Flow Characterization of a Three-Dimensional Separated Annular Diffuser

2009 ◽  
Author(s):  
Jason J. Dunn ◽  
Mark Ricklick ◽  
J. S. Kapat
Keyword(s):  
Vertical Wall ◽  
Three Dimensional ◽  
Separated Flow ◽  
Outer Wall ◽  
Reynolds Numbers ◽  
Pressure Gradients ◽  
Cfd Models ◽  
Flow Characterization ◽  
Annular Diffuser

Experiments were performed on two annular diffusers to characterize the flow separation along the outer wall. Both diffusers had the same fully developed inlet flow condition, however, the expansion of the two diffusers differed such that one diffuser replicated a typical compressor discharge diffuser found in a real machine while the other would create a natural separated flow along the outer wall. Both diffusers were tested at two Reynolds numbers, 5×104 and 1×105, with and without a vertical wall downstream of the exit to replicate the dump diffuser that re-directs the flow from the compressor outlet to the combustor. It was shown that the separation happens quite quickly within the diffuser after which the pressure recovery remains fairly constant. The results also further validate claims that CFD models can not accurately predict flows with high adverse pressure gradients.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

The Effect of Angle and Flow Rate Upon Hemodynamics in Distal Vascular Graft Anastomoses: A Numerical Model Study

1994 ◽  
Vol 116 (3) ◽  
pp. 331-336 ◽  
Author(s):  
Ding-Yu Fei ◽  
James D. Thomas ◽  
Stanley E. Rittgers
Keyword(s):  
Numerical Model ◽  
Stagnation Point ◽  
Arterial Wall ◽  
Artery Bypass ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
In Vivo Studies ◽  
Stagnation Points

Flow in distal end-to-side anastomoses of iliofemoral artery bypass grafts was simulated using a steady flow, three-dimensional numerical model. With the proximal artery occluded, anastomotic angles were varied over 20, 30, 40, 45, 50, 60 and 70 deg while the inlet Reynolds numbers were 100 and 205. Fully developed flow in the graft became somewhat skewed toward the inner wall with increasing angle for both Reynolds numbers. Separated flow regions were seen along the inner arterial wall (toe region) for angles ≥ 60 deg at Re = 100 and for angles ≥ 45 deg at Re = 205 while a stagnation point existed along the outer arterial wall (floor region) for all cases which moved downstream relative to the toe of the anastomosis with decreasing angles. Normalized shear rates (NSR) along the arterial wall varied widely throughout the anastomotic region with negative values seen in the separation zones and upstream of the stagnation points which increased in magnitude with angle. The NSR increased with distance downstream of the stagnation point and with magnitudes which increased with the angle. Compared with observations from chronic in vivo studies, these results appear to support the hypothesis of greater intimal hyperplasia occurring in regions of low fluid shear.

Experimental and Numerical Study of the Flow Around a Semi-Submerged Rectangular Cylinder

2012 ◽  
Author(s):  
Tufan Arslan ◽  
Stefano Malavasi ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson
Keyword(s):  
Particle Image ◽  
Model Simulation ◽  
Numerical Study ◽  
Three Dimensional ◽  
Separated Flow ◽  
Piv Measurements ◽  
Rectangular Cylinder ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd

The present work is motivated by phenomena occurring in the flow field around structures partly submerged in water. A three dimensional unsteady flow around a rectangular cylinder is studied for four different submergence ratios by using computational fluid dynamics (CFD) tools with LES turbulence model. Simulation results are compared to particle image velocimetry (PIV) measurements at Reynolds number Re = 12100 and Froude number Fr = 0.26. Focus in our investigation is on the characterization of the behaviour of vortex structures generated by separated flow. Another target in the study is to obtain better knowledge of the hydrodynamic forces acting on a semi-submerged structure. Computed force coefficients are compared with experimental measurements.

Three-dimensional study of separated flow over a square cylinder by large eddy simulation

2005 ◽  
Vol 219 (3) ◽  
pp. 225-234 ◽  
Author(s):  
M Farhadi ◽  
M Rahnama
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Mean Flow ◽  
Central Difference ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy

Large eddy simulation of flow over a square cylinder in a channel is performed at Reynolds numbers of 22 000 and 21 400. The selective structure function (SSF) modelling of the subgrid-scale stress terms is used and the convective terms are discretized using quadratic upstream interpolation for convective kinematics (QUICK) and central difference (CD) schemes. A series of time-averaged velocities, turbulent stresses, and some global flow parameters such as lift and drag coefficients and their fluctuations are computed and compared with experimental data. The suitability of SSF model has been shown by comparing the computed mean flow velocities and turbulent quantities with experiments. Results show negligible variation in the flow parameters for the two Reynolds numbers used in the present computations. It was observed that both QUICK and CD schemes are capable of obtaining results close to those of the experiments with some minor differences.

Turbulent Flow Around a Semi-Submerged Rectangular Cylinder

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Tufan Arslan ◽  
Stefano Malavasi ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson
Keyword(s):  
Three Dimensional ◽  
Separated Flow ◽  
Piv Measurements ◽  
Eddy Simulation ◽  
Rectangular Cylinder ◽  
Image Velocimetry ◽  
Large Eddy ◽  
3D Unsteady Flow ◽  
Computational Fluid Dynamics Cfd

The present work is motivated by phenomena occurring in the flow field around structures partly submerged in water. A three-dimensional (3D) unsteady flow around a rectangular cylinder is studied for four different submergence ratios by using computational fluid dynamics (CFD) tools with the large eddy simulation (LES) turbulence model. The simulation results are compared to particle image velocimetry (PIV) measurements at the Reynolds number Re = 12,100 and the Froude number Fr = 0.26. The focus in our investigation is on the characterization of the behavior of vortex structures generated by separated flow. Another target in the study is to obtain a better knowledge of the hydrodynamic forces acting on a semi-submerged structure. The computed force coefficients are compared with experimental measurements.

scholarly journals NONSYMMETRIC BRANCHING OF FLUID FLOWS IN 3D VESSELS

2018 ◽  
Vol 59 (4) ◽  
pp. 533-561
Author(s):  
N. C. OVENDEN ◽  
F. T. SMITH
Keyword(s):  
Three Dimensional ◽  
Fluid Flows ◽  
Outer Wall ◽  
Reynolds Numbers ◽  
Arbitrary Cross Section ◽  
Shear Stresses ◽  
Flux Change ◽  
End Pressures ◽  
Branching Flow ◽  
Unsteady Effects

Nonsymmetric branching flow through a three-dimensional (3D) vessel is considered at medium-to-high flow rates. The branching is from one mother vessel to two or more daughter vessels downstream, with laminar steady or unsteady conditions assumed. The inherent 3D nonsymmetry is due to the branching shapes themselves, or the differences in the end pressures in the daughter vessels, or the incident velocity profiles in the mother. Computations based on lattice-Boltzmann methodology are described first. A subsequent analysis focuses on small 3D disturbances and increased Reynolds numbers. This reduces the 3D problem to a two-dimensional one at the outer wall in all pressure-driven cases. As well as having broader implications for feeding into a network of vessels, the findings enable predictions of how much swirling motion in the cross-plane is generated in a daughter vessel downstream of a 3D branch junction, and the significant alterations provoked locally in the shear stresses and pressures at the walls. Nonuniform incident wall-shear and unsteady effects are examined. A universal asymptotic form is found for the flux change into each daughter vessel in a 3D branching of arbitrary cross-section with a thin divider.

The Effect of Reynolds Number on Microfan Performance

2004 ◽  
Author(s):  
David Quin ◽  
Ronan Grimes ◽  
Ed Walsh ◽  
Mark Davies ◽  
Stefan Kunz
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Electronic Systems ◽  
Piv Measurements ◽  
Flow Characterization ◽  
Image Velocimetry ◽  
Macro Scale

Miniaturisation of modern electronics means that future compact electronic systems are likely to be too hot to be held in the users hand. Simultaneous increases in heat dissipation will also require the development of novel compact cooling technologies. In systems such as mobile phones and palmtop computers, macro scale fans cannot be used to overcome this problem, as they are too large. As a solution, the implementation of micro fan technology is proposed. Previous investigators have shown that reduction of the Reynolds number of turbomachinery results in reduced efficiency. To experimentally investigate this predicted phenomenon, a series of geometrically similar axial flow fans have been fabricated. These range in size from the macro to the micro scale with the Reynolds numbers varying linearly with fan dimensions. Through detailed Particle Image Velocimetry (PIV) measurements and pressure flow characterization of these fans, this investigation aims to quantify the reduction in efficiency, which occurs as the Reynolds number is reduced. This paper concludes that the extent to which fan efficiency is reduced by Reynolds number is in surprisingly good agreement with relatively simple predictions developed by the authors in previous investigations. Reduced Reynolds number was also seen to alter the velocity distribution at the fan outlet. This is an important point as it indicates a change in the physics of the flow with reducing scale.

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