Turbulent Boundary Layer over a Piezoelectrically Excited Traveling Wave Surface

Abstract

Skin friction drag plays a significant role in determining the fuel efficiency of a vehicle. Reducing the skin friction thus has implications in a number of applications such as aircraft, ships, and automobiles. In recent years, a large amount of studies have researched various active drag reduction methods. One particular method involves active wall motion with the use of spanwise traveling waves. These out-of-plane traveling waves interact with the vortices in the turbulent boundary layer and weaken the bursting events that are responsible for increased skin friction drag. Computational and experimental studies have shown that these spanwise traveling waves are able to reduce the skin friction by upwards of 13% in turbulent flow. However, previous studies generated traveling waves using bulky actuation setups requiring arrays of discrete actuators that limited the achievable bandwidth and traveling wave patterns. In order for traveling waves to be a practical drag reduction method, a more implementable wave generation method is necessary. A promising traveling wave generation method is known as two-mode excitation. This technique takes advantages of a surface's inherent structural properties to generate steady-state traveling waves in an open-loop fashion. In addition, the waves can be excited at most frequencies and using a small number of low-profile piezoelectric actuators. Previous research into two-mode excitation has primarily focused on one-dimensional beams. Traveling waves have been generated on a two-dimensional surface, but this was done from a fundamental standpoint with the resultant waves propagating in arbitrary directions. Before the two-mode excitation method can be applied for drag reduction, traveling waves must be generated on two-dimensional surfaces with tailorable propagation patterns. The goal of this research is the development and testing of an implementable traveling wave generation method that alters the turbulent boundary layer with the aim of reducing skin friction drag. The first objective is to further develop the two-mode excitation method in order to tailor the traveling waves generated on a two-dimensional plate. Then, these tailored traveling waves are experimentally tested to determine their effect on the turbulent boundary layer. By directly investigating the boundary layer, a more fundamental approach is taken than only focusing on the skin friction drag. Finally, the overall effect of the traveling waves on the boundary layer are compared with standing waves. vii None of this would have been possible without the support of my family. My parents, Robert and Jacqueline, you raised me to be the person I am today. You have always been there with support and encouragement, and I am eternally grateful. I want to thank my brothers, Brian and Robert, and their wives, Katie and Lindsay. You are always there to chat and you provided many late nights of fun. Finally, I want to thank Alexis Gushiken and the endless support she has given. You always know when to motivate, encourage, o...

Turbulent drag reduction by spanwise wall forcing. Part 1: Large-eddy simulation

“…The profiles of ∆U * (figure 4d ) better highlight this systematic increase in the logarithmic shift. This behaviour is similar to that seen in previous turbulent drag reduction studies, including turbulent flow with the spanwise wall oscillation (Di Cicca et al 2002;Touber & Leschziner 2012;Hurst et al 2014), turbulent flow with the streamwise travelling wave (Hurst et al 2014;Gatti & Quadrio 2016), turbulent flow of a polymer solution (Ptasinski et al 2003;White & Mungal 2008), and turbulent flow over piezoelectrically excited travelling waves (Musgrave & Tarazaga 2019). These studies report the thickening of the viscous sublayer with a shortening and shifting of the logarithmic portion.…”

Turbulent drag reduction by spanwise wall forcing. Part 1. Large-eddy simulations

“…The magnitude of the shift increases as DR increases. These observations are also reported in the previous turbulent DR studies, including turbulent flow with the spanwise wall oscillation (Di Cicca et al 2002;Touber & Leschziner 2012;Hurst et al 2014), turbulent flow with the streamwise travelling wave (Hurst et al 2014;Gatti & Quadrio 2016), turbulent flow of a polymer solution (Ptasinski et al 2003;White & Mungal 2008) and turbulent flow over piezoelectrically excited travelling waves (Musgrave & Tarazaga 2019). Gatti & Quadrio (2016) derived their predictive model (1.5) based on similar observations of the velocity profiles in region I, and as a result, GQ's prediction works well in this region (figure 3d).…”

Guidelines and procedure for tailoring high-performance, steady-state traveling waves for propulsion and solid-state motion

“…This enables solid state-propulsion for robotics [6][7][8][9] and the conveyance of objects [10][11][12] such as powder [13][14][15], and they are often discussed in the context of acoustic levitation [16,17]. Traveling waves can also be used to reduce skin friction drag [18][19][20][21], adapting to changing flow conditions while remaining streamlined. However, the traveling wave methods used in these studies often have significant limitations.…”