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.

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.

Partially Premixed Flame Stabilization in the Presence of a Combined Swirl and Bluff Body Influenced Flowfield: An Experimental Investigation

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Rajesh Sadanandan ◽  
Aritra Chakraborty ◽  
Vinoth Kumar Arumugam ◽  
Satyanarayanan R. Chakravarthy
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Reverse Flow ◽  
Fluid Dynamic ◽  
Thermal Power ◽  
Swirl Flow ◽  
Flame Stabilization ◽  
Dynamic Strain ◽  
Low Velocity ◽  
Divergent Flow

Abstract Optical and laser diagnostic measurements in a nonpremixed model gas turbine (GT) burner have been performed to investigate the effect of an increase in thermal power on the flame stabilization. The model GT burner has a large bluff body base with an annular swirl region, leading to a convergent-divergent flow field at the burner exit. Under the investigated conditions, the flame stabilizes predominantly in the diverging section characterized by the swirl flow with a central recirculation zone. With increasing thermal power, the reverse flow of hot burned gases is strengthened, with the hydroxyl radical (OH) planar laser induced fluorescence (PLIF) images indicating an increase in the temperature of the burned gases. The preferred flame stabilization location coincides with the inner shear layer between the reactant inflow and the reverse flow of hot burned gases. At high thermal power, the flame seems to stabilize in regions of high fluid dynamic strain rate, highlighting the influence of the reverse flowing burned gases in the evolution of the flammable mixture upstream. However, simultaneous and time-resolved measurements of the flow-field and scalar field are needed for direct quantification of this. The results are in agreement with the flame stabilization theories based on partial fuel-air mixing and streamline divergence. The flow is seen to decelerate upstream of the flame front and the flame stabilizes in a region of low velocity, created as a result of heat release diverging the streamlines ahead of it.

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

Transition of a Steady to a Periodically Unsteady Flow for Various Jet Widths of a Combined Wall Jet and Offset Jet

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Tanmoy Mondal ◽  
Manab Kumar Das ◽  
Abhijit Guha
Keyword(s):  
Flow Field ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Progressive Increase ◽  
Separation Distance ◽  
Wall Jet ◽  
Two Dimensional ◽  
Two Jets ◽  
Offset Jet

In the present paper, a dual jet consisting of a wall jet and an offset jet has been numerically simulated using two-dimensional unsteady Reynolds-Averaged Navier–Stokes (RANS) equations to examine the effects of jet width (w) variation on the near flow field region. The Reynolds number based on the separation distance between the two jets (d) has been considered to be Re = 10,000. According to the computational results, three distinct flow regimes have been identified as a function of w/d. For w/d ≤ 0.5, the flow field remains to be always steady with two counter-rotating stable vortices in between the two jets. On the contrary, within the range of 0.6 ≤ w/d < 1.6, the flow field reveals a periodic vortex shedding phenomenon similar to what would be observed in the wake of a two-dimensional bluff body. In this flow regime, the Strouhal number of vortex shedding frequency decreases monotonically with the progressive increase in the jet width. For w/d ≥ 1.6, the periodic vortex shedding is still evident, but the Strouhal number becomes insensitive to the variation of jet width.

scholarly journals Experimental investigation of distance between v-gutters on flame stabilization and NOx emissions

2019 ◽  
Vol 23 (5 Part B) ◽  
pp. 2971-2981 ◽  
Author(s):  
Dias Umyshev ◽  
Abay Dostiyarov ◽  
Andrey Kibarin ◽  
Galya Tyutebayeva ◽  
Gaziza Katranova ◽  
...  
Keyword(s):  
Bluff Body ◽  
Flame Stabilization ◽  
Temperature Fields ◽  
Flame Stability ◽  
Bluff Bodies ◽  
Nox Emissions ◽  
Exhaust Gas ◽  
Gas Temperature ◽  
Inlet Velocity ◽  
Exhaust Gas Temperature

Blow-off performance and NOx emissions of the propane and air mixture in a rectangular combustion chamber with bluff bodies were investigated experimentally and numerically. The effects of distance between bluff bodies on NOx emissions, the blow-off limit, and exhaust gas temperature were examined. It was observed that NOx emissions are highly dependent on distance between V-gutters. The re-circulation zone behind the bluff body expands in width based on the decrease of distance between V-gutters, and expands in length with the increase of inlet velocity. The temperature fields behind the bluff body show a similar change, the temperature behind the bluff body reaches its highest when the distance between V-gutters reaches 20 mm, meaning it has better flame stability. The blow-off limit is significantly improved with the decrease of distance between V-gutters. The blow-off limit is greatly improved by reducing the distance between the V-gutters. Maximum blow-off limit of 0.11 is reached in the case of 20 mm, compared with 0.16 at 50 mm at a speed of 10 m/s.

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%.

Drag Reduction of a Simple Bluff Body by Changing the Rear End and Use the Ground Effect

2009 ◽  
Author(s):  
Jesper Marklund ◽  
Lennart Lofdahl
Keyword(s):  
Flow Field ◽  
Drag Reduction ◽  
Bluff Body ◽  
Ground Effect ◽  
Model Testing ◽  
Scale Model ◽  
Bluff Bodies ◽  
Ground Vehicle ◽  
University Of Technology ◽  
Force Reduction

The flow field around bluff bodies constitutes a classic area within fluid dynamics and has been the topic for much research through the years. However, in the use for road vehicles with the effect of the ground, the behavior is changed very much from more classical aviation usage. In this paper we are investigating the drag force reduction on a vehicle like simplified model with rear open diffuser when stationary ground simulation is considered. The objective with this work was to study the rear end of a bluff body and optimize it for drag with ground vehicle like boundaries. Here the testing contains two common body variants, square back, boat tailed/fastback in generic forms. Scale model testing combined with simulations is used to explain behavior and flow field. The model testing is performed in the L2 scale model wind tunnel at Chalmers University of Technology in Gothenburg, Sweden. Simulations are done with the commercial CFD code Fluent. A diffuser on a car is normally used to create down force but here it is tested to see if the energy in the flow can be used to optimize reduction of drag. One part of the study is to show the potential in optimizing the rear end underbody for drag, by varying the diffuser angle. The results show a potential in drag reduction by using a diffuser and varying effect depending on other rear end geometries.

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.

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