Estimation of CLARK Y-14 Airfoil’s Lift Hysteresis in Low-Speed Flow

Abstract

A phenomenon called hysteresis is responsible for the difference in the separation and the reattachment angles of an airfoil which is seen within the vicinity of the stalling angle of attack. The reason for this is the difference in the expected lift distribution of an airfoil for a particular angle of attack when recovery from stall is achieved. This leads to asymmetric flow parameters around a body even when the boundaries remain symmetric. Empirical results were obtained for a two-dimensional Clark Y-14 airfoil by varying the angle of attack for different Reynold’s numbers in order to estimate how lift characteristics are affected by the formation of hysteresis loops at different Reynolds numbers. It was seen that the extent of the clockwise hysteresis loops of the Clark Y-14 increased with the increase of the Reynolds number up to the Reynolds number of 134072 before starting to decrease again. The stalling angles followed a similar pattern before starting to decrease at a Reynolds number of 164543. These trends observed for the Clark Y-14 airfoil is similar to that of the Eppler 591 and NACA 0018 by Lance W.Traub and W.A Timmer respectively (Timmer, 2008), (Traub, 2016). When analyzing the coefficient of pressure variation for the Clark Y-14 airfoil at a particular Reynolds number, it was seen that a laminar separation bubble was formed for the forward stroke which shifted towards the leading edge of the airfoil which was common for all the Reynolds numbers. In the forward stroke, it could be seen that a laminar separation bubble was formed whereas for the backward stroke no such laminar separation bubble was formed for the same angle of attack which gave rise to the hysteresis loops of the Clark Y-`14 airfoil. It was observed that the laminar separation bubble had a direct impact on the formation of the hysteresis loops giving rise to static stall hysteresis as mentioned in previous research published by various authors. The empirical results obtained were further validated using Computation Fluid Dynamics.