Abstract
In global skin-friction measurement of aircraft, the fluorescent oil film method can characterize the distribution of skin friction well. However, in an actual wind tunnel test, the wing of the aircraft will inevitably produce corresponding vibrations due to the influence of wind, which will change the relative position between fluorescent oil film and UV (ultraviolet) excitation light source (position fixed). This also directly affects gray value imaging of fluorescent oil films. Based on this, a mathematical model is established to judge the stability of the gray value of fluorescent oil film in this vibrational environment; then, the model can be solved to obtain the vibrational range constraint that enables the gray value of fluorescent oil film to be stabilized. In order to simplify the calculation process, the light vector angle is used to describe the constraint, which also makes the results more intuitive. Through experimental analysis and demonstration, the prediction accuracy of this model can reach 95.61%, which has certain practical engineering application significance.
Highlights
Skin friction is one of the most important physical quantities in aerodynamics, as an essential component of the total resistance in an aircraft
In the case with measurement point 1 in Table 2, the gray value of measurement point 1 remains stable as the light vector angle varies between [0°, 2.862°]. e median value of Metrical data is used as a reference to facilitate the calculation of errors
By researching the stability of fluorescent oil film greyscale values under wing vibration conditions, a mathematical theory was derived and analyzed, which was validated by practical tests
Summary
Skin friction is one of the most important physical quantities in aerodynamics, as an essential component of the total resistance in an aircraft. In order to facilitate the calculation of the model, the vector angle and distance factor of UV light are introduced to represent the variable space vector between fixed UV excitation light source and fluorescent oil film, using the light vector angle to characterize the wing vibration as a constraint. The stability of the gray value of fluorescent oil film has been studied to limit the interference factors in the measurement of skin friction resistance and to provide a range of applications for the use with fluorescent oil films. By obtaining information on the spatial vector variation between the fluorescent oil film and the fixed UV excitation light source, UV vector angles are used to describe the range of spatial vector variations which facilitate model calculations. En, the equation can be expanded as follows: ΔS ⎛⎜⎜⎜⎝1 − RR →→2122⎞⎟⎟⎟⎠ · I1 < 1
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