A wing structure water power noise control device with internal wall heating outer porous medium

Abstract

The present application relates to a kind of wing structure water dynamic noise control device of internal wall heating outer porous medium, belong to the field of ship vibration noise control.The device of the present application includes wing structure trailing edge, heat insulation layer, heat preservation layer, first electric heating sheet, first temperature sensor, second temperature sensor, second electric heating sheet, third temperature sensor, fourth temperature sensor, first outer porous medium, second outer porous medium, third outer porous medium, electric heating sheet controller, first fixing bolt, second fixing bolt, third fixing bolt, fourth fixing bolt.The present application utilizes the control effect of wall heating and porous medium, mainly influenced by the characteristics of viscosity, proposes the combination control device of internal wall heating and outer porous medium, can significantly reduce the water dynamic noise generated by wing structure trailing edge flow separation.

Description

Technical Field

[0001] This invention relates to a hydrodynamic noise control device with an airfoil structure that is internally heated and covered with a porous medium, belonging to the field of ship vibration and noise control. Background Technology

[0002] Underwater vehicles widely employ airfoil appendages, whose surfaces experience boundary layer flow separation and vortex shedding. These flow phenomena induce significant turbulent pressure fluctuations, leading to a substantial increase in hydrodynamic noise, which severely impacts the acoustic stealth performance of underwater vehicles and greatly amplifies their self-noise. Flow control methods, by controlling the flow field, can effectively suppress turbulent pressure fluctuations, thereby reducing hydrodynamic noise at its source.

[0003] Recent studies have shown that active and passive flow control methods, such as wall heating and porous media, can effectively reduce turbulent pulsating pressure and have the potential to control hydrodynamic noise. Water viscosity decreases with increasing temperature, and wall heating utilizes this property to influence flow. However, surface flow on underwater vehicles is typically forced convection, where viscosity has a limited impact on the flow. Conventional porous media control methods often directly replace airfoil sections with porous media, which not only affects the structural strength of the underwater vehicle but also reduces the already limited internal space. Therefore, external porous media covering is more suitable for hydrodynamic noise control.

[0004] The control effects of both porous media and wall heating are related to the viscosity of water. In porous media, the water velocity is effectively reduced, the flow is significantly affected by viscosity, and temperature has a more pronounced impact on the flow. Therefore, wall heating enhances the suppression of turbulent pulsating pressure. Furthermore, the effects of porous media on flow manifest as viscous drag and inertial drag; the reduction in water viscosity caused by wall heating enhances the control effect of porous media on flow separation and vortex control. Therefore, combining internal wall heating with external porous media can achieve a synergistic effect, expected to yield superior flow control and significantly reduce hydrodynamic noise. Summary of the Invention

[0005] This invention addresses the hydrodynamic noise problem caused by flow separation and vortex shedding at the trailing edge of airfoils by proposing a hydrodynamic noise control device for airfoils with internal wall heating and an outer porous medium coating. The device utilizes electrically heated plates inside the trailing edge of the airfoil for wall heating, and covers the trailing edge with a porous medium of varying porosity and pore count per inch. This effectively reduces the viscosity of water near the wall and dissipates pressure fluctuations in the turbulent boundary layer, thereby reducing the hydrodynamic noise of the airfoil.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows:

[0007] A hydrodynamic noise control device for an airfoil structure with internal wall heating and an outer porous medium coating includes an airfoil trailing edge, a heat insulation layer, a thermal insulation layer, a first electric heating element, a first temperature sensor, a second temperature sensor, a second electric heating element, a third temperature sensor, a fourth temperature sensor, a first outer porous medium coating, a second outer porous medium coating, a third outer porous medium coating, an electric heating element controller, a first fixing bolt, a second fixing bolt, a third fixing bolt, and a fourth fixing bolt. The first and second electric heating elements are respectively attached to the inner sides of the trailing edge of the airfoil structure, and thermal insulation is attached to the other side of the first and second electric heating elements. The airfoil structure has a heat insulation layer on the other side of the insulation layer. The first and second electric heating elements are connected to the electric heating element controller by wires. The outer edge of the airfoil structure is covered with three layers of porous media, which are the first outer porous media, the second outer porous media, and the third outer porous media from the inside out. The outer porous media are fixed to the outer edge of the airfoil structure by the first fixing bolt, the second fixing bolt, the third fixing bolt, and the fourth fixing bolt. The first temperature sensor and the second temperature sensor are placed on the two sides of the airfoil structure trailing edge, respectively, and the third temperature sensor and the fourth temperature sensor are placed away from the airfoil structure trailing edge.

[0008] Furthermore, the first and second electric heating elements are flexible etched foil heating elements, with an adhesive on one side.

[0009] Furthermore, the insulation layer is made of insulation cotton, and the heat insulation layer is made of polyurethane foam.

[0010] Furthermore, the first temperature sensor, the second temperature sensor, the third temperature sensor, and the fourth temperature sensor are all digital temperature sensors; the electric heating element controller is connected to the first temperature sensor, the second temperature sensor, the first electric heating element, and the second electric heating element via cables.

[0011] Furthermore, the first, second, and third outer porous media are all open-cell foamed iron-nickel alloys, and the porosity and number of pores per inch of the three porous media increase sequentially from the inside to the outside; the first, second, and third outer porous media are all provided with through holes for the fixing bolts to pass through.

[0012] Furthermore, the airfoil trailing edge surface has blind hole threads and through hole threads.

[0013] Furthermore, the first fixing bolt, the second fixing bolt, the third fixing bolt, and the fourth fixing bolt are all cross-head countersunk bolts.

[0014] The beneficial effects of this invention are:

[0015] Conventional flow control methods based on porous media typically replace a portion of the airfoil structure with a porous medium. This approach not only affects the structural strength of the underwater vehicle but also compresses its internal space, making it difficult or even impossible to apply in high-pressure underwater environments. Applying a porous medium to the entire exterior of the airfoil structure results in a significant increase in drag, leading to a prominent trade-off between drag and acoustic performance. This invention uses a custom mold to create a porous medium that fits tightly to the trailing edge of the airfoil, covering its exterior without altering the material of the trailing edge and thus not affecting the structural strength of the underwater vehicle. Since the porous medium only covers the trailing edge, its impact on drag performance is also very limited. Furthermore, this invention only applies a thin electric heating element to the interior of the trailing edge of the airfoil, significantly saving internal space compared to conventional porous media control methods.

[0016] The permeability of a porous medium reflects the ease with which fluid passes through it. This parameter is directly proportional to porosity and inversely proportional to the number of pores per inch. To ensure smooth water flow through a porous medium, the outer porous medium needs to have a small number of pores per inch. However, a decrease in the number of pores per inch leads to an increase in pore diameter and surface roughness, thus increasing high-frequency hydrodynamic noise. This invention employs a multi-layered structure of outer porous medium. While maintaining a relatively constant permeability, the porosity and number of pores per inch of the third outer porous medium are greater than those of the second outer porous medium, and vice versa. This design ensures smooth water flow while increasing the number of pores per inch and decreasing the pore diameter, thereby reducing the surface roughness of the porous medium. Therefore, the increase in high-frequency hydrodynamic noise is no longer significant.

[0017] This invention employs a combined control method of internal wall heating and external porous media coating, both of which are affected by water viscosity. On one hand, the permeation and dissipation effect of the porous media significantly reduces flow instability at the trailing edge of the airfoil structure, while simultaneously lowering the water velocity near the wall, thus enhancing the control effect of wall heating on turbulent pulsating pressure. On the other hand, wall heating reduces the viscosity of water near the wall, preventing excessive resistance from the porous media. Therefore, internal wall heating and external porous media coating can mutually enhance the control effect, and this invention is expected to achieve a more significant noise reduction effect. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a hydrodynamic noise control device with an airfoil structure that is heated internally and covered with a porous medium externally.

[0019] Figure 2This is a top view of the heating device on the internal wall of the trailing edge of the airfoil structure.

[0020] Figure 3 It is a top view of the airfoil structure with a porous medium covering the trailing edge.

[0021] Figure 4 This is a left view of the airfoil structure with a porous medium covering its trailing edge.

[0022] Figure 5 This is a front view of the airfoil structure with a porous medium covering its trailing edge.

[0023] Among them, 1 is the trailing edge of the airfoil structure, 2 is the heat insulation layer, 3 is the thermal insulation layer, 4 is the first electric heating element, 5 is the first temperature sensor, 6 is the second temperature sensor, 7 is the second electric heating element, 8 is the third temperature sensor, 9 is the fourth temperature sensor, 10 is the first outer porous medium, 11 is the second outer porous medium, 12 is the third outer porous medium, 13 is the electric heating element controller, 14 is the first fixing bolt, 15 is the second fixing bolt, 16 is the third fixing bolt, and 17 is the fourth fixing bolt. Detailed Implementation

[0024] Specific implementation method one: Combining Figure 1-5 This implementation method is described as follows: Figure 1-5 As shown in this embodiment, a hydrodynamic noise control device for an airfoil structure with internal wall heating and an outer porous medium coating includes an airfoil trailing edge 1, a heat insulation layer 2, a thermal insulation layer 3, a first electric heating element 4, a first temperature sensor 5, a second temperature sensor 6, a second electric heating element 7, a third temperature sensor 8, a fourth temperature sensor 9, a first outer porous medium 10, a second outer porous medium 11, a third outer porous medium 12, an electric heating element controller 13, a first fixing bolt 14, a second fixing bolt 15, a third fixing bolt 16, and a fourth fixing bolt 17. The first electric heating element 4 and the second electric heating element 7 are respectively attached to the inner two sides of the airfoil trailing edge 1, and the thermal insulation layer is attached to the other side of the first electric heating element 4 and the second electric heating element 7. 3. The other side of the insulation layer 3 is covered with the heat insulation layer 2. The first electric heating element 4 and the second electric heating element 7 are connected to the electric heating element controller 13 by wires. The outer side of the airfoil tail edge 1 is covered with three layers of porous media, which are, from the inside to the outside, the first outer porous media 10, the second outer porous media 11 and the third outer porous media 12. The outer porous media are fixed to the outside of the airfoil tail edge 1 by the first fixing bolt 14, the second fixing bolt 15, the third fixing bolt 16 and the fourth fixing bolt 17. The first temperature sensor 5 and the second temperature sensor 6 are placed on the two sides of the airfoil tail edge 1 to monitor the temperature of the heated wall. The third temperature sensor 8 and the fourth temperature sensor 9 are placed away from the airfoil tail edge 1 to monitor the water flow temperature.

[0025] The trailing edge 1 of the airfoil structure is made of 316L stainless steel with a thickness of 6mm. It has the characteristics of high strength, corrosion resistance and low thermal conductivity, and can maintain stable performance at high temperatures. Four M10 blind holes are opened on the outer surface of the trailing edge for fixing the porous medium covering it. Two M14 through holes are also opened for fixing the first temperature sensor 5 and the second temperature sensor 6.

[0026] The first temperature sensor 5, the second temperature sensor 6, the third temperature sensor 8, and the fourth temperature sensor 9 are all digital temperature sensors. The first temperature sensor 5 and the second temperature sensor 6 are fixed to the trailing edge 1 of the airfoil structure by M14 threads at the tail. The average temperature of the first temperature sensor 5 and the second temperature sensor 6 is recorded as the temperature of the heated wall surface. The third temperature sensor 8 and the fourth temperature sensor 9 are fixed at a position away from the heated wall surface at the trailing edge. The average temperature of the third temperature sensor 8 and the fourth temperature sensor 9 is recorded as the temperature of the unheated wall surface. All temperature sensors are watertight using fluororubber O-rings.

[0027] The first electric heating element 4 and the second electric heating element 7 are custom flexible etched foil heating elements with a thickness of 3mm. Their shape is completely consistent with the trailing edge 1 of the airfoil structure. They have two holes with a diameter of 15mm for the first temperature sensor 5 and the second temperature sensor 6 to pass through. The heating element is tightly attached to the inner wall of the trailing edge 1 of the airfoil structure with an adhesive.

[0028] The insulation layer 2 is made of insulation cotton with a thickness of 5mm, and the insulation layer 3 is made of polyurethane foam with a thickness of 5mm. The dimensions of the insulation layer 2 and the insulation layer 3 are slightly larger than the first electric heating element 4 and the second electric heating element 7, ensuring that the heating elements are completely covered. These two materials have excellent heat insulation performance and can effectively prevent the heat output from the electric heating element from dissipating into the airfoil structure.

[0029] The electric heating element controller 13 is connected to the first temperature sensor 5, the second temperature sensor 6, the first electric heating element 4, and the second electric heating element 7. It can not only display the temperature of the heated and unheated wall surfaces, but also contains a PID controller that can automatically adjust the heating power to ensure that the temperature of the heated wall surface is maintained at the target temperature.

[0030] The first outer porous medium 10, the second outer porous medium 11, and the third outer porous medium 12 are all made of open-cell foamed iron-nickel alloy. The first outer porous medium 10 has a porosity of 87% and 10 pores per inch, the second outer porous medium 11 has a porosity of 93% and 20 pores per inch, and the third outer porous medium 12 has a porosity of 95% and 30 pores per inch. There are interconnected pores between the first outer porous medium 10 and the second outer porous medium 11, and between the second outer porous medium 11 and the third outer porous medium 12, forming a transition region where the porosity and pores per inch increase rapidly. This design ensures that the permeability of the outer porous medium remains basically unchanged while also ensuring that the surface of the outer porous medium has a small roughness. In addition, the outer porous medium has through holes with a diameter of 11 mm.

[0031] The first fixing bolt 14, the second fixing bolt 15, the third fixing bolt 16, and the fourth fixing bolt 17 are all M10 cross-head countersunk bolts made of titanium alloy.

[0032] The mechanism by which this invention controls hydrodynamic noise is mainly reflected in the following two aspects. Firstly, wall heating reduces the viscosity of water near the wall; for every degree Celsius increase in temperature, the water viscosity decreases by approximately 2%, leading to a reduction in wall shear stress. The root mean square value of the turbulent pulsating pressure is directly proportional to the wall shear stress. The relationship between the water flow velocity and the free flow velocity in the porous medium is as follows:

[0033] ①

[0034] In formula ①, Porosity The velocity in a porous medium, This is the intrinsic mean velocity. Because... The porous medium reduces the water flow velocity, and the temperature has a more significant impact on the water flow. Therefore, the porous medium coating improves the hydrodynamic noise control effect of the internal wall heating.

[0035] On the other hand, porous media primarily influence the flow field through resistance, specifically viscous drag and inertial drag. When the resistance caused by the porous media is too great, water flow becomes difficult to pass through, leading to additional turbulent pulsating pressure. The resistance effect of porous media can be expressed as:

[0036] ②

[0037] In formula ② Viscosity, For density, The coefficient of viscosity resistance. This represents the inertial drag coefficient. The viscosity of water does not change linearly with temperature; when the initial temperature of water is low, the effect of temperature on viscosity is significant. The global average temperature of ocean water is approximately 4°C. At this temperature, the viscosity of seawater is approximately 0.001563 Pa·s. When the temperature rises to 30°C, the viscosity of water decreases to 0.0008357 Pa·s, a normalized change of approximately 46.5%. In the deep seawater where underwater vehicles frequently operate, wall heating does not require a high temperature difference to significantly change the viscosity of the local water flow, and does not require a large heating power. The softening temperature of high-temperature polyurethane foam is approximately 80°C, while the softening temperature of rubber and plastic insulation cotton can reach 140°C, far exceeding the temperature required for wall heating (30°C). Therefore, the wall heating of this invention will not cause the insulation layer or heat insulation layer to soften, leading to structural detachment or loss of insulation effect. Furthermore, by Figure 1 It is known that the wall heating components such as heating plates are attached to the inside of the trailing edge of the airfoil structure, while the porous medium covers the outside of the trailing edge of the airfoil structure. The porous medium is made of foamed iron-nickel alloy. Heating the wall to about 30°C will not change the pore characteristics of the foamed iron-nickel alloy. Therefore, it will not affect the control effect of the outer porous medium on turbulent pulsating pressure and hydrodynamic noise.

[0038] The flow control effects of both internal wall heating and the external porous medium coating are highly correlated with viscosity. Internal wall heating reduces the viscosity of water near the wall. As shown in Equation ②, the reduced water viscosity weakens the resistance of the porous medium to the water flow. In this case, the external porous medium effectively dissipates turbulent pulsating pressure without causing additional turbulent pulsating pressure due to excessive resistance. As shown in Equation ①, the external porous medium reduces the water velocity near the wall. Lower water velocity results in a lower convective heat transfer coefficient, reducing the water's ability to carry away heat from the wall and decreasing the heat required to maintain wall heating. This makes the effect of temperature on water viscosity more significant. In summary, internal wall heating and the external porous medium coating mutually enhance the control of turbulent pulsating pressure, thereby more effectively suppressing the main source of hydrodynamic noise. Therefore, this invention achieves excellent hydrodynamic noise control.

Claims

1. A hydrodynamic noise control device for an airfoil structure with internal wall heating and an outer porous medium coating, characterized in that: The structure includes an airfoil trailing edge, a heat insulation layer, a thermal insulation layer, a first electric heating element, a first temperature sensor, a second temperature sensor, a second electric heating element, a third temperature sensor, a fourth temperature sensor, a first outer porous medium, a second outer porous medium, a third outer porous medium, an electric heating element controller, a first fixing bolt, a second fixing bolt, a third fixing bolt, and a fourth fixing bolt. The first and second electric heating elements are respectively attached to the inner sides of the airfoil trailing edge. A thermal insulation layer is attached to the other side of the first and second electric heating elements, and a thermal insulation layer is attached to the other side of the thermal insulation layer. A first and a second electric heating element are connected to an electric heating element controller via a cable. The outer edge of the airfoil structure is covered with three layers of porous outer medium, which are, from the inside out, the first, second, and third porous outer mediums. The porous outer mediums are fixed to the outer edge of the airfoil structure by the first, second, third, and fourth fixing bolts. The first and second temperature sensors are placed on the two sides of the airfoil structure's trailing edge, respectively, while the third and fourth temperature sensors are placed away from the trailing edge of the airfoil structure.

2. The airfoil structure hydrodynamic noise control device with internal wall heating and external porous medium coating according to claim 1, characterized in that: The first and second electric heating elements are flexible etched foil heating elements, each with an adhesive on one side.

3. The airfoil structure hydrodynamic noise control device with internal wall heating and external porous medium coating according to claim 1, characterized in that: The insulation layer is made of rubber and plastic insulation cotton, and the heat insulation layer is made of high-temperature resistant polyurethane foam.

4. The airfoil structure hydrodynamic noise control device with internal wall heating and external porous medium coating according to claim 1, characterized in that: The first temperature sensor, the second temperature sensor, the third temperature sensor, and the fourth temperature sensor are all digital temperature sensors; the electric heating element controller is connected to the first temperature sensor, the second temperature sensor, the first electric heating element, and the second electric heating element via cables.

5. The airfoil structure hydrodynamic noise control device with internal wall heating and external porous medium coating according to claim 1, characterized in that: The first, second, and third outer porous media are all open-cell foamed iron-nickel alloys. The porosity and number of pores per inch of the three outer porous media increase sequentially from the inside to the outside. The first, second, and third outer porous media are all provided with through holes for fixing bolts to pass through.

6. The airfoil structure hydrodynamic noise control device with internal wall heating and external porous medium coating according to claim 1, characterized in that: The trailing edge surface of the airfoil structure has blind hole threads and through hole threads.

7. The airfoil structure hydrodynamic noise control device with internal wall heating and external porous medium coating according to claim 1, characterized in that: The first, second, third, and fourth fixing bolts are all Phillips head countersunk bolts.

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