Influence of passive flow control methods on flow topology and stability deritives of muldicon wing

Abstract

Sweep backward delta wings lead to flow separation and generate an effective vortex lift at high angle of attack (AOA). Despite of many studies in flow topology for the low sweep wings at a medium to higher AOA, most of them have been limited to steady-state measurements. Whereas nonlinearity in the aerodynamic stability derivatives is still not well understood and rarely reported in the literature. The aims of this study were to characterize and mitigate the unsteadiness and uncertainties of the flow at a medium to higher AOA with more consistent and predictable aerodynamic derivatives for the low sweep MULDICON wing. The experimental and Computational Fluid Dynamics methods were used to investigate the surface flow topology for the clean MULDICON wing for AOA, a = 5° to 30° with angle intervals of 5° for Re = 4.50×105. The wind tunnel testing involved the aerodynamic load's measurement (steady-state and dynamic) and the transient pure-yawing testing conducted at the Universiti Teknologi Malaysia Low-Speed wind Tunnel for the AOA, a = -4° to 30°, and yaw angle, ß = ± 20° with angle intervals of 2°, at Re = 3.0×105, 3.75×105 and 4.5×105 respectively. The influence of the passive flow control methods (2-dimensional and 3-dimensional roughness heights, and vortex generators (VGs) placed at 10 % & 15 % of the mean aerodynamic chord (MAC)) were investigated at a medium to a higher AOA. The standard deviation variance data quantified the unsteadiness and uncertainties of flow topology. Analysis done suggested that the aerodynamic stability derivatives can be further improved at a medium to a higher angle of attack by improving the flow physics over the wing. A strong correlation between flow topology and pitching moment coefficient was exhibited, thus the previous computational studies for the MULDICON were validated. The aerodynamic center was found not to be fixed for the MULDICON wing and shifted forward towards the wing apex with the increase in a. For a = 10°, the flow became asymmetric. Power spectral density (PSD) plots from the dynamic loading data quantified the flow separation (apex vortex, leading-edge vortex, and vortex breakdown) over the MULDICON wing and the different vortex structures detected by the several peaks in the PSD plots. The transient pure-yawing test showed that the increase in a lead to higher directional stability and oscillation was highly damped at a higher a. The transient pure-yawing test for a > 20°, indicated that there are self-sustained and self-excited oscillations. The quantification of the system’s total energy at a higher AOA, i.e. for a = 26° confirmed the fact that the stall occurred at a = 26° where the significant total energy was associated with the system, which lead to the wing to stall. The ?????? curve, the error bars, and relative standard deviation data showed that the onset of the leading-edge vortex was delayed to a higher AOA for the VGs at 10% MAC case. The ?????? curve became more consistent and predictable for a = 5º to 20º. Time series data showed a small-amplitude oscillation frequency for VGs at 10% for a = 5°, 10° and 15° and no significant effects for all flow control cases at a higher AOA. Application of VGs at 10% of MAC made the stability derivatives more consistent and predictable for a = 5º to 20º for low sweep lambda configurations.º.