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<p>One of the important features of flow at Reynolds number less than 3.0 × 10<sup>5</sup> is presence of laminar separation bubble over airfoil surface. The laminar separation bubble is categorised as short or long bubble and there is lack of clarity about the same. Drag polar indicates drag rise at moderate lift coefficient for flow at Reynolds number below 10<sup>5</sup> and the physics of such behaviour is not well understood. In the present study numerical computations have been carried out over Eppler 387 airfoil using two transition models- transition SST model and k-k<sub>L</sub>-ω model. The steady and unsteady simulations have been performed using Fluent software at two Reynolds numbers of 0.6 × 10<sup>5</sup> and 1.0 × 10<sup>5</sup>, with three turbulence intensities of 0.03%, 0.1% and 0.5% at the inlet of the domain are used to compute the flow. Based on the studies, a new definition of short and long bubble has been postulated and the reason for drag rise at moderate lift coefficient for Reynolds number less than 10<sup>5</sup>, is attributed to occurrence of long bubble on the airfoil surface, has been clearly demonstrated.</p>

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Laminar Separation Bubble and Aerodynamics of Drag Rise for Flow at Low Reynolds Number with Moderate Lift Coefficient

  • 期刊论文

  • 发表日期：

    2025年5月9日

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  • Ashish Kumar Gupta,
  • P. A. Aswatha Narayana,
  • G. Ramesh

摘要

One of the important features of flow at Reynolds number less than 3.0 × 105 is presence of laminar separation bubble over airfoil surface. The laminar separation bubble is categorised as short or long bubble and there is lack of clarity about the same. Drag polar indicates drag rise at moderate lift coefficient for flow at Reynolds number below 105 and the physics of such behaviour is not well understood. In the present study numerical computations have been carried out over Eppler 387 airfoil using two transition models- transition SST model and k-kL-ω model. The steady and unsteady simulations have been performed using Fluent software at two Reynolds numbers of 0.6 × 105 and 1.0 × 105, with three turbulence intensities of 0.03%, 0.1% and 0.5% at the inlet of the domain are used to compute the flow. Based on the studies, a new definition of short and long bubble has been postulated and the reason for drag rise at moderate lift coefficient for Reynolds number less than 105, is attributed to occurrence of long bubble on the airfoil surface, has been clearly demonstrated.