We evaluate two leading-edge-based dynamic stall-onset criteria (namely, the maximum magnitudes of the leading-edge suction parameter and the boundary enstrophy flux) for mixed and trailing-edge stall. These criteria have been shown to successfully predict the onset of leading-edge stall at Reynolds numbers of O(10^5), where the leading-edge suction drops abruptly. However, for mixed/trailing-edge stall, leading-edge suction tends to persist even when there is significant trailing-edge reversed flow and stall is underway, necessitating further investigation into the effectiveness of these criteria. Using wall-resolved large-eddy simulations and the unsteady Reynolds-averaged Navier–Stokes method, we simulate one leading-edge stall and three mixed/trailing-edge stall cases at Reynolds numbers of 200,000 and 300,000. We contrast the progression of flow features such as trailing-edge separation and vortex formation across different stall types and evaluate the stall-onset criteria relative to critical points in the flow. We find that the criteria nearly coincide with the instance of leading-edge suction collapse and are reached in advance of dynamic stall vortex formation and lift stall for all four cases. We conclude that the two criteria effectively signal dynamic stall onset in cases where the dynamic stall vortex plays a prominent role.
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Effects of Compressibility on Leading-Edge Dynamic Stall Criteria
The current work evaluates the effectiveness of two leading-edge dynamic stall criteria in mild to moderately compressible regimes using numerical simulations. The two criteria under consideration, namely, the maximum magnitudes of the leading edge suction parameter (max(𝐿𝐸 𝑆𝑃)) and boundary enstrophy flux (max(|𝐵𝐸𝐹|)), have previously been found to be effective at signaling dynamic stall in the incompressible regime. Based on unsteady Reynolds-averaged Navier-Stokes simulations at a Reynolds number of 2 × 105 and freestream Mach numbers between 0.1 - 0.5, we observe that these criteria are directly applicable in the mild to moderately compressible regimes, since they are reached shortly after suction collapse at the leading edge and well in advance of dynamic stall vortex formation for all the cases. This is attributed to compressibility effects promoting adverse-pressure-gradient(APG)-induced stall for the flow conditions considered. For the highest Mach number of 0.5, shock wave interactions with the separated shear layer are observed. It is noted that although compressibility leads to separation at a lower APG, the maximum APG scaled by the local flow density remains in the
same range for all the cases.
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- Award ID(s):
- 1935255
- NSF-PAR ID:
- 10467866
- Publisher / Repository:
- American Institute of Aeronautics and Astronautics
- Date Published:
- ISBN:
- 978-1-62410-704-7
- Format(s):
- Medium: X
- Location:
- San Diego, CA and Online
- Sponsoring Org:
- National Science Foundation
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We evaluate two leading-edge-based dynamic stall onset criteria, namely, the maximum magnitudes of the Leading Edge Suction Parameter and the Boundary Enstrophy Flux, for mixed and trailing-edge stall. These criteria have been shown to successfully predict the onset of leading-edge stall at Reynolds numbers >= O(10^5), where the leading-edge suction drops abruptly. However, for mixed/trailing-edge stall, leading-edge suction tends to persist even when there is significant trailing-edge reversed flow and stall is underway, necessitating further investigation of the effectiveness of these criteria. Using wall-resolved, large-eddy simulations and unsteady Reynolds-Averaged Navier-Stokes method, we simulate one leading-edge stall and three mixed/trailing-edge stall cases at Reynolds numbers 2x10^5 and 3x10^6. We contrast the progression of flow features such as trailing-edge separation and vortex formation across different stall types and evaluate the stall onset criteria relative to critical points in the flow. We find that the criteria nearly coincide with the instance of leading-edge suction collapse and are reached in advance of dynamic stall vortex formation and lift stall for all four cases. We conclude that the two criteria effectively signal dynamic stall onset in cases where the dynamic stall vortex plays a prominent role.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2023-3371
