A method for correcting additional drag in the transition zone of wind tunnel tests

Abstract

The present invention discloses a correction method for the additional drag of a transition zone in a wind tunnel test, which belongs to the field of wind tunnel tests. Through variable Reynolds number force measurement tests with different transition zone thicknesses, the zero-lift drag coefficient of a scaled-down model of an aircraft generated by different transition zone thicknesses and test Reynolds numbers is obtained. By establishing a correction formula for the additional drag of the transition zone related to the transition zone thickness and the test Reynolds number, the additional drag of the transition zone is corrected to obtain more accurate test results. The present invention can be used for the correction of the additional drag of the transition zone in low-speed conventional and high / variable Reynolds number fixed transition tests, and can obtain more accurate drag results of scaled-down models of wind tunnel tests.

Description

Technical Field

[0001] The invention belongs to the field of wind tunnel tests, and in particular relates to a method for correcting additional resistance of a transition zone in a wind tunnel test. Background Art

[0002] The fixed transition test simulates the transition position and structure of the boundary layer on the full-size aircraft surface by forcing the transition of the boundary layer on the scaled model surface, making the flow simulation more realistic and the test results more accurate. However, the zero-lift drag of the fixed transition test results includes the different effects of laminar and turbulent boundary layer friction resistance and the additional drag of the transition zone. The test results after deducting the additional drag of the transition zone are more accurate. Fixed transition tests in high- and low-speed wind tunnels at home and abroad only give the difference in zero-lift drag of the scaled aircraft model before and after the transition zone is attached, and believe that the difference is the effect of the transition zone. The difference in boundary layer structure and the additional drag of the transition zone are not distinguished, which is not accurate enough. Summary of the invention

[0003] Based on the above problems, the present invention provides a method for correcting the additional resistance of the transition zone in a wind tunnel test, which can correct the additional resistance of different transition zone thicknesses, and can also correct the additional resistance of different wind tunnel test Reynolds numbers with the same transition zone thickness.

[0004] The technical solution adopted by the present invention is as follows: A method for correcting the additional resistance of the transition zone in a wind tunnel test, the steps are as follows:

[0005] Step 1: Establish a linear fitting formula for the zero-lift drag coefficient and the transition zone thickness h at each Reynolds number, as follows:

[0006] C x0 (h) = k(Re) × h + b(Re) (1)

[0007] Among them, C x0 (h) is the zero-lift drag coefficient at different transition zone thickness h;

[0008] Step 2: Establish a quadratic polynomial fitting formula of k(Re) with the horizontal coordinate 0.1lgRe, as follows:

[0009] k(Re)=A×(0.1lgRe) 2 +B×(0.1lgRe)+C (2)

[0010] Among them, A, B, and C are constants;

[0011] Step 3: Establish a quadratic polynomial fitting formula of b(Re) with the horizontal coordinate 0.1lgRe, as follows:

[0012] b(Re)=D×(0.1lgRe) 2+E×(0.1lgRe)+F (3)

[0013] Among them, D, E, and F are constants;

[0014] Step 4: Substitute formulas (2) and (3) into formula (1) and calculate the zero-lift drag coefficient when the transition zone thickness is h and h = 0 under a certain test Reynolds number, and make a difference to obtain the transition zone additional drag correction ΔC x0 , the formula is as follows:

[0015] ΔC x0 =C x0 (h)-C x0 (h=0)=(A×(0.1lgRe) 2 +B×(0.1lgRe)+C)×h (4).

[0016] Advantages and beneficial effects of the present invention: The present invention can be used for the additional drag correction of the transition zone in low-speed conventional and high / variable Reynolds number fixed transition tests, and can obtain more accurate drag results of the wind tunnel test scale model. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The zero-lift drag coefficient diagram of the aircraft model under different transition zone thicknesses and test Reynolds numbers;

[0018] Figure 2 When the thickness of the transition zone is 0.2 mm, 0.25 mm and 0.3 mm respectively, the variation law of the zero-lift drag coefficient of the aircraft scale model with the Reynolds number is: Figure 1 Two-dimensional form;

[0019] Figure 3 The graph is a graph showing the variation of the zero-lift drag coefficient of the aircraft scale model with the thickness of the transition zone when the Reynolds numbers are 2 million, 4 million, 6 million and 8 million respectively;

[0020] Figure 4 The linear fitting formula of zero lift drag coefficient with transition zone thickness h, the slope k(Re) of which changes with Reynolds number;

[0021] Figure 5 The graph of the variation of the intercept b(Re) of the linear fitting formula of the zero lift drag coefficient with the transition zone thickness h with the Reynolds number;

[0022] Figure 6 Variation of zero-lift drag coefficient with Reynolds number before and after correction for additional drag in the transition zone. DETAILED DESCRIPTION

[0023] The present invention is further described below with reference to the accompanying drawings:

[0024] Example 1

[0025] A method for correcting the additional drag of the transition zone in a wind tunnel test, the steps are as follows:

[0026] Step 1: Figure 3 As shown, the linear fitting formula of zero lift drag coefficient with transition zone thickness h at various Reynolds numbers is established as follows:

[0027] C x0 (h) = k(Re) × h + b(Re) (1)

[0028] Among them, C x0 (h) is the zero-lift drag coefficient for different transition zone thickness h.

[0029] Step 2: Figure 4 As shown, a quadratic polynomial fitting formula of k(Re) with the horizontal coordinate 0.1lgRe is established as follows:

[0030] k(Re)=A×(0.1lgRe) 2 +B×(0.1lgRe)+C (2)

[0031] Among them, A, B, and C are constants.

[0032] Step 3: Figure 5 As shown, a quadratic polynomial fitting formula of b(Re) with the horizontal coordinate 0.1lgRe is established as follows:

[0033] b(Re)=D×(0.1lgRe) 2 +E×(0.1lgRe)+F (3)

[0034] Among them, D, E, and F are constants.

[0035] Step 4: Substitute formulas (2) and (3) into formula (1) and calculate the zero-lift drag coefficient when the transition zone thickness is h and h = 0 under a certain test Reynolds number, and make a difference to obtain the transition zone additional drag correction ΔC x0 , the formula is as follows:

[0036] ΔC x0 =C x0 (h)-C x0 (h=0)=(A×(0.1lgRe) 2 +B×(0.1lgRe)+C)×h (4)

[0037] For the free transition, the present invention has a high consistency between the transition position and thickness of the boundary layer on the surface of the aircraft model at high Reynolds number and the actual flight Reynolds number of the aircraft, and its zero-lift drag coefficient is more realistic. For the fixed transition variable Reynolds number test with a certain transition zone thickness, the additional drag of the transition zone increases with the increase of Reynolds number because the thickness of the boundary layer on the surface of the model decreases with the increase of Reynolds number. Figure 6 The zero-lift drag coefficient of the aircraft after correcting the additional drag in the transition zone at medium and high Reynolds numbers is highly consistent with the results of the free transition test, which shows the rationality and accuracy of this correction method.

Claims

1. A method for correcting the additional drag of the transition zone in a wind tunnel test, characterized in that: The steps are as follows: Step 1: Establish a linear fitting formula for the zero-lift drag coefficient and the transition zone thickness h at each Reynolds number, as follows: C x0 (h)=k(Re)×h+b(Re) (1) Among them, C x0 (h) is the zero-lift drag coefficient at different transition zone thickness h; Step 2: Establish a quadratic polynomial fitting formula of k(Re) with the horizontal coordinate 0.1lgRe, as follows: k(Re)=A×(0.1lgRe) 2 +B×(0.1lgRe)+C (2) Among them, A, B, and C are constants; Step 3: Establish a quadratic polynomial fitting formula of b(Re) with the horizontal coordinate 0.1lgRe, as follows: b(Re)=D×(0.1lgRe) 2 +E×(0.1lgRe)+F (3) Among them, D, E, and F are constants; Step 4: Substitute formulas (2) and (3) into formula (1) and calculate the zero-lift drag coefficient when the transition zone thickness is h and h = 0 under a certain test Reynolds number, and make a difference to obtain the transition zone additional drag correction ΔC x0 , the formula is as follows: ΔC x0 =C x0 (h)-C x0 (h=0)=(A×(0.1lgRe) 2 +B×(0.1lgRe)+C)×h (4)。

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