Numerical Study On Turbulent Channel Flow Over A Compliant Wall

Turbulent flow is commonly found in nature and engineering. Since thehigh friction drag it brings continues to be a challenge, investigations onturbulent drag reduction are of great importance on the cutting of energyexpense and the environmental protection. People’s interests on compliantwall originate from studies on dolphin’s swimming. Though bears a poorerdrag reduction potentiality than active control strategies, compliant wall stillgains attention because it does not require extra power input and sensorinstallation which is beyond the current technical capabilities. Compliantwall’s delay of boundary layer transition is close to practical application,while its influence on fully-developed turbulence is far from being fullyunderstood.Direct numerical simulations (DNS) of channel flow with an isotropicviscous-elastic compliant wall as the lower wall are performed with improvedprogram here. The Reynolds number is set to be2000, and the domain size is0.8π H×2H×0.8πH, where H is the half channel height. The velocity of thecompliant wall is employed as the basic boundary conditions of the channelflow, and the fluctuating pressure is used to drive the compliant wall. Themain results are as follows:1. The program is improved to fix the current application. To reduce theresidual divergence, the time integration is changed to2ndorder projectionmethod from time-splitting method. The projection method is based on theHodge decomposition theorem, and keeps the residual divergence to be zero.Since the fluctuating pressure on the wall is used as the loading of thecompliant wall, the staggered mesh and2ndorder finite-difference method isapplied to the normal direction.2. Effects of different boundary layer conditions (namely periodicalboundary, clamped boundary and simply-supported boundary) are studiedthrough the dynamic analysis of compliant wall and the DNS of compliantwall turbulence. Different boundary conditions cause different wall deformation root mean square (RMS), but no significant change of thecorrelation of the wall velocity and the fluctuating pressure near the wall isfound.3. Effects of compliant wall parameters are studied. Among the sets ofparameter employed in this thesis, only the change of the damping coefficientcauses significant drag increase. In compliant wall’s dynamic analysis, thechange of the tension coefficient brings a much bigger wall deformationRMS change, while in coupled computation, the difference is greatly reduced.The smaller damping coefficient, with large deformation RMS, causes muchmore complex change of fluctuating vortex, fluctuating pressure, theproduction of turbulent kinetic, etc. The correlation of the wall velocity andthe fluctuating pressure near the wall is also found to be significantlychanged.