Surface water drop collection coefficient measurement test piece and method for icing wind tunnel test

Abstract

The invention provides a surface water drop collection coefficient measurement test piece and method for an icing wind tunnel test, and relates to the technical field of airplane icing wind tunnel tests.The surface water drop collection coefficient measurement test piece comprises a to-be-measured test piece model, a groove is formed in the surface of the to-be-measured test piece model, and a plurality of partition plates are arranged in the groove at intervals to divide the groove into a plurality of strip-shaped grooves; the strip-shaped groove is filled with water absorption sponge, the appearance of the water absorption sponge is matched with the inner structure of the strip-shaped groove, the water absorption sponge is completely embedded into the strip-shaped groove, and the upper surface of the water absorption sponge is flush with a groove opening of the strip-shaped groove. The depth of the groove is greater than the height of the partition plate; the to-be-tested test piece model further comprises a surface skin, the surface skin covers a notch of the groove and is smoothly connected with the surfaces, on the two sides of the notch, of the to-be-tested test piece model, and a plurality of water inlet holes are formed in the surface skin in an array arrangement mode. The invention can simply, quickly and accurately measure the water drop collection coefficient on the surface of the test piece.

Description

Technical Field

[0001] The invention relates to the technical field of aircraft ice wind tunnel tests, and in particular to a surface water droplet collection coefficient measurement test piece and method for ice wind tunnel tests. Background Art

[0002] The icing problem is one of the major hidden dangers that threaten the flight safety of aircraft. There are a large number of supercooled water droplets in the cloud layer that are below zero but still exist in the form of liquid water. Due to inertia, supercooled water droplets cannot bypass the windward side of the aircraft with the airflow. After hitting the surface of the aircraft, they will quickly exchange heat and mass with the aircraft skin and the atmospheric environment, causing the aircraft's load-bearing surface to ice. Icing will cause changes in the aircraft's aerodynamic shape, increase the wind resistance of the wing, reduce lift, reduce the aircraft's critical angle of attack, and reduce the aircraft's maneuverability and stability; when the engine air inlet and power unit are frozen, the detached ice is sucked in, causing engine damage and flameout.

[0003] To ensure flight safety, it is necessary to predict icing to determine the impact of ice on aircraft performance, and then install anti-icing systems on key components for icing protection. The impact of supercooled water droplets is the cause of aircraft icing. The location and magnitude of the impact directly determine the location and severity of icing, which is called the water droplet impact characteristics. It is usually reflected by the local water droplet collection coefficient (i.e., the ratio of the actual water collection amount of the surface microelement to its maximum possible water collection amount).

[0004] At present, the calculation of surface water droplet collection coefficient mainly adopts the numerical calculation method of simulation software, but the ice wind tunnel test plays an important role as the reliability basis of numerical calculation. The generally accepted method for measuring water droplet collection coefficient is to use the dyeing method, that is, to collect water droplets on the wing surface using materials such as absorbent paper, and then calculate the water droplet collection coefficient. The current data extraction methods include colorimeter method, laser reflection spectroscopy method and CCD reflectometer method. The result is obtained by obtaining the amount of dye in the blotting paper, and then the water droplet collection coefficient is obtained through experimental calibration. Since the absorbent paper is easy to saturate, the spray time is usually no more than 2-4s, but it is difficult for the atomized water droplets to reach a uniform state when the spray system is just started, which may cause a certain error in the measured water droplet collection coefficient. In addition, since the supercooled liquid droplet (SLD) has unique dynamic characteristics such as deformation, fragmentation, splashing, and rebound during the impact process, it is difficult to accurately measure the water droplet collection coefficient of SLD using the dyeing method.

[0005] In addition, the prior art also proposes a method for calculating the water droplet collection coefficient based on the frost ice shape, that is, a two-dimensional ice shape diagram is drawn according to the frost ice shape at a certain position of the test piece under a simulated low temperature environment to obtain the actual water droplet collection rate at the local position, and then the local water droplet collection coefficient is indirectly obtained by calculating the theoretical maximum water droplet collection rate. However, when the temperature of the water droplets in the water mist sprayed by the spray device is high, the water droplets will not freeze immediately when they hit the airfoil surface and then overflow, so the water droplet collection coefficient cannot be accurately determined for the freezing of open ice; at the same time, this method only uses the two-dimensional plane where the cross section of the wing along the span direction is located to represent the typical surface water droplet impact characteristics, ignoring the influence of the wing span direction. Summary of the invention

[0006] In view of this, an embodiment of the present application provides a test piece and method for measuring the surface water droplet collection coefficient for ice wind tunnel testing, so as to achieve the purpose of simply, quickly and accurately measuring the water droplet collection coefficient on the surface of the test piece.

[0007] The embodiment of the present application provides the following technical solution: a surface water droplet collection coefficient measurement test piece for ice wind tunnel test, comprising:

[0008] A test piece model to be tested, wherein a groove is provided on the surface of the test piece model to be tested, wherein a plurality of partitions are arranged in the groove to separate the groove into a plurality of strip grooves, wherein the strip grooves are filled with a water-absorbing sponge, wherein the shape of the water-absorbing sponge is adapted to the groove structure of the strip grooves, so that the water-absorbing sponge is completely embedded in the strip grooves, and the upper surface of the water-absorbing sponge is flush with the notch of the strip grooves; wherein the depth of the groove is greater than the height of the partition;

[0009] The test piece model to be tested also includes a surface skin, which covers the notch of the groove and is smoothly connected to the surface of the test piece model to be tested on both sides of the notch. A plurality of water inlet holes are arranged in an array on the surface skin.

[0010] According to an embodiment of the present application, the water-absorbing sponge is a polyurethane water-absorbing sponge, and the side and lower surfaces of the polyurethane water-absorbing sponge are both treated with an acrylic waterproof coating.

[0011] According to one embodiment of the present application, the test piece model to be tested is a wing model, the width of the groove is 5%c, the depth of the groove is 1.05%c, the width of the strip groove is 1%c, and the depth of the strip groove is 1%c; wherein c is the chord length of the wing.

[0012] According to an embodiment of the present application, the aperture d of the water inlet hole is 0.5 mm.

[0013] According to an embodiment of the present application, the test piece model is made of aluminum alloy material.

[0014] The present application also provides a method for measuring a surface water droplet collection coefficient measurement test piece for an ice wind tunnel test as described above, comprising:

[0015] Dry and weigh the absorbent sponge used in the test piece model, and record the mass m1 of the absorbent sponge before the test begins;

[0016] The water-absorbing sponge is placed in the strip groove so that the upper surface of the water-absorbing sponge is flush with the notch of the strip groove, the notch of the groove is covered with the surface skin, and the surfaces of the to-be-tested specimen model on both sides of the notch are smoothly connected to obtain the to-be-tested specimen model;

[0017] The test piece model to be tested is installed in the test section of the wind tunnel and is located at the same level as the spray valve of the wind tunnel spray system;

[0018] Set the velocity v of the droplets sprayed by the spray system in the test and the liquid water content LWC of the spray in the test, start the spray system, start spraying water droplets to the test specimen model, and record the spray time t;

[0019] Remove the surface skin, take out the water-absorbing sponge in each of the strip grooves and weigh it, and record the mass m2 of the water-absorbing sponge after the test;

[0020] The surface water droplet collection coefficient of the test specimen model is calculated based on the mass m1 of the absorbent sponge before the test, the mass m2 of the absorbent sponge after the test, the velocity v of droplets sprayed by the spray system, the liquid water content LWC of the spray, the spray time t and the total area of ​​the upper surface of the absorbent sponge.

[0021] According to one embodiment of the present application, the calculation formula of the surface water droplet collection coefficient of the test piece model to be tested is as follows:

[0022]

[0023] Wherein, m1 is the mass of the absorbent sponge before the test, in kg; m2 is the mass of the absorbent sponge after the test, in kg; v is the velocity of droplets sprayed by the spray system, in m / s; t is the spray time, in s; s is the total area of ​​the upper surface of the absorbent sponge, in m 2 ; LWC is the liquid water content in the spray, in kg / m 3 .

[0024] According to an embodiment of the present application, the spraying time t lasts at least 20-30 seconds.

[0025] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least: the embodiment of the present invention is a method for measuring the surface water droplet collection coefficient using an embedded water-absorbing sponge. Compared with the traditional method, the advantages of the embodiment of the present invention are:

[0026] (1) Excellent water retention performance: Due to its excellent water retention performance and large water absorption capacity, the absorbent sponge can allow a longer spraying time (up to minutes), thereby reducing the measurement error caused by uneven spraying when the spray system is turned on.

[0027] (2) Simplified test process: Since the absorbent sponge is directly embedded in the wing model, this method simplifies the test device setup and subsequent data processing process, and also eliminates the need for expensive instruments such as spectrometers. Compared with using absorbent paper, the absorbent sponge can more conveniently collect and measure the amount of water absorbed, and then calculate the water droplet collection coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 is a schematic diagram of the slotted structure of the wing model to be tested in an embodiment of the present invention;

[0030] Figure 2 is a schematic diagram of the local detailed structure of the wing model to be tested in an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the structure of the water-absorbing sponge in an embodiment of the present invention;

[0032] Figure 4 Schematic diagram of the relative position structure of the water-absorbing sponge and the strip grooves in the embodiment of the present invention;

[0033] Figure 5 is a schematic diagram of a surface skin structure in an embodiment of the present invention;

[0034] Figure 6 Schematic diagram of the water inlet hole structure on the surface skin in an embodiment of the present invention;

[0035] Figure 7 is a schematic diagram of the structure of a test wind tunnel in an embodiment of the present invention;

[0036] Among them, 1-power section, 2-corner section, 3-protective net, 4-heat exchange section, 5-spray valve, 6-test section, 601-test piece model, 602-strip groove, 603-partition, 604-water-absorbing sponge, 605-surface skin, 606-water inlet hole. DETAILED DESCRIPTION

[0037] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0038] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0039] The traditional measurement method relies on using materials such as absorbent paper to collect water droplets on the wing surface and then calculate the water droplet collection coefficient. Considering that this method has some obvious limitations, including limited water absorption capacity and the inability to measure the collection coefficient of supercooled large water droplets; therefore, based on the measurement requirements of the water droplet collection coefficient in the ice wind tunnel test, the embodiment of the present invention proposes a simple and fast method to measure the water droplet collection coefficient on the surface of the test piece. In the following scheme, the aircraft wing is used as an example, but it is also applicable to other types of test pieces.

[0040] like Figure 1 As shown, an embodiment of the present invention provides a surface water droplet collection coefficient measurement test piece for ice wind tunnel test, comprising:

[0041] A test piece model 601 to be tested, wherein a groove is provided on the surface of the test piece model 601 to be tested, wherein a plurality of partitions 603 are arranged in the groove to separate the groove into a plurality of strip grooves 602, wherein the strip grooves 602 are filled with a water-absorbing sponge 604, wherein the shape of the water-absorbing sponge 604 is adapted to the groove structure of the strip groove 602, so that the water-absorbing sponge 604 is completely embedded in the strip groove 602, and the upper surface of the water-absorbing sponge 604 is flush with the notch of the strip groove 602; wherein the depth of the groove is greater than the height of the partition 603;

[0042] The test piece model 601 also includes a surface skin 605, which covers the notch of the groove and is smoothly connected to the surface of the test piece model 601 on both sides of the notch. A plurality of water inlet holes 606 are arranged in an array on the surface skin 605.

[0043] In a specific implementation, the water-absorbing sponge 604 is a polyurethane water-absorbing sponge, and the side and lower surfaces of the polyurethane water-absorbing sponge are both treated with acrylic waterproof coating.

[0044] In a specific implementation, the diameter d of the water inlet hole 606 is 0.5 mm.

[0045] In one embodiment, the test piece model 601 is a wing model, the width of the groove is 5%c, the depth of the groove is 1.05%c, the width of the strip groove 602 is 1%c, and the depth of the strip groove 602 is 1%c; wherein c is the chord length of the wing.

[0046] Taking the wing model as an example, the preparation process of the surface water droplet collection coefficient measurement test piece is as follows:

[0047] (1) First, prepare the aluminum alloy material to make the wing model to be tested, and select the 5% chord length area in the middle of the airfoil for slotting and cutting (such as Figure 1 As shown in FIG. 1 ), n strip grooves 602 are cut out, the width and depth of each strip groove 602 are both 1% of the chord length, the distance between the strip groove 602 and the wing surface is 0.05% of the chord length, and a distance is reserved for installing the wing surface skin 605 (as shown in FIG. Figure 2 shown).

[0048] (2) Prepare n pieces of long polyurethane absorbent sponges with a size of 5%*1%*1% chord length (such as Figure 3 As shown), the surfaces of the absorbent sponge except the upper surface are treated with acrylic waterproof coating to ensure that after the water droplets are absorbed by the upper surface of the sponge, they will not seep out from other surfaces and remain in the strip groove 602.

[0049] (3) Place the polyurethane water-absorbing sponge in the strip groove 602 of the wing so that it is completely embedded in the strip groove 602 and the upper surface is flush with the strip groove 602 (e.g. Figure 4 shown).

[0050] (4) Use aluminum alloy material to make the surface skin 605 (such as Figure 5 As shown), the skin thickness is 0.05% of the chord length, and holes are punched in the skin in an array arrangement, and the diameter of each circular hole is set to d = 0.5 mm (as shown Figure 6 as shown) to ensure that water droplets can be absorbed by the sponge through the capillary action of the holes.

[0051] (5) Cover the skin on the surface of the wing groove so that it is smoothly connected to the wing surface to obtain the final test piece. The connection between the skin and the wing can be fixed with bolts or tape.

[0052] Among them, the material, slot position, number of slots and size of the test specimen are not fixed and can be flexibly adjusted according to the test arrangement; but the depth of the slots must ensure that the slots on the upper and lower surfaces of the wing do not affect each other.

[0053] The present application also provides a method for measuring a surface water droplet collection coefficient measurement test piece for an ice wind tunnel test as described above, comprising:

[0054] Dry and weigh the absorbent sponge 604 used in the test specimen model 601, and record the mass m1 of the absorbent sponge 604 before the test.

[0055] The water-absorbing sponge 604 is placed in the strip groove 602, so that the upper surface of the water-absorbing sponge 604 is flush with the notch of the strip groove 602, and the notch of the groove is covered with the surface skin 605, and the surfaces of the to-be-tested specimen model 601 on both sides of the notch are smoothly connected to obtain the to-be-tested specimen model 601;

[0056] The test piece model 601 is installed in the test section of the wind tunnel and is located at the same level as the spray valve of the wind tunnel spray system;

[0057] Set the velocity v of the droplets sprayed by the spray system in the test and the liquid water content LWC of the spray in the test, start the spray system, start spraying water droplets to the test piece model 601, and record the spray time t;

[0058] Remove the surface skin 605, take out the water-absorbing sponge 604 in each of the strip grooves 602, weigh it, and record the mass m2 of the water-absorbing sponge 604 after the test.

[0059] The surface water droplet collection coefficient of the test specimen model 601 is calculated based on the mass m1 of the absorbent sponge 604 before the test, the mass m2 of the absorbent sponge 604 after the test, the velocity v of droplets sprayed by the spray system, the liquid water content LWC of the spray, the spray time t and the total area of ​​the upper surface of the absorbent sponge 604.

[0060] In specific implementation, the operating steps of the above-mentioned surface water droplet collection coefficient measurement test piece are as follows:

[0061] 1. Test wind tunnel (such as Figure 7(as shown) The main body includes a test section 6, a power section 1, a heat exchange section 4 and four corner sections 2, and a protective net 3 is provided in the corner section 2. The power system adopts a high-power fan, and the accuracy and stability of the wind speed index are guaranteed by frequency conversion control; the spray system realizes the atomization and spraying of water droplets, and can simulate a certain range of supercooled large water droplets; the heat exchange section 4 is equipped with a heat exchanger to realize the control of the wind tunnel temperature; the test specimen (the model of the test specimen to be tested 601) is placed in the test section 6. Before conducting the test, first install the test specimen and the instrument. According to the test arrangement, make each test part. First, dry and weigh the polyurethane absorbent sponge, and record the mass m1 of the sponge before the start of the test. Then place the sponge in the strip groove 602 of the wing so that the sponge is flush with the strip groove 602 of the wing. Use a porous skin to cover the groove of the wing to ensure that the connection is smooth to obtain the test specimen. The test specimen is installed horizontally in the test section of the wind tunnel, and is located at the same level as the spray valve 5 of the spray system.

[0062] 2. Start the spray system, set the spray droplet velocity v and the spray liquid water content LWC during the test, and start spraying water droplets to the test piece. The spray time t should last at least 20-30 seconds to ensure that the sprayed water droplets reach a uniform state. The specific spray time needs to be determined by the size of the sponge and the spray parameters. After the spray is completed, record the specific spray time t and turn off the spray system.

[0063] 3. Remove the porous skin on the wing surface, take out the water-absorbing sponge inside each strip groove 602 and weigh it to record the mass m2 of the water-absorbing sponge after the test. By recording the mass change of the water-absorbing sponge, the water absorption mass data can be obtained.

[0064] The water drop collection coefficient can be derived and calculated based on the increased mass of the water-absorbing sponge 604, that is, the water absorption mass. The water drop collection coefficient is the ratio of the actual amount of water collected in a local area of ​​the object surface to the maximum amount of water that can be collected in the area, which characterizes the water drop impact range on the surface of the component and the distribution of water in the impact area. The specific derivation formula of the water drop collection coefficient is as follows:

[0065]

[0066] Among them, m Δ is the mass of the absorbent sponge before and after the test, in kg; m1 is the mass of the absorbent sponge before the test, in kg; m2 is the mass of the absorbent sponge after the test, in kg; v is the speed of the water mist sprayed by the spray system, in m / s; t is the start-up time (spraying time) of the spray system, in s; s is the total area of ​​the upper surface of the absorbent sponge, in m 2 ; LWC is the liquid water content in the spray, in kg / m 3In the above formula, the data of m1 and m2 are obtained by measurements before and after the test, v, t, and LWC are obtained by setting the spray system parameters in the test, and s is calculated according to the size of the test specimen.

[0067] The embodiment of the present invention measures the water droplet collection coefficient of the airfoil surface by using a wing model with an embedded water-absorbing sponge, thereby achieving the purpose of simply, quickly and accurately measuring the water droplet collection coefficient of the test piece surface.

[0068] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A test piece for measuring the surface water droplet collection coefficient for ice wind tunnel testing, characterized in that: include: A test piece model to be tested, wherein a groove is provided on the surface of the test piece model to be tested, wherein a plurality of partitions are arranged in the groove to separate the groove into a plurality of strip grooves, wherein the strip grooves are filled with a water-absorbing sponge, wherein the shape of the water-absorbing sponge is adapted to the groove structure of the strip grooves, so that the water-absorbing sponge is completely embedded in the strip grooves, and the upper surface of the water-absorbing sponge is flush with the notch of the strip grooves; wherein the depth of the groove is greater than the height of the partition; The test piece model to be tested also includes a surface skin, which covers the notch of the groove and is smoothly connected to the surface of the test piece model to be tested on both sides of the notch. A plurality of water inlet holes are arranged in an array on the surface skin.

2. The surface water droplet collection coefficient measurement test piece for ice wind tunnel test according to claim 1, characterized in that: The water-absorbing sponge is a polyurethane water-absorbing sponge, and the side surface and the lower surface of the polyurethane water-absorbing sponge are both treated with acrylic waterproof coating.

3. The surface water droplet collection coefficient measurement test piece for ice wind tunnel test according to claim 1, characterized in that: The test piece model to be tested is a wing model, the width of the groove is 5%c, the depth of the groove is 1.05%c, the width of the strip groove is 1%c, and the depth of the strip groove is 1%c; wherein c is the chord length of the wing.

4. The surface water droplet collection coefficient measurement test piece for ice wind tunnel test according to claim 1, characterized in that: The aperture d of the water inlet hole is 0.5 mm.

5. The surface water droplet collection coefficient measurement test piece for ice wind tunnel test according to claim 1, characterized in that: The to-be-tested specimen model is made of aluminum alloy material.

6. A method for measuring a surface water droplet collection coefficient test piece for ice wind tunnel testing according to any one of claims 1 to 5, characterized in that: include: Dry and weigh the absorbent sponge used in the test piece model, and record the mass m1 of the absorbent sponge before the test begins; The water-absorbing sponge is placed in the strip groove so that the upper surface of the water-absorbing sponge is flush with the notch of the strip groove, the notch of the groove is covered with the surface skin, and the surfaces of the to-be-tested specimen model on both sides of the notch are smoothly connected to obtain the to-be-tested specimen model; The test piece model to be tested is installed in the test section of the wind tunnel and is located at the same level as the spray valve of the wind tunnel spray system; Set the velocity v of the droplets sprayed by the spray system in the test and the liquid water content LWC of the spray in the test, start the spray system, start spraying water droplets to the test specimen model, and record the spray time t; Remove the surface skin, take out the water-absorbing sponge in each of the strip grooves and weigh it, and record the mass m2 of the water-absorbing sponge after the test; The surface water droplet collection coefficient of the test specimen model is calculated based on the mass m1 of the absorbent sponge before the test, the mass m2 of the absorbent sponge after the test, the velocity v of droplets sprayed by the spray system, the liquid water content LWC of the spray, the spray time t and the total area of ​​the upper surface of the absorbent sponge.

7. The measuring method according to claim 6, characterized in that: The calculation formula of the surface water droplet collection coefficient of the test piece model is as follows: Wherein, m1 is the mass of the absorbent sponge before the test, in kg; m2 is the mass of the absorbent sponge after the test, in kg; v is the velocity of droplets sprayed by the spray system, in m / s; t is the spray time, in s; s is the total area of ​​the upper surface of the absorbent sponge, in m 2 ; LWC is the liquid water content in the spray, in kg / m 3 .

8. The measuring method according to claim 6, characterized in that: The spraying time t lasts at least 20-30s.

Images