Modelling and simulation of flow through a flowbench

AIM

To create a 3D model of a flow bench and run flow analysis and then obtaining a plot of lift vs mass flow rate.

OBJECTIVE

• Run a Grid dependence test i.e for three grids run your simulation at a particular valve lift and obtain the results.
• To find effect of valve lift on mass flow rate by once deciding the best grid.
• Run a parametric sweep to show the effect of valve lift on mass flow rate

THEORY

The flow bench with any fluid is a device used for testing the internal aerodynamic or fluid qualities of an engine component or any component. It can also act as a tool to measure the air flow capabilities of anything tht flows through it.

In Engine, it is used primarily for testing the intake and exhaust ports of cylinder heads of IC engines. Inlet manifolds, ports, valve profiles, exhaust systems, intercoolers, throttle bodies, air cleaners, 2 stroke porting etc are the list of items that can be tested to measure the air flow capabilities. It is an invaluable tool to any one interested in increasing the performance of combustion engines.Engine modifiers and designers will work on the flowbenches in order to get the excellent properties.

A flow bench consists of an air pump of some sort, testing element , pressure and temperature measuring instruments such as manometerd, and various controls. 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.

It also allows us to study air flow characteristics like velocity, turbulence, swirl, tumble, distribution etc. It’s both the quality and quantity of air flow that counts.

FLOW SETUP

MODEL

Inputs Parameters

Analysis Type: Internal

Type of fluid: Air

Type of flow: Laminar and Turbulant

Wall conditions: Adiabatic with 0 micrometer roughness,

Initial conditions: Pressure(101325Pa), Temperature(293.2K).

Boundary conditions

@INLET Total pressure of 101325Pa

@OUTLET Static pressure of 50000pa

Grid dependence test is run i.e 3 different size of grids at a particular valve lift to simulate and deciding which one will be best for rest of simulation and was run to get cut plots for pressure and velocity.

CASE 1- GRID MESH SIZE 4

VELOCITY PLOTS

CASE 2- GRID MESH SIZE 5

VELOCITY PLOTS

CASE 3- GRID MESH SIZE 6

VELOCITY PLOTS

• After all three simulations of different grid sizes, the fine mesh quality i.e mesh size 6 is selected for parametric studies.
• For much accurate results local mesh is created at the surface of valve.
• Smaller is the mesh size, more accurate is the result.
• As we increase the mesh size i.e the mesh becomes finer and finer the value of mass flow rate in our case is converged to 0.0012kg/s. So, we consider the above mesh for parametric study of valve lift.
• Now considering the mesh size 6 we will run the parmetric studies for various valve lifts and find out the mass flow rates for various lifts.

PARAMETRIC STUDY FOR VARIOUS VALVE LIFTS @MESH SIZE 6

CASE 1 For 0.9mm lift (FROM CLOSED POSITION)

VELOCITY PLOTS

FLOW TRAJECTORIES

CASE 2 For 2.675mm lift (FROM CLOSED POSITION)

VELOCITY PLOTS

FLOW TRAJECTORIES

CASE 3 For 4.45mm lift (FROM CLOSED POSITION)

VELOCITY PLOTS

FLOW TRAJECTORIES

CASE 4 For 6.225mm lift (FROM CLOSED POSITION)

VELOCITY PLOTS

FLOW TRAJECTORIES

CASE 5 For 8mm lift (FROM CLOSED POSITION)

VELOCITY PLOTS

FLOW TRAJECTORIES

The above table represents mass flow rate for different valve lifts. Negative sign indicates that mass is leaving the control volume and is just sign convention, so considering the magnitude. Plotting graph between valve lift and mass flow rate, it is shown below.

CONCLUSIONS

• As the valve lift increases mass flow rate of the outlet also increases simultaneously.
• Initially, mass flow rate increases rapid rate with valve lift then decreases, approximately follows exponential distribution.
• From velocity cutplots, it can be concluded that as valve lift increases the velocity of fluid entering into the cylinder also increases
• In addition to that it can be noted that as valve lift increases the flow trajectories velocity became uneven, it may be due to sudden rushing of fluid into the cylinder and hitting the walls causing it to have uneven trajectories.