Wake dynamics and surface pressure variations on two-dimensional normal flat plates

Arman Hemmati,David H Wood,Robert J Martinuzzi

doi:10.1063/1.5079634

Abstract

The relationship between vortex dynamics and surface pressure fluctuations on the leeward face of a two-dimensional normal thin flat plate was studied using Direct Numerical Simulations for incompressible flow at a Reynolds number of 1200. The vortex shedding frequency was observed in the spectra of pressure fluctuations on both faces of the plate, while a lower frequency spectral peak was only evident on the leeward pressure fluctuations. Local sharp peaks of low pressure in the separated shear layers coincide with increases in the leeward face pressure fluctuations. These observations are tied to the vortex dynamics using the invariant Q, commonly used for vortex identification. Q is also proportional to the source term for the Poisson equation for the instantaneous pressure. The pressure, which is the only contributor to the plate drag, varies significantly in response to alterations to the vortex shedding, which can be observed in differences of vortex trajectories. At minimum drag, the pressure fluctuations are small, which is attributed to lower values of Q associated with weaker vortices.

Highlights

The turbulent wakes of bluff bodies such as circular cylinders,1–6 rectangular cylinders,7–9 thin flat plates10–17 and flat disks18–25 have been studied to understand the vortex formation and interaction processes
These instances occur during regime L. (M1) corresponds to the more commonly occurring regime M, in which the lift fluctuations are typical of regular vortex shedding
The current results suggest that interrupting the vortex shedding process should reduce the surface pressure fluctuations, and lower the aerodynamic force variations, even though the large structures are not confined to the edges of the plate

Summary

Introduction

The turbulent wakes of bluff bodies such as circular cylinders, rectangular cylinders, thin flat plates and flat disks have been studied to understand the vortex formation and interaction processes. Direct Numerical Simulations (DNS) provide the instantaneous pressure and velocity fields, which allows an investigation of the relationships between wake dynamics and surface pressure variations. These relationships have been studied in detail for pipe and turbulent boundary layers flows.. Identifying changes to the wake topology using pressure measurements on the plate surfaces can significantly improve the design of flow control systems, and improve the performance of wind turbines, fastmaneuvering aircraft, and propeller fins. Lower drag is fundamental to achieving high efficiency and fast propulsion in swimming (or flying) bodies, which can be accomplished by designing control systems that use surface pressure sensors to enforce low-drag vortex shedding regimes. The development of smaller vortices with lower rates of flow mixing has major implications for pollution control systems and techniques to reduce contamination

Results

Discussion

Conclusion