On the challenges in experimental characterization of flow separation over airfoils at low Reynolds number

Abstract

Measurements and computations of the separation and reattachment locations are reported for the steady flow over a SD7003 airfoil at different angles of attack and chord Reynolds number in the range 2 × 10⁴–4 × 10⁴. The experiments are based on multi-line molecular tagging velocimetry, and the computations employ an implicit large eddy simulation approach. Comparisons of experimental results with current computations and previous experiments point to challenges involved in the experimental determination of the separation bubble characteristics. The results also underline the importance of the facility-dependent freestream turbulence level on the experimental data. The collective effect of experimental uncertainty and facility-dependent issues, examined systematically herein, appear to clarify the discrepancy among the various experimental and computational results. The findings also suggest that accurate characterization of the separation bubble over airfoils at low Reynolds number is more difficult than generally recognized and presents a challenge in comparing results between different experiments, and between experiments and computations. Moreover, this complicates the validation of computational data against experiments within this flow regime.