A device for accurately evaluating background noise during cavity testing

Abstract

This invention provides a device for accurately evaluating background noise during orifice testing, comprising a first electromagnet, a first plate, a second electromagnet, a second plate, a third electromagnet, a third plate, a fourth electromagnet, a fourth plate, a first power supply, an electromagnetic heating block, a second power supply, a first pad, a second pad, a Tesla coil, and a third power supply. The first electromagnet is connected to the first plate, the second electromagnet to the second plate, the third electromagnet to the third plate, and the fourth electromagnet to the fourth plate. The first power supply is connected to the first, second, third, and fourth electromagnets. The electromagnetic heating block is connected to the second power supply. The first and second pads are placed at the interface of the leading and trailing edges of the orifice, respectively. The first and second pads are each connected to one end of the Tesla coil, and the other end of the Tesla coil is connected to the third power supply. This device utilizes mass effect, electromagnetic damping, and heating drag reduction techniques to effectively improve the flow field characteristics of orifice testing.

Description

Technical Field

[0001] This invention relates to a device for accurately evaluating background noise during cavity testing, belonging to the field of acoustic measurement. Background Technology

[0002] During operation, underwater vehicles generate sound waves of a specific frequency through their flow holes. This is caused by fluid oscillations resulting from the sudden interruption of the continuous fluid flow due to the opening, which impacts the trailing edge and body of the orifice. When measuring the hydrodynamic noise of the orifice, it is generally necessary to test the background noise of a gravity-type low-noise water tunnel. The background noise measurement procedure involves allowing the gravity-type water tunnel to flow freely through a hydrophone inside a reverberation chamber. However, this method has a significant drawback: because the working section of the gravity-type water tunnel is in a laminar flow state during free flow, even at high flow velocities, the turbulence is very low due to the honeycomb rectifier at the front end of the working section. Therefore, the radiated noise generated by the laminar flow excitation in the gravity-type water tunnel is received by the reverberation chamber. When the orifice is inserted, the flow field is suddenly interrupted by the orifice opening, completely disrupting the laminar flow state and transforming it into a turbulent state. Since the rear half of the working section of the gravity-type low-noise water tunnel lacks a honeycomb rectifier, the background noise generated by the turbulent excitation in this turbulent state is the "true" background noise in the experimental study. Therefore, how to evaluate the background noise during the cavity testing process will become a bottleneck in accurately verifying the accuracy of numerical calculation methods for the cavity turbulence development process and sound generation process.

[0003] Meanwhile, during the installation of the cavity in the working section of the gravity-type low-noise water tunnel, errors in machining precision can cause small depressions or protrusions at the interface when the cavity is placed into the working section. These depressions or protrusions disrupt the flow state, causing abrupt changes in the boundary layer at the wall, prematurely transitioning from laminar to turbulent flow, and increasing the turbulence intensity of the flow field within the working section and the pipe. Especially when a "step effect" occurs between the cavity model and the working section interface, flow separation is more likely to occur, leading to additional vibration and noise, and enhancing the background noise during underwater acoustic testing. To ensure a good seal at the connection, O-rings are generally used for sealing, and bolts and nuts are used for tightening. However, using multiple bolts and nuts to connect the model introduces the problem that vibrations from the working section can easily be transmitted to the cavity model through the bolts and nuts. While O-rings can provide some vibration damping, rubber O-rings are effective at suppressing high-frequency vibrations but have poor damping effects on low-frequency vibrations. Because no active control methods are used, the vibration damping effect during cavity testing is very limited. Summary of the Invention

[0004] The purpose of this invention is to provide a device for accurately evaluating background noise during orifice testing. This device utilizes techniques such as mass effect, electromagnetic damping, and heating drag reduction to effectively improve the flow field characteristics of orifice testing.

[0005] The objective of this invention is achieved as follows: It includes a first electromagnet, a first plate, a second electromagnet, a second plate, a third electromagnet, a third plate, a fourth electromagnet, a fourth plate, a first power source, an electromagnetic heating block, a second power source, a first pad, a second pad, a Tesla coil, and a third power source. The first electromagnet is connected to the first plate, the second electromagnet is connected to the second plate, the third electromagnet is connected to the third plate, and the fourth electromagnet is connected to the fourth plate. The first power source is connected to the first, second, third, and fourth electromagnets. The electromagnetic heating block is connected to the second power source. The first pad is placed at the interface of the front edge of the cavity, and the second pad is placed at the interface of the tail edge of the cavity. The first and second pads are respectively connected to one end of the Tesla coil, and the other end of the Tesla coil is connected to the third power source.

[0006] Furthermore, the first electromagnet is composed of a stud made of silicon steel and a copper coil; the second electromagnet is composed of a stud made of silicon steel and a copper coil; the third electromagnet is composed of a stud made of silicon steel and a copper coil; and the fourth electromagnet is composed of a stud made of silicon steel and a copper coil.

[0007] Furthermore, the first plate is a stainless steel plate; the second plate is a stainless steel plate; the third plate is a stainless steel plate; and the fourth plate is a stainless steel plate.

[0008] Furthermore, the first power source is a DC power source; the second power source is a high-frequency AC power source; and the third power source is an AC power source.

[0009] Furthermore, the electromagnetic heating block consists of a microcrystalline glass panel and an excitation coil.

[0010] Furthermore, the first pad has a composite structure, with the first layer made of rubber; the second layer has a wavy structure with spikes and is made of stainless steel; the third layer has a structure with pits on the outer surface and is made of rubber; the fourth layer has a wavy structure with spikes and is made of stainless steel; and the fifth layer is made of rubber.

[0011] Furthermore, the second pad has a composite structure, with the first layer made of rubber, the second layer having a wavy structure with spikes made of stainless steel, the third layer having a pitted structure made of rubber, the fourth layer having a wavy structure with spikes made of stainless steel, and the fifth layer made of rubber.

[0012] Compared with the prior art, the advantages of this invention are as follows: First, the first, second, third, and fourth electromagnets, composed of studs and coils, can attract the first, second, third, and fourth plates to the outer wall of the cavity under the action of the first power source. The strong attraction of the magnets and the mass effect of these plates increase the wall impedance of the cavity, making the cavity less prone to elastic deformation under the action of fluid. Second, the electromagnetic attraction also acts as a magnetic damper. When the first, second, third, and fourth plates vibrate, shear friction also occurs, which can effectively suppress the elastic deformation of the cavity wall under turbulence and improve the strength of the cavity, especially the shear oscillation process of fluid in a rigid cavity. Third, the studs are installed on the outer surface of the cavity wall by means of threads, without disrupting the flow field of the inner wall of the cavity. Moreover, after the studs are screwed into the outer surface of the cavity, they will disrupt the structural modes of the cavity itself, causing the vibration modes of the cavity wall to change. The device attenuates low-frequency spikes in the cavity, making it less prone to coupled vibrations under fluid action. Finally, this device changes the previous method of evaluating background noise during experimental testing in gravity-type low-noise water tunnels. When the working section of the water tunnel is not placed with a model, the background noise is only generated by laminar flow excitation of the pipe. However, after the model is placed in the working section of the water tunnel, the flow field within the working section is disrupted, making it impossible to measure the background noise. If the background noise generated before the model is placed is used as a reference, the flow field states of the two are inconsistent, and the generation characteristics and intensity of hydrodynamic noise will change. Thus, the background noise collected in the early stage loses its reference value. The device of this invention obtains background noise by suppressing the noise generated by the cavity itself after the model is placed, which is "pure" background noise. This will help solve the problem of accurate evaluation of the model established in the theoretical and numerical calculation research of cavity pulsating pressure and hydrodynamic noise, and improve the accuracy of the data obtained in the experimental testing process.

[0013] The advantages of this invention also lie in the following: First, the spiked wave-shaped structure within the first and second pads, along with an external Tesla coil and a third power source, forms a plasma flow control device. Utilizing the ionization and discharge characteristics of plasma, energy is supplied to the fluid moving in the water tunnel, effectively solving the flow separation problem caused by the abrupt boundary change between the orifice mounting plane and the working cover plane of the water tunnel. This reduces the high hydrodynamic noise generated by the increased turbulence due to the interface abrupt change. Second, the recesses on the inner surfaces of the first and second pads, as a passive flow control technology, can reduce fluid resistance. Combined with the plasma control device, this forms a combination of active and passive flow control. The flow control system is further enhanced by the fact that the high-frequency magnetic lines generated by the electromagnetic heating block, after passing through the microcrystalline glass panel, can form strong eddies at the leading edge of the cavity. This heats the incoming flow at the front of the cavity, increases its temperature, reduces the viscosity of the water medium, and mitigates the high turbulence issues caused by misalignment of the sealing and interface planes. Simultaneously, the heated incoming flow is more likely to approach a laminar flow state, improving the accuracy of experimental measurement data. Finally, this device for accurately evaluating background noise during cavity testing causes virtually no damage to the inner wall of the cavity and does not affect the internal flow field. However, it significantly reduces the impact of elastic vibration of the cavity wall on the internal flow field, providing a guarantee for accurately evaluating the turbulent pulsating pressure and hydrodynamic noise of the cavity. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a device for accurately evaluating background noise during a cavity test;

[0015] Figure 2 A schematic diagram of a device for accurately evaluating background noise during a cavity test (rotated 90° clockwise);

[0016] Figure 3 A schematic diagram of a device for accurately evaluating background noise during a cavity test (rotated 180° clockwise);

[0017] Figure 4 A schematic diagram of a device for accurately evaluating background noise during a cavity test (rotated 270° clockwise);

[0018] Figure 5 This is a schematic diagram of the first electromagnet;

[0019] Figure 6 This is a schematic diagram of the second electromagnet;

[0020] Figure 7 This is a schematic diagram of the third electromagnet;

[0021] Figure 8 This is a schematic diagram of the fourth electromagnet;

[0022] Figure 9 This is a schematic diagram of the microcrystalline glass panel and the excitation coil;

[0023] Figure 10 This is a schematic diagram of the first pad block;

[0024] Figure 11 This is a schematic diagram of the second pad block;

[0025] Wherein, 1 is a cavity, 2 is a first electromagnet, 3 is a first plate, 4 is a second electromagnet, 5 is a second plate, 6 is a third electromagnet, 7 is a third plate, 8 is a fourth electromagnet, 9 is a fourth plate, 21 is a stud, 22 is a copper coil, 41 is a stud, 42 is a copper coil, 61 is a stud, 62 is a copper coil, 81 is a stud, 82 is a copper coil, 111 is a microcrystalline glass panel, 112 is an excitation coil, 131 is the first layer of the first pad 13, 132 is the second layer of the first pad 13, 133 is the third layer of the first pad 13, 134 is the fourth layer of the first pad 13, 135 is the fifth layer of the first pad 13, 141 is the first layer of the second pad 14, 142 is the second layer of the second pad 14, 143 is the third layer of the second pad 14, 144 is the fourth layer of the second pad 14, and 145 is the fifth layer of the second pad 14. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0027] The present invention includes a cavity 1, a first electromagnet 2, a first plate 3, a second electromagnet 4, a second plate 5, a third electromagnet 6, a third plate 7, a fourth electromagnet 8, a fourth plate 9, a first power source, an electromagnetic heating block, a second power source, a first pad, a second pad, a Tesla coil, and a third power source. The first electromagnet 2 is connected to the first plate 3, the second electromagnet 4 is connected to the second plate 5, the third electromagnet 6 is connected to the third plate 7, and the fourth electromagnet 8 is connected to the fourth plate 9. The first power source 10 is connected to the first electromagnet 2, the second electromagnet 4, the third electromagnet 6, and the fourth electromagnet 8. The electromagnetic heating block 11 is connected to the second power source 12. The first pad 13 is placed at the interface of the front edge of the cavity 1, and the second pad 14 is placed at the interface of the rear edge of the cavity 1. The first pad 13 and the second pad 14 are respectively connected to one end of the Tesla coil 15, and the other end of the Tesla coil 15 is connected to the third power source 16.

[0028] The first electromagnet 2 of the present invention is composed of a stud 21 made of silicon steel and a copper coil 22. The stud made of silicon steel serves as the magnetic core, with one end screwed into the first side wall plate of the cavity 1. Insulated copper wires are tightly wound around the surface of the stud to form an electromagnet.

[0029] The first plate 3 of this invention is a stainless steel plate, belonging to martensitic stainless steel. After being attracted by the first electromagnet 2, it increases the wall mass of the cavity 1.

[0030] The second electromagnet 4 of the present invention is composed of a stud 41 made of silicon steel and a copper coil 42. The stud made of silicon steel serves as the magnetic core, with one end screwed into the second side wall plate of the cavity 1. Insulated copper wires are tightly wound around the surface of the stud to form an electromagnet.

[0031] The second plate 5 of this invention is a stainless steel plate, belonging to martensitic stainless steel. After being attracted by the first electromagnet 4, it increases the wall mass of the cavity 1.

[0032] The third electromagnet 6 of the present invention is composed of a stud 61 made of silicon steel and a copper coil 62. The stud made of silicon steel serves as the magnetic core, with one end screwed into the third side wall plate of the cavity 1. Insulated copper wires are tightly wound around the surface of the stud to form an electromagnet.

[0033] The third plate 7 of this invention is a stainless steel plate, belonging to martensitic stainless steel. After being attracted by the third electromagnet 6, it increases the wall mass of the cavity 1.

[0034] The fourth electromagnet 8 of the present invention is composed of a stud 81 made of silicon steel and a copper coil 82. The stud made of silicon steel serves as the magnetic core, with one end screwed into the fourth side wall plate of the cavity 1. Insulated copper wires are tightly wound around the surface of the stud to form an electromagnet.

[0035] The fourth plate 9 of this invention is a stainless steel plate, belonging to martensitic stainless steel. After being attracted by the fourth electromagnet 8, it increases the wall mass of the cavity 1.

[0036] The first power source of this invention is a DC power source, model KPS series, brand WANPTEK, which can provide DC power between 20V and 300V to supply current to the first electromagnet 2, the second electromagnet 4, the third electromagnet 6, and the fourth electromagnet 8.

[0037] The electromagnetic heating block of the present invention is composed of a microcrystalline glass panel 111 and an excitation coil 112. The microcrystalline glass panel 111 is placed near the front edge of the cavity 1, and the excitation coil 112 is placed on top of the microcrystalline glass panel 111.

[0038] The second power source of the present invention is a high-frequency AC power source that generates an ultra-high frequency current higher than 20kHz, which can drive the excitation coil 112 to generate an alternating magnetic field. After passing through the microcrystalline glass panel 111, a large number of dense eddy currents are generated near the leading edge of the cavity 1, thereby heating the incoming flow.

[0039] The first pad of the present invention has a composite structure. The first layer 131 is made of rubber, the second layer 132 is a wavy structure with spikes and is made of stainless steel, the third layer 133 is a structure with pits on the outer surface and is made of rubber, the fourth layer 134 is a wavy structure with spikes and is made of stainless steel, and the fifth layer 135 is made of rubber. The first pad is placed at the front edge of the cavity 1 to complete the sealing of the front edge of the cavity 1.

[0040] The second pad of the present invention has a composite structure. The first layer 141 is made of rubber, the second layer 142 is a wavy structure with spikes and is made of stainless steel, the third layer 143 is a structure with pits and is made of rubber, the fourth layer 144 is a wavy structure with spikes and is made of stainless steel, and the fifth layer 145 is made of rubber. The second pad is placed at the rear edge of the cavity 1 to complete the sealing of the rear edge of the cavity 1.

[0041] The Tesla coil of this invention is used for voltage boosting, and the resonant transformer boosts the voltage of the power supply to between 5 and 30 kilovolts. This is used to drive the front spikes of the second layer 132 and the fourth layer 144 embedded in the first pad of the rubber damping layer, as well as the front spikes of the second layer 142 and the fourth layer 144 in the second pad, to discharge, forming a plasma device to achieve the plasma effect. This heats the incoming flow and wake near the mounting interface of the cavity 1, reducing the turbulence caused by the "step effect" of model installation.

[0042] The third power source of this invention is an AC power source, used to supply electrical energy to the Tesla coil.

Claims

1. A device for accurately evaluating background noise during cavity testing, characterized in that: It includes a first electromagnet, a first plate, a second electromagnet, a second plate, a third electromagnet, a third plate, a fourth electromagnet, a fourth plate, a first power supply, an electromagnetic heating block, a second power supply, a first pad, a second pad, a Tesla coil, and a third power supply. The first electromagnet is connected to the first plate, the second electromagnet is connected to the second plate, the third electromagnet is connected to the third plate, and the fourth electromagnet is connected to the fourth plate. The first power supply is connected to the first electromagnet, the second electromagnet, the third electromagnet, and the fourth electromagnet. The electromagnetic heating block is connected to the second power supply. The first pad is placed at the interface of the front edge of the cavity, and the second pad is placed at the interface of the tail edge of the cavity. The first pad and the second pad are respectively connected to one end of the Tesla coil, and the other end of the Tesla coil is connected to the third power supply. The first electromagnet is composed of a stud made of silicon steel and a copper coil; the second electromagnet is composed of a stud made of silicon steel and a copper coil; the third electromagnet is composed of a stud made of silicon steel and a copper coil; the fourth electromagnet is composed of a stud made of silicon steel and a copper coil. The first sheet is made of stainless steel; the second sheet is made of stainless steel. The third plate is made of stainless steel; the fourth plate is made of stainless steel.

2. The apparatus for accurately evaluating background noise during a cavity test according to claim 1, characterized in that: The first power supply is a DC power supply; the second power supply is a high-frequency AC power supply; and the third power supply is an AC power supply.

3. The apparatus for accurately evaluating background noise during a cavity test according to claim 1, characterized in that: The electromagnetic heating block consists of a microcrystalline glass panel and an excitation coil.

4. The apparatus for accurately evaluating background noise during a cavity test according to claim 1, characterized in that: The first pad has a composite structure. The first layer is made of rubber; the second layer is a wavy structure with spikes and is made of stainless steel; the third layer is a structure with pits on the outer surface and is made of rubber; the fourth layer is a wavy structure with spikes and is made of stainless steel; and the fifth layer is made of rubber.

5. The apparatus for accurately evaluating background noise during a cavity test according to claim 1, characterized in that: The second pad has a composite structure. The first layer is made of rubber, the second layer is a wavy structure with spikes and is made of stainless steel, the third layer is a structure with pits and is made of rubber, the fourth layer is a wavy structure with spikes and is made of stainless steel, and the fifth layer is made of rubber.

Images