AHMED BODY SIMULATION
AIM:
To perform grid dependency test on Ahmed body and study the pressure and velocity characteristics.
AHMED BODY:-Ahmed body is generic car body. the air flow around the ahmed body captures the essential flow features around automobile .it has very simple shape and it allows us to capture the charateristics featurs that are relevent to bodies in the automobile industry.
GEOMETRY:
To simulate the flow we have to cover the ahmed body with a enclosure for external fluid flow domain.
UPSTREAM-2m
DOWNSTREAM-2m
ABOVE and BOTH SIDES-0.5m
MESH:
A baseline mesh was generated using default mesh settings.
BOUNDARY CONDITIONS:
INLET:velocity inlet=50m/s,temperature=300k
OUTLET:pressure outlet
SOLVER SETTINGS:
STEADY STATE,FLUID =AIR,TURBULANT FLOW(K-EPSILON),HYBRID INITIALIZTION,IMPLICIT METHOD
RESULT:
GRID DEPENDENCY TEST:
CASE1:
GEOMETRY:
ENCLOSURE 1-: upstream=2m,downstream=2m,above and both sides=0.5m
ENCLOSURE 2-:all sides expect below=0.26
MESH:
MESH TYPE:MULTI ZONE
MESH SIZE:150mm(BOTH ENCLOSURE)
INFLATION LAYER: TOTAL THICKNESS(12.5mm)
BOUNDARY CONDITIONS:
INLET:velocity inlet=50m/s,temperature=300k
OUTLET:pressure outlet
SOLVER SETTINGS:
STEADY STATE,FLUID =AIR,TURBULANT FLOW(K-EPSILON),HYBRID INITIALIZTION,IMPLICIT METHOD
RESULT:
CASE2:
GEOMETRY:
ENCLOSURE 1-: upstream=2m,downstream=2m,above and both sides=0.5m
ENCLOSURE 2-:all sides expect below=0.26
MESH:
MESH TYPE:MULTI ZONE
MESH SIZE:100mm(BOTH ENCLOSURE)
INFLATION LAYER: TOTAL THICKNESS(12.5mm)
BOUNDARY CONDITIONS:
INLET:velocity inlet=50m/s,temperature=300k
OUTLET:pressure outlet
SOLVER SETTINGS:
STEADY STATE,FLUID =AIR,TURBULANT FLOW(K-EPSILON),HYBRID INITIALIZTION,IMPLICIT METHOD
RESULT:
CASE3:
GEOMETRY:
ENCLOSURE 1-: upstream=2m,downstream=2m,above and both sides=0.5m
ENCLOSURE 2-:all sides expect below=0.26
MESH:
MESH TYPE:MULTI ZONE
MESH SIZE:50mm(BOTH ENCLOSURE)
INFLATION LAYER: TOTAL THICKNESS(12.5mm)
BOUNDARY CONDITIONS:
INLET:velocity inlet=50m/s,temperature=300k
OUTLET:pressure outlet
SOLVER SETTINGS:
STEADY STATE,FLUID =AIR,TURBULANT FLOW(K-EPSILON),HYBRID INITIALIZTION,IMPLICIT METHOD
RESULT:
WHY THE PRESSURE GOES NEGATIVE ?
The body pressure goes negative because as the flow passes the body there is a increase in the velocity and thus to contour the increased velocity the pressure goes negative.due to reciculation of air at rear end of the car the pressure becomes negative as there is backflow behing the ahmed body.
Due to an accelerstion in flow over the body due to recirculation of flow the pressure contours on the ahmed body are negative in nature.