An active film cooling leading edge test system applied to an arc wind tunnel

Abstract

The present invention provides a film cooling active cooling wing leading edge test system applied to an arc wind tunnel. This system uses the atmospheric environment at standard atmospheric pressure as the cold air source and relies on the relatively high vacuum degree in the wind tunnel to achieve the input of cold air. The present invention includes a sonic throat, an electric pressure regulating valve, a pressure sensor, an electromagnetic solenoid valve, and a heat flux sensor. A cooling air hole is arranged at a uniform interval along the highest heat flux line on the wing leading edge at several distances. The range of the ratio of the radius of the cooling air hole to the radius of the wing leading edge is 1 / 10 to 1 / 5. Two to three heat flux measurement points are arranged between two intake air holes to detect the heat flux density between the two air holes, and at the same time, one heat flux measurement point is arranged on each side of the cold air hole. Before the test, the air flow rate is changed by replacing sonic throats with different diameters, and according to the distribution of the measured values of each heat flux sensor, the electric pressure regulating valves on each branch pipeline are adjusted to adjust the pressure of the branch, solving the problem of the active film cooling thermal protection aerodynamic heat test for the wing leading edge material of a hypersonic aircraft.

Description

Technical Field

[0001] The present invention relates to the field of aerospace aerodynamic heat ablation tests, particularly for reusable vehicle heat protection materials. Background Art

[0002] When a hypersonic vehicle flies at high speed in the atmosphere, it undergoes severe aerodynamic heating. As an important local component on the vehicle, the leading edge of the wing has to withstand intense aerodynamic heating. With the development of hypersonic reusable vehicles, it is required that the heat protection materials on the vehicle surface can be reused multiple times. The traditional passive thermal protection, such as ablation thermal protection, can no longer meet the heat protection requirements of this type of vehicle. Instead, active thermal protection is mostly adopted, and the principle is to rely on the cooling medium to carry away most of the heat flux.

[0003] Due to the limitation of the power problem of hypersonic vehicles, there are certain restrictions on the mass of each part of the vehicle. For the leading edge with active film cooling, it is required to achieve a relatively uniform test effect with the minimum air flow rate, which puts higher requirements on the position of the cold wall heat flux measurement points on the leading edge and the control of the cooling gas pressure. First, when the cold air flow meets the supersonic oncoming flow on the leading edge, if the total pressure of the cold air is relatively high, a shock wave is likely to be generated upstream of the cold air holes, resulting in local high heat flux regions on the leading edge. If the total pressure of the cold air is relatively low, the high-temperature oncoming flow will surely enter the cold air holes, and the cooling effect will be poor. Therefore, it is necessary to find a more appropriate dimensionless ratio of the total pressure of the cold air flow to the surface pressure of the leading edge through the ground test system, so that the cold air flow can flow in the boundary layer on the leading edge before it can be officially applied to the model. Summary of the Invention

[0004] The technical problem solved by the present invention is: overcoming the deficiencies of the prior art, providing a film active cooling leading edge test system for an arc wind tunnel, and improving the film cooling effect of the leading edge by adjusting the pressure of each cold air branch.

[0005] The technical solution adopted by the present invention is: a film active cooling leading edge test system for an arc wind tunnel, where the leading edge is located in the high-temperature flow field downstream of the nozzle exit. The test system of the present invention includes a sonic throat, a first electromagnetic solenoid valve, N cooling branches, and a heat flux sensor;

[0006] Each cooling branch includes an electro - pressure regulating valve, a pressure sensor, and a second electromagnetic switching valve; there are N cooling air holes, 4N - 1 heat flux measurement points, and N cooling channels on the leading edge of the wing. The cooling channels are connected to the cooling air holes, and heat flux sensors are installed at the heat flux measurement points; the upstream of the sonic throat is connected to normal - temperature air under standard atmospheric pressure to provide a cold air source. The downstream of the sonic throat is connected to the first electromagnetic switching valve, and they are both placed outside the test chamber. The output of this first electromagnetic switching valve is connected to the test chamber through a connecting pipe and is connected to N cooling branches, and the N cooling branches are connected to the N cooling channels on the leading edge of the wing; on each cooling branch, the output of the electro - pressure regulating valve is connected to the input of the second electromagnetic switching valve, and the pressure sensor measures the pressure between the electro - pressure regulating valve and the second electromagnetic switching valve; according to the distribution of the measured values of each heat flux sensor on the leading edge of the wing, the electro - regulating valves on each cooling branch are adjusted to adjust the pressure of the branch and improve the film cooling effect on the leading edge of the wing; N≥1.

[0007] Further, the sonic throat is a converging circular flow channel. The large - diameter end is the upstream of the sonic throat and is connected to the atmosphere; the small - diameter end is the downstream of the sonic throat and is connected to N cooling branches through a connecting pipe, N≥1.

[0008] Further, both the electro - pressure regulating valve and the second electromagnetic switching valve are connected to the cooling branch through a sealed joint, and the pressure sensor is connected to the cooling branch through a three - way valve. The N cooling branches, the leading edge of the wing, and the heat flux sensors are all placed inside the test chamber.

[0009] Further, the vacuum degree inside the test chamber is less than 1 kPa.

[0010] Further, the N cooling air holes on the leading edge of the wing are evenly arranged along the direction of the highest heat flow line on the arc surface. The distance between adjacent two cooling air holes is 20 - 30 mm, and the diameter is 1 / 10 - 1 / 5 of the radius of the arc surface of the leading edge of the wing, N≥1.

[0011] Further, the distribution of the positions of the heat flux measurement points is as follows:

[0012] (1) On both sides of each cooling air hole perpendicular to the direction of the nozzle incoming flow, one heat flux measurement point is symmetrically arranged with the center of the cooling air hole, and the distance between each heat flux measurement point and the center of the current cooling air hole is 3 - 5 mm;

[0013] (2) Along the nozzle incoming flow, one heat flux measurement point is arranged on the highest heat flow line at the upstream position of each cooling air hole, and its distance from the center of the cooling air hole is 5 - 10 mm; [[ID=_{22}]]

[0014] (3) One heat flux measurement point is arranged in the middle of adjacent two cooling air holes.

[0015] Further, the method for determining the position of the highest heat flux line on the leading edge of the wing is as follows: Define the straight line connecting the midpoints of the arcs at both ends of the leading edge arc surface of the wing as the center line. For the leading edge of the wing without deflection, the highest heat flux line is located on the center line of the leading edge arc surface; for the deflected leading edge of the wing, the highest heat flux line is located on the leading edge surface on the windward side determined by the following formula and is parallel to the center line of the leading edge arc surface;

[0016]

[0017] In the above formula: ε is the angle between the plane passing through the highest heat flux line and the center of the arc surface and the plane passing through the center line of the arc surface and the center of the arc surface, α is the deflection angle, and β is the windward angle.

[0018] Further, the heat flux sensor includes a calorimetric block, a heat insulation sleeve, and a K-type thermocouple. The calorimetric block is externally sleeved with a heat insulation sleeve, and the axial bottom end of the calorimetric block is connected to the K-type thermocouple.

[0019] Further, the control signal of the electric pressure regulating valve 2 is a DC P-Q mA, and the current value of the control signal has a linear relationship with the opening degree of the valve. The valve is closed at P mA, and the valve is fully open at Q mA, where P>1, Q>1, and P<Q;

[0020] According to the distribution of the heat flux measurement values on the leading edge 5 of the wing, the pressure of each cooling branch is adjusted by adjusting the electric pressure regulating valve 2. Specifically:

[0021] If the heat flux value around the current cooling air hole is higher than the heat flux value at the middle position between the current cooling air hole and the adjacent downstream cooling air hole, at this time, the intake air volume of the current cooling air hole is large. Reduce the current value of the control signal, reduce the intake air pressure, and reduce the intake air volume until the heat flux value at the measurement point around the current cooling air hole is lower than, or equal to, the heat flux value between the two cooling air holes;

[0022] If the heat flux value around the current cooling air hole is lower than the heat flux value at the middle position between the current cooling air hole and the adjacent downstream cooling air hole, at this time, the intake air volume of the current cooling air hole is small. Increase the current value of the control signal, increase the intake air pressure, and increase the intake air volume until the heat flux value at the measurement point around the current cooling air hole is higher than, or equal to, the heat flux value between the two cooling air holes;

[0023] Convert the current signal into a corresponding linear displacement, and linearly increase the opening degree of the valve by increasing the current value of the control signal.

[0024] Further, the calculation formula for the mass of the cold air source is:

[0025]

[0026] In the above formula, m is the mass of the cold air, unit: kg / s; is the area at the downstream exit of the sonic throat, unit: m 2 ; p0 is the atmospheric pressure, with a value of 0.1 MPa; T0 is the atmospheric ambient temperature, unit: K.

[0027] The beneficial effects of the present invention compared with the prior art are as follows:

[0028] (1) The present invention uses the atmospheric environment as the cooling gas supply source, and jointly with the sonic throat, directly calculates the mass flow rate of air according to the isentropic flow principle of aerodynamics. At the same time, if required by the test, the mass flow rate of the cooling gas can be changed by replacing the sonic throat with different outlet diameters, and the operation is simple and convenient.

[0029] (2) The present invention arranges heat flux measurement points at the upstream, both sides, and the center positions of the two cooling holes downstream of the cooling holes only at the leading edge of the wing, and can immediately monitor the heat flux uniformity of the key parts on the leading edge of the wing.

[0030] (3) According to the distribution of the measured values of each heat flux measurement point on the leading edge of the wing, the present invention can adjust the pressure of each branch through the electric pressure regulating valves on different cold air branches, so as to further improve the film cooling effect on the leading edge of the wing. Brief Description of the Drawings

[0031] Figure 1 is a schematic diagram of the leading-edge active film cooling test system of the embodiment of the present invention;

[0032] Figure 2 is a schematic diagram of the flow channel of the sonic throat of the embodiment of the present invention;

[0033] Figure 3 is a schematic diagram of the distribution of heat flux measurement points on the film-cooled leading edge of the wing of the embodiment of the present invention; Detailed Embodiment

[0034] The present invention will be further described in detail below with reference to the drawings:

[0035] The present invention provides a test system applied to the leading-edge active film cooling of an arc wind tunnel. Using the atmospheric environment as the gas source, the mass flow rate of the cold air is changed by replacing the sonic throat 1 with different outlet diameters, and at the same time, the pressure in each cold air branch is adjusted. Finally, the dimensionless ratio of the total pressure of the cold air in each branch to the static pressure on the leading edge is found, realizing a better cooling effect of the leading-edge active film, laying a foundation for the model application.

[0036] As Figure 1 shown is a schematic diagram of the leading-edge active film cooling test system, including a sonic throat 1, a first electromagnetic switch valve, N cooling branches, and a heat flux sensor.

[0037] Each cooling branch includes an electro-pneumatic pressure regulating valve 2, a pressure sensor 3, and a second electromagnetic switching valve 4; there are N cooling air holes, heat flux measurement points, and N cooling channels on the wing leading edge 5. The cooling channels are connected to the cooling air holes, and heat flux sensors are installed at the heat flux measurement points; the upstream of the sonic throat 1 is connected to normal-temperature air under standard atmospheric pressure, and the downstream of the sonic throat 1 is connected to the first electromagnetic switching valve. They are all placed outside the test chamber. The output of this first electromagnetic switching valve is connected to the test chamber through a connecting pipe and is connected to each cooling branch, and each cooling branch is connected to the cooling channels on the wing leading edge 5; on each cooling branch, the output of the electro-pneumatic pressure regulating valve 2 is connected to the input of the second electromagnetic switching valve 4, and the pressure sensor 3 measures the pressure between the electro-pneumatic pressure regulating valve 2 and the second electromagnetic switching valve 4. The N cooling branches, the wing leading edge 5, and the heat flux sensors are all placed inside the test chamber; the wing leading edge 5 is placed in the high-temperature flow field downstream of the nozzle exit.

[0038] Under standard atmospheric pressure conditions, air enters the test chamber through the sonic throat 1 and the first electromagnetic switching valve downstream thereof, enters each cold air branch, and then passes through the electro-pneumatic pressure regulating valve 2, the pressure sensor 3, the second electromagnetic switching valve 4, and the cooling channels of the wing leading edge 5 to be connected to the cooling air holes on the leading edge. In this embodiment, both the electro-pneumatic pressure regulating valve 2 and the second electromagnetic switching valve 4 are connected to the cooling branch through sealed joints, and the pressure sensor 3 is connected to the cooling branch through a three-way valve.

[0039] In order to ensure the required supersonic flow field at the front of the wing leading edge of the nozzle and to ensure sonic flow at the exit of the sonic throat, a certain degree of vacuum needs to be maintained in the test chamber, preferably less than 1 kPa.

[0040] Figure 2 It shows a schematic diagram of the sonic throat flow passage. Combining the motion and energy equations, the required cold air mass flow rate through the sonic throat can be derived through isentropic flow, and its calculation formula is:

[0041]

[0042] Among them, m is the mass flow rate, unit: kg / s; is the area at the exit of the sonic throat, unit: m 2 ; p0 is the atmospheric pressure, with a value of 0.1 MPa; T0 is the atmospheric ambient temperature, K.

[0043] The electro-pneumatic pressure regulating valve 2 in the test chamber can adjust the pressure according to the heat flux distribution near the cooling air holes on each cold air branch and the wing leading edge 5. The pressure sensor 3 downstream of the electro-pneumatic pressure regulating valve 2 is used to measure the surface pressure of the wing leading edge in the high-temperature supersonic flow field. Close the first electromagnetic switching valve downstream of the sonic throat 1 and open the second electromagnetic switching valve 4 of each branch. The surface pressure at the positions of each cooling air hole on the wing leading edge during the test can be measured through the pressure sensor 3 of the branch, denoted as P b1 、P b2, P b3 , ……, P bM . Similarly, when the first electromagnetic switching valve is opened and the second electromagnetic switching valves 4 on each branch are closed, the measured values of the pressure sensors 3 on each branch represent the total cooling gas pressure of each branch, denoted as P 01 , P 02 , P 03 , ……, P 0M . The ratio of the total cooling gas pressure of each branch to the surface pressure at the position of the corresponding cooling air hole is the dimensionless ratio of the total cooling gas pressure of each branch to the pressure at the leading edge 5 of the wing, i.e., P 01 / P b1 , P 02 / P b2 , P 03 / P b3 , ……, P 0M / P bM .

[0044] The leading edge 5 of the wing downstream of the second electromagnetic switching valve 4 on each branch has a cross-section in the shape of a triangle, rectangle, or trapezoid, with the top spliced by arc surfaces; it is fixed in the high-temperature supersonic flow field at the nozzle exit through a water-cooled bracket. A number of cooling air holes are evenly arranged along the flow field direction, and the recommended interval between two adjacent cooling air holes is 20 - 30 mm. The diameter of the cooling air holes is 1 / 10 - 1 / 5 of the diameter of the leading edge 5 of the wing. The cooling channels connected to the cooling air holes are placed inside the leading edge 5 of the wing and wrapped with heat-insulating materials to avoid being ablated by the hot air flow.

[0045] The position of the cold air inlet hole on the leading edge 5 of the wing is set at the position with the highest heat flux on a certain cross-section of the leading edge 5 of the wing. The straight line connecting the midpoints of the arcs at both ends of the arc surface of the leading edge 5 of the wing is defined as the center line. For the leading edge 5 of the wing without a deflection angle, the highest heat flux line is located on the center line of the arc surface of the leading edge 5 of the wing; for the deflected leading edge 5 of the wing, the highest heat flux line is located on the surface of the leading edge 5 of the wing on the windward side determined by the following formula and is parallel to the center line of the arc surface of the leading edge 5 of the wing;

[0046]

[0047] In the above formula: ε is the angle between the plane passing through the highest heat flux line and the center of the arc surface and the plane passing through the center line of the arc surface and the center of the arc surface, α is the deflection angle, and β is the windward angle.

[0048] Figure 3 Schematic diagram showing the distribution of cold air holes and cold wall heat flux on the leading edge 5 of the wing. The distribution of the heat flux measurement point positions is as follows:

[0049] (1) On both sides of each cooling air hole perpendicular to the nozzle incoming flow direction, one heat flux measurement point is symmetrically arranged with respect to the center of the cooling air hole, and the distance between each heat flux measurement point and the center of the current cooling air hole is 3 - 5 mm;

[0050] (2) Along the oncoming flow of the nozzle, a heat flux measurement point is arranged on the highest heat flux line at the upstream position of each cooling air hole, and the distance from the center of the cooling air hole is 5 - 10 mm;

[0051] (3) A heat flux measurement point is arranged in the middle between two adjacent cooling air holes.

[0052] When the cooling air pressure is relatively high, it forms an obstacle to the hypersonic oncoming flow, generating a shock wave upstream of the cold air hole, resulting in a high heat flux area upstream and on both sides of the cold air hole. As the cooling air pressure decreases, finally the cooling air can only flow within the leading edge boundary layer. At this time, the shock wave disappears, and the local high heat flux area also disappears. Moreover, the cold wall heat flux on the leading edge surface between the two cold air holes is significantly lower than that without cooling air, achieving a better cooling effect. At this time, the dimensionless ratio of the total pressure of the cooling air in each branch to the pressure on the leading edge is the result to be obtained by this test system. The specific implementation requires adjusting the pressure of each cooling branch by adjusting the electric pressure regulating valve 2. The method is as follows:

[0053] The control signal of the electric pressure regulating valve 2 is DC 4 - 20 mA, and the current value of the control signal has a linear relationship with the opening of the valve. The valve is closed at 4 mA and fully open at 20 mA;

[0054] If the heat flux value around the current cooling air hole is higher than the heat flux value at the middle position between the current cooling air hole and the adjacent downstream cooling air hole, at this time the air intake of the current cooling air hole is large. Reduce the current value of the control signal, reduce the intake pressure, and reduce the air intake until the heat flux value measured around the current cooling air hole is lower than or equal to the heat flux value between the two cooling air holes;

[0055] If the heat flux value around the current cooling air hole is lower than the heat flux value at the middle position between the current cooling air hole and the adjacent downstream cooling air hole, at this time the air intake of the current cooling air hole is small. Increase the current value of the control signal, increase the intake pressure, and increase the air intake until the heat flux value measured around the current cooling air hole is higher than or equal to the heat flux value between the two cooling air holes;

[0056] Convert the current signal into the corresponding linear displacement, and linearly increase the opening of the valve by increasing the current value of the control signal.

[0057] By replacing the sonic throat 1, the active film cooling test of the wing leading edge under different flow rate conditions is realized.

[0058] The heat flux sensor used in this embodiment is a plug calorimeter; a calorimetric block is vertically placed inside the heat flux sensor; the calorimetric block is made of oxygen-free copper material; the calorimetric block has a cylindrical structure; the diameter of the calorimetric block is 3 mm; the axial length of the calorimetric block is 5 mm. A heat insulation sleeve is sleeved outside the calorimetric block, and the axial length of the heat insulation sleeve is 6.5 mm; the wall thickness of the heat insulation sleeve is 1 mm; the axial bottom end of the calorimetric block is connected to a K-type thermocouple; the measuring range of the K-type thermocouple is 0 - 1300 °C. The thermocouple is led out through a water-cooled bracket from the internal channel of the wing leading edge 5.

[0059] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. An active film cooling wing leading edge test system applied to an arc wind tunnel, where the wing leading edge (5) is located in the flow field downstream of the nozzle outlet in the test chamber, and is characterized in that: It includes a sonic throat (1), a first electromagnetic switching valve, N cooling branches, and a heat flux sensor; Each cooling branch includes an electric pressure regulating valve (2), a pressure sensor (3), and a second electromagnetic switching valve (4); there are N cooling air holes, 4N - 1 heat flux measurement points, and N cooling channels on the leading edge of the wing (5). The cooling channels are connected to the cooling air holes, and the heat flux sensor is installed at the heat flux measurement points; the upstream of the sonic throat (1) is connected to normal temperature air under standard atmospheric pressure to provide a cold air source. The downstream of the sonic throat (1) is connected to the first electromagnetic switching valve and is placed outside the test chamber together. The output of this first electromagnetic switching valve is connected to the test chamber through a connecting pipe and is connected to N cooling branches. The N cooling branches are connected to the N cooling channels on the leading edge of the wing (5); on each cooling branch, the output of the electric pressure regulating valve (2) is connected to the input of the second electromagnetic switching valve (4), and the pressure sensor (3) measures the pressure between the electric pressure regulating valve (2) and the second electromagnetic switching valve (4); according to the distribution of the measured values of each heat flux sensor on the leading edge of the wing (5), the electric pressure regulating valve (2) on each cooling branch is adjusted to adjust the pressure of the branch and improve the film cooling effect of the leading edge of the wing (5); N ≥ 1; During the test, the mass flow rate of the cold air source is calculated by the following formula: In the above formula, m is the mass flow rate of cold air, unit: kg / s; is the area at the downstream outlet of the sonic throat (1), unit: m 2 ; p0 is the atmospheric pressure, with a value of 0.1 MPa; T0 is the atmospheric ambient temperature, unit: K.

2. The test system for the leading edge of a gas film actively cooled wing applied to an arc wind tunnel according to claim 1, characterized in that: The sonic throat (1) is a converging circular flow channel. The large-diameter end is the upstream of the sonic throat (1) and is connected to the atmosphere; the small-diameter end is the downstream of the sonic throat (1).

3. The active film cooling wing leading edge test system for an arc wind tunnel according to claim 1, characterized in that: Both the electric pressure regulating valve (2) and the second electromagnetic switching valve (4) are connected to the cooling branch through a sealed joint, and the pressure sensor (3) is connected to the cooling branch through a three-way valve.

4. An active film cooling wing leading edge test system for an arc wind tunnel according to claim 1, characterized in that: The vacuum degree in the test chamber is less than 1 kPa.

5. The active film cooling wing leading edge test system for an arc wind tunnel according to claim 1, wherein: The cooling air holes on the leading edge of the wing (5) are evenly arranged N along the direction of the highest heat flow line on the arc surface. The distance between adjacent two cooling air holes is 20 - 30 mm, and the diameter is 1 / 10 - 1 / 5 of the radius of the leading edge arc surface, N ≥ 1.

6. The test system for the leading edge of a gas film actively cooled wing applied to an arc wind tunnel according to claim 5, characterized in that: The distribution of the positions of the heat flux measurement points is as follows: On both sides of each cooling air hole perpendicular to the flow direction of the nozzle, one heat flux measurement point is symmetrically arranged with the center of the cooling air hole, and the distance between each heat flux measurement point and the center of the current cooling air hole is 3 - 5 mm; Along the flow of the nozzle, one heat flux measurement point is arranged on the highest heat flow line at the upstream position of each cooling air hole, and the distance from the center of the cooling air hole is 5 - 10 mm; One heat flux measurement point is arranged in the middle between adjacent two cooling air holes.

7. An air film active cooling wing leading edge test system applied to an arc wind tunnel according to claim 1, characterized in that: The heat flux sensor includes a calorimetric block, a heat insulation sleeve, and a K-type thermocouple. The calorimetric block is externally sleeved with a heat insulation sleeve, and the axial bottom end of the calorimetric block is connected to the K-type thermocouple.

8. An active film cooling wing leading edge test system for an arc wind tunnel according to claim 1, characterized in that: The control signal of the electric pressure regulating valve (2) is a DC P - Q mA. The current value of the control signal has a linear relationship with the opening of the valve. The valve is closed at P mA and fully open at Q mA, P > 1, Q > 1, P < Q; According to the distribution of the heat flux measurement values on the leading edge of the wing (5), the pressure of each cooling branch is adjusted by adjusting the electric pressure regulating valve (2). Specifically: When the heat flux value around the current cooling air hole is higher than the heat flux value at the midpoint between the current cooling air hole and the adjacent downstream cooling air hole, the air intake volume of the current cooling air hole is large at this time. Then, reduce the current value of the control signal, lower the intake pressure, and decrease the air intake volume until the heat flux value measured at the points around the current cooling air hole is lower than or equal to the heat flux value between the two cooling air holes. When the heat flux value around the current cooling air hole is lower than the heat flux value at the midpoint between the current cooling air hole and the adjacent downstream cooling air hole, the air intake volume of the current cooling air hole is small at this time. Then, increase the current value of the control signal, increase the intake pressure, and increase the air intake volume until the heat flux value measured at the points around the current cooling air hole is higher than or equal to the heat flux value between the two cooling air holes. Convert the current signal into the corresponding linear displacement, and linearly increase the opening degree of the valve by increasing the current value of the control signal.

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