Bluff body drag control by boundary layer disturbances

Simulations for the Cambridge swirl bluff-body spray burner are performed near blow-out conditions. A hybrid stress blended eddy simulation (SBES) model is utilized for sub-grid turbulence closure. SBES blends the RANS-SST model at the boundary layer with large eddy simulation dynamic Smagorinsky model outside the boundary layer. The injected N-heptane spray droplets are tracked using a typical Eulerian-Lagrangian approach. Heat transfer coupling between the bluff-body walls and the near-walls fluid is accounted for by coupling the solid and fluid energy equations at the bluff-body surface. Mixing and chemistry are modeled using the Flamelet Generated Manifold (FGM) model. The study investigates how successful the FGM model is in predicting finite rate effects like local extinction and flame lift-off height. To this end, two near blow-out spray flames, the H1S1 (75% to blow-out) and H1S2 (88% to blow-out) are simulated. Good results are shown matching the spray Sauter mean diameter (SMD) and axial velocity mean and rms experimental data. The results also show that the FGM model captured reasonably well the flame structure and lift-off height as well as the spray pattern. Overall the spray droplets mean D32 and mean axial velocity were under-predicted, while the rms distribution matched reasonably well for the H1S1 flame. The mean flame brush lift-off height is estimated based on the statistically stationary mean flame brush and is estimated to be around 6 mm from the bluff-body base. Instantaneous local flame extinction is observed. The H1S2 flame, however, showed similar but slightly better match with the measurements for the mean spray data compared to the H1S1 flame, with slight under-prediction for D32 at Z = 10 mm and Z = 20 mm. Future work will investigate the sensitivity of the simulation to the spray boundary conditions and grid resolution.

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Experimental Study on Bluff Body Drag Reduction with Fluidic Oscillators

52nd Aerospace Sciences Meeting ◽

10.2514/6.2014-0403 ◽

2014 ◽

Cited By ~ 26

Author(s):

Rene Woszidlo ◽

Timo Stumper ◽

C. Nayeri ◽

Christian O. Paschereit

Keyword(s):

Experimental Study ◽

Drag Reduction ◽

Bluff Body ◽

Body Drag

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Boundary Layer Influence on the Unsteady Horseshoe Vortex Flow and Surface Heat Transfer

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27633 ◽

2007 ◽

Cited By ~ 2

Author(s):

D. R. Sabatino ◽

C. R. Smith

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Bluff Body ◽

Leading Edge ◽

Horseshoe Vortex ◽

Surface Heat ◽

Wall Region ◽

Thermochromic Liquid Crystal ◽

Surface Heat Transfer ◽

End Wall

The spatial-temporal flow-field and associated surface heat transfer within the leading edge, end-wall region of a bluff body were examined using both particle image velocimetry and thermochromic liquid crystal temperature measurements. The horseshoe vortex system in the end-wall region is mechanistically linked to the upstream boundary layer unsteadiness. Hairpin vortex packets, associated with turbulent boundary layer bursting behavior, amalgamate with the horseshoe vortex resulting in unsteady strengthening and streamwise motion. The horseshoe vortex unsteadiness exhibits two different natural frequencies: one associated with the transient motion of the horseshoe vortex, and the other with the transient surface heat transfer. Comparable unsteadiness occurs in the end-wall region of the more complex airfoil geometry of a linear turbine cascade. To directly compare the horseshoe vortex behavior around a turning airfoil to that of a simple bluff body, a length scale based on the maximum airfoil thickness is proposed.

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Wake Interaction of a Square Cylinder With a Splitter Plate Boundary Layer at a Low Reynolds Number

Volume 1A: Symposia, Part 2 ◽

10.1115/ajkfluids2015-01793 ◽

2015 ◽

Author(s):

Smriti Srivastava ◽

Sudipto Sarkar

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Bluff Body ◽

Acoustic Noise ◽

Vortex Formation ◽

Plate Boundary ◽

Wake Flow ◽

Stream Velocity ◽

Square Cylinder ◽

Plate Length

One of the most important researches in bluff body aerodynamics is to control the shear layer evolution leading to vortex formation. This kind of research is closely associated with reduction of aerodynamics forces and acoustic noise. Passive and active control of wake-flow from bluff bodies have received a great deal of attention in the last few decades [1–4]. Keeping this in mind, authors investigate the interaction of a square cylinder (side of the square = a) wake with a flat plate (length L = a, width w = 0.1a) boundary layer positioned at various downstream locations close to the cylinder. The gap-to-side ratios are maintained at G/a = 0, 0.5, 1 and 2 (where G is the gap between square cylinder and plate), and the simulation is performed at a Reynolds number, Re = 100 (Re = U∞a/v, where U∞ is free stream velocity and v is kinematic viscosity). Instantaneous flow visualization, aerodynamic forces and vortex shedding frequencies for all cases are described to gain insight about the changes associated with wake of the cylinder when a short plate is kept in its downstream.

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Extremum seeking to control the amplitude and frequency of a pulsed jet for bluff body drag reduction

Experiments in Fluids ◽

10.1007/s00348-016-2243-4 ◽

2016 ◽

Vol 57 (10) ◽

Cited By ~ 6

Author(s):

Rowan D. Brackston ◽

Andrew Wynn ◽

Jonathan F. Morrison

Keyword(s):

Drag Reduction ◽

Bluff Body ◽

Extremum Seeking ◽

Pulsed Jet ◽

Body Drag

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The dispersion of contaminant released from instantaneous sources in laminar flow near stagnation points

Journal of Fluid Mechanics ◽

10.1017/s0022112074000498 ◽

1974 ◽

Vol 66 (4) ◽

pp. 753-766 ◽

Cited By ~ 3

Author(s):

P. C. Chatwin

Keyword(s):

Boundary Layer ◽

Laminar Flow ◽

Bluff Body ◽

Velocity Potential ◽

Tangent Plane ◽

The Body ◽

Centre Of Mass ◽

Stagnation Points ◽

Molecular Diffusivity ◽

Instantaneous Source

This paper considers the dispersion of a cloud of passive contaminant released from an instantaneous source in the steady two-dimensional laminar flow near the forward stagnation point on a bluff body. The body is replaced by its tangent plane y = 0 with x measuring distance along the plane. Far away from y = 0 the flow is irrotational with velocity potential ½l(x2 – y2), where l is a positive constant. When the boundary layer is ignored the equation governing the distribution of concentration can be solved exactly. Consequences of this solution are that for large times the centre of mass moves parallel to the body at a speed proportional to exp (lt) while the cloud spreads out along the body symmetrically about the centre of mass with the magnitude of the spread also proportional to exp (lt). However, this solution is unrealistic because most of the contaminant is confined to a layer adjoining the body of thickness of order (k/l)½, where k is the molecular diffusivity, and this layer normally lies within the boundary layer, which is of thickness of order (v/l)½, where v is the kinematic viscosity. An approximate analysis, based on ideas similar to those supporting the Pohlhausen method in boundary-layer theory, suggests that when the boundary layer is taken into account the conclusions above remain true provided that exp (lt) is replaced by exp (βlt), where β is a constant depending on v/k. Calculations give values of β ranging from 0·73 when v/k = 0·5 to 0·10 when v/k = 103.

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