The Effect of Sweep-Angle Variation on the Turbulence Structure in a Separated, Three-Dimensional Flow

Kaltenbach, Hans-Jakob

doi:10.1007/s00162-002-0078-5

Cited by 11 publications

(10 citation statements)

References 34 publications

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“…This is consistent with reported results for a separated turbulent boundary layer by Dianat & Castro (1991). The production term P , becomes negative in this region which indicates strong deviation from equilibrium conditions as mentioned by Kaltenbach (2003). Above the shear layer zone, it is observed that turbulent transport in conjunction with convection becomes a source of turbulence kinetic energy.…”

Section: Turbulence Kinetic Energy and Budgetssupporting

confidence: 91%

“…The profiles of cases C and D have values higher and lower than those predicted by the ZPG law, respectively. Near the reattachment zone, the flow is far from equilibrium owing to the presence of large scale vortices (Kiya & Sasaki 1985) and impingement of vortical structures on the wall (Shih & Ho 1994;Simpson 1996;Na & Moin 1998;Kaltenbach 2003;Dejoan & Leschziner 2004;Hudy et al 2007). The profiles measured from the top wall for case B collapse again and differ slightly from that of case C and D, where lower values are observed in inertial sublayer, indicative of APG.…”

Section: Mean Flowmentioning

confidence: 92%

“…In this region, disorganized vortices near the reattachment zone get distorted (Song & Eaton 2004) owing to mean flow straining and recovery of the boundary layer occurs, thus forming more organized vortical structures (Le et al 1997;Lee & Sung 2002) further downstream of reattachment. Similar to Kaltenbach (2003), downstream of the reattachment zone, densely packed structures exist consisting of entangled filaments with a preferential orientation aligned with the mean flow. Additionally, the complete flow separation from the top of the wire produces a shear layer with intense disorganized vortical structures.…”

Section: Instantaneous Flow Structuresmentioning

confidence: 99%

“…is the friction velocity and τ w is the overall average shear stress at the walls. Owing to the presence of the wire and its induced secondary flows, a local average wall shear stress can be defined along direction s, similar to Simpson (1996) and Kaltenbach (2003), given by…”

Section: Simulation Parametersmentioning

confidence: 99%

“…In this study, the flow is highly three dimensional owing to existence of transverse pressure gradient and transverse shear and sweep independence of flow exists for sweep angles up to 40 o . Kaltenbach (2003) used DNS of the flow behind a swept backward-facing step to study effect of skewing on turbulence structure and identified origin of axial vorticity and provided details of strain field. They found that strain induced stretching-compression and skewing of mean flow influences turbulence structure only in the vicinity of separation.…”

Section: Introductionmentioning

confidence: 99%

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Direct simulation of turbulent swept flow over a wire in a channel

2010

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Turbulent swept flow over a cylindrical wire placed on a wall of a channel is investigated using direct numerical simulations. This geometry is a model of the flow through the wire-wrapped fuel pins, the heat exchanger, typical of many nuclear reactor designs. Mean flow along and across the wire axis is imposed, leading to the formation of separated flow regions. The Reynolds number based on the bulk velocity along the wire axis direction and the channel half height is 5400 and four cases are simulated with different flowrates across the wire. This configuration is topologically similar to backward-facing steps or slots with swept flow, except that the dominant flow is along the obstacle axis in the present study and the crossflow is smaller than the axial flow, i.e. the sweep angle is large. Mean velocities, turbulence statistics, wall shear stress and instantaneous flow structures are investigated. Particular attention is devoted to the statistics of the shear stress on the walls of the channel and the wire in the recirculation zone. The flow around the mean reattachment region, at the termination of the recirculating bubble, does not exhibit the typical decay of the mean shear stress observed in classical backward-facing step flows owing to the presence of a strong axial flow. The evolution of the mean wall shear stress angle after reattachment indicates that the flow recovers towards equilibrium at a rather slow rate, which decreases with sweep angle. Finally, the database is analysed to estimate resolution requirements, in particular around the recirculation zones, for large-eddy simulations. This has implications in more complete geometrical models of a wire-wrapped assembly, involving hundreds of fuel pins, where only turbulence modelling can be afforded computationally.

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Section: Turbulence Kinetic Energy and Budgetssupporting

confidence: 91%