4:10 pm Presentation
“On the Promotion of Instabilities for Hydro-Kinetic Energy Harvesting Through Flexible Materials and Wave-Like Analogs”
Presented by DIEGO F. MURIEL (Prof. Katz)
The implementation of flexible materials for micro-energy harvesting is limited by the required high flow velocities to start exploitable oscillations. Initial configurations consist of membranes or plates with minimal or no induced curvature. Upon the action of an external flow, the harvester will oscillate presenting attractive possibilities for energy extraction. We demonstrate that forcing a plate into a wave-like deformation reduces minimum required flow velocities and provides consistent large amplitude oscillatory motions. First, we present the capacity to extract energy through a self-powered water pump, and second, we build a reduced-order model to explore the underlying physics. We show that the main driving mechanisms are a marginally stable deformation, a destabilizing effect of the compressive force, and an unsteady flow field that exists prior to the onset of large amplitude oscillatory motions. Our results open possibilities for new configurations of energy harvesters, and we argue the physical concepts can be translated to areas such as locomotion and propulsion.
4:35 pm Presentation
“Effect of Free-Stream Vortical Disturbances on Thermal Turbulent Boundary Layer”
Presented by JIHO YOU (Prof. Zaki)
Direct numerical simulations are performed to examine the impact of free-stream vortical forcing on a thermal turbulent boundary layer. When the boundary layer is buffeted by the external perturbations, the wall heat-transfer rate is increased relative to the canonical configuration where the free stream is quiescent. The change in the Stanton number is attributed to the distortion of the base temperature profile and enhanced production of the scalar variance. Both terms are increased due to the wall-normal heat flux, which is itself a result of the enhanced Reynolds stresses in response to the free-stream vortical forcing. The enhanced production of temperature variance leads to the formation of high thermal fluctuations that are maintained in the forced flow. In addition, the free-stream disturbances modify the spectral content of the boundary layer, and enlarge the scales of the hydrodynamic and thermal structures in the logarithmic layer. Near the near wall, the thermal structures are also strengthened due to their modulation by the outer velocity motions.