TY - GEN
T1 - A controls-based methodology for generating turbulence in direct and large-eddy simulations of wall-bounded flows
AU - Krishnan, Vivek
AU - Milano, Michele
AU - Squires, Kyle
PY - 2007
Y1 - 2007
N2 - An integral control scheme is used to optimize a method for generating turbulent fluctuations for DNS and LES of wall-bounded flows. Similar to previous investigations, the method employs a series of control planes in which a body force is applied to the wall-normal momentum equation that amplifies and shapes velocity fluctuations seeded into the flow towards a target resolved shear-stress profile. The focus of the current work is on a methodology for specifying the controller gains and ensuring numerical stability without the introduction of criteria that override the control commands in order to prevent unphysical effects. The first method used to analyze the control process is based on identification of a linear model formed from the openloop response of the shear stress to random inputs at the control planes. Optimal gains for the controller are specified based on the location of the poles of the linear model in the closedloop configuration. The second method consists of measuring the response of the non-linear system to preset gain values and incrementally increasing the gains until the onset of numerical instabilities. The schemes have been tested using computations of turbulent channel flow at Reynolds numbers based on friction velocity and channel halrwidth of 400 and 5000. Simulation results obtained using both methods show that using the second approach the resolved shear stress reaches the target levels at the control planes, without ad hoc tuning of the control parameters. The predicted optimal gain values at the control planes are sensitive to the stirring force used to create fluctuations. In addition, the magnitude of the stirring force also affects rms values of the velocity fluctuations downstream of the control planes.
AB - An integral control scheme is used to optimize a method for generating turbulent fluctuations for DNS and LES of wall-bounded flows. Similar to previous investigations, the method employs a series of control planes in which a body force is applied to the wall-normal momentum equation that amplifies and shapes velocity fluctuations seeded into the flow towards a target resolved shear-stress profile. The focus of the current work is on a methodology for specifying the controller gains and ensuring numerical stability without the introduction of criteria that override the control commands in order to prevent unphysical effects. The first method used to analyze the control process is based on identification of a linear model formed from the openloop response of the shear stress to random inputs at the control planes. Optimal gains for the controller are specified based on the location of the poles of the linear model in the closedloop configuration. The second method consists of measuring the response of the non-linear system to preset gain values and incrementally increasing the gains until the onset of numerical instabilities. The schemes have been tested using computations of turbulent channel flow at Reynolds numbers based on friction velocity and channel halrwidth of 400 and 5000. Simulation results obtained using both methods show that using the second approach the resolved shear stress reaches the target levels at the control planes, without ad hoc tuning of the control parameters. The predicted optimal gain values at the control planes are sensitive to the stirring force used to create fluctuations. In addition, the magnitude of the stirring force also affects rms values of the velocity fluctuations downstream of the control planes.
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U2 - 10.1115/FEDSM2007-37319
DO - 10.1115/FEDSM2007-37319
M3 - Conference contribution
AN - SCOPUS:40449129952
SN - 0791842886
SN - 9780791842881
T3 - 2007 Proceedings of the 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007
SP - 1367
EP - 1376
BT - 2007 Proceedings of the 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007
T2 - 2007 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007
Y2 - 30 July 2007 through 2 August 2007
ER -