Graduate Seminar in Fluid Mechanics 530.807
3:00 p.m. Presentation
“Uncertainty in Stability Predictions for High-Speed Boundary Layers”
Presented by JUNHO PARK (Adviser: Prof. Zaki)
The parabolized stability equations are widely adopted in prediction of laminar-to-turbulence transition in high-speed boundary layers. The analysis is performed for mean flow profiles from the similarity solution to the compressible boundary-layer equations, over wide ranges of Reynolds and Mach numbers. But in real flows, the base state deviates from the similarity solution due to, for instance, variations in the base flow due to roughness or variations in the base temperature due to thermal boundary conditions. In this presentation, we revisit the boundary-layer stability problem, and formulate its sensitivity analysis using the Lagrangian multiplier and adjoint methods. The sensitivity to base-flow and base-temperature distortions will be analyzed, and we will quantify the uncertainty in the growth rates of instability waves. The interpretation of the sensitivity curves motivates the optimal strategy to delay transition.
3:25 p.m. Presentation
“Direct Simulation of a Jet in Channel Crossflow with Conjugate Heat Transfer”
Presented by ZHAO WU (Adviser: Prof. Meneveau)
We present a DNS study of a hot laminar jet discharged into a cold turbulent channel stream through a circular orifice in one of the steel channel walls. The channel wall has a finite thickness and its outer side is cooled under Robin type thermal boundary conditions for a realistic external environment, leading to a conjugate heat transfer system. This test case may be used to study the thermal failure problem as found, for example, in power plant piping T-junctions. The near-wall mean flow structures, a horseshoe vortex ahead and on the sides of the jet orifice, a recirculation behind the jet and a counter-rotating vortex pair downstream, lead to a complex convective and turbulent wall heat transfer pattern around the orifice. The main findings are:
- Wall maps of Nusselt number and r.m.s temperature for conjugate heat transfer are quite different to the iso-thermal and adiabatic wall cases.
- Discontinuities of temperature dissipation rate are found at the fluid-solid interface.
- At the high wavenumber range, the spanwise temperature spectra decrease exponentially, and the exponential decay rate increases as one goes deeper into the solid.