Transient growth in a flat plate boundary layer under a stream with uniform shear

One of the simplest problems involving external vorticity in boundary layer flows is the flow over a semi-infinite plate under a stream of uniform shear. We study the transient growth phenomenon in this flow to investigate the role of freestream shear on energy amplification and analyze the differences with the Blasius flow. The initial optimal disturbance that triggers the maximum growth is found to be streamwise vortices, as in other shear flows. Compared to the Blasius boundary layer, higher optimum energy and larger spanwise wavelength of streamwise vortices have been observed. We provide scaling laws for the maximum optimal amplification, which is found to increase exponentially with the freestream shear gradient.SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Transient growth in a flat plate boundary layer under a stream with uniform shear

One of the simplest problems involving external vorticity in boundary layer flows is the flow over a semi-infinite plate under a stream of uniform shear. We study the transient growth phenomenon in this flow to investigate the role of freestream shear on energy amplification and analyze the differences with the Blasius flow. The initial optimal disturbance that triggers the maximum growth is found to be streamwise vortices, as in other shear flows. Compared to the Blasius boundary layer, higher optimum energy and larger spanwise wavelength of streamwise vortices have been observed. We provide scaling laws for the maximum optimal amplification, which is found to increase exponentially with the freestream shear gradient.SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Transient growth in a boundary layer under uniform freestream shear

info:eu-repo/semantics/publishe

Experimental studies on the frequency selection in flat plate wakes: Mean-flow stability analyses and low-dimensional modeling

We investigate the global frequency selection of two-dimensional vortex shedding in the flat plate wake. The analysis is based on the mean-flow velocity profiles obtained from experimental measurements carried out for two values of Reynolds number, 1850 and 3350, which are based on the plate thickness and the free-stream velocity. Two different trailing edge geometries of the flat plate are considered in this study: blunt and circular. By performing local spatiotemporal analyses on the measured mean-flow velocity profiles, we estimate the global shedding frequency of the flow. This is in excellent agreement with the shedding frequency measured experimentally. To complement the study, we carry out a low-dimensional modeling based on the proper orthogonal decomposition (POD) of the flow fields which is novel for flat plate wakes. We observe that a model based on only two POD modes produces an accurate estimate of the global shedding frequency. Our results also highlight the role of the interaction strength between the mean flow and the higher harmonics thereby experimentally supporting the theoretical criterion outlined in Sipp and Lebedev [J. Fluid Mech. 593, 333 (2007)10.1017/S0022112007008907].SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe