Modelling and simulation of flow through a flowbench - Solidworks CFD

1. AIM:

- To create a 3D model of a flow bench and run flow analysis on it.

2. INTRODUCTION:

- An air flow bench is a device used for testing the internal aerodynamic qualities of an engine component and is related to the more familiar wind tunnel.

- It is used primarily for testing the intake and exhaust ports of cylinder heads of internal combustion engines. It is also used to test the flow capabilities of any component such as air filters, carburetors, manifolds or any other part that is required to flow gas.

- A flow bench consists of an air pump of some sort, a metering element, pressure and temperature measuring instruments such as manometers, and various controls.

- The test piece is attached in series with the pump and measuring element and air is pumped through the whole system.

- Therefore, all the air passing through the metering element also passes through the test piece. Because the volume flow rate through the metering element is known and the flow through the test piece is the same, it is also known.

- The mass flow rate can be calculated using the known pressure and temperature data to calculate air densities, and multiplying by the volume flow rate.

3. OBJECTIVES:

- To perform 3 grid dependency tests and explain the outcomes.

- To find the effect of valve lift on mass flow rates.

- Plot the information.

4. FLOW SIMULATION SETUP:

1. Create a CAD model of the flowbench in solidworks.

2. Enable the Flow simulation add-in and Open the wizard.

3. Now, to set the boundary conditions, we need to give a pressure difference as below.

4. The next most important step is to check the grid dependency. This basically refers to the mesh size. Finer the mesh, greater is the accuracy of the results of the simulation. Initially, the mesh size is set to 3 and the simulation is run. Similarly, the simulation is run at mesh sizes 4 and 5 respectively.

*Finalization criteria is the level of detailing and accurate values. Since Local machine(computer) cannot handle level 5 mesh at higher speeds, level 4 mesh is finalized.

5. After selecting the best grid, the local mesh refinement was done around the valve walls to improve the accuracy of the results.

6. Set the global goals as well as the local goals. In our case, the main goal is to find out the mass flow rate at various positions of the valve at the outlet lid, i.e at different valve lifts.

7. Finally, create the lids as the inlet and the outlet must be perfectly closed. The simulation study was conducted for 0.003 seconds approximately.

8. Run the simulation using parametric study as follows:

9. Select the governing dimension which controls the valve lift as the input variable.Enter the range of the valve lift(min. 0.001m and max. 0.009m) and the number of iterations for which the simulation must be run.

10. Select the output parameter as the main surface goal, i.e the mass flow rate and the required cut plots.

11. Check the scenario tab and run the simulation.

5. OBSERVATIONS, RESULTS AND CONCLUSION:

The below GIF shows the change in Pressure, Velocity and Flow Trajectories as the valve lift increases in the steps 1mm, 3mm, 5mm, 7mm and 9mm.

Pressure:

Velocity:

Flow Trajectories:

Animation:

The Mass flow rates obtained at the outlet lid at different valve lifts are:

This data can graphically be visualized by a plot:

Conclusions:

- Solidworks puts a negative sign when fluid comes out of the outlet lid. Hence considering the magnitude of values of mass flow rate, we can deduce that as valve lift increases, the mass flow rate also increases.

- The slope of increasing mass flow rate is reducing after increase in valve lift, Thus it is eminent that at some point, the slope will be zero and thus increase in valve lift will have no effect on mass flow rate.

- This is observed in the last design point where slope is not exactly zero, but close to zero, thus mass flow rate increasing by a very small amount of 0.0002 `(kg)/s`