scholarly journals On the recirculating flow of three-dimensional asymmetric bluff bodies

2020 ◽  
Vol 61 (12) ◽  
Author(s):  
Antoine Legeai ◽  
Olivier Cadot
Keyword(s):  
Bluff Body ◽  
Reference Model ◽  
Three Dimensional ◽  
Bluff Bodies ◽  
Recirculating Flow ◽  
Bistable Dynamics ◽  
Geometrical Variation ◽  
Static Instability ◽  
State Selection

Abstract The paper investigates the role of geometrical asymmetric modifications of a rectangular flat-backed body on the properties of the recirculating flow at a Reynolds number $$Re=1.8\times 10^5$$ R e = 1.8 × 10 5 . The reference model has two reflectional symmetries denoted $$s_y$$ s y and $$s_z$$ s z in both spanwise directions. The flow is subjected to the static instability that leads to two mirrored wake states breaking the symmetry $$s_y$$ s y . Two families of geometrical variation of the fore-body and after-body are studied, each breaking one of the reflectional symmetries of the reference model. Geometrical modifications that preserve $$s_y$$ s y evidence possibilities of bistable dynamics suppression although the static instability persists. Geometrical modifications that do not preserve $$s_y$$ s y produces a large unbalance of both wake states in accordance to recent observations on real cars (Bonnavion et al. in J Wind Eng Ind Aerodyn 184:77–89, 2019). Results offer perspectives for potential drag reduction induced by appropriate coupling of bluff body geometry and wake state selection. Graphic abstract

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

1994 ◽  
Author(s):  
Z. Gu ◽  
M. A. R. Sharif
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Flame Stabilization ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Combustion Chambers ◽  
Recirculating Flow ◽  
Conservative Form ◽  
Curvilinear Grid ◽  
Predictor Corrector

Abstract The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

scholarly journals Bluff body drag manipulation using pulsed jets and Coanda effect

2016 ◽  
Vol 805 ◽  
pp. 422-459 ◽  
Author(s):  
Diogo Barros ◽  
Jacques Borée ◽  
Bernd R. Noack ◽  
Andreas Spohn ◽  
Tony Ruiz
Keyword(s):  
Bluff Body ◽  
Three Dimensional ◽  
Base Pressure ◽  
Coanda Effect ◽  
Wake Time ◽  
Recirculating Flow ◽  
Flow Deviation ◽  
Coandǎ Effect ◽  
And Control ◽  
The Impact

The impact of fluidic actuation on the wake and drag of a three-dimensional blunt body is investigated experimentally. Jets blowing tangentially to the main flow force the wake with variable frequency and amplitude. Depending on the forcing conditions, two flow regimes can be distinguished. First, in the case of broadband actuation with frequencies comprising the natural wake time scale, the convection of the jet structures enhances wake entrainment, shortens the length of the recirculating flow and increases drag. Secondly, at higher actuation frequencies, shear-layer deviation leads to fluidic boat tailing of the wake. It additionally lowers its turbulent kinetic energy thus reducing the entrainment of momentum towards the recirculating flow. The combination of both mechanisms produces a rise in the base pressure and reduces the drag of the model. Both actuation regimes are characterized by complementary velocity, pressure and drag measurements at several upstream conditions and control parameters. By adding curved surfaces to deviate the jets by the Coanda effect, periodic actuation is reinforced and drag reductions of approximately 20 % are achieved. The unsteady Coanda blowing not only intensifies the flow deviation and the base pressure recovery but also preserves the unsteady high-frequency forcing effect on the turbulent field. The present results encourage further development of fluidic control to improve the aerodynamics of road vehicles and provide a complementary insight into the relation between wake dynamics and drag.

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.

Large-scale vortex structures in turbulent wakes behind bluff bodies. Part 2. Far-wake structures

1987 ◽  
Vol 174 ◽  
pp. 271-298 ◽  
Author(s):  
T. R. Steiner ◽  
A. E. Perry
Keyword(s):  
Large Scale ◽  
Bluff Body ◽  
Three Dimensional ◽  
Bluff Bodies ◽  
Mean Velocity ◽  
Wake Flows ◽  
Wake Patterns ◽  
Large Scale Vortex ◽  
High Reynolds ◽  
Far Wake

An investigation of a selection of high-Reynolds-number bluff-body flows was conducted. Here in Part 2 phase-averaged velocity-field results will be presented for several far-wake flows generated by nominally two-dimensional and three-dimensional bodies. In these far-wake flows the shed vortices have approached a nearly constant convection velocity. Some mean velocity and phase-averaged and global Reynoldsstress measurements are also presented. The turbulent wake of a lift-producing three-dimensional body has been examined. Also included are the phase-averaged wake patterns behind a flapping flag and a windmill. The topological structure of these patterns is discussed and a preliminary classification of wake patterns is presented.

scholarly journals An Observational Study of Vortex Spacing in Island Wake Vortex Streets

2006 ◽  
Vol 134 (8) ◽  
pp. 2285-2294 ◽  
Author(s):  
George S. Young ◽  
Jonathan Zawislak
Keyword(s):  
Aspect Ratio ◽  
Bluff Body ◽  
Three Dimensional ◽  
Width Ratio ◽  
Bluff Bodies ◽  
Von Karman ◽  
Vortex Streets ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Island Wake ◽  
Von Kármán

Abstract Vortex streets are a frequent occurrence in stratocumulus-topped flow downwind of mountainous islands. Theoretical studies dating back to von Kármán, supported by laboratory and numerical studies, have yielded similarity theories for the size and spacing of these vortices behind bluff bodies. Despite dynamical differences between such two-dimensional flows and the three-dimensional flow past isolated islands, satellite case studies suggest these geometric similarities may also hold for the atmospheric case. In this study, two of the resulting dimensionless ratios are measured using satellite imagery. One is the aspect ratio between cross-street and along-street spacing of the vortices. The second is the ratio of the cross-street spacing to the crosswind width of the island. A 30-image sample from the Aqua and Terra Moderate Resolution Imaging Spectroradiometer satellites is analyzed to obtain these ratios. The resulting set of values for the two dimensionless ratios is tested against the values found in bluff body studies. The aspect ratio is tested against the value of 0.28 resulting from von Kármán’s inviscid theory, and the dimensionless width ratio is tested against the value of 1.2 from Tyler’s laboratory study of flow around a bluff body. It is found that atmospheric vortex streets do indeed follow the geometric similarity theories, but with different values for the two ratios than those predicted by von Kármán and Tyler. The aspect ratio is larger than predicted as is the dimensionless width ratio. Both differences are consistent with the turbulent diffusion of vorticity in the wake of the island. The vortex streets more closely follow inviscid theory close to the island, with vortex expansion taking place a few vortex diameters downwind of the island.

scholarly journals The Simultaneous Role of an Alveolus as Flow Mixer and Flow Feeder for the Deposition of Inhaled Submicron Particles

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
F. S. Henry ◽  
S. Haber ◽  
D. Haberthür ◽  
N. Filipovic ◽  
D. Milasinovic ◽  
...  
Keyword(s):  
Particle Deposition ◽  
Three Dimensional ◽  
Submicron Particles ◽  
Flow Structures ◽  
Central Channel ◽  
Recirculating Flow ◽  
Convective Mixing ◽  
Flow Mixing ◽  
Spiral Structures

In an effort to understand the fate of inhaled submicron particles in the small sacs, or alveoli, comprising the gas-exchange region of the lung, we calculated the flow in three-dimensional (3D) rhythmically expanding models of alveolated ducts. Since convection toward the alveolar walls is a precursor to particle deposition, it was the goal of this paper to investigate the streamline maps’ dependence upon alveoli location along the acinar tree. On the alveolar midplane, the recirculating flow pattern exhibited closed streamlines with a stagnation saddle point. Off the midplane we found no closed streamlines but nested, funnel-like, spiral, structures (reminiscent of Russian nesting dolls) that were directed towards the expanding walls in inspiration, and away from the contracting walls in expiration. These nested, funnel-like, structures were surrounded by air that flowed into the cavity from the central channel over inspiration and flowed from the cavity to the central channel over expiration. We also found that fluid particle tracks exhibited similar nested funnel-like spiral structures. We conclude that these unique alveolar flow structures may be of importance in enhancing deposition. In addition, due to inertia, the nested, funnel-like, structures change shape and position slightly during a breathing cycle, resulting in flow mixing. Also, each inspiration feeds a fresh supply of particle-laden air from the central channel to the region surrounding the mixing region. Thus, this combination of flow mixer and flow feeder makes each individual alveolus an effective mixing unit, which is likely to play an important role in determining the overall efficiency of convective mixing in the acinus.

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%.

Aerodynamic behaviour of bodies in the wakes of other bodies

1971 ◽  
Vol 269 (1199) ◽  
pp. 425-437 ◽  
Keyword(s):  
Bluff Body ◽  
Three Dimensional ◽  
Future Research ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Limited Information ◽  
Irrotational Flow ◽  
Two Bodies

Wakes of two-dimensional bluff bodies are described, with emphasis on the properties of the wake which influence the loads on other bodies placed in the wake. The unsteady irrotational flow outside the true wake is included in the discussion. Some limited information on the wakes of three-dimensional bluff bodies is also considered. The interaction between two bodies is subdivided into two categories: (i) when the bodies are close together and the upstream body is influenced by the downstream one and (ii) when the bodies are so far apart that only the downstream body is affected. Experiments are described in which the load on an aerofoil in the wake of a two-dimensional bluff body was measured. The results are presented in the form of an aerodynamic admittance and these experiments are used to illustrate the type of problem associated with the determination of the loads on a bluff body in a wake. Experiments are also described which show the large variation of time-averaged load which can be developed on a body which is part of a closely packed complex of bodies, as the orientation of the complex to the wind is varied. Finally, some ideas for future research are outlined.

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.

The Effect of the Pocket on the Heat Transfer of Endwall With Bluff Body in the Rear Part of Gas Turbine

2017 ◽  
Author(s):  
Jian Liu ◽  
Safeer Hussain ◽  
Lei Wang ◽  
Gongnan Xie ◽  
Bengt Sundén ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Bluff Body ◽  
Guide Vane ◽  
Rectangular Channel ◽  
High Heat ◽  
Bluff Bodies ◽  
Recirculating Flow ◽  
High Heat Transfer ◽  
Rear Part

A pocket cavity is generated at the connection of two parts, such as the transition part between the low pressure turbine (LPT) and outlet guide vane (OGV) in a gas turbine engine. A bluff body, working as a heat transfer enhancement part or supporting strength part, has tremendous engineering applications in turbomachinery. In the present work, the effect of the pocket on the heat transfer of endwall with a bluff body in the rear part of gas turbine is investigated. A simplified triangular pocket cavity is built in a rectangular channel and two bluff bodies, a cylinder or a cuboid is attached downstream on the endwall. The heat transfer and fluid flow on the endwall are investigated experimentally and numerically. Liquid Crystal Thermography (LCT) is employed to measure the heat transfer over the pocket surface with Reynolds number ranging from 87,597, to 218,994. The turbulent flow details are provided by numerically calculations based on the commercial software Fluent 17.0. Based on the results, high heat transfer areas are usually found at the boundary of the pocket cavity and vortex street shedding regions around the bluff body. When a pocket cavity is placed in the upstream of a bluff body, the endwall heat transfer around the bluff body is obviously decreased due to the disturbance by the pocket. There are no recirculating flows in front of the tested cylinder while this is not applicable for the cuboid case. The recirculating flow behind the bluff bodies forms a three-dimensional flow structure rotating in two directions.

Sign in / Sign up

Export Citation Format

Share Document