STUDY OF 3-DIMENSIONAL INTERTACTINS BETWEEN WAKE VORTICES AND FLOWS NEAR SEPARATION LINES

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Three dimensional separated flow over axisymmetric paraboloid at incidence angles ; α=30, 40 and 50 deg has been investigated by three approaches such as particle image velocimetry, numerical study. and measurement with constant temperature anemometer.Partcle image velocimetry : Supplying tracers with a fog machine or plastic balloons. Laser light sheet is used in studying the structure of the vortices in cross-sections of flow, for which two-color Laser dual sweep has been employed. The user-friendly PIV technique has been developed with separating Argon laser beam into Blue and Green by dichroic mirror, and the flow reversal can be detected. Velocimetry results at α=30, or 40 deg shows at most 20% deviation from the following anemometer results, where Reynolds numbers is 9000 referred to the base diameter.Numerical simulation : The attempt of numerical simulation of the flow is performed with a pseudo-compressibility method with Beam and Warming method . The results are compared with … More the anemometry experiment. and it was realized that the prediction is good for the 40deg and 50 deg cases where strong vortices appear.Hot wire anemometry. The flow at the same condition as in PIV study has been investigated experimentally with a hot wire anemometer. Reynolds numbers are 9.0×10^3 and 1.8×10^4 referred to the base diameter. X-type probe has been used to measure three dimensional velocity fields. Velocity fluctuations at sampling time of 4kHz have been also evaluated. The output signals show the change of R.M.S.value and Reynolds stress in various cross-sections and that the spatial correlation factors are small at the locations of large R.M.S.value. Laser light sheet method is used in studying the structure of the vortices in separated flow. The development of lateral vortices in each cross-section of the body is visualized. The variation of vortex patterns is shown for each cross-section, angle of attack and Reynolds number. With both results of anemometry and visualization, it has been confirmed that at large αsuch as 50 deg, the leeside vortex interacts unsteadily with the velocity fluctuations in the wake behind the body. Less