STEADY STATE SIMULATION OF FLOW OVER A THROTTLE BODY

ABSTRACT: In this project, a study of steady state simulation of flow over a throttle body is performed. The results were analysed and interpreted during the study. The throttle valve is placed inside an elbow shaped pipe.

INTRODUCTION: A throttle is a mechanism used to regulate fluid flow in a system. It is a disc shaped structure in a cylindrical tube that is rotated by some mechanism such as accelerator pedal or thrust lever. This rotation causes an opening which allows the fluid to flow over it. For maximum flow the throttle valve is opened by 90 degree. As fluid starts flowing through the pipe, it encounters throttle in between where flow is disturbed.

In this project we are going to do a steady state analysis of flow over a throttle valve. Hence the valve is going to be fixed at an angle of 90 during the entire simulation.

CASE SETUP: Geometry for the challenge was imported. And it was checked for proper dimensional units. Boundaries were created then namely: Throttle, Elbow, Inlet and outlet. After this geometry was checked for any errors using diagnosis tool.

Application: General flow

Material: Gas simulation, Global Transpot parameters were set as default.

Simulation Parameters: Run parameters- Pressure based steady state solver, simulation mode was taken as full hydrodynamic. Solver parameters were kept as default.

Boundary conditions: Elbow(Boundary id 1) and throttle were assigned WALL boundary type with wall motion kept as stationary for both as it is a steady state simulation. Inlet(Boundary id 3) boundary type inflow and pressure =150000 Pa, species inflow O2 and N2. Outflow (Boundary id 4) boundary type outflow and pressure=100000 Pa, species :- O2 and N2. All boundaries are assigned Region 0.

Regions and initialization:Temperature 300 K, and pressure= 101325, species Air (O2 and N2).

Physical modeling: Turbulence modelling with RNG `k-epsilon`.

Base Grid: dx=.004,dy=.004,dz=.004.

Output/Post processing Variable: Post variable selection, Interval for writing 3D output file-1000 cycles, interval for writing text output-1 cycle, time interval for writing restarting output- 1000 cycles.

User defined functions: None.

Geometry:-

RESULTS AND OBSERVATIONS:

1. Mesh and total cell count:

Total Cell count

To create proper mesh near the throttle Adaptive mesh refinement technique was used.

2. PRESSURE CONTOUR:

From the pressure contour we can observe that the pressure in the vicinity of the throttle varies greatly due to the throttle. When flowing fluid encounters throttle valve ( since in this simulation throttle valve remains constant) there is a change in velocity (it decreases) and hence the pressure rises. The same phenomenon is observed when the fluid flows over the shaft of the throttle. Due to the streamlines formed there is a pressure drop in the areas adjacent to it indicated by blue color.

3. MASS FLOW RATE:

Mass flow rate initially fluctuates and is asymmetric. After a certain duration it gains steady state and the mass flow rate at inlet is equal to the mass flow rate at outlet.

4. VELOCITY:

Velocity profile near the throttle varries when flow encounters the throttle. There is some side leakage as well and it can be viewed by red color contour between throttle and elbow. As the fluid flows over the throttle its velocity increases marginally over its course of flow. This occurs due to the decrease in pressure in the region after the throttle.