Experimental investigation of flow past a sphere in the regime of boundary layer transition

Abstract eng:
The flow over a smooth sphere is experimentally investigated for 1.5 × 105 ≤ Re ≤ 5.5 × 105 via unsteady force and 2–D Particle Image Velocimetry(PIV) measurements. For Re > 3.3 × 105 , it is observed from the force measurements that the drag coefficient significantly reduces with increase in Re. This phenomenon, popularly known as the drag crisis, occurs in the critical flow regime due to the transition of the boundary layer over the sphere from laminar to turbulent state. The statistics from the force measurements reveal that the fluctuations in the force coefficients increase with Re in the subcritical regime. A steep fall in the fluctuations is observed in the critical regime. The normal Reynolds stresses in the separated shear layer, from the PIV measurements, are found to be one order lower in magnitude for the supercritical regime in comparison to the subcritical regime.

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