Test piece and method for measuring surface water droplet collection coefficient for ice wind tunnel test

Abstract

The present invention provides a test piece and method for measuring the surface water droplet collection coefficient for ice wind tunnel tests, which relates to the technical field of aircraft ice wind tunnel tests and includes: a test piece model to be tested, a groove is provided on the surface of the test piece model to be tested, a plurality of partitions are arranged at intervals in the groove to divide the groove into a plurality of strip grooves, the strip grooves are filled with absorbent sponges, the shape of the absorbent sponges is adapted to the groove structure of the strip grooves, the absorbent sponges are completely embedded in the strip grooves, and the upper surface of the absorbent sponges is flush with the notch of the strip grooves; wherein the depth of the groove is greater than the height of the partitions; the test piece model to be tested also includes a surface skin, the surface skin 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, and a plurality of water inlet holes are provided on the surface skin in an array arrangement. The present invention can simply, quickly and accurately measure the water droplet collection coefficient of the test piece surface.

Description

Technical Field

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

[0002] Icing is one of the major hidden dangers threatening aircraft flight safety. Clouds contain large numbers of supercooled water droplets, which are still in the form of liquid water at temperatures below zero. Due to inertia, these droplets cannot flow around the windward side of the aircraft. Upon impacting the aircraft surface, they rapidly exchange heat and mass with the aircraft skin and the atmosphere, causing ice to form on the aircraft's load-bearing surfaces. Icing can alter the aircraft's aerodynamic shape, increasing wing drag, reducing lift, and lowering the aircraft's critical angle of attack, reducing the aircraft's maneuverability and stability. When ice forms on the engine inlet and power unit, loose ice is ingested, causing engine damage and flameout.

[0003] To ensure flight safety, icing prediction is necessary to determine its impact on aircraft performance and, subsequently, to install anti-icing systems on key components for icing protection. Supercooled water droplet impact is the cause of aircraft icing. The location and magnitude of the impact directly determine the location and severity of icing, known as the droplet impact characteristic. This is typically measured using the local droplet collection coefficient (i.e., the ratio of the actual amount of water collected by a surface element to its maximum possible amount).

[0004] Currently, the calculation of surface droplet collection coefficients primarily relies on numerical methods using simulation software. However, ice wind tunnel testing plays an important role in ensuring the reliability of numerical calculations. The currently accepted method for measuring the droplet collection coefficient is dyeing, which involves collecting droplets on the wing surface using materials such as blotting paper and then calculating the droplet collection coefficient. Current data extraction methods include colorimetry, laser reflectance spectroscopy, and CCD reflectometry. Results are obtained by measuring the amount of dye in the blotting paper, and the droplet collection coefficient is then determined through experimental calibration. Because blotting paper is easily saturated, spraying time typically does not exceed 2-4 seconds. However, it is difficult for the spray system to achieve a uniform atomized droplet state upon initial startup, which can lead to errors in the measured droplet collection coefficient. Furthermore, due to the unique dynamic characteristics of supercooled liquid droplets (SLDs) during impact, such as deformation, breakup, splashing, and rebound, dyeing methods are difficult to accurately measure the droplet collection coefficient of SLDs.

[0005] Another existing method for calculating the droplet collection coefficient based on frost ice shape is to create a two-dimensional ice pattern based on the frost ice shape at a specific location on a test piece under a simulated low-temperature environment. This pattern then generates the actual droplet collection rate at that location. The local droplet collection coefficient is then indirectly determined by calculating the theoretical maximum droplet collection rate. However, when the temperature of the droplets in the spray mist is high, the droplets do not immediately freeze upon impacting the airfoil surface, causing overflow. Therefore, the droplet collection coefficient cannot be accurately determined for clear ice. Furthermore, this method only uses the two-dimensional plane of the wing's spanwise cross-section to represent the typical surface droplet impact characteristics, ignoring the influence of the wing's spanwise 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 of the test piece surface.

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

[0008] A test piece model to be tested, wherein a groove is formed 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 partitions;

[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 one 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 specimen 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 one 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 the surface water droplet collection coefficient of a test piece for ice wind tunnel testing, as described above, comprising:

[0015] Dry and weigh the absorbent sponge used in the test specimen 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 specimen model 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 during the test and the liquid water content LWC of the spray during the test, start the spray system, start spraying water droplets toward the test specimen model, and record the spraying 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 the 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 start of the test, in kg; m2 is the mass of the absorbent sponge after the end of the test, in kg; v is the velocity of the droplets sprayed by the spray system, in m / s; t is the spraying 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, unit is kg / m 3 .

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

[0025] Compared with the prior art, the beneficial effects achieved by at least one of the above technical solutions adopted in the embodiments of this specification include at least the following: 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 traditional methods, the advantages of the embodiment of the present invention are:

[0026] (1) Excellent water retention: Due to its excellent water retention 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: Because the absorbent sponge is embedded directly into the wing model, this method simplifies the test setup and subsequent data processing, eliminating the need for expensive instruments such as spectrometers. Compared with using absorbent paper, the absorbent sponge can more easily collect and measure the amount of water absorbed, thereby calculating 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 following briefly introduces the drawings required for use in the embodiments. 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 any creative work.

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

[0030] Figure 2 1 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 an embodiment of the present invention;

[0033] Figure 5 is a schematic diagram of the 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 Schematic diagram of the test wind tunnel structure 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. 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 embodiments 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 embodiments, 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 features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0039] Traditional measurement methods rely on using materials such as absorbent paper to collect water droplets on the wing surface and then calculate the water droplet collection coefficient. 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 need to measure the water droplet collection coefficient in ice wind tunnel tests, the present invention proposes a simple and rapid method to measure the water droplet collection coefficient on the surface of the test piece. The following scheme uses an aircraft airfoil as an example, but is equally 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 testing, comprising:

[0041] A test piece model 601 to be tested has a groove formed on its surface, and a plurality of partitions 603 are arranged in the groove to separate the groove into a plurality of strip grooves 602. The strip grooves 602 are filled with absorbent sponges 604. The shape of the absorbent sponges 604 matches the groove structure of the strip grooves 602, so that the absorbent sponges 604 are completely embedded in the strip grooves 602, and the upper surface of the absorbent sponges 604 is flush with the notch of the strip grooves 602. The depth of the groove is greater than the height of the partitions 603.

[0042] The test piece model 601 further 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 specimen 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 (such as Figure 1 As shown), n strip grooves 602 are cut out, the size of each strip groove 602 is 1% of the chord length in width and depth, 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. 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 and make it smoothly connected with 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] The material, slot location, number of slots, and size of the test specimen are not fixed and can be flexibly adjusted according to the test arrangement; however, the slot depth 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 the surface water droplet collection coefficient of a test piece for ice wind tunnel testing, 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 begins;

[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. The notch of the groove is covered with the surface covering 605, and the surface of the to-be-tested specimen model 601 on both sides of the notch is smoothly connected to obtain the to-be-tested specimen model 601.

[0056] The test specimen 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 during the test and the liquid water content LWC of the spray during the test, start the spray system, start spraying water droplets toward the test specimen model 601, and record the spraying time t;

[0058] Remove the surface skin 605, take out the water-absorbing sponge 604 in each of the strip-shaped grooves 602, weigh them, 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 the 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 601) is placed in the test section 6. Before conducting the test, the test specimen and the instrument are first installed. According to the test arrangement, each test part is made. First, the polyurethane water-absorbing sponge is dried and weighed, and the mass m1 of the sponge before the start of the test is recorded. Then the sponge is placed in the strip groove 602 of the wing so that the sponge is flush with the strip groove 602 of the wing. The groove of the wing is covered with a porous skin 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 test droplet velocity v and the test liquid water content LWC, and begin spraying water droplets onto the test piece. The spray time t should last at least 20-30 seconds to ensure a uniform spray of droplets. The specific spray time depends on 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 from the wing surface, take out the absorbent sponge inside each strip groove 602, and weigh it to record the mass m2 of the absorbent sponge after the test. By recording the mass change of the absorbent sponge, the water absorption quality data can be obtained.

[0064] The water droplet collection coefficient can be derived and calculated based on the increased mass of the absorbent sponge 604, i.e., the water absorption mass. The water droplet 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 that area. It represents the impact range of the water droplet on the component surface and the distribution of water within the impact area. The specific formula for the water droplet 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 start of the test, in kg; m2 is the mass of the absorbent sponge after the test, in kg; v is the velocity 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, unit is kg / m 3In the above formula, m1 and m2 data are obtained from measurements before and after the test, v, t, and LWC are obtained from the settings of the spray system parameters during the test, and s is calculated based on 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 description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection 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 formed on the surface of the test piece model to be tested, and a plurality of partitions are arranged at intervals in the groove to divide the groove into a plurality of strip grooves, and the strip grooves are filled with a water-absorbing sponge, and the shape of the water-absorbing sponge is adapted to the groove structure of the strip groove so that the water-absorbing sponge is completely embedded in the strip groove, and the upper surface of the water-absorbing sponge is flush with the notch of the strip groove; wherein the depth of the groove is greater than the height of the partition, and the side and lower surfaces of the water-absorbing sponge are treated with a waterproof coating; 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 specimen 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 testing according to claim 1, characterized in that: The aperture d of the water inlet is 0.5 mm.

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

6. A method for measuring the surface water droplet collection coefficient of a 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 specimen 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 specimen model 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 during the test and the liquid water content LWC of the spray during the test, start the spray system, start spraying water droplets toward the test specimen model, and record the spraying 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 the 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 specimen model is as follows: Wherein, m1 is the mass of the absorbent sponge before the start of the test, in kg; m2 is the mass of the absorbent sponge after the end of the test, in kg; v is the velocity of the droplets sprayed by the spray system, in ; t is the spraying time, in seconds; s is the total area of ​​the upper surface of the absorbent sponge, in seconds ; LWC is the liquid water content in the spray, unit is .

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

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