A previous numerical study by Davis and Moore of vortex shedding from rectangles in infinite domains is extended to include the effects of confining walls. The major changes to the numerical modeling are the addition of a direct solver for the pressure equation and the use of an infinite‐to‐finite mapping downstream of the rectangle. The parameters in the problem are now Reynolds number, rectangle aspect ratio, blockage ratio, and upstream velocity profile. As each of these is varied, the effects upon the forces acting on the rectangle and the structure of the wake are discussed. Streakline plots composed of multishaped passive marker particles provide a clear visualization of the vortices. These plots are compared with smoke‐wire photographs taken from a wind tunnel test. Strouhal numbers obtained both computationally and experimentally are compared for two values of the blockage ratio. Moving recirculation zones which appear between the wake and the walls are discussed.

A numerical-experimental study of confined flow around rectangular cylinders

A numerical analysis of forced-convection heat transfer from a horizontal stationary circular cylinder dissipating a uniform heat flux in a crossflow of air is conducted by solving the full two-dimensional steady-state Navier-Stokes and energy equations in the range of the Reynolds numbers from 100 to 500 (based on diameter). A numerical study by this author for Reynolds numbers less than 100 was previously conducted and therefore is not repeated here. Dependence on the Reynolds number of the flow and thermal fields, vorticity and pressure distributions, separation angle, drag coefficient, and local and average Nusselt number around the cylinder are shown. Correlations for the separation angle and drag coefficient as functions of Reynolds number are suggested. Quantities such as vorticity, pressure, and Nusselt number at the forward and rear (base) stagnation points are also calculated and correlated as functions of Reynolds number. The local and average values of the Nusselt numbers are shown to be in go...

Steady-State Numerical Solution of the Navier-Stokes and Energy Equations around a Horizontal Cylinder at Moderate Reynolds Numbers from 100 to 500

Numerical study of vortex shedding from different shaped bluff bodies

The impulsive start of a circular cylinder in a shock tube was characterized with time-resolved particle image velocimetry measurements (TR-PIV) at 50 kHz using a pulse-burst laser. Three Reynolds numbers Re of 1.07, 1.63 and 2.46 × 105 were studied adding insight into the transient process near the drag crisis. In all cases, vorticity was maximum in the first pair of vortices formed. In a fashion analogous to previous studies at Re ≤ 104, a single symmetric vortex pair was first shed from the cylinder at Re = 1.07 × 105 prior to the eventual transition to a von Karman vortex street. In contrast, at Re ≥ 1.63 × 105, two or more symmetric vortex pairs were first shed. The non-dimensional time for the wake to begin to exhibit asymmetry was also found to be lower at the two higher Re. The time required to reach a fully antisymmetric wake (peak von Karman shedding) was roughly five times the asymmetric onset time. Altogether, the study indicates a transformation in the impulsive wake structure and associated time scales to occur at Re near 1.6 × 105.

Pulse-burst PIV of an impulsively started cylinder in a shock tube for Re > 10 5

Flow around impulsively started square prisms

The growth of the vortex-pair developed behind a circular cylinder was investigated experimentally, when the cylinder was moved impulsively in a water tank. The experimental conditions were Re = Ud/ν = 1022×103, d/h =0.040.67 where U is the cylinder speed, d the cylinder diameter and h the distance between side walls of the tank. The detailed patterns of the vortex sheets and path lines around the cylinder were visualized by means of electrolysis and Al-dust methods. When the ratio d/h is decreased to 0.1, the effects of the tank walls on the flow are substantially negligible. The vortex sheets roll up near the separation points when Re> 520 and a secondary small vortex-pair is formed on the upstream side of the main vortices. The pattern of the vortex sheets shedding from the secondary vortices changes as Re is increased. This phenomenon is closely related to the manner of growth and collapse of the main vortices. The wall effects were examined within the range of d/h = 0.10.67. When d/h>0.5, the separation of flow occurs also at the side walls and "wall vortices" are formed. These vortices deform the pattern of main vortices behind the cylinder.

Yutaka Kakehi

Papers

Unsteady Flow Past a Circular Cylinder Started Impulsively