DOI: 10.1615/TSFP9
ON THE DESIGN OF OPTIMAL COMPLIANT WALLS FOR TURBULENCE CONTROL
SINOPSIS
This paper employs the theoretical framework developed by Luhar et al. (2015, J. Fluid Mech., 768, 415-441) to consider the design of compliant walls for turbulent skin friction reduction. Specifically, the effects of simple springdamper walls are contrasted with the effects of more complex walls incorporating tension, stiffness and anisotropy. Despite the differing physical responses, all the walls tested exhibit two important common features. First, the effect of the walls (positive or negative) is greatest at conditions close to resonance, with sharp transitions in performance across the resonant frequency or phase speed. In general, turbulent flow structures with frequencies (or phase speeds) below resonance are further amplified, while higher-frequency structures are suppressed. Compliant walls are also predicted to have a more pronounced effect on the slowermoving low frequency structures because such structures generally have larger wall-pressure signatures. Second, two-dimensional (spanwise constant) structures are particularly susceptible to further amplification. This is consistent with previous experiments and simulations, suggesting that mitigating the rise of such two-dimensional structures is essential to designing performance-improving walls. The above observations are used to develop specific design guidelines for compliant walls.