Investigation of the shear flows over a sunroof opening based on a linear inviscid instability analysis |
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Authors: | H S Kook S R Shin K D Ih D B Kim D H Yu |
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Institution: | (1) School of Mechanical and Automotive Engineering, Kookmin University, Seoul, 136-702, Korea;(2) Research & Development Division for Hyundai Motor Company & Kia Motors Corporation, 772-1 Jangduk-dong, Hwaseong-si, Gyeonggi, 445-706, Korea;(3) Jeonbuk Automotive Parts Industry Innovation, 1641-4 Soryong-dong, Gunsan-si, Jeonbuk, 573-882, Korea |
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Abstract: | The large-scale shear flows over the sunroof opening of a mid-sized SUV measured using a PIV system were investigated. The
shear flows were measured for five different cases of deflector protrusion (one case was the baseline test without deflector)
at two different free stream flow velocities below the critical velocity where the buffeting noise level reached a maximum.
The structures of the shear flows were observed to differ, apparently depending on whether the radiated buffeting noise is
relatively strong or not. For strongly buffeting experimental cases, the momentum thicknesses of the shear layers were observed
to grow rapidly and saturated at a station near the downstream edge of the sunroof opening, where the saturation of the transverse
velocity fluctuations was also observed, and where the vortex coalescence process was presumably completed. On the other hand,
no discrete large-scale vortex structures were observed for none-buffeting or weakly buffeting cases. Streamwise growth of
the velocity fluctuations was found to be well predicted by a linear hydrodynamic instability analysis for the strongly buffeting
cases. Numerical results obtained from a linear inviscid instability analysis using a hyperbolic tangent mean velocity profile
were used to calculate the amplification factors with the initial momentum thickness and the streamwise fluctuation wavenumber.
The shear flows were found to form large-scale discrete vortices when the linear inviscid amplification factors exceeded a
threshold amplification factor. |
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Keywords: | Sunroof buffeting noise Sunroof deflectors Flow over a cavity Momentum thickness Linear hydrodynamic instability analysis |
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