Week 4: Project - Transient simulation of flow over a throttle body
Objective: To setup and run transient flow simulation for flow over a throttle body in Converge CFD and post process the results in Paraview.
Case Setup:
The transient flow analysis is basically done to study the variation in flow and change in the physical properties of the fluid during the throttle movement. The throttle
Mesh size considered : 2e-03 m
Fixed embedding is applied to the area near the throttle plate to give better analysis results near the throttle plate.
Simulation type:
General flow (Time-based)
Pressure based Transient solver
Fluid considered: Air
Simulation time parameters:
Start time: 0 s
End time: 0.01 s
Calculation of end time:
Approximate length of flow travel= Ly= 0.10 m
Max velocity = 220 m/s
Time= Distance/ Speed
Hence, flow time = 0.1/220= 4.545 * 10^-4 s
The above end time obtained is just for the flow established for a single cycle or one time.
To observe the flow for an adequate period of time i.e 20 times,
Simulation time = 20*4.545*10^-4 = 0.009 s
Initial time step = 1e-09 s
Minimum time step= 1e-09 s
Maximum time step= 1 s
Boundary conditions:
Inlet pressure = 1.5 e+05 Pa
Outlet pressure = 1.0 e+05 Pa
Elbow wall : Law of wall (Stationary) , Tempertaure= 300 K
Throttle plate:
Wall motion type: Rotating
Surface movement : Throttle plate is moved by giving an input in the form a file.
Turbulence model: Reynolds- Averaged Navier Stokes (RANS)
Fixed Embedding : Scale -3, Embeded Layers-2
Time interval for writing 3D output files: 0.001 s
Time interval for writing text output : 1e-06 m
Time interval for writing restarting output: 0.0001 s
Results:
The movement of the throttle is as shown below:
Velocity contour:
In the velocity contour plot we can see that the maximum velocity of 360 m/s is observed near the minimum area between the throttle and the elbow wall.
The reason being the at a constant flow rate the velocity is high at small cross sectional area.
The throttle plate creates a disturbance in the normal staedy flow thus showing a variation in the velocity contour.
Pressure contour:
A pressure difference of 50 kPa exists between inlet and outlet end of the pipe.
Due to the throttle valve movement there is a variable pressure difference created and hence the variation.
A high pressure and low pressure region can be seen to be created at the same time at certain throttle positions.
Streamlines showing flow pattern:
The streamlines depict how exactly the flow varies with the position of the throttle. A turbulence is created when the throttle is titled to a certain angle.
Plots:
Velocity plot:
The obstruction created by the throttle plate to the normal flow. The appearance of turbulence can be seen from 0.0005 s when the throttle plate starts to move 0.004 s when the throttle plate reaches to its original position.
Pressure plot:
The pressure plot shows that there is a low pressure region created when the throttle plate starts tilting creating minimum flow area.
Mass flow rate plot:
Instead of gradual increase in the mass flow rate , ripples are observed in the mass flow rate plot indicating a variation in the mass flow due to throttle movement.
Total cell count:
The cell count increases from 0- 0.002 s and then remains constant from 0.002-0.004 s as the throttle is at the same position.
From 0.004-0.008 seconds we can see that there is a decrease in the cell count but it more gradual as compared to the previous increase and later becoming constant till 0.01 s.