Laval nozzles, the structure of the expansion section is fixed and cannot be adjusted. To adapt to different cryogenic wind tunnel test conditions, this invention proposes a Laval nozzle with adjustable nitrogen droplet size and density range, comprising a connected inlet contraction section and an outlet expansion section; wherein the structure and length of the outlet expansion section are adjustable. Specifically, when the outlet expansion section is shorter, the nitrogen expands faster, resulting in smaller droplet size; when the outlet expansion section is longer, the nitrogen expands slower, resulting in larger droplet size. Therefore, the Laval nozzle with adjustable expansion rate can flexibly adjust the droplet size range according to experimental needs, adapting to different cryogenic wind tunnel test conditions.

[0053] like Figure 3 and Figure 4 As shown, the Laval nozzle 6 includes a contraction section 26, an expansion section 27, an adjusting rod 30, a piston 31, a track support 32, a rod connection hole 33, an expansion section extension housing 34, and a central support 35.

[0054] The central support 35 is fixed to the housing of the Laval nozzle contraction section 26. The adjusting rod 30 is divided into two sections: one section connects the central support 35 to one end of the piston 31, and the other section connects the other end of the piston 31 to the expansion section expansion housing 34. The track support 32 is fixed to the outlet housing of the expansion section 27, and the track support 32 has a rod connection hole 33 so that the adjusting rod 30 can be connected to the expansion section expansion housing 34; the bottom of the track support 32 has a track so that the expansion section expansion housing 34 can move stably.

[0055] The piston 31 pushes the expansion section extension housing 34 to move along the track support 32 until it connects with the Laval nozzle outlet.

[0056] Furthermore, multi-stage expansion section housings and multi-stage track supports can be installed to achieve multi-stage expansion rate adjustment of the Laval nozzle. Polytetrafluoroethylene (PTFE) seals are used between expansion sections and expansion section housings, or between multi-stage expansion section housings.

[0057] The structural diagram of speed measuring section 10 is shown below. Figure 4 As shown. Quartz glass observation windows are provided on both the front and rear sides of the speed measuring section to ensure camera imaging. Supplemental lighting is provided by the supplementary lighting instrument 12, and the high-speed camera 11 captures the droplets, using nitrogen droplets as tracer particles for speed measurement. The speed measuring section cover 37 is made of stainless steel and is sealed to the speed measuring section observation window 38 using a flange and PVC sealing ring. The speed measuring section cover 37 is connected to the speed measuring section body 36 by a flange, and the two are sealed using a groove and indium seal method.

[0058] The heat exchanger 20 and the fan 22 are used to control the inlet temperature and inlet pressure of the Laval nozzle 6, respectively, thereby adjusting the particle size of the nitrogen droplets generated by the Laval nozzle. They can also make the nitrogen droplets exist continuously and diffuse with the mainstream to the velocity measurement section 10, where the mainstream flow velocity is captured by a high-speed camera.

[0059] In addition, some of the nitrogen that was not discharged from the nitrogen discharge section 18 is recycled back into the liquid nitrogen injection section 4.

[0060] It should be noted that the non-contact flow field measurement device provided by this invention theoretically only needs to include a liquid nitrogen tank 1, a Laval nozzle 6, a liquid nitrogen injection section 4, a bend 5, a high-speed flow section 7, and a velocity measurement section 10. However, in order to clearly describe the entire wind tunnel structure, [the following is omitted as it is not directly related to the preceding text]. Figure 1 The examples are provided for illustration only and are not intended to limit the scope of the invention.

[0061] Based on the above-mentioned non-contact flow field measurement device, the present invention also provides a non-contact flow field measurement method using nitrogen droplets as tracer particles, comprising the following steps:

[0062] 1. Determine the density and particle size range of the nitrogen droplets.

[0063] The nitrogen droplet density needs to reach 10 droplets / mm 3 ~10,000 pieces / mm 3 If the number of nitrogen droplets is too small, they are difficult to capture; if the number of nitrogen droplets is too large, they will agglomerate and affect the flow characteristics of the nitrogen droplets, thus failing to give full play to the characteristics of the tracer particles.

[0064] Nitrogen droplet size ranges from 1 to 100 μm. Droplets smaller than 1 μm are invisible, while those larger than 100 μm are too heavy, causing a difference in velocity with the airflow and affecting the accuracy of non-contact measurements. Based on calculations combining the Stokes number and nitrogen droplet evaporation rate, the size of nitrogen droplets in a cryogenic wind tunnel should fall within this range.

[0065] 2. Adjust the nitrogen droplet size by regulating the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle. Refer to the following formula for parameter adjustments:

[0066] d=aP b T c K

[0067] Where d represents the nitrogen droplet size in mm, and a, b, and c are fitting coefficients with values ​​of 8.75 × 10⁻⁶. 4 7.36, -4.10, where P and T represent the inlet pressure and inlet temperature of the Laval nozzle, respectively, in MPa and K. K is the fitting correction coefficient, used to correct for errors caused by the expansion rate of the Laval nozzle.

[0068] K = 1 + (1.8 × 10) -4 ×ε)

[0069] Wherein, K ranges from 1 to 3, and ε represents the expansion rate of the Laval nozzle. In this embodiment, the expansion rate of the Laval nozzle ranges from 3000 to 10000 s. -1 .

[0070] By adjusting the inlet pressure and temperature of the Laval nozzle, the distribution density of nitrogen droplets can be adjusted. The parameter adjustments are based on the following formula:

[0071] log10(N) = eP f T g

[0072] Where N represents the number of nitrogen droplets, in units of droplets / mm. 3 e, f, and g are fitting coefficients with values ​​of 0.23, -0.40, and 0.81, respectively. P and T represent the inlet pressure and inlet temperature of the Laval nozzle, respectively, in MPa and K.

[0073] The above formula is applicable to pressures of 0.3–0.6 MPa and temperatures of 93–115 K.

[0074] 3. After determining the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle, nitrogen droplets that meet the requirements are generated based on the above-mentioned non-contact flow field measurement device. Then, using the nitrogen droplets as tracer particles, the flow velocity can be measured by capturing the nitrogen droplets with a high-speed camera, thus completing the non-contact flow field measurement.

[0075] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 non-contact flow field measurement device using nitrogen droplets as tracer particles, characterized in that, include: Liquid nitrogen tank (1), Laval nozzle (6), and liquid nitrogen injection section (4), bend (5), high-speed flow section (7) and velocity measurement section (10) connected in sequence. The liquid nitrogen tank (1) is connected to the liquid nitrogen injection section (4) via a valve to provide cryogenic liquid nitrogen; the cryogenic liquid nitrogen is injected into the liquid nitrogen injection section (4) and vaporized before entering the first bend (5) and the high-speed flow section (7) in sequence. The Laval nozzle (6) is fixed in the high-speed flow section (7) by a bracket, which is used to spontaneously condense a portion of the nitrogen gas entering the Laval nozzle (6) into nitrogen droplets; the nitrogen droplets, as tracer particles, are mixed with the remaining nitrogen gas in the high-speed flow section (7) at the outlet of the Laval nozzle (6) and then enter the velocity measurement section (10) to complete the non-contact flow field measurement. The Laval nozzle (6) includes a contraction section (26), an expansion section (27), an adjusting rod (30), a piston (31), a track support (32), a rod connection hole (33), an expansion section extension housing (34), and a center support (35). The central support (35) is fixed to the contraction section (26); The adjusting rod (30) is divided into two sections. One section connects the central support (35) to one end of the piston (31), and the other section connects the other end of the piston (31) to the expansion section expansion housing (34). The track support (32) is fixed to the outlet of the expansion section (27), and the track support (32) has a tie rod connection hole (33) so that the adjusting tie rod (30) can be connected to the expansion section expansion shell (34). The bottom of the track support (32) has a track so that the expansion section expansion shell (34) can move stably. The piston (31) is used to push the expansion section extension housing (34) along the track support (32) until it is connected to the Laval nozzle outlet.

2. The non-contact flow field measurement device according to claim 1, characterized in that, The adjusting rod (30), piston (31), track support (32), rod connecting hole (33), and expansion section expansion housing (34) are all multi-stage, realizing multi-stage expansion rate adjustment of the Laval nozzle.

3. The non-contact flow field measurement device according to claim 2, characterized in that, The expansion section (27) and the expansion section extension shell (34) or the multi-stage expansion section extension shell (34) are sealed with polytetrafluoroethylene.

4. The non-contact flow field measurement device according to any one of claims 1 to 3, characterized in that, The non-contact flow field measurement device also includes a connected expansion section (8) and a rectification section (9). The expansion section (8) and the rectification section (9) are located between the high-speed flow section (7) and the velocity measurement section (10) and are used to uniformly mix the nitrogen droplets and the remaining nitrogen gas.

5. The non-contact flow field measurement device according to any one of claims 1 to 3, characterized in that, The non-contact flow field measurement device also includes a heat exchanger (20) and a fan (22). The heat exchanger (20) and the fan (22) are used to control the inlet temperature and inlet pressure of the Laval nozzle (6), thereby adjusting the particle size of the nitrogen droplets generated by the Laval nozzle.

6. The non-contact flow field measurement device according to any one of claims 1 to 3, characterized in that, The speed measuring section (10) is equipped with observation windows on both sides. One side is illuminated by a supplementary light instrument, and the other side is captured by a high-speed camera to capture nitrogen droplets.

7. The non-contact flow field measurement device according to any one of claims 1 to 3, characterized in that, The Laval nozzle (6) is made of stainless steel.

8. A non-contact flow field measurement method using nitrogen droplets as tracer particles, characterized in that, include: Adjust the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle according to the following formulas to ensure that the nitrogen droplet size range generated by the Laval nozzle meets the requirements: in, Indicates the nitrogen droplet size, a , b , c Represents the fitting coefficient. , , These represent the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle, respectively. Indicates the fitting correction coefficient; Adjust the inlet pressure and inlet temperature of the Laval nozzle according to the following formula to ensure that the nitrogen droplet density range generated by the Laval nozzle meets the requirements: in, N Indicates the number of nitrogen droplets. e , f , g These are the fitting coefficients; After determining the inlet pressure, inlet temperature, and expansion rate of the Laval nozzle, nitrogen droplets that meet the requirements are generated based on the non-contact flow field measurement device described in any one of claims 1 to 7 to complete the non-contact flow field measurement.

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