Week 4.1: Project Steady state simulation of flow over a throttle body

Abstract:

In this project, a steady state simulation of throttle valve is studied using CONVERGE cfd. Pressure based solver with RNG k-epsilon turbulent model is used for simulation. Parameters like mass flow rate, velocity distribution, pressure variation across the throttle region is observed and analyzed. Embedded scaling is done to refine the mesh at the throttle interface and capture the physics of flow accurately.

Aim:

Steady state simulation over a throttle body.

Objective:

1. Set up and run the steady state simulation for flow over throttle body.
2. Post process the results and show pressure and velocity contours.
3. Show the mesh (i.e surface with edges)
4. Show the plots for pressure, velocity, mass flow rate and total cell count.
5. Create an animation in which it throttle movement should be visible.

Introduction:

A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.

In an IC engine the throttle is a means of controlling an engine's power by regulating the amount of fuel or air entering the engine. In a motor vehicle the control used by the driver to regulate power is sometimes called the throttle, accelerator, or gas pedal. For a gasoline engine, the throttle most commonly regulates the amount of air and fuel allowed to enter the engine. Recently, for a GDI engine, the throttle regulates the
amount of air allowed to enter the engine. The throttle of a diesel, when present, regulates the air flow into the engine.

Historically, the throttle pedal or lever acts via a direct mechanical linkage. The butterfly valve of the throttle is operated by means of an arm piece, loaded by a spring. This arm is usually directly linked to the accelerator.

The throttle on a gasoline engine is typically a butterfly valve. In a fuel injected engine,the throttle valve is placed on the entrance of the intake manifold, or housed in thethrottle body. In a carbureted engine, it is found in the carburetor. When a throttle iswide open, the intake manifold is usually at ambient atmospheric pressure. When thethrottle is partially closed, a vaccuum develops as the intake drops below ambient pressure.

Simulation Case setup:

• Open converge studio console and import the drawing to the graphics panel.
• To ensure better flow simulation, we delete the outer covering of the elbow wall --> selecttriangle entity selection --> choose angle mode --> select the outer elbow wall --> selectdelete

figure 1

• Follow the similar procedure for the inlet and outlet section

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• The inlet and outlet section are open and will generate open edge error.
• To remove the error we provide patching --> select edge tab --> select open edge mode --> go to repair section --> select the inlet and outlet edge --> select patch and the apply. Theopenings will get closed.

Patch-1: Considered to be inlet

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Patch-2: Considered to be outlet

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• Go to option --> select bounding box. The dimension of the box will be highlighted

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• To ensure make the diagnosis check to remove all the geometrical errors

Diagnosis check: (ctrl+D)

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• Case setup:

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• Select application option --> select time based option.

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• Go to materials --> select gas simulation --> click ok

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• Click the default values for the Gas simulation values.

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• Go to simulation parameters --> select run parameters --> choose steady state solver withfull hydrodynamic case.

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• Go to steady state monitor --> provide monitor variable as mass flow rate --> select targettype boundary --> select target as outlet.
• Provide the minimum no of cycles for steady state solver --> provide monitor delay start,sample size.

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• Select simulation time parameter -->provide end time as 15000 cycles --> provide initialand min time step of 1e-9 and max time step of 1.

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• Go to solver parameter setting --> choose density based --> go to equation --> selectpressure and set precondition to none --> go to solver control and define the cfl limit to (0.5).

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• Go to boundary --> define all boundary region name with ID.

figure 14.1

• Choose the inlet boundary, and select the boundary type as INFLOW

figure 14.2

• Choose the outlet boundary and select the boundary type as OUTFLOW

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• For elbow wall, choose boundary type as WALL

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• For throttle, select the boundary type as WALL.
• To select the throttle body by change to surface option --> click the throttle and the whole body get selected.

figure 17.1

figure 17.2

• Go to initialization --> choose region give name as region 0 --> specify the composition of species.

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• Go to turbulent model --> select RNG kepsilon.

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• For grid control --> provide the grid sizes in x, y, z direction as 2mm.

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• Define fixed embedding to refine the grid at the throttle section --> select fixedembedding --> select boundary ID as throttle --> give embedding scale of 3 and layers 2.

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• Go to post variable selection --> select the variables for post processing.
• Go to output files --> provide the no of output files to be dumped.

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Simulation run:

1.Export all the case set up from the converge studio
2.Go to Cygwin64 --> go to desired path or directory
3.Type the command mpiexec.exe -n 2 converge-intelmpi.exe to run the simulation.
4.To post convert the output files, go to Cygwin64 --> type the command as ex -n 2 post_convert_msmpi_64.exe

Post processing:

Meshing of the elbow wall region:

Meshing at the throttle section with embedding effect:

Mass flow rate:

The mass flow rate is high initially and becomes stable at 0.007kg/s after reaching10000 cycles. The fluctuation of mass flow is due to variation of inlet static pressure anddecrease in velocity. The outlet mass flow rate increases and becomes stable

Density variation:

Inlet density variation is caused due to mass flow variation. The inlet density attainsstability at 1.45kg/m3 after reaching 10000 cycles. At outlet section density increases and reaches stability at 1.3kg/m3 at 8000 cycles. The fluctuation is caused due tovariation of mass flow at the throttle region.

Total pressure:

The inlet total pressure remains constant all over the cycles of iterations. The outlet pressure increases and becomes stable at 135000Pa after reaching 10000 cycles. This variation of pressure is due to mass flow moving at the outlet section from the cornersof throttle wall and causing rise in total pressure.

Static pressure:

The inlet static pressure is very high initially and after encountering the valve gradually decreases and becomes stable at 12000Pa after reaching 10000 cycles. The outlet pressure remains constant because of less variation of mass flow at outlet.

Average velocity:

The inlet average velocity variation is very high at starting and then reaches stability at190m/s after reaching 12000 cycles. The high outlet velocity is due to low is due to Procesors used for computation.

Total cell counts:

The total no of cell count used for running the simulation is around 36000 cells, while inprocessor 0 no of cells used is 17000 and for processor 1 no of cell count is 18500. thesimulation is runned parallely in two processor to reduce the computational time.

Velocity contour:

The velocity vector and the plane of throttle exposes the maximum velocity of 3.2e2m/sat the inlet section. While at the outlet section the velocity drops to 100m/s. The staticpressure increases and the flow becomes seperated. the outlet velocity is low which supports low mass flow rate at the outlet.

Velocity animation:

Pressure contour:

The inlet pressure is high and encountered at the throttle front region and themagnitude is about 1.5e5 Pa. The air while passing through the corners reduces the total pressure and flow seperation takes place. The pressure reaches around 80000Pa acrossthe throttle corner section and back portion.

Pressure animation:

Results:

From the steady state simulation of throttle valve, it is seen that pressure at the inlet ishigher than the outlet. The mass flow variation is encountered at the throttle valve frontposition. The velocity at the inlet position is higher, but some region of high velocity isseen to leak from the corner of the throttle section. At the outlet the flow seeration takesplace from the throttle surface and the outlet velocity reeduces down to attain a steadystate value . The density variation also a function of mass flow variation and pressuredifference. The flow seperation can be seen to take place when pressure tends to dropdown.

Conclusion:
1.The steady state simulation is performed to observe the effect of flow seperation acrossthe region of throttle section. The maximum velocity of 3.2e2m/s is observed at the inletand low velocity of 50m/s at the outlet.
2.The pressure variation is seen to be fluctuating at the inlet and while encountering thevalve, the pressure rises up. The outlet pressure becomes low and further detaches theflow seperation.
3.The grid refinement is done at the throttle section to capture accurately the flowbehaviour. With refinement the computational cell count is higher and time taken tocomplete the simulation increases.