EFFECT OF REAR END TAPER ON DRAG FOR

EFFECT OF REAR END TAPER ON DRAG FOR A BLUFF BODY : 

EFFECT OF REAR END TAPER ON DRAG FOR A BLUFF BODY THARANGA JAYATHUNGA SID: 3601183

INTRODUCTION : 

INTRODUCTION Aerodynamics is the analysis regarding the air flow around a body. Aerodynamic drag force has a direct effect on the fuel consumption and maximum speed. Drag coefficient (C D ) is one of the governing factor on the drag force and depends on the body shape.

INTRODUCTION: 

INTRODUCTION Body shape of a vehicle is aerodynamically bluff. Air flow separation is occurring at the rear end of the vehicle. There is a developed adverse pressure gradient at the back. This is the cause for the pressure drag.

INTRODUCTION: 

INTRODUCTION Degree of taper at the rear end affect the drag force.

INTRODUCTION: 

INTRODUCTION Rear and taper and boat tailing are drag reduction methods.

RESEARCH TOPIC: 

RESEARCH TOPIC Aim of the research is to generate an understanding of interaction of side boat tailing and end taper on the drag of a bluff body.

METHODOLOGY : 

METHODOLOGY CFD simulations was performed and Star CCM+ software Version 6.04.014. Ahmed model and Windsor model tested for validation. Windsor models is tested for side boat tailing and end taper interaction. Detail optimization of Windsor model. Tested for theoretical best values for end taper and side boat tailing angles.

METHODOLOGY: 

METHODOLOGY Tapered length of the model. Length ratio= Length of the tapered/Total length of the model Ratio used here is 0.2 (209mm). CAD modeling. CATIA version 5R20 is used for the CAD modeling. AhmedCAD.jpg Windsor CAD.jpg

METHODOLOGY: 

METHODOLOGY Star CCM+ modeling. Number of cells is around 1 million for every cases that are tested. Number of faces for each case kept around 300000. Mesh type is polyhedral. Prism layer mesh is used for the boundary layers and the thickness is 10mm. K-ε model is used for the turbulence modelling. Number of iterations limit to 1000. Domainortho.jpg

METHODOLOGY: 

METHODOLOGY Following table is showing all the combinations of side boat tailing and end taper, that are examined.

RESULTS: 

RESULTS C D value obtained for the Ahmed model is 0.25. AhmedCAD.jpg C D value obtained for the Windsor model is 0.295. Windsor model is in the square back configuration.

RESULTS: 

RESULTS ∆ C D for each configuration of the Windsor model.

RESULTS: 

RESULTS Largest value for ∆C D obtained when the end taper angle 8 0 and side boat tail angle 8 0 (18% reduction) . S8T8_Vector Scene 1.jpg Wakeregion.jpg Windsor_Vector Scene 1.jpg S8T8_Geometry Scene 6.jpg stmlin2 - Copy.avi

RESULTS: 

RESULTS Wake region is narrowed due to the geometry changes. Vortices in the near wake region are comparatively small. Pressure loss has been reduced by around 22% due to the changes. There is a noticeable change in the free stagnation point. Comparatively more orderly flow is obtained in here. Flow coming from the under the body has different characteristics in here .

RESULTS: 

RESULTS Figure shows the trend of variation of ∆C D With Side boat tail angle for typical end taper angle.

RESULTS: 

RESULTS Starting from 0 0 -8 0 ∆C D is increased and after 8 0 ∆C D getting reduced up to 20 0 . strmlineS8T20.jpg When the Slant angle increases strength in the 3D trailing vortices are becoming stronger. In the far wake region there are two separate flows.

DETAIL OPTIMIZATION: 

DETAIL OPTIMIZATION All the edges as showing in the following figure is rounded and ∆C D value obtained is 92. DEtailopt1.jpg Detailopt CP.jpg

RESULTS: 

RESULTS For the tapered length ratio 0.2 (209mm), end taper angle 12.5 0 and side boat tail angle 10 0 obtained ∆C D value is 49. When the tapered length change to 222mm ∆C D obtained is 54.

CONCLUSIONS: 

CONCLUSIONS C D value for the (square back) Windsor model is 0.295. Largest ∆C D is obtained for the side boat tail angle 8 0 and end taper angle 8 0 . ∆C D value is 53. Around 22% base pressure increase compare with square back. 18% decrease in C D. Theoretical optimum values for side boat tail end taper given ∆C D value is 52. Aspect ratios of the boat tail and end taper have an effect on drag reduction.

CONCLUSIONS: 

CONCLUSIONS Drag coefficient is influenced by after body rounding. After body rounding at the side boat tail and end taper 8 0 configuration gives 31% reduction in drag coefficient . Aspect ratios of the boat tail and end taper have an effect on drag reduction. Drag coefficient is influenced by after body rounding. Body rounding at the side boat tail and end taper 8 0 configuration gives 31% reduction in drag coefficient.

THANK YOU: 

THANK YOU