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Unsteady dynamics in a subsonic duct flow with a bluff body

A series of reduced-order numerical simulations on a specific bluff body type (v-gutters) in a subsonic duct flow is done to assess the unsteady wake dynamics. Two of the v-gutter's geometrical parameters are varied: the v-gutter's base angle ($θ$) and the size of a slit ($ξ$) at the leading-edge of the v-gutter. Turbulent flow kinematics and pressure field are analyzed to evaluate the unsteadiness at a freestream Mach number of $M_\infty = 0.25$ and a freestream Reynolds number based on bluff body's transverse length (L) of $Re_L=0.1 \times 10^6$. Five v-gutter angles are considered ($θ$, $^\circ = π/6, π/4, π/3, 5π/12, π/2$) and three slit sizes ($ξ$, mm =0,0.25,0.5) are considered only for a particular $θ= [π/6]$. In general, high fluctuations in velocity and pressure are seen for the bluffest body in consideration ($θ= π/2$) with higher drag ($c_d$) and total pressure loss ($Δp_0$). On the other hand, the presence of a slit on a streamlined body ($θ= π/6$) tends to efficiently stabilize the wake and thus, producing almost a periodic shedding structure with lower $c_d$ and $Δp_0$. For $θ= [π/6]$, broadened spectra in vortex shedding is seen with a peak at $[fL/u_\infty] \sim 0.08$. For $θ\geq [π/4]$, a dominant discrete shedding frequency is seen with a gradual spectral decay. Similarly, the effects of $ξ$ on the $θ= [π/6]$ case produce a discrete shedding frequency instead of a broadened one, as told before. The shedding frequency increases to a maximum of $[fL/u_\infty] \sim 0.26$ for the maximum slit size of $ξ= 0.5$. More insights on the shedding vortices, momentum deficit in the wake, varying energy contents in the flow field, and the dominant spatiotemporal structures are also provided.