Performing and Analyzing Transient simulation of flow over a throttle body
Objective:
Performing Transient simulation of flow over throttle body.
Here we are more concern about pressure velocity and mass flow rates are getting effected due to the rotation of throttle over a time periods which will be disscussed more in the report below.Flow time through elbow data is calculate from steady state analysis for the same geomentry.Rotation is provided manually by creating a file which say when to rotated as per time
Steps involved in running Transient Simulation
1)Geomentry Creation
2)Boundary flagging
3)Diagnosing the geomentry
4)Case Setup
5)Solve
5)Post processing the results
Geomentry
Geomentry has import as STL format.Geomentry cleaning such has unnessary faces are cleared for example extra thickness is removed. After that boundary flagging is done by creating 4 boundaries namely Inlet ,Outlet,elbow_surface and Throttle.
then Diagnosis is performed to check any error are present.If present necessary corrections are made.Then moved to case setup
Case Setup
=>In case setup we choose time based model and then we leave the input parameters under material are kept default the only thing we select air as our fluid,Gas simulation and Reaction mechanism.
=>Going to simulation parameter we are going to choose Transient and hydrosimulation(The main difference between Hydro and non-hydro is that no navier stokes equtions are solved in non-hydro it is only used to check our mesh changes while running simulation).Then rest of then are set to default.We are going to unselect the Shared memory flag
If we look at the bounding box figure provided in the geomentry section we will take length to a round figure of 0.2 m and the rounded up velocity value calculated during performing a steady state simulation
Under Simulation time parameter cycles to run the simulation is set start time to 0 sec and final time to 0.01sec with Initial and minimum time step of 1e-9 and maximum time step to 1 and rest are set to defaults
=>Coming to boundary there are 4 boundaries are flagged with different Boundary ID, they are
>Inlet:Set to inflow Here are we are specifying pressure of 150000 Dirichlet BC to pressure
>Outlet:Set to outflow Specifying Pressure as 100000 Dirichlet BC to pressure
>Elbow_Surface : Set to walls neumann BC are appliled for temperature
>Throttle:Set to walls neumann BC are applied for temperature
Wall Motion:Rotating>Moving>Axis
Rotation Rate is given by creating a file
| Time(Milli Sec) | Rotation in degrees |
| 0 | 0 |
| 2 | 25 |
| 4 | 25 |
| 8 | 0 |
Rotation center and rotation about is calculated by measuring the arc of the vertices of throttle
All the boundaries are set to region0 with air at 101325 pa and 300K
=>Region 0 is created at initial condition and events.Here were are performing turbulance simulation.In turbulance model RNG K-epsilon is choosen
=>Base grid dx=dy=dz=0.002 and fixed emmbeding with scale=3 and layers= 2 at the top and bottom wall to capture the velocity at walls more accuratly.
=>Then postprossesing output files are set to defaults because the data which we are looking is already in default selections
Then we need to export the input files to a folder to start running a simulation.then by using CYgwin we are directing to the input file and simulation is stared by using an executable file and simulation is runned by using a single processor. After successfully running the simulation we can post process the results and check the general outcomes whether simulation ran properly and are they making any sense.
Mesh
After Post converting results the data is viewed by using paraview.Converge uses Cartician cut cell method for meshing.Cut-cell Cartesian approach is the fact that you have a body-fitted mesh. This ultimately means that your mesh fits perfectly with your geometry, reducing the number of inaccuracies that propagate through the rest of the domain. Because of this, the cut-cell Cartesian approach makes handling complex and moving geometries much easier and accurate by cutting the cells rather than stretching and compressing the cells to fit.
Link for the simulation video
https://youtu.be/L5kC9Ot0QRI
Velocity Contour
Here we are concentrated about flow getting disturbed because of throttle valve.There is a small gap at the axis of rotation and the velocity is so high because rest of the are aais blocked by the throttle and we can also see red zone over axis of rotationof the throttle where velocity is high due to low pressure (Look at the pressure Contour for more Understanding).By observing velocity contour there is a rise in velocity at outlet(Look at the pressure Contour for more Understanding)but these contours dont give more detailing because this is transient simulation and trottle is moving with respect to time the contour shown below is at the end of te time step
Pressure Contour
Pressure is low at the gap under the trottle body due to high velocity region and we can see a red pressure zone because of flow getting obstructed because of throttle body but these contours dont give more detailing because this is transient simulation and trottle is moving with respect to time the contour shown below is at the end of te time step
Velocity Stream Line
How velocity magnitude is getting effected due to rotation of throttle body over a period of time can be observed more clearly fom the animation provided below
Link for the simulation video
https://youtu.be/bTdfPwJJjCU
Average Velocity Plot
Here we can obsere more wave like formation starting from 0 to 8 milli seconds because here the throttle is rotated as the time change but when time reaches 8 milli seconds it is going to get stabilize. Here we can observe the effect of velocity because of variation in throttle position.
Pressure Plot
Here we can obsere more wave like formation starting from 0 to 8 milli seconds because here the throttle is rotated as the time change but when time reaches 8 milli seconds it is going to get stabilize. Here we can observe the effect of pressure because of variation in throttle position.
Mass Flow Rate Plot
Here we can obsere more wave like formation starting from 0 to 8 milli seconds because here the throttle is rotated as the time change but when time reaches 8 milli seconds it is going to get stabilize or more like line or slighly look like a cure because trottle is already brough back to its orginal position when it reached 8 milli seconds. mass flow rate is not constant upto 8 millin seconds so by this we can able to capture the data how mass flow rate is gettimg effected because of rotating throttle valve.So if we want more flow rate we will rotate open throttle valve full we want to reduce the flow rate we will use the trottle body
Total Cells
Here we added additional option called adaptive mesh refinement because we are trying to improvise the mesh as the throttle rotates as the time varies . Because of throttle rotating we found more fluctuating mesh generation between 0 to 2milli seconds and 4 to 6milli seconds inbetween 2 to 54 milli seconds the trottle is remained at 25 degrees constant because of theat mesh size is constant same case after 8 milli seconds because trottle is brought back to originaal position so mesh generation remains contant up to the end
Conclusion:
Sucessfully we performed a transient simulation. During running transient case we need data related to velocity that has been calculated by performing a steady state simulation for the same geomentry to calculate the flow time so that we can able to take more time than the flow time to make sense of results .More fluctuation is observed when the trottle is rotating can be clearly observed in the animation provided above. So here we observed how velocity pressure and mass flow rated are getting effected because of rotation of the throttle body from the plotted graphs because much data is not extrated through contours other than the velocity stream lines.Thus our objective is fullfilled