The effects of wake splitter plates on bluff-body flow in the range 104 < R < 5 × 104. Part 2

1975 ◽  
Vol 71 (1) ◽  
pp. 145-160 ◽  
Author(s):  
C. J. Apelt ◽  
G. S. West
Keyword(s):  
Cross Sections ◽  
Flow Separation ◽  
Bluff Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Flat Plates ◽  
Pressure Distributions ◽  
Splitter Plates ◽  
Bluff Body Flow

The work reported in part 1 has been extended to cover flows past circular cylinders with wake splitter plates having 2 [les ] L/D [les ] 7 and to include flows past normal flat plates with splitter plates having L/D [les ] 3·7. Pressure distributions and wake Strouhal numbers were measured and visualization studies carried out. The results obtained indicate that no further changes would be produced by lengthening the splitter plates beyond the limits tested.The combined results of parts 1 and 2 provide coherent descriptions of the effects of wake splitter plates for all values of L/D of significance for the two profiles, which are representative of two distinct classes of bluff bodies, viz., those with cross-sections of curvilinear shape for which the flow separation points are not determined uniquely by the geometry and those for which the separation points are fixed.

A Free-Streamline Model for Bluff Bodies in Confined Flow

1977 ◽  
Vol 99 (3) ◽  
pp. 585-592 ◽  
Author(s):  
V. J. Modi ◽  
S. E. El-Sherbiny
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Flow Model ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Flat Plates ◽  
Surface Loading ◽  
Confined Flow ◽  
Potential Flow Model

A potential flow model is presented for two-dimensional symmetrical bluff bodies under wall confinement. It provides a procedure for predicting surface loading on a bluff body over a range of blockage ratios. Experimental results with normal flat plates and circular cylinders for blockage ratios up to 35.5 percent substantiate the validity of the approach.

Vortex shedding from bluff bodies in oscillatory flow: A report on Euromech 119

1980 ◽  
Vol 99 (2) ◽  
pp. 225-245 ◽  
Author(s):  
P. W. Bearman ◽  
J. M. R. Graham
Keyword(s):  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Bluff Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Unidirectional Flow ◽  
Low Reynolds Number Flows ◽  
Wide Range ◽  
Bluff Body Flow ◽  
Reynolds Number Flows

European Mechanics Colloquium number 119 was held at Imperial College on 16–18 July 1979, when the subject of vortex shedding from bodies in unidirectional flow and oscillatory flow, was discussed. A wide range of experimental work was presented including low-Reynolds-number flows around circular cylinders, the influence of disturbances on bluff body flow, the measurement of fluctuating forces and the influence of oscillations of the stream. About a third of the 33 papers presented concentrated on theoretical aspects and the majority of these were concerned with the ‘method of discrete vortices’.

Numerical characterization of three-dimensional bluff body shear layer behaviour

2016 ◽  
Vol 799 ◽  
pp. 1-26 ◽  
Author(s):  
Daniel T. Prosser ◽  
Marilyn J. Smith
Keyword(s):  
Shear Layer ◽  
Turbulent Flows ◽  
Bluff Body ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Time Averaging ◽  
Bluff Bodies ◽  
Face Shape

Three-dimensional bluff body aerodynamics are pertinent across a broad range of engineering disciplines. In three-dimensional bluff body flows, shear layer behaviour has a primary influence on the surface pressure distributions and, therefore, the integrated forces and moments. There currently exists a significant gap in understanding of the flow around canonical three-dimensional bluff bodies such as rectangular prisms and short circular cylinders. High-fidelity numerical experiments using a hybrid turbulence closure that resolves large eddies in separated wakes close this gap and provide new insights into the unsteady behaviour of these bodies. A time-averaging technique that captures the mean shear layer behaviours in these unsteady turbulent flows is developed, and empirical characterizations are developed for important quantities, including the shear layer reattachment distance, the separation bubble pressure, the maximum reattachment pressure, and the stagnation point location. Many of these quantities are found to exhibit a universal behaviour that varies only with the incidence angle and face shape (flat or curved) when an appropriate normalization is applied.

The wakes of cylindrical bluff bodies at low Reynolds number

1978 ◽  
Vol 288 (1354) ◽  
pp. 351-382 ◽  
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
The Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Near Wake ◽  
Cross Sectional ◽  
Molecular Diffusivity ◽  
Splitter Plates ◽  
Low Reynolds

Experiments on the near wake of a cylinder will be discribed in an attempt to present a coherent picture of the events encountered as the Reynolds number increases from small values up to values of a few thousand. Much work on this subject has already been done, but there are gaps in our description of these flows as well as more fundamental deficiencies in our understanding of them. The subject has been reviewed several times and most recently by Berger & Wille (1972) whose paper covers much of the ground that will be discussed again here. The present work may be regarded as built upon this latest review. I remember with gratitude many helpful discussions with the late Rudolph Wille who contributed so much to this subject. The investigation has concentrated on circular cylinders, but the wakes of bluff cylinders of different cross sectional shapes have also been observed. Bluff cylinders in general are considered in §§4 and 5, together with the effect of splitter plates on circular cylinders in §9. The experiments concern, almost exclusively, flow visualization of the wakes by means of dye washed from the bodies. The patterns of dye observed are, therefore, filament line representations of the flow leaving the separation lines on the body. It must be stressed that the dye does not make visible the vorticity bearing fluid because at low Reynolds number, vorticity diffuses considerably more rapidly than does dye. The ratio of the molecular diffusivity of momentum to that of mass of dye is of the order of 100.

scholarly journals The wake of two side-by-side square cylinders

2011 ◽  
Vol 669 ◽  
pp. 432-471 ◽  
Author(s):  
Md MAHBUB ALAM ◽  
Y. ZHOU ◽  
X. W. WANG
Keyword(s):  
Flow Separation ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Recirculation Bubble ◽  
Vortex Interactions ◽  
Square Cylinders ◽  
Gap Flow ◽  
Spacing Ratio ◽  
Multiple Structures ◽  
Particle Imaging

Aerodynamic interference between two cylinders involves most of the generic flow features associated with multiple structures, thus providing an excellent model for gaining physical insight into the wake of multiple cylindrical structures. This work aims to provide an experimental systematic study of the flow behind two side-by-side square cylinders. The square cylinder is a representative model for bluff bodies with sharp corners, characterized by a fixed flow separation point, which are distinct from those of continuous curvature with oscillating separation points, typically represented by the circular cylinder. Experiments were performed at a Reynolds number Re of 4.7 × 104 and a cylinder centre-to-centre spacing ratio T/d (d is the cylinder height) of 1.02–6.00. The flow was measured using different techniques, including hot wires, load cell, particle imaging velocimetry and laser-induced fluorescence flow visualization. Four distinct flow regimes and their corresponding T/d ranges are identified for the first time on the basis of the flow structure and the Strouhal number. Physical aspects in each regime, such as interference between shear layers, gap flow deflection and changeover, multiple flow modes, entrainment, recirculation bubble, vortex interactions and formation lengths, are investigated in detail and are connected to the characteristics of the time-averaged and fluctuating fluid forces. The flow displays a marked difference in many facets from that behind two side-by-side circular cylinders, which is linked to their distinct flow separation natures. A crucial role played by the gap flow and its passage geometry in contributing to the observed difference is also unveiled.

Effects of an Underbody Device on the Characteristics of a Trailer Truck Wake Region

2018 ◽  
Author(s):  
M. Ibrahim ◽  
M. Agelin-Chaab
Keyword(s):  
Drag Coefficient ◽  
Flow Separation ◽  
Bluff Body ◽  
Aerodynamic Drag ◽  
Pressure Fluctuations ◽  
Industrial Applications ◽  
Bluff Bodies ◽  
Wake Region ◽  
Ansys Fluent ◽  
Recirculating Flow

The aerodynamics of bluff bodies and flow separation are encountered in many industrial applications. Flow separation causes significant pressure fluctuations that can yield undesirable effects such as vibration, noise, and drag. It is well-known that at highway speeds, over 50% of the fuel is used by a road vehicle to overcome aerodynamic drag. Due to these reasons, bluff body aerodynamics has been the subject of intensive research interests for many decades. In this paper, a new concept of an underbody aerodynamic device is used to modify the turbulent wake region of a bluff body. In particular, the underbody device was designed in order to allow for the recirculating flow to reattach and exit the underside of the bluff body while increasing the average speed of the flow and preventing side winds from disturbing the flow. This significantly reduces the underbody recirculation zone, which is a major source of drag. In addition, this ensures that the flow exits with minimum turbulence to reduce the size of the bluff body’s wake. The studies were conducted using the RANS based turbulence model, k-ω SST in ANSYS Fluent. A width-based Reynolds number of 1.1 × 106 was used to conduct the simulations in order to validate the baseline model with NASA’s wind tunnel data; which include the surface pressure coefficients and a drag coefficient. The paper focuses on the changes in the model’s wake that were introduced due to the device and their influence on the underside flow. The results showed that the device significantly reduced the recirculation at the underside of the bluff body. This was found to increase the coefficient of pressure at the base of the model, which reduced the size of the wake. These changes in the flow field resulted in an overall drag coefficient reduction of 4.1%.

Designing a High Fidelity Wake Simulator for Research Using Linear Cascades

2009 ◽  
Author(s):  
Jonathon Pluim ◽  
Curtis Memory ◽  
Jeffrey Bons ◽  
Jen-Ping Chen
Keyword(s):  
Turbine Blade ◽  
Cross Sections ◽  
Bluff Body ◽  
Axial Direction ◽  
Low Pressure ◽  
Shear Stresses ◽  
Bluff Bodies ◽  
High Lift ◽  
Low Pressure Turbine ◽  
Experimental Findings

Owing to the extensive use of wake generators in the study of turbine and compressor airfoils in linear cascades, a study was undertaken to determine the most accurate model for the wakes generated by upstream blade rows. Velocity (PIV) measurements were taken to compare wake properties of several bluff bodies with different cross sections to the wake of an ultra high lift low pressure turbine profile. These measurements were taken at two Reynolds numbers, a low and a high one to simulate a separated and attached wake, respectively, for both the blade and two of the shape configurations. The L1A turbine blade profile was determined to shed a wake typical of high lift turbine blade profiles. It is shown that the wake of the turbine blade is highly dependent on Reynolds number. In order to make an appropriate comparison, all bluff body data were extracted along a plane parallel to the equivalent inlet plane of a rotor stage in the stationary frame of reference. It was found that no single rod shape matched all of the blade wake characteristics. From among the shapes used in this study, a 30° isosceles wedge placed 6 diameters upstream of the cascade inlet in the axial direction and skewed 15° from the rod relative flow was found to yield the closest match for the low Re case due to the asymmetry in the velocity and Reynolds shear stresses in this wake compared with the wake of the low pressure turbine blade. The same configuration placed 10 diameters upstream yielded the best comparison to a higher Re, more attached L1A wake. Large Eddy Simulations of various shapes largely corroborate the experimental findings.

The Form Drag of Three-Dimensional Bluff Bodies Immersed in Turbulent Boundary Layers

1982 ◽  
Vol 104 (3) ◽  
pp. 326-333 ◽  
Author(s):  
H. Sakamoto ◽  
M. Moriya ◽  
S. Taniguchi ◽  
M. Arie
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Boundary Layers ◽  
Bluff Body ◽  
Three Dimensional ◽  
Turbulent Boundary Layers ◽  
Bluff Bodies ◽  
Smooth Wall ◽  
Form Drag ◽  
Pressure Distributions

Measurements of the pressure distributions on the three-dimensional bluff bodies are correlated with the characteristics of the smooth-wall turbulent boundary layers in which the bodies are immersed. The bluff bodies selected for measurement were a cube and a vertical circular cylinder which can be considered as typical examples of three-dimensional bluff bodies. Experimental data were collected to investigate the effects of (1) the variation of the height of bluff bodies h, (2) the characteristics of the smooth-wall boundary layers in which they are immersed, on the form drag acting on the three-dimensional bluff bodies. For flow with zero-pressure gradient, the form drag coefficients of the cube and the vertical circular cylinder defined by CDτ=D/(1/2ρuτ2h2) are found to be expressed as a power-law function of huτ/ν in the range of h/δ less than about 1.0, where D is the form drag, uτ the shear velocity, ν the kinematic viscosity and δ the thickness of the undisturbed boundary layer at the location of the bluff bodies. For h/δ>1.0, the drag coefficients are independent of the parameter uτ/U0, being uniquely related to h/δ. Further, the pressure distributions along the front centerline of each bluff body can be expressed by a single curve irrespective of both the height of the bluff body and the boundary layer characteristics and show a good agreement with the dynamic pressure in an undisturbed boundary layer at the location of the bluff bodies in the range of about 0.2<y/h<0.7, where y is the distance from the wall.

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