Effects of Uniform Blowing or Suction on the Amplitude Modulation in Spatially Developing Turbulent Boundary Layers

Authors: Kametani, K., Örlü, R., Schlatter, P., Fukagata, K.
Document Type: Conference
Pubstate: Published
Journal: IUTAM Symposium on Advances in Computation, Modeling and Control of Transitional and Turbulent Flows, Goa, India, Dec. 15–18, 2014
Volume:    185-194
Year: 2016


Large-eddy simulations of spatially evolving turbulent boundary layers with uniform blowing or suction were performed at a moderate Reynolds number (based on free-stream velocity and momentum thickness) of up to Re=2500 in the uncontrolled case. Aiming at the control of external flows, the influence on the skin friction drag and turbulent statistics is investigated with the control amplitude of 0.1% of Uinf. While uniform blowing reduces the skin-friction coefficient and enhances the amplitude of all components of the turbulence intensities, uniform suction reverses the effect on the skin friction and scales turbulent intensities with wall units throughout the inner layer. A net-energy saving rate S of around 13% could be achieved by blowing over the controlled surface. Since the locally defined S develops in the streamwise direction, the global S increases as the streamwise length of the controlled region is expanded. The fact that the control gain has similar trend in the streamwise direction indicates that the control efficiency increases the streamwise length of the uniform blowing region. The 2D amplitude modulation map shows that the correlation between the energy of the small scale turbulence and the large scale modulation velocity is remarkably increased (decreased) around the diagonal and off-diagonal peaks by blowing (suction). These results are directly linked to the observed enhancement of turbulence intensities in the inner layer for the blowing and obtained inner-scaling for the suction case.