Modelling and simulation of flow through a flowbench
Project Title: Modeling and simulation flow through flow-bench
Objective:
1. Create a model of flow-bench.
2. Cary out the flow simulation if flow-bench.
3. Do the parametric study by changing the valve position.
4. Study the effect of valve lift on the mass flow rate.
Theory:
What’s a flow-bench
A flow-bench or ‘airflow bench’ is a tool to measure the airflow capabilities of anything that’s required to do this. It is (and has been for decades) an invaluable tool to anyone interested in increasing the performance of combustion engines. Inlet manifolds, ports, valve profiles, exhaust systems, intercoolers, throttle bodies, air cleaners, 2 strokes porting etc. the list of items that can be tested is endless. Engine modifiers and designers (and even those dealing with fluid dynamics and aeronautics) will find this an excellent project
The actual airflow figures are generally the goal but the ability to flow air under controlled conditions also allows the user to study airflow characteristics like velocity, turbulence, swirl, tumble, distribution etc. and anyone who’s really done the ‘hard yards’ of engine development will tell you this is the secret. It’s the ‘quality’ of airflow, not necessarily just ‘quantity’ that counts.
Principle:
A flow-bench needs a source of airflow, a system to measure the actual airflow, a method to control the test pressure of air being applied and an area to mount the device under test. The test piece is mounted and a certain pressure, called test pressure (eg 28” of water) is applied to it and the resulting airflow measured.
The chosen way to measure the airflow is by measuring the pressure drop across an ‘orifice’ with a known characteristic. Greater airflow will cause a greater pressure drop. Simple ‘water column’ manometers are used to measure the test pressure and the flow rate, no need for complex tables or spreadsheets. This method is not only easy but it’s very accurate, it is independent of all the atmospheric variables (air temp and pressure) that plague other methods. Any variations are applied to the test piece as well as the measuring system (it’s called ‘ratiometric’ measuring). It is the method also used by the industry-standard flow benches from the Superflow company.
Problem Statement:
For this project, you will create a 3D model of a flow bench and run flow analysis. You will be obtaining a plot of lift vs mass flow rate
You need to do the following
- Grid dependence test
- For three grids run your simulation at a particular valve lift and explain your results
- Effect of valve lift on mass flow rate
- Once you have decided the best grid, run a parametric sweep to show the effect of valve lift on the mass flow rate
Solution:
Modelling:
The circular base is created for a cylinder of diameter 0.05 m.
The cylinder of height 0.1 m is created.
For air inlet, one inlet manifold is created at top side of the cylinder.
The first cylinder is solid.
For CFD simulation we need a hollow cylinder where the air will enter through inlet manifold.
For that shell command is used.
For the parametric study, we need one valve so that at the centre of the inlet manifold one valve is created.
Fig shows the cut section view of the flow-bench assembly.
TO give inlet boundary condition inlet lid is created at the start of the manifold.
To give outlet boundary condition outlet lid is created at the outlet.
Isometric view of the flow-bench assembly.
FLow Setup
Computational domain
Fig shows the computational domain of flow-bench.
Inlet Lid
At the inlet total pressure boundary condition is given. value of total pressure is 201235 Pa.
Outlet Lid
At the outlet, the static boundary condition is given. Value of static pressure is 101235 Pa.
Type of analysis
An internal steady-state analysis is done.
Working fluid
Working fluid air is considered.
Initial conditions
Initial boundary condition
Pressure 101325 Pa
Temperature 293.2 K
Grid Independence Test:
Grid 1
Mesh for First grid test
Total mesh count is 5307 cells.
Pressure distribution around the valve
Velocity distribution around the valve
Mass flow rate is 0.0244 kg/sec
The total net force acting on to the valve is 9.025 N.
Grid 2
Mesh structure for 2nd grid test
Global mesh setting fo 2nd grid test
Local mesh setting for 2nd grid test
Mesh count is 24317 cells
Velocity distribution around the valve.
Pressure distribution around the valve
Mass flow rate is 0.0241 kg/s.
Total net force acting on the valve is 9.063 N.
Grid 3
Mesh structure for grid 3 test
The global setting for 3rd grid test.
Local mesh setting for 3rd grid test.
Mesh count for 3rd grid test is 174482 cells.
Pressure distribution around the valve.
Velocity distribution around the valve
Mass flow rate is 0.0244 kg/sec.
The net total force acting on to the valve is 9.130 N.
Parametric Study
2nd grid configuration is considered for parametric study
Input parameter
Input parameter for the parametric study is valve lift.
Total 6 configurations are considered from 0.003 m to 0.006 m.
Output parameter
Output parameter for the parametric study is the mass flow rate at outlet and velocity contour.
Parametric table
Table od 6 design point completion.
Mass flow rate at different design points.
Mass flow rate Vs Valve position
In this simulation outlet mass flow rate is measured so values are negative.
As the valve lift changes from 0.03 m to 0.06 m mass flow rate is increasing.
Velocity Contours:
Velocity contour at the design point 1
Velocity contour at the design point 2
Velocity contour at the design point 3
Velocity contour at the design point 4
Velocity contour at the design point 5
Velocity contour at the design point 6
Conclusion:
1 As the valve lift changes in positive direction mass flow rate also increase in a positive direction.