An experimental study of surface-mounted bluff bodies immersed in thick turbulent boundary layers
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Date
2020-04
Authors
Amorin, Helen Afi
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Abstract
This is a study of an experimental investigation of the effects of spanwise aspect ratio on the turbulent properties of separation bubbles over a surface-mounted bluff body. In this study, the streamwise aspect ratio was kept constant at 𝑙/ℎ = 2.36 and the spanwise aspect ratio was varied from 1 to 20. The body was immersed in a turbulent boundary layer whose thickness is equivalent to 4.8 times the body height. The Reynolds number, based on the body height and freestream velocity, was 12500. A time-resolved particle image velocimetry (TR-PIV) method was used to measure the velocity field within the separation bubble to quantify the influence of varying spanwise aspect ratio on the mean flow and turbulent characteristics. Two distinct separation bubbles developed on top and downstream of the bluff bodies. The results showed that the reattachment lengths of both separation bubbles are influenced by the aspect ratio; they increased monotonically as aspect ratio increased from 𝑤/ℎ = 1 to 8, and reach asymptotic values and do not vary significantly with aspect ratio larger than 8. The effects of aspect ratios on the mean velocities, Reynolds stresses, triple velocity correlations and turbulence production are also examined over the bluff body. Galilean decomposition, quadrant decomposition, joint probability density function (JPDF), two-point auto-correlation function and proper orthogonal decomposition (POD) are also used to investigate the impact of spanwise aspect ratio on the structures present in the flow field.
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Keywords
Turbulent flow, Aspect ratio effect, Separated and reattached flow, Time-resolved PIV