MSc Project
-
Upload
shreyasr88 -
Category
Technology
-
view
1.728 -
download
1
description
Transcript of MSc Project
CFD Project- Shreyas Ragavan- MSc Advanced Mechanical
Engineering (2010-11)
Aerodynamic Drag Sensitivity Analysis of a Land Speed Record (LSR) Racing Vehicle
Target Speed : 490.346 kmph
(1% more than the current record)
Rolls Royce Viper 522 series Turbojet+
afterburner engine (~5000 lbs thrust)
Half- Vehicle Model (Gambit)Length= 8m Wheel Radius = 0.1 m Jet engine is roughly half the total length
PROJECT BACKGROUND :
• The vehicle is part of the ‘Stay Gold’ Jet Car Project and the objective is to set a new British Land Speed Record
• The average speed over two straight passes of 402 m with acceleration and deceleration zones of 1300 m is taken into account.
• Current Record : 485.49 kmph over a 500m stretch• Target Speed : 490.47 kmph
PROJECT GOALS :
A. To understand external vehicle aerodynamics and flow representation along with the established methods of reducing aerodynamic drag.
B. Explore the methodology and limitations behind applying CFD. Setup a Simulation, investigate parameters like grid independence as well as different turbulence models.
C. Investigate and apply strategic geometric modifications and optimisation techniques of the chosen parameters
APPROACH & SETUPPossible modifications ?
Suitable Domain Size ?
Efficient Mesh distribution over the volume?
VOLUME MESH DISTRIBUTION
PARAMETERS AND BOUNDARY CONDITIONS
1. Pressure Based Solver
2. 2nd Order solutions with assumed smooth wall
3. Turbulence defined : Length scale and Intensity
4. Operating speeds : 136.207 m/s and 100m/s
5. Rotating wheels and moving ground
6. Energy Equation with Mass continuity used for the Jet with its inlet at ambient conditions
Grid improvement- Reduction in Skewness
Difference between coarsest and finest mesh
GRID INDEPENDENCE
1 e+06 1.25 e+06 1.48 e+06 1.56 e+06 1.98 e+060.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.4
0.41
0.42
KE realizable
SST KW
SA
KE- RNG
Turbulence Models Tested
Coeffi
cie
nt
of
Dra
g (
Cd
)
Domain Cell Count
AREAS OF FLOW DISTURBANCE
Regions of Turbulence
APPLYING MESH MORPHING (USING OPTIMAL SOLUTIONS- SCULPTOR)
• Creating an ‘ Arbitary Shape Volume’ (ASD) over the desired area of deformation
• Controlling the mesh Deformation
• Preparing Acceptable mesh files for Fluent
Final ASD
Initial ASD
Illustration of deformation limitation by converting the middle plane into a ‘Super plane’
ASD shown with Mesh.Length-wise planes in RedTransverse planes in Green
ILLUSTRATION OF THE CELLS BEING DEFORMED
Stretched Cellson pushing the nose downwards
Original Model
PRESSING THE NOSE DOWN-WARDS
Smaller stagnant flow Zone
Original Model
PINCHING THE BODY INWARDS
Original Model
ADDING GEOMETRY : CYLINDERS
Adding Two cylinders , Front and Rear.
• Heights : Front- 0.02 m Rear - 0.05 m • Radius : 50% of the wheel rim width it is
placed in front of• Bottom of both cylinders are aligned with
lower surface of the vehicle
Cylinder heights Reduced by 50% from the top.
Smaller low velocity area
Baseline
With cylinder
Variation of Cp
SUMMARY OF RESULTSType of change Change in Geometry and
dimensions
Percentage increase
or reduction in Cd
Addition of Geometry
through remodelling and
re-meshing
Cylinders with the same height
as the vehicle.
+27.4 %
Cylinders with 50% height
reduction
+19.5%
Mesh Morphing/ Geometry
Deformations
Pressing the nose down
0.02m
0.04 m
0
-3.2%
Pressing the Back inwards
0.02m
0.03m
+4%
+7.5
Extending the nose
(0.005- 0.025m)
0
Pushing out the side
(0.01- 0.03m) 0.53%
CONCLUSIONS OF THE STUDY :
Even relatively minor geometric changes have an effect on the overall drag coefficient and the forces being experienced by the vehicle.◦ Provided they are implemented at the right position in the vehicle.
High mesh densities are required to perform appreciable deformations in the mesh.
The exposed wheels have been established to contribute to the drag on a very large scale. It is also established that the wheel covers must be carefully designed so as to not contribute further to the drag.
Areas of improvement required: ◦ More accurate CAD representation
◦ Obtaining reliable Test and Design specifications of the jet engine
◦ Improved Boundary conditions including running the compressible solver at lower Reynolds Numbers