Flow past a disk under different levels of stratification

The wave field of a horizontally-moving circular disk in a stratified fluid is studied using large eddy simulations. Five levels of stratification (body Froude numbers of Fr = 0.5, 1, 1.5, 2 and 5) are studied at Reynolds number of 5000. The wavelength and amplitude of steady lee waves are compared with linear-theory analysis. Good agreement is found if an 'equivalent body' that includes the separation region is employed for the linear theory. Unsteady wake generated waves in a stationary-body frame are linked to the vortex shedding frequency. Study of these waves in a stationary-ambient frame, along with the linear dispersion relationship, helps understand their propagation angle. The partition between steady and unsteady components of the wave flux is found to depend on Fr. Spectral Proper Orthogonal Decomposition (SPOD), when applied to the wake, shows the suppression of the natural vortex shedding frequency of the disk at Fr < O(1). A new parameter is introduced to identify the critical Fr for the onset of this suppression.