A vorticity-based criterion to characterise leading edge dynamic stall onset

Journal Article · 25 January 2022 · Journal of Fluid Mechanics

DOI: https://doi.org/10.1017/jfm.2021.1149 · OSTI ID:1981804

Sudharsan, Sarasija  ^[1]; Ganapathysubramanian, B.  ^[1]; Sharma, A.  ^[1]

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1. Iowa State University, Ames, IA (United States)

We propose a more conservative, physically-intuitive criterion, namely, the boundary enstrophy flux ( BEF), to characterise leading-edge-type dynamic stall onset in incompressible flows. Our results are based on wall-resolved large-eddy simulations of pitching aerofoils, with fine spatial and temporal resolution around stall onset. We observe that |BEF| reaches a maximum within the stall onset regime identified. By decomposing the contribution to BEF from the flow field, we find that the dominant contribution arises from the laminar leading edge region, due to the combined effect of large clockwise vorticity and favourable pressure gradient. A relatively small contribution originates from the transitional/turbulent laminar separation bubble (LSB) region, due to LSB-induced counter-clockwise vorticity and adverse pressure gradient. This results in BEF being nearly independent of the integration length as long as the region very close to the leading edge is included. This characteristic of BEF yields a major advantage in that the effect of partial or complete inclusion of the noisy LSB region can be filtered out, without changing the BEF peak location in time significantly. Next, we analytically relate BEF to the net wall shear and show that its critical value (=max(|BEF|) ) corresponds to the instant of maximum net shear prevailing at the wall. Finally, we have also compared BEF with the leading edge suction parameter ( LESP) and find that the former reaches its maximum value between 0.3° and 0.8° of rotation earlier.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States). Argonne Leadership Computing Facility (ALCF); Iowa State University, Ames, IA (United States)
• Sponsoring Organization: Air Force Office of Scientific Research (AFOSR); National Science Foundation (NSF); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1981804
• Journal Information: Journal of Fluid Mechanics, Journal Name: Journal of Fluid Mechanics Vol. 935; ISSN 0022-1120
• Publisher: Cambridge University PressCopyright Statement
• Country of Publication: United States
• Language: English