Time-Averaged and Fluctuated Wall Shear Stresses Downstream from an Orifice in a Circular Pipe

概要

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In the present study, the distributions of time-averaged and fluctuated wall shear stresses downstream from an orifice were measured using a Flow Vector Sensor of MEMS (Micro Electro Mechanical System). The air flow was supplied to a circular pipe from a blow-down wind tunnel. The diameter of the pipe is D = 194 mm and the diameter of the orifice is d = 97mm, yielding a diameter ratio of 0.5. The axial distance from separation (orifice) to reattachment was approximately 2.5D. Near the wall in the recirculating region, the minimum mean wall shear stress was located at approximately x/D = 1.75, and the maximum rms value of the wall shear stress was approximately x/D = 1 - 2. The experimental results were found to approximately agree with the numerical results obtained previously by Large-eddy simulation. It seems that using the fluctuated wall shear stress to estimate the FAC(Flow-Accelerated Corrosion) rate of the circular pipe wall downstream from the orifice is appropriate.