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.

scholarly journals Influence of Diffuser Angle on a Bluff Body in Ground Effect

2003 ◽  
Vol 125 (2) ◽  
pp. 332-338 ◽  
Author(s):  
Andreas Ruhrmann ◽  
Xin Zhang
Keyword(s):  
Flow Field ◽  
Flow Separation ◽  
Bluff Body ◽  
Vortex Breakdown ◽  
Three Dimensional ◽  
Ground Effect ◽  
Surface Flow ◽  
Ride Height ◽  
Force Reduction ◽  
Underbody Diffuser

The forces and pressures on a generic bluff body in ground effect were investigated. The bluff-body model was equipped with interchangeable underbody diffuser ramps and side plates. Five different diffuser angles were tested: 5, 10, 15, 17, and 20 deg to the horizontal. The experiments were undertaken in a low-speed wind tunnel equipped with a moving ground. Load cells, pressure taps, and surface flow visualization were the techniques used to evaluate the flow field. The flow field is characterized by vortex flow and three-dimensional flow separation. A region of hysteresis was found for the 15, 17, and 20 deg diffusers. As the ride height is varied, five different flow types can be identified with three subtypes within the region of hysteresis. The force reduction phenomenon was found to be caused by both vortex breakdown and flow separation.

scholarly journals Bionic shape design of electric locomotive and aerodynamic drag reduction

2018 ◽  
Vol 4 (48) ◽  
pp. 99-109
Author(s):  
Zhenfeng WU ◽  
Yanzhong HUO ◽  
Wangcai DING ◽  
Zihao XIE
Keyword(s):  
Flow Field ◽  
Drag Reduction ◽  
Bluff Body ◽  
Aerodynamic Drag ◽  
Geometric Characteristic ◽  
Shape Design ◽  
Shape Optimisation ◽  
Electric Locomotive ◽  
Geometric Models ◽  
Characteristic Lines

Bionics has been widely used in many fields. Previous studies on the application of bionics in locomotives and vehicles mainly focused on shape optimisation of high-speed trains, but the research on bionic shape design in the electric locomotive field is rare. This study investigated a design method for streamlined electric locomotives according to the principles of bionics. The crocodiles were chosen as the bionic object because of their powerful and streamlined head shape. Firstly, geometric characteristic lines were extracted from the head of a crocodile by analysing the head features. Secondly, according to the actual size requirements of the electric locomotive head, a free-hand sketch of the bionic electric locomotive head was completed by adjusting the position and scale of the geometric characteristic lines. Finally, the non-uniform rational B-splines method was used to establish a 3D digital model of the crocodile bionic electric locomotive, and the main and auxiliary control lines were created. To verify the drag reduction effect of the crocodile bionic electric locomotive, numerical simulations of aerodynamic drag were performed for the crocodile bionic and bluff body electric locomotives at different speeds in open air by using the CFD software, ANSYS FLUENT16.0. The geometric models of crocodile bionic and bluff body electric locomotives were both marshalled with three cars, namely, locomotive + middle car + locomotive, and the size of the two geometric models was uniform. Dimensions and grids of the flow field were defined. And then, according to the principle of motion relativity, boundary conditions of flow field were defined. The results indicated that the crocodile bionic electric locomotive demonstrated a good aerodynamic performance. At the six sampling speeds in the range of 40–240 km/h, the aerodynamic drag coefficient of the crocodile bionic electric locomotive decreased by 7.7% on the average compared with that of the bluff body electric locomotive.

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.

Drag Reduction of Bluff Bodies by Surface Control Based on a Force Theory

2007 ◽  
Author(s):  
Shih-Hao Yang ◽  
Chien C. Chang ◽  
Chin-Chou Chu ◽  
Shi-Hua Liao ◽  
R. L. Chern
Keyword(s):  
Circular Cylinder ◽  
Drag Reduction ◽  
Bluff Body ◽  
The Body ◽  
Bluff Bodies ◽  
Rational Basis ◽  
Surface Control

In the present study, we show how drag reduction of a bluff body can be achieved on a rational basis of a force theory. The force theory indicates where is the best location to apply the surface control to minimize the drag on the body. In particular, the method of drag reduction is illustrated for flow around a circular cylinder. It is shown that drag reduction for the circular cylinder can be as efficient as 46.5%.

scholarly journals Research on Control Technology of Jet and Rectifying Cone Combined Flow Field

2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Hongqing Lv ◽  
Lei Xu ◽  
Zhenqing Wang ◽  
Xiaobin Zhang
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Drag Reduction ◽  
High Speed ◽  
Bluff Body ◽  
Hot Spot ◽  
Pressure Ratio ◽  
Main Flow ◽  
Control Technology ◽  
Reduction Effect

As an active flow field control technology, reverse jet and rectifier cone can significantly affect the flow field around the high-speed aircraft and reduce the drag and heat of high-speed aircraft to a certain extent. In this paper, the CFD numerical method is used to simulate and analyze the flow around the bluff body front rectifier cone and the reverse jet interference flow field. Further considering the combination of the two, the flow field structure around the bluff body under the combination of rectifying cone and reverse jet flow was simulated. Research shows, for the flow field of a single reverse jet, the pressure ratio of the reverse jet to the main flow has a significant effect on the drag reduction performance. With the change of the pressure ratio of the jet to the main flow, two modes of long jet and short jet will appear. The structure of the short jet modal flow field is relatively stable. However, with the increase of attack angle, the shear layer of free flow will attach to the shock wave and form hot spot, which is a great threat to high-speed aircraft. When the rectifier cone and the reverse jet are combined, within a certain angle of attack, the wall will not form a reattachment shock wave. The area behind the bow shock and in front of the aircraft head is a free-state zone, which has a good cooling effect on the aircraft head. At the same time, the static pressure on the wall is reduced, which has a very good drag reduction effect.

Computational and Neuro-Fuzzy Study of the Effect of Small Objects on the Flow and Thermal Fields of Bluff Bodies

2006 ◽  
Author(s):  
Ahmed F. Abdel Gawad
Keyword(s):  
Drag Reduction ◽  
Bluff Body ◽  
Three Dimensional ◽  
The Body ◽  
Bluff Bodies ◽  
Small Object ◽  
Two Dimensional ◽  
Neuro Fuzzy ◽  
Body Cooling ◽  
Two Dimensional Flows

The aim of the present study is to find computationally the optimum parameters that affect the drag reduction of bluff bodies using a small object (obstacle). These parameters include the size of the obstacle as well as the gap between the obstacle and the bluff body. Two- and three-dimensional bodies were investigated in turbulent flow fields. The research was focused on the cases of the rectangular-section obstacle. Four values of the obstacle size were studied, namely: 4%, 10%, 35%, and 100% of the size of the bluff body. The effect of the obstacle on the thermal field of the two-dimensional body was also studied. Comparisons were carried out with the available experimental measurements. A proposed neuro-fuzzy approach was used to predict the drag reduction of the entire system. Results showed that system drag reductions up to 62% (two-dimensional flows) and 48% (three-dimensional flows) can be obtained. Also, enhancement of the body cooling up to 75% (two-dimensional flows) may be achieved. Generally, useful comments and suggestions are stated.

Nature-inspired solutions to bluff body aerodynamic problems: A review

2021 ◽  
Vol 15 (2) ◽  
pp. 8095-8140
Author(s):  
Naseeb Ahmed Siddiqui ◽  
Martin Agelin-Chaab
Keyword(s):  
Drag Reduction ◽  
Body Shape ◽  
Bluff Body ◽  
Bluff Bodies ◽  
Flow Modification ◽  
Fast Running ◽  
Passive Devices ◽  
Flow Control Devices ◽  
Control Devices ◽  
Bluff Body Flow

This review investigates the nature-inspired techniques for the optimization of the aerodynamic forces on bluff bodies. To provide a rich understanding of these nature-inspired phenomena, three distinct zones of the species fishes (nektons), birds (avians) and the fast running land animals are considered. This allows contextualizing different capabilities of the species in different environmental necessities. The review follows a trend in which drag reduction capabilities of individual parts of these species, including body shape & size, tails, fins, surface structure, wings, and wingtips, have been explored in detail. By focusing on specific parts, the review examined the methods and physics involved, which provides space to narrate the development of ideas and our current understanding of the nature-inspired drag reduction and their application to bluff body aerodynamics. Consequently, nature-inspired promising areas for future endeavor related to the bluff body has been discussed in detail. It was found that, though, aerospace field has found several bird inspired application but the bluff body flow modification have only few. Similar is the case with fishes and land animals which have not been explored yet for aerodynamic use on the bluff bodies. The crucial importance of passive devices are also highlighted along with the review of their application on the bluff bodies inspired by nature. Furthermore, several of nature-inspired techniques are proposed and compared to facilitate the research in this direction. It provides a fundamental method  to develop nature-inspired flow control devices for the bluff bodies.

The Force and Pressure of a Diffuser-Equipped Bluff Body in Ground Effect

2000 ◽  
Vol 123 (1) ◽  
pp. 105-111 ◽  
Author(s):  
Andrea E. Senior ◽  
Xin Zhang
Keyword(s):  
Flow Separation ◽  
Bluff Body ◽  
Three Dimensional ◽  
Ground Effect ◽  
Surface Flow ◽  
Force Balance ◽  
Diffuser Flow ◽  
Subsequent Loss ◽  
Force Reduction ◽  
Low Speed Wind Tunnel

The force and pressure behavior of a generic diffuser in ground effect were investigated. The diffuser model is a bluff body with a rear diffuser at 17 deg to the horizontal, and side-plates. Measurements were conducted in a low speed wind tunnel equipped with a moving ground facility. Techniques employed were force balance, pressure taps, and surface flow visualization. The diffuser flow in ground effect was characterized by vortex flow and three-dimensional flow separation. Four types of force behavior were observed: (a) down-force enhancement at high ride heights characterized by an attached symmetric diffuser flow, (b) maximum down-force at moderate ride heights characterized by a symmetric diffuser flow and separation on the diffuser ramp surface, (c) down-force reduction at low ride heights characterized by an asymmetric diffuser flow and flow separation, and (d) low down-force at very low ride heights, also characterized by an asymmetric diffuser flow and flow separation. The down-force reduction near the ground is attributed to flow separation at the diffuser inlet and subsequent loss of suction in the first half of the diffuser.

Effect of Body Aspect Ratio and Tank Size on the Hydrodynamics of a Rotating Bluff Body During the Initial Spin-Up Period

2001 ◽  
Vol 123 (3) ◽  
pp. 649-655
Author(s):  
D. Maynes ◽  
M. Butcher
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Bluff Body ◽  
Initial Period ◽  
The Body ◽  
Bluff Bodies ◽  
Physical Description ◽  
Time Scaling ◽  
Rectangular Cylinders ◽  
Tank Geometry

Hydrodynamic torque measurements on rotating bluff bodies are presented for 32 different bodies and three different sized tanks for Reynolds numbers in the range 104-105. The present results focus on the initial period, build-up regime, where the torque remains constant before the tank walls have impacted the flow field in the vicinity of the body. The results show that during the build-up regime, the torque coefficient is a function only of the aspect ratio and increases to a maximum at an aspect ratio near unity, followed by a decrease for further increases in the aspect ratio. This behavior is similar to a uniform flow past rectangular cylinders of varied width and a physical description for the observed variation is proposed. A nondimensional time scale describing the time until the tank geometry impacts the flow field near the body is also presented. This time scaling is based on all of the measurements and appears to be quite general, predicting the spin-up time for bodies differing in volume by three orders of magnitude and tanks differing by two orders of magnitude.

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