A negative pressure Laval nozzle flow characteristics experimental system and experimental method

Abstract

The present invention discloses a negative pressure Laval nozzle flow characteristic experimental system and an experimental method thereof, including an experimental device and a test assembly, wherein the experimental device includes a pressure stabilizing tank, the top of the pressure stabilizing tank is connected to the nozzle through a connecting pipe, the pressure stabilizing tank is connected to a vacuum pump through a pipeline, and the pressure stabilizing tank is provided with a pressure regulating valve; the test assembly includes a joint pressure sensor and a flow meter arranged at the nozzle inlet through a three-way joint, a pressure stabilizing tank pressure sensor arranged in cooperation with the pressure stabilizing tank, a plurality of pipe wall pressure sensors arranged on the side wall of the nozzle, a force sensor arranged between the connecting pipe and the pressure stabilizing tank, a temperature sensor arranged on the side of the connecting pipe, and one or more of a nozzle outlet pressure sensor. The present invention can realize the test of physical parameters related to the flow field inside the nozzle, intuitively reflect the flow field characteristics inside the nozzle, thereby realizing nozzle performance comparison and profile structure optimization, and can be used as an experimental teaching device to demonstrate air flow characteristic experiments to enhance the teaching effect.

Description

Technical Field

[0001] The invention belongs to the technical field of nozzle experiments, and in particular relates to a negative pressure Laval nozzle flow characteristic experiment system and an experiment method thereof. Background Art

[0002] Laval nozzles can be divided into positive pressure and negative pressure structural schemes according to the different pressurization methods at the nozzle inlet and outlet. The positive pressure type is to pressurize the nozzle inlet, and the nozzle outlet is placed in the atmosphere, relying on the positive pressure at the inlet to drive the airflow movement; the negative pressure type uses vacuum to form negative pressure at the nozzle outlet, and the nozzle inlet is placed in the atmosphere, and air is sucked into the nozzle to form a supersonic airflow. At present, most of the experimental devices involving nozzles use a positive pressure structural scheme, and the experimental cost is relatively high. The negative pressure structural schemes available on the market can generally only test the pressure parameters on the axis, and other physical quantities cannot be measured.

[0003] On the one hand, although the reference materials explain the principle of the Laval nozzle and the characteristics of its internal flow field, most of the experimental devices related to the flow field inside the nozzle can only test the pressure at a certain point on the nozzle axis, and cannot complete multi-point testing of the side wall pressure. This makes it impossible for students to have an intuitive understanding of the internal flow field characteristics of the nozzle, affecting the teaching effect. On the other hand, the positive pressure nozzle experimental device is relatively expensive, has a relatively small expansion ratio, unstable total pressure, large pressure fluctuations, and unstable flow field parameters inside the nozzle, making it impossible to optimize the nozzle profile structure based on the parameters. Summary of the invention

[0004] One of the purposes of the present invention is to design a low-cost negative pressure Laval nozzle flow characteristics experimental system that is easy to promote on a large scale, on this basis to complete the measurement of the internal flow field parameters of the nozzle, and further achieve the purpose of optimizing the nozzle profile structure.

[0005] The second purpose of the present invention is to provide an experiment and teaching method for a negative pressure Laval nozzle flow characteristics experiment system to solve the problem of incomplete test parameters and data of the nozzle experimental device in the background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A negative pressure Laval nozzle flow characteristics experimental system, an experimental device and a test assembly, wherein the experimental device comprises a pressure stabilizing tank, the top of which is connected to the nozzle through a connecting pipe, the pressure stabilizing tank is connected to a vacuum pump through a pipeline, and the pressure stabilizing tank is equipped with a pressure regulating valve;

[0008] The test assembly includes a joint pressure sensor and a flow meter arranged at the nozzle inlet through a three-way joint, a pressure-stabilizing tank pressure sensor arranged in cooperation with a pressure-stabilizing tank, a plurality of pipe wall pressure sensors arranged on the side wall of the nozzle, a force sensor arranged between the connecting pipe and the pressure-stabilizing tank, a temperature sensor arranged on the side of the connecting pipe, and one or more nozzle outlet pressure sensors. The joint pressure sensor, flow meter, pressure-stabilizing tank pressure sensor, pipe wall pressure sensor, force sensor, temperature sensor, and nozzle outlet pressure sensor are all arranged in cooperation with a dynamic information acquisition and analysis instrument.

[0009] Preferably, a plurality of threaded through holes are sequentially provided on the side wall of the nozzle from top to bottom, one end of any threaded through hole is connected to a stainless steel pipe, and the stainless steel pipe and the pipe wall pressure sensor are connected via a ferrule joint.

[0010] Preferably, the connecting tube and the force sensor are connected via threads, a medium flow channel is provided inside the force sensor, and the inner diameter of the connecting tube is consistent with the diameter of the medium flow channel.

[0011] Preferably, a sealing ring is provided between the force sensor and the connecting pipe.

[0012] Preferably, the nozzle is threadedly connected to the connecting pipe, and the inner diameter of the connecting pipe is not less than the maximum inner diameter of the nozzle.

[0013] Preferably, the nozzle is a conical profile nozzle, a double arc profile nozzle, or a cubic polynomial profile nozzle.

[0014] An experimental method using a negative pressure Laval nozzle flowability experimental system is applied, wherein the experiment includes a nozzle wall pressure test experiment, and the nozzle wall pressure test experiment includes the following steps:

[0015] Step 1: Assemble the test system, the nozzle is connected to the pressure regulating tank through a connecting pipe, the pipe wall pressure sensors are arranged on the side of the nozzle from top to bottom, and the nozzle outlet pressure sensor is arranged on one side of the connecting pipe;

[0016] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within a preset time after stabilization, and obtain the nozzle wall pressure curve through the dynamic information acquisition and analysis instrument.

[0017] Preferably, the experiment further includes a nozzle flow rate test experiment, and the nozzle flow rate test experiment includes the following steps:

[0018] Step 1: Assemble the test system, connect one end of the tee joint to the inlet of the nozzle, connect the other two ends of the tee joint to the flow meter and the joint pressure sensor respectively, connect the nozzle to the pressure regulating tank through the connecting pipe, and set the nozzle outlet pressure sensor on one side of the connecting pipe;

[0019] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition analyzer to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition analyzer to obtain the average flow rate and joint pressure after stabilization.

[0020] Preferably, the experiment also includes a nozzle tension test experiment, and the nozzle tension test experiment includes

[0021] Step 1: Assemble the test system, connect the nozzle to the connecting pipe, the connecting pipe is connected to the pressure regulating tank through the force sensor, and the nozzle outlet pressure sensor is set on the side of the connecting pipe;

[0022] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition and analysis instrument to obtain the nozzle tension value after stabilization.

[0023] Preferably, the experiment also includes an airflow temperature test experiment, and the airflow temperature test experiment includes

[0024] Step 1: Assemble the test system, connect the nozzle to the pressure regulating tank through the connecting pipe, and set the temperature sensor on the side of the connecting pipe;

[0025] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition and analysis instrument to obtain the stabilized airflow temperature and temperature change curve.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The pressure inside the nozzle is detected by multiple pipe wall pressure sensors, the flow rate at the nozzle inlet is detected by a flow meter, the thrust of the nozzle is detected by a force sensor, and the temperature of the nozzle outlet is measured by a temperature sensor. The flow field characteristics inside the nozzle are tested and the flow field characteristics inside the nozzle are intuitively reflected, thereby achieving performance comparison and surface structure optimization of the nozzle. On the other hand, the device and experimental method can be used as an experimental teaching device for "Fluid Mechanics" or "Aerodynamics" to demonstrate air flow characteristics experiments to enhance the teaching effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of Example 1 of the present invention.

[0029] Figure 2 Schematic diagram of the structure of the pipe wall pressure sensor.

[0030] Figure 3Schematic diagram of the location of the pressure measuring points on the nozzle wall in Example 1.

[0031] Figure 4 This is a schematic diagram of the flow meter connection structure of Example 4 of the present invention.

[0032] Figure 5 This is a schematic diagram of the structure of Example 5 of the present invention.

[0033] Figure 6 This is the pressure variation curve of the conical profile nozzle in Example 1.

[0034] Figure 7 This is the pressure change curve of the double arc profile nozzle in Example 2.

[0035] Figure 8 This is the pressure variation curve of the cubic polynomial profile nozzle in Example 3.

[0036] Fig. 9 This is the pressure variation curve of the surge tank in Example 4.

[0037] Fig.10 This is the variation curve of the nozzle outlet pressure in Example 5.

[0038] Fig.11 This is the pressure variation curve of the surge tank in Example 5.

[0039] Fig.12 This is the temperature change curve in Example 6.

[0040] Fig.13 This is a general dimension drawing of the nozzle.

[0041] Fig.14 This is a comparison diagram of the nozzle profile.

[0042] Markings in the figure: 1-nozzle, 2-connecting pipe, 3-force sensor, 4-pressure regulating tank, 5-pressure regulating valve, 6-pipeline, 7-vacuum pump, 8-tube wall pressure sensor, 9-nozzle outlet pressure sensor, 10-connector pressure sensor, 11-flow meter, 12-tee connector, 13-vacuum KF quick-release male thread connector, 14-ferrule connector, 16-stainless steel pipe. DETAILED DESCRIPTION

[0043] The technical solution of the invention will be further described below in conjunction with the accompanying drawings and embodiments. The scope of protection claimed by the present invention includes but is not limited to the scope described in the embodiments.

[0044] A negative pressure Laval nozzle flow characteristics experimental system, experimental device and test components, such as Figure 1As shown, the experimental device includes a pressure stabilizing tank, the top of which is connected to the nozzle through a connecting pipe, the pressure stabilizing tank is connected to the vacuum pump through a pipeline, and the pressure stabilizing tank is equipped with a pressure regulating valve;

[0045] like Figure 2-5 As shown, the test assembly includes a joint pressure sensor and a flow meter arranged at the nozzle inlet through a three-way joint, a pressure-stabilizing tank pressure sensor arranged in cooperation with a pressure-stabilizing tank, a plurality of pipe wall pressure sensors arranged on the side wall of the nozzle, a force sensor arranged between the connecting pipe and the pressure-stabilizing tank, a temperature sensor arranged on the side of the connecting pipe and one or more of a nozzle outlet pressure sensor. The joint pressure sensor, flow meter, pressure-stabilizing tank pressure sensor, pipe wall pressure sensor, force sensor, temperature sensor, and nozzle outlet pressure sensor are all arranged in cooperation with a dynamic information acquisition and analysis instrument.

[0046] In the present invention, the nozzle is vertically arranged, the inlet end of the nozzle faces upward, and the outlet end of the nozzle faces downward; the nozzle test device can be divided into two types according to the different installation methods of the nozzle, one is horizontal placement, and the other is vertical placement. The horizontal placement has the advantages of convenient installation and easy operation. At present, most of the nozzle cooling experiments adopt horizontal placement, but in the process of testing thrust, it is difficult to eliminate the error of the influence of gravity on the test, and the test accuracy will be affected to a certain extent. Therefore, the present invention adopts a vertically arranged nozzle.

[0047] An external thread is set at the lower part of the nozzle, and an internal thread is set at the upper part of the connecting pipe. The nozzle and the connecting pipe are connected by threads. At the same time, the nozzle is connected to the pressure-stabilizing tank through the connecting pipe. The right side of the pressure-stabilizing tank is connected to the vacuum pump through a pipeline. The vacuum pump is turned on to discharge the gas in the pressure-stabilizing tank to the outside. Due to the pressure difference between the inside and outside of the experimental device, the gas flows from the outside to the upper end of the nozzle to the lower end. A pressure regulating valve is set on the left side of the pressure-stabilizing tank. The pressure of the pressure-stabilizing tank is changed by adjusting the pressure regulating valve on the pressure-stabilizing tank. After unscrewing the pressure regulating valve, air enters the pressure-stabilizing tank from the pressure regulating valve. Observe the pressure reading in the pressure-stabilizing tank. After reaching the specified pressure and balancing again, test the wall pressure, thrust, flow, temperature and other data in the nozzle, and obtain the wall pressure, thrust, flow, temperature and other data under different outlet pressures and different expansion ratios.

[0048] The joint pressure sensor, pipe wall pressure sensor, and nozzle outlet pressure sensor are all PVG550 diaphragm resistor composite vacuum gauges; the selection of the pressure sensor in the present invention is obtained through error calibration experiments, specifically, the suction end of the vacuum pump is connected to a tee, and the tee is connected to the pressure sensor to be tested. By measuring the pressure value at the same position multiple times, if the repeatability of the pressure sensor is good, the error of the pressure sensor is small; then, using the pressure sensor as a reference, other types of sensors connected to the tee can be roughly calibrated. This method can be used to select a pressure sensor with higher accuracy as the joint pressure sensor, pipe wall pressure sensor, and nozzle outlet pressure sensor of the present invention.

[0049] In the present invention, the connecting pipe has only one through hole for installing a nozzle outlet pressure sensor or a temperature sensor.

[0050] The connecting pipe and the force sensor are connected via threads, a medium flow channel is arranged inside the force sensor, and the inner diameter of the connecting pipe is consistent with the diameter of the medium flow channel.

[0051] In the present invention, the connecting tube and the force sensor are respectively provided with matching external threads and internal threads to realize a detachable connection between the connecting tube and the force sensor; by setting the diameter between the connecting tube and the force sensor, the diameter difference between the connecting tube and the force sensor is prevented from affecting the detection data of the force sensor.

[0052] A sealing ring is arranged between the force sensor and the connecting pipe, and the sealing reliability between the force sensor and the connecting pipe is ensured by the sealing ring, thereby improving the accuracy of the measurement data of the force sensor.

[0053] The nozzle is threadedly connected to the connecting pipe, and the inner diameter of the connecting pipe is not less than the maximum inner diameter of the nozzle.

[0054] In the present invention, by setting the inner diameters of the connecting pipe and the nozzle, it is prevented that the inner diameter of the connecting pipe is too small to affect the pressure in the nozzle, thereby affecting the detection result of the pipe wall pressure sensor.

[0055] The principle of the present invention is as follows: the vacuum pump starts working under the drive of a high-power motor, and continuously extracts the air in the pressure-surge tank, forming a negative pressure environment at the nozzle outlet, so that the nozzle pressure ratio NPR (nozzle pressure ratio) continues to increase and remain stable. The air medium is subjected to atmospheric pressure, flows through the Laval nozzle, contracts first and then expands to reach the pressure-surge tank, and finally is discharged to the atmosphere through the vacuum pump. At the beginning, the nozzle NPR is small, the nozzle flow is also small, the vacuum pump's suction volume is greater than the intake volume at the nozzle inlet, the pressure in the pressure-surge tank continues to decrease, and the nozzle NPR continues to increase; after a period of time, the air flow in the Laval nozzle gradually reaches congestion, and the nozzle flow no longer changes at this time. When the vacuum pump's own exhaust volume and the nozzle's intake volume reach a relative balance, the flow field in the nozzle can be regarded as flow at this time. In the contraction section of the nozzle, the airflow gradually accelerates from a static state to a subsonic speed, and reaches the speed of sound at the throat; in the expansion section, the airflow is further accelerated, and finally forms a supersonic airflow.

[0056] The invention discloses an experimental method for a negative pressure Laval nozzle fluidity experimental system, which comprises a nozzle wall pressure test experiment, a nozzle flow test experiment, a nozzle tension test experiment and an airflow temperature test experiment.

[0057] Embodiment 1, the conical profile nozzle wall pressure test experiment specifically comprises the following steps:

[0058] Step 1: Assemble the test system, connect the conical profile nozzle to the pressure-stabilizing tank through a connecting pipe, set the pipe wall pressure sensors on the side of the nozzle from top to bottom, and set the nozzle outlet pressure sensor on one side of the connecting pipe.

[0059] More specifically, the side wall of the conical nozzle has 10 threaded holes arranged from top to bottom, and the positions of the threaded holes refer to Figure 3 As shown, one end of any threaded through hole is connected to a stainless steel tube, and the stainless steel tube and the tube wall pressure sensor are connected via a ferrule joint. In order to minimize the interference of the threaded through hole at the tube wall pressure measuring point on the flow field in the nozzle, the diameter of the wall threaded through hole is selected to be 0.5 mm.

[0060] In the present invention, the stainless steel pipe is L-shaped, and the heights of all the stainless steel pipes are different. During installation, the stainless steel pipes are installed in order from low to high. The stainless steel pipe is connected to the compression sleeve joint through threads, and the pipe wall pressure sensor is clamped on the compression sleeve joint, so that the pipe wall pressure sensor can be quickly disassembled and used conveniently. At the same time, the pipe wall pressure is led out for measurement through the mode of the stainless steel pipe and the clamping sleeve, which expands the installation space of the pipe wall pressure sensor and solves the problem of difficulty in installing multiple pipe wall pressure sensors.

[0061] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within a preset time after stabilization, and obtain the nozzle wall pressure curve through the dynamic information acquisition and analysis instrument.

[0062] In the present invention, the atmospheric pressure on the day of the test is 102.09KPa, the temperature is 295.35K, and the humidity is 77%. The dynamic information acquisition and analysis instrument can collect the detection data of the sensor, and judge whether the nozzle outlet pressure ratio remains stable by judging whether the nozzle outlet pressure in the nozzle outlet pressure sensor remains constant within a preset time. If so, the vacuum pump is turned off. The wall pressure changes of the 1st to 4th positions of the conical nozzle obtained by the dynamic information acquisition and analysis instrument are as follows: Figure 6 As shown, Figure 6 (a) shows the change of the pipe wall pressure at the first position. Figure 6 (b) shows the change of the pipe wall pressure at the second position. Figure 6 (c) shows the change of the pipe wall pressure at the third position. Figure 6 (d) shows the change of pipe wall pressure at the 4th position.

[0063] Example 2, double arc profile nozzle pipe wall pressure test, the conical profile nozzle of Example 1 is replaced with a double arc profile nozzle, and the same operation as step 2 in Example 1 is performed to obtain the pipe wall pressure changes at positions 1 to 4 of the double arc profile nozzle as shown in FIG. Figure 7 As shown, Figure 7 (a) shows the change of the pipe wall pressure at the first position. Figure 7 (b) shows the change of the pipe wall pressure at the second position. Figure 7 (c) shows the change of the pipe wall pressure at the third position. Figure 7 (d) shows the change of pipe wall pressure at the 4th position.

[0064] Example 3, a test of the pipe wall pressure of a cubic polynomial profile nozzle, the double arc profile nozzle of Example 2 is replaced with a cubic polynomial profile nozzle, and the same operation as step 2 in Example 1 is performed to obtain the changes in the pipe wall pressure at the 1st to 4th positions of the cubic polynomial profile nozzle as shown in FIG. Figure 8 As shown, Figure 8 (a) shows the change of the pipe wall pressure at the first position. Figure 8 (b) shows the change of the pipe wall pressure at the second position. Figure 8 (c) shows the change of the pipe wall pressure at the third position. Figure 8 (d) shows the change of pipe wall pressure at the 4th position.

[0065] It can be seen from Examples 1-3 that the wall pressures P1 to P4 of the conical profile, double arc profile, and cubic polynomial profile have the same change trend, all of which gradually decrease from atmospheric pressure and tend to stabilize. By comparison, it is found that the wall pressure of the conical profile nozzle is quite different from that of the latter two profile nozzles, and the pressure inside the conical nozzle is generally higher, which is consistent with the smaller expansion degree and small expansion area ratio of the conical nozzle. The difference in wall pressure between the double arc and the cubic polynomial is very small, with the largest difference being P2, which is 3.7%. It can be seen that there is no obvious difference in the flow state of the two.

[0066] Example 4, nozzle flow rate test experiment, specifically:

[0067] Step 1: Assemble the test system, connect one end of the tee joint to the inlet of the nozzle, connect the other two ends of the tee joint to the flow meter and the joint pressure sensor respectively, connect the nozzle to the pressure regulating tank through the connecting pipe, and set the nozzle outlet pressure sensor on one side of the connecting pipe.

[0068] In the present invention, the three-way joint is T-shaped, and the inlet end of the nozzle arranged in conjunction with the three-way joint is provided with an external thread to realize the threaded connection with the lower joint of the three-way joint. The left end joint of the three-way joint is connected to the joint pressure sensor through a vacuum KF quick-release external thread joint, and the right end is connected to the flow meter. The flow meter here is a float flow meter, which is vertically arranged and the air inlet end is arranged at the lower part.

[0069] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition analyzer to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition analyzer to obtain the average flow rate and joint pressure after stabilization.

[0070] In the present invention, since air enters from the air inlet at the lower end of the float flowmeter, flows out from the air outlet at the upper end of the float flowmeter, and enters the three-way joint and the nozzle in sequence, the air pressure at the air inlet end of the nozzle is inconsistent with the external atmospheric pressure. By setting a joint pressure sensor, the air pressure at the air inlet end of the nozzle at this time is obtained, and the theoretical flow value is calculated based on the air pressure at the air inlet end of the nozzle, rather than calculating the theoretical flow value based on the external atmospheric pressure, thereby reducing the error between the actually detected flow value and the theoretical value.

[0071] More specifically, the nozzle here is a conical nozzle without a threaded through hole on the side. The total inlet pressure obtained by the test is: 78200Pa, and the average flow rate obtained by the test is 6.6m 3 / h, the simulation value is 6.75m 3 / h, the error between the two is only 2%; in the process of testing the flow rate, the pressure in the surge tank was tested, and the pressure curve is as follows Fig. 9As shown, after turning on the vacuum pump, the pressure is basically stable after about 5 seconds, and the pressure is about 2142.6Pa.

[0072] Example 5, nozzle tension test experiment, specifically:

[0073] Step 1: Assemble the test system, connect the nozzle to the connecting pipe, the connecting pipe is connected to the pressure regulating tank through the force sensor, and the nozzle outlet pressure sensor is set on the side of the connecting pipe.

[0074] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition and analysis instrument to obtain the nozzle tension value after stabilization.

[0075] On the day of the test of this embodiment, the air pressure was 102.09KPa, the temperature was 295.25K, and the humidity was 75%. The force measurement experiment was completed, and the tension generated inside the conical profile nozzle without a threaded through hole on the side was measured to be 85N; at the same time, the nozzle outlet pressure curve 10 was obtained by the dynamic information acquisition analyzer, and the pressure after stabilization was 3005Pa, and the pressure curve of the pressure regulating tank was as shown in Fig.11 As shown, the pressure after stabilization is 3001Pa; it should be noted here that in the force measurement experiment, the force sensor reading is not the actual force generated by the nozzle, but the pressure signal generated by the strain gauge after the internal vacuum is evacuated.

[0076] Example 6, air flow temperature test experiment, specifically:

[0077] Step 1: Assemble the test system, connect the nozzle to the pressure regulating tank through the connecting pipe, and set the temperature sensor on the side of the connecting pipe.

[0078] Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition and analysis instrument to obtain the stabilized airflow temperature and temperature change curve.

[0079] In this embodiment, the temperature variation curve of the conical nozzle is as follows: Fig.12 As shown, after 1700s, the temperature finally stabilized at around 130K.

[0080] In the present invention, it should be noted that the conical surface nozzle, double arc profile nozzle and cubic polynomial profile nozzle mentioned in all embodiments refer to Fig.14 As shown in the figure, the expansion angle of the conical nozzle is 17.23°; for the double arc profile nozzle and the cubic polynomial profile nozzle, the general nozzle dimensions are as follows: Fig.13As shown; the double arc is drawn by drawing method, and the radius of the arc of the expansion section is 206.76; the cubic parabola is: y=ax3+bx2+cx+d, where a= 4.2838e-05, b=-0.0088, c= 0.6902, d= 3.6631; the conical surface nozzle, double arc surface nozzle and cubic polynomial surface nozzle are all made of acrylic material, and the throat radius, expansion section length, upstream and downstream curvature radius of the throat, initial expansion angle, and outlet expansion angle of the three are consistent, and the throat radius R t It is 4mm, the expansion section length La is 72mm, the upstream curvature radius of the throat R1 is 6mm, the downstream curvature radius of the throat R2 is 1.6mm, the initial expansion angle b1 is 28°, the outlet expansion angle b2 is 5°, and the outlet radius Re is 23.66mm.

[0081] In the present invention, the flow field characteristics inside the nozzle, including the tube wall pressure, inlet flow rate, nozzle temperature, etc., can be obtained through the above experimental tests. The flow field characteristics obtained through the tests can be used to optimize the nozzle structure.

Claims

1. A negative pressure Laval nozzle flow characteristics experimental system, characterized in that: An experimental device and a test assembly, wherein the experimental device comprises a pressure stabilizing tank, the top of which is connected to the nozzle through a connecting pipe, the pressure stabilizing tank is connected to a vacuum pump through a pipeline, and the pressure stabilizing tank is equipped with a pressure regulating valve; The test assembly includes a joint pressure sensor and a flow meter arranged at the nozzle inlet through a three-way joint, a pressure-sustaining tank pressure sensor arranged in cooperation with a pressure-sustaining tank, a plurality of pipe wall pressure sensors arranged on the side wall of the nozzle, a force sensor arranged between the connecting pipe and the pressure-sustaining tank, and a temperature sensor arranged on the side of the connecting pipe. The joint pressure sensor, flow meter, pressure-sustaining tank pressure sensor, pipe wall pressure sensor, force sensor, temperature sensor, and nozzle outlet pressure sensor are all arranged in cooperation with a dynamic information acquisition and analysis instrument; A plurality of threaded through holes are sequentially provided on the side wall of the nozzle from top to bottom, one end of any threaded through hole is connected to a stainless steel pipe, and the stainless steel pipe and the pipe wall pressure sensor are connected via a ferrule joint; the connecting pipe and the force sensor are connected via a threaded connection, a medium flow channel is arranged inside the force sensor, and the inner diameter of the connecting pipe is consistent with the diameter of the medium flow channel.

2. A negative pressure Laval nozzle flow characteristics experimental system as claimed in claim 1, characterized in that: A sealing ring is arranged between the force sensor and the connecting pipe.

3. A negative pressure Laval nozzle flow characteristics experimental system as claimed in claim 1, characterized in that: The nozzle is threadedly connected to the connecting pipe, and the inner diameter of the connecting pipe is not less than the maximum inner diameter of the nozzle.

4. A negative pressure Laval nozzle flow characteristics experimental system as claimed in claim 1, characterized in that: The nozzle is a conical profile nozzle, a double arc profile nozzle, or a cubic polynomial profile nozzle.

5. An experimental method using a negative pressure Laval nozzle flow characteristics experimental system according to any one of claims 1 to 4, characterized in that: The experiment includes a nozzle wall pressure test experiment, and the nozzle wall pressure test experiment includes the following steps: Step 1: Assemble the test system, the nozzle is connected to the pressure regulating tank through a connecting pipe, the pipe wall pressure sensors are arranged on the side of the nozzle from top to bottom, and the nozzle outlet pressure sensor is arranged on one side of the connecting pipe; Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within a preset time after stabilization, and obtain the nozzle wall pressure curve through the dynamic information acquisition and analysis instrument.

6. The experimental method according to claim 5, characterized in that The experiment also includes a nozzle flow test experiment, and the nozzle flow test experiment includes the following steps: Step 1: Assemble the test system, connect one end of the three-way interface to the inlet of the nozzle, connect the other two ends of the three-way interface to the flow meter and the interface pressure sensor respectively, connect the nozzle to the pressure regulating tank through the connecting pipe, and set the nozzle outlet pressure sensor on one side of the connecting pipe; Step 2: Turn on the vacuum pump, and use the dynamic information acquisition analyzer to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition analyzer to obtain the average flow rate and interface pressure after stabilization.

7. The experimental method according to claim 5, characterized in that The experiment also includes a nozzle tension test experiment, and the nozzle tension test experiment includes Step 1: Assemble the test system, connect the nozzle to the connecting pipe, the connecting pipe is connected to the pressure regulating tank through the force sensor, and the nozzle outlet pressure sensor is set on the side of the connecting pipe; Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition and analysis instrument to obtain the nozzle tension value after stabilization.

8. The experimental method according to claim 5, characterized in that The experiment also includes an airflow temperature test experiment, which includes Step 1: Assemble the test system, connect the nozzle to the pressure regulating tank through the connecting pipe, and set the temperature sensor on the side of the connecting pipe; Step 2: Turn on the vacuum pump, and use the dynamic information acquisition and analysis instrument to obtain parameters to determine whether the nozzle pressure drop ratio remains stable. If so, turn off the vacuum pump within the preset time after stabilization, and use the dynamic information acquisition and analysis instrument to obtain the stabilized airflow temperature and temperature change curve.

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