Exhaust apparatus for measuring turbulent pressure fluctuations in a downwardly open cavity
By using Tesla coil plasma flow control and multi-layer damping layer design, the problem of gas exhaust at the bottom of the downward-facing cavity was solved, thus improving the accuracy and precision of turbulent pulsating pressure measurement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN ENG UNIV
- Filing Date
- 2023-04-14
- Publication Date
- 2026-07-24
AI Technical Summary
In gravity-type low-noise water tunnels, circulating water tanks, or cavitation water cylinders, air at the bottom of the downward-facing orifice is difficult to expel effectively, causing gas to mix into the fluid and affecting the accuracy of turbulent pulsating pressure measurements and test results.
The plasma flow control and the filtration effect of the breathable and waterproof membrane generated by the Tesla coil are combined with the design of multi-layer damping layer and gas box. The plasma discharge device changes the fluid flow mode, and the damping layer and gas box filter out air bubbles, reducing the impact of air bubbles on the measurement results.
It effectively removes gas from the bottom of the cavity, reduces the error of turbulent pulsating pressure measurement caused by bubbles, improves acoustic measurement accuracy, reduces background noise interference, and enhances the adaptability and stability of the device.
Smart Images
Figure CN116358773B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an exhaust device for measuring the turbulent pulsating pressure of a downward-opening cavity, belonging to the field of acoustic measurement. Background Technology
[0002] Currently, a common problem encountered when measuring pulsating pressure in orifices using gravity-type low-noise water tunnels, circulating water tanks, or cavitation water cylinders is how to expel the air at the bottom of the downward-facing orifice as the incoming flow velocity changes. This is because during the test preparation phase, the air inside the orifice can only be vented using the bottom venting bolt. During the test, this venting bolt must be tightened to prevent bottom leakage and ensure accurate measurement results. However, during the test, residual air in the water tunnel or tank inevitably mixes with the fluid. Since the orifice opening is downward, the gas is most likely to accumulate at the bottom, resulting in an air layer covering the bottom of the orifice. Furthermore, according to Bernoulli's equation, higher flow velocities result in lower pressure. At high flow velocities, air inside the water will also precipitate due to the reduced pressure, thus accumulating at the bottom of the orifice. Because the trapped air is a medium with excellent compressibility and elastic deformation, it can achieve the same effect as vibration damping pads and vibration isolation pads under the action of hydrostatic pressure. This reduces the excitation intensity of the turbulent motion in the cavity on the cavity, increases the sources of error in the experimental measurement process, and makes the experimental results unable to well verify the results of theoretical analysis and numerical calculation. Summary of the Invention
[0003] The purpose of this invention is to provide an exhaust device for measuring the turbulent pulsating pressure of a downward-opening cavity. This device utilizes the flow control of plasma generated by a Tesla coil and the filtration effect of a breathable and waterproof membrane inside the gas chamber to reliably remove bubbles generated during the measurement of turbulent pulsating pressure in the cavity due to changes in flow velocity, thereby reducing the impact of bubbles on the experimental measurement results and showing good prospects for engineering applications.
[0004] The objective of this invention is achieved as follows: it includes a damping layer, a self-tapping screw, a first flexible tube, an air chamber, a second flexible tube, a cable, a Tesla coil, and a power source. The damping layer is applied to the bottom of the cavity, the self-tapping screw is embedded in the damping layer, one end of the first flexible tube is connected to the middle of the damping layer, the other end of the first flexible tube is connected to one end of the air chamber, the other end of the air chamber is connected to one end of the second flexible tube, one end of the cable is connected to the damping layer and the bottom of the cavity respectively, the other end of the cable is connected to the Tesla coil, and the other end of the Tesla coil is connected to the power source.
[0005] Furthermore, the damping layer consists of a three-layer structure: the first layer is made of rubber, the second layer is a metal mesh structure with spikes, and the third layer is made of rubber with an inclined angle, with an opening in the middle of the damping layer.
[0006] Furthermore, the self-tapping screws are inserted into the damping layer, and their positions are staggered with the spikes in the damping layer.
[0007] Furthermore, the first flexible hose is a flexible rubber tube used to vent air from the cavity; the second flexible hose is a flexible rubber tube used to vent air from the air chamber.
[0008] Furthermore, the gas chamber is a rectangular structure made of plastic with through holes at the top and bottom. The outside of the gas chamber is wrapped with rigid foam, and the inside of the gas chamber is filled with a seven-layer structure, from bottom to top: the first layer is a breathable and waterproof membrane, the second layer is composed of solid plastic balls, the third layer is a breathable and waterproof membrane, the fourth layer is composed of coarse glass beads, the fifth layer is a breathable and waterproof membrane, the sixth layer is composed of fine glass beads, and the seventh layer is a breathable and waterproof membrane.
[0009] Furthermore, the cable is a double-strand insulated wire embedded in the wall of the first flexible tube. One end of the cable is connected to the Tesla coil, and the first strand of the double-strand wire at the other end of the cable is connected to the second layer in the damping layer. The second strand of the double-strand wire at the other end of the cable is connected to the bottom of the cavity.
[0010] Compared with the prior art, the advantages of this invention are as follows: First, the damping layer placed at the bottom of the cavity is a multi-layered structure with inclined surfaces, which allows the bubbles entering the cavity to gather well in the middle of the damping layer and enter the first flexible tube through the opening in the middle of the damping layer. Since the vortices inside the cavity rarely touch the bottom of the cavity, the inclined surface structure of the damping layer can effectively avoid affecting the motion mode of the large vortices inside the cavity. Moreover, the hydrostatic pressure of the fluid inside the cavity is much greater than the pulsating pressure of the turbulent flow. Therefore, the micro-deformation of the damping layer after being deformed by hydrostatic pressure and then by the pulsating pressure of turbulent flow is very small, and its influence on the operation mode of the turbulent vortex can be ignored. Second, the plasma discharge device is composed of a spiked mesh structure embedded in the damping layer, a Tesla coil, a power supply, and self-tapping screws. This design alters the fluid flow pattern at the bottom of the damping layer, simultaneously heating the fluid and facilitating the smooth arrival of air bubbles at the bottom of the pores in the middle of the damping layer and their entry into the first flexible tube. Furthermore, the exterior of the air chamber is made of rigid foam, whose acoustic impedance differs significantly from that of water, creating excellent reflection. This effectively conceals the noise generated during filtration by the air bubbles, which rubs against the solid plastic balls, glass beads, and the breathable waterproof membrane, reducing background noise interference. Finally, when filtering air bubbles and water, the surface tension and viscosity of water molecules prevent water from passing through the breathable waterproof membrane, allowing only air bubbles to pass through. Therefore, the water chamber ensures gas escape while preventing water from escaping from the pores.
[0011] The advantages of this invention are further as follows: First, the glass beads and the breathable and waterproof membrane inside the air-holding box form a multi-layered bubble filtration device. Because the glass beads have smooth surfaces, the pores formed after stacking facilitate the rapid upward movement of bubbles. After passing through the multi-layered waterproof and breathable membrane, the bubbles enter the second flexible tube and are then discharged to the water surface. Since the multi-layered waterproof and breathable membrane effectively slows down the upward speed of the bubbles after filtration, and the second flexible tube is very close to the water surface, the gas movement speed of the bubbles is very low, and the frictional effect on the second flexible tube is negligible, thus avoiding strong background noise interference. Second, the buoyancy generated by the rigid foam outside the air-holding box in the water allows the air-holding box to float. Because the first flexible tube is made of rubber and is a flexible structure, it does not increase the mass of the back of the cavity, reducing the impact on the stiffness of the cavity wall. Third, the first flexible tube connected in the middle of the damping layer passes through the middle of the cavity. This design only requires a through hole at the bottom of the cavity. A sealing mechanism is formed by a damping layer, adhesive, and a first flexible tube, preventing water leakage at the bottom of the cavity. Simultaneously, the multi-layered breathable and waterproof membrane inside the gas chamber ensures no water leaks out after withstanding hydrostatic pressure. Furthermore, as the flow velocity on the outer surface of the cavity increases, the turbulent pulsating pressure inside the cavity intensifies, and the pressure of the multi-layered breathable and waterproof membrane in the gas chamber changes accordingly with the changes in hydrostatic and turbulent pulsating pressure. Therefore, the device of this invention has excellent adaptability. Finally, after installation, the device automatically adjusts according to the water level in the reverberation chamber, avoiding the inconvenience of having to completely drain the water from the reverberation chamber when adjusting the cavity for venting. Moreover, because the reverberation chamber can be kept filled with water for extended periods, the impact of air bubbles adhering to the reverberation chamber on the test results is reduced, improving the accuracy of acoustic measurements. Attached Figure Description
[0012] Figure 1 A block diagram of an exhaust device for measuring the turbulent pulsating pressure of a downward-opening cavity;
[0013] Figure 2 This is a schematic diagram of the cross-sectional structure of the damping layer;
[0014] Figure 3 This is a schematic diagram of the structure of the gas-holding box;
[0015] Among them, 1 is the working section, 2 is the cavity, 3 is the damping layer, 4 is the self-tapping screw, 5 is the first flexible tube, 6 is the air box, 7 is the second flexible tube, 8 is the cable, 9 is the Tesla coil, 10 is the power supply, 31 is the first layer of damping layer 3, 32 is the second layer of damping layer 3, 321 is the spike, 33 is the third layer of damping layer 3, 61 is the rigid foam on the outside of the air box, 62 is the breathable and waterproof membrane, 63 is the fine glass bead, 64 is the breathable and waterproof membrane, 65 is the fine glass bead, 66 is the breathable and waterproof membrane, 67 is the coarse glass bead, 68 is the breathable and waterproof membrane, 81 is the first strand of cable 8, and 82 is the second strand of cable 8. Detailed Implementation
[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0017] The present invention includes a working section 1, a cavity 2, a damping layer 3, a self-tapping screw 4, a first flexible tube 5, an air tank 6, a second flexible tube 7, a cable 8, a Tesla coil 9, a power supply 10, and the damping layer 3 is attached to the bottom of the cavity 2. The self-tapping screw 4 enters into the damping layer 3 and is connected to the bottom of the cavity 2. One end of the first flexible tube 5 is connected to the middle of the damping layer 3, and the other end of the first flexible tube 5 is connected to one end of the air tank 6. The other end of the air tank 6 is connected to one end of the second flexible tube 7. The cable 8 is connected to one end of the Tesla coil 9, and the other end of the Tesla coil 9 is connected to the power supply 10.
[0018] The working section 1 of the present invention is composed of an organic glass and a stainless steel metal frame structure. There is an inverted "T" shaped recess at the upper part of the working section 1, and there is a non-permeable threaded hole at the edge of the recess for mounting the cavity 2.
[0019] The cavity 2 of the present invention is made of stainless steel plate. The cavity 2 has a height of 520mm, a wall thickness of 10mm, a length of 190mm, a width of 150mm, and an opening length of 150mm and a width of 120mm. The cavity 2 is a small-opening cavity. There is a through hole at the top of the cavity 2 for venting. There is a through hole at the edge of the cavity 2 so that it can be fixed to the working section 1 by bolts through the threaded holes at the edge of the working section 1.
[0020] The damping layer 3 of the present invention consists of a three-layer structure. The first layer 31 is made of rubber, specifically styrene-butadiene rubber (SBR) made from a copolymer of butadiene and styrene. The second layer 32 is a metal mesh structure with spikes 321, the base of which is a mesh made of titanium alloy. Spikes 321 are welded at each mesh node. The third layer 33 is made of rubber with an inclined angle, specifically isobutylene and diene polymer (IIR). A through hole is opened in the middle of the damping layer 3, the size of which is the same as the size of the top of the cavity 2. The spikes 321 of the damping layer 32 penetrate the outer surface of the damping layer 33 and are exposed. The first layer 31, the second layer 32, and the third layer 33 of the damping layer 3 are bonded together with epoxy resin. Epoxy resin is coated on the outer surface of the first layer 31 of the damping layer 3 and applied to the bottom of the cavity 2.
[0021] The self-tapping screw 4 of the present invention is a semi-circular internal hexagonal self-tapping screw with a specification of M2, which is arranged alternately with the spikes 321 in the damping layer 3.
[0022] The first flexible hose 5 of the present invention is a flexible rubber hose or PVC hose, used to vent air from the cavity 2.
[0023] The gas-filled box 6 of this invention is a rectangular structure made of plastic, with through holes at the top and bottom. The exterior of the gas-filled box 6 is wrapped with rigid foam 61, which is a high-density polystyrene foam board. The interior of the gas-filled box 6 is filled with a seven-layer structure, from bottom to top: layer 62, layer 63, layer 64, layer 65, layer 66, layer 67, and layer 68. Layer 62 is a breathable and waterproof membrane made of polyethylene and polypropylene, model number N20338d. Layer 63 consists of solid plastic spheres, model number KDR1L1650266705148. Layer 64 is a breathable and waterproof membrane, model number N20338d. The fourth layer 65 is composed of coarse glass beads with a density of 2.4-2.6 kg / m3, a hardness between 6 and 8 on the Mohs scale, and a particle size of 9.5 mm. The fifth layer 66 is a breathable and waterproof membrane, model N20338d. The sixth layer 67 is composed of fine glass beads with a density of 2.4-2.6 kg / m3, a hardness between 6 and 8 on the Mohs scale, and a particle size of 2 mm. The seventh layer 68 is a breathable and waterproof membrane, model N20338d. The buoyancy generated by the rigid foam 61 and the air tank 6, as well as the first layer 62, second layer 63, third layer 64, fourth layer 65, fifth layer 66, sixth layer 67, and seventh layer 68 inside the air tank 6, is not less than the weight of the air tank 6, ensuring that the air tank 6 is in a floating state.
[0024] The second hose 7 of the present invention is a PVC hose, used to discharge gas from the gas tank 6.
[0025] The cable 8 of the present invention is a double-strand insulated wire, model JHS2, a pure copper deep-sea cable. One end of the cable 8 is connected to the Tesla coil 9, and the first strand 81 of the double strand at the other end of the cable 8 is connected to the second layer 32 in the damping layer 3. The second strand 82 of the double strand at the other end of the cable 8 is connected to the bottom of the cavity 2.
[0026] The Tesla coil 9 of the present invention is used to transform the voltage of the power supply. The resonant transformer boosts the voltage of the power supply to between 5 and 30 kilovolts, which is used to drive the spikes 321 of the second layer 32 in the damping layer 3 to discharge. Together with the staggered self-tapping screws 4, they form a plasma device to realize the plasma effect.
[0027] The power supply 10 of this invention is an AC power supply with a voltage of 220V and a frequency of 50Hz, and is connected to the Tesla coil 9 through a cable 101.
Claims
1. An exhaust device for measuring the turbulent pulsating pressure of a downward-opening cavity, characterized in that: The device includes a damping layer, self-tapping screws, a first flexible tube, an air chamber, a second flexible tube, cables, a Tesla coil, and a power supply. The damping layer is applied to the bottom of the cavity, and the self-tapping screws are embedded in the damping layer. One end of the first flexible tube is connected to the middle of the damping layer, and the other end of the first flexible tube is connected to one end of the air chamber. The other end of the air chamber is connected to one end of the second flexible tube. One end of the cable is connected to the damping layer and the bottom of the cavity, and the other end of the cable is connected to the Tesla coil. The other end of the Tesla coil is connected to the power supply. The damping layer consists of three layers: the first layer is made of rubber, the second layer is a metal mesh structure with spikes, and the third layer is made of rubber with an inclined angle. There is an opening in the middle of the damping layer. The first flexible hose is a flexible rubber tube used to vent air from the cavity; the second flexible hose is a flexible rubber tube used to vent air from the air tank. The gas chamber is a rectangular structure made of plastic with through holes at the top and bottom. It is wrapped with rigid foam on the outside and filled with seven layers from bottom to top. The first layer is a breathable and waterproof membrane, the second layer is made of solid plastic balls, the third layer is a breathable and waterproof membrane, the fourth layer is made of coarse glass beads, the fifth layer is a breathable and waterproof membrane, the sixth layer is made of fine glass beads, and the seventh layer is a breathable and waterproof membrane. The cable is a double-strand insulated wire embedded in the wall of the first flexible tube. One end of the cable is connected to the Tesla coil, and the first strand of the double-strand wire at the other end of the cable is connected to the second layer in the damping layer. The second strand of the double-strand wire at the other end of the cable is connected to the bottom of the cavity.
2. The exhaust device for measuring the turbulent pulsating pressure of a downward-opening cavity according to claim 1, characterized in that: The self-tapping screws are inserted into the damping layer, and their positions are interspersed with the spikes in the damping layer.