Modelling and simulation of flow through a flowbench

AIM : Modelling and simulation of a flow through a flow bench.

OBJECTIVE :

• To create a 3D model of a flow bench and run flow analysis.
• To plot a graph of valve lift vs mass flow rate .

INTRODUCTION:

Flow Bench : 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.

PROCEDURE :

First we model the flow bench as required and ran a new flow simulation study. We made shells as required and further also provided lids to the parts as required .

We then provided input parameters such as air as working fluid and other thermodynamics properties through wizard.

We then provided boundary conditions such as velocity of 100m/s at inlet and static pressure at the outlet lids respectively.

We then provided a Surface Goal and Global Goal for the mass flow rate.

After that we provided global mesh with adjust mesh refinement and also insert a local mesh.

Initially our valve lift was 2mm and for different valve lift we made a new parametric study and ran the simulation for valve lift of 2,4,6,8 mm respectively.

Parametric study : Variable valve lift (VVL) is an automotive piston engine technology which varies the height a valve opens in order to improve performance, fuel economy or emissions. There are two main types of VVL: discrete, which employs fixed valve lift amounts, and continuous, which is able to vary the amount of lift. Continuous valve lift systems typically allow for the elimination of the throttle valve.

The velocity along with pressure plots for different valve conditions are as shown below.

We have also provided Cut plots and flow trajectories for the same.

GRID DEPENDENCY TEST :

Grid convergence is the term used to describe the improvement of results by using successively smaller cell sizes for the calculations. A calculation should approach the correct answer as the mesh becomes finer, hence the term grid convergence.

As we go on making the mesh finer and finer the results are more and more clear which we can easily see form the below images.

4 level of refinement 5 level of refinement 6 level of refinement

For time saving and optimum solution of the problem we can go with 5 or 6 level of refinement of mesh.

RESULTS AND PLOTS :

We can clearily see from the below graph that how the pressure and velocity changes as the fluid(air) passes through the flow bench.

Both pressure and velocity are initially higher ,but as they flow through the flow bench both decreases due to the change in cross section area.This happens upto a certain lift and then both increases which can be seen in the further write up.

Cut Plot and Pressure Plot are as shown below :

Pressure at valve lift of 2mm Velocity at valve lift of 2mm

Pressure at valve lift of 4mm Velocity at valve lift of 4mm

Pressure at valve lift of 6mm Velocity at valve lift of 6mm

Pressure at valve lift of 8mm Velocity at valve lift of 8mm

Velocity Plots for different valve lift as shown below:

• At 2mm valve lift

• At 4mm valve lift

• At 6mm valve lift

• At 8mm valve lift

Pressure Plots for different valve lift as shown below:

• At 2mm valve lift

• At 4mm valve lift

• At 6mm valve lift

• At 8mm valve lift

Flow Trajectories :

• At 2mm valve lift

• At 4mm valve lift

• At 6mm valve lift

• At 8mm valve lift

CONCLUSION :

We obtain the different values of mass flow rate for different valve lift .The plot between them is as shown below.

Thus we can conclude from the above graph that initially with slight increase in valve lift the mass flow rate slowly increases,but after a certain valve of valve lift (in our case 5 mm approx) the mass flow rate becomes constant and it has no relationship with the valve lift .

This same impact is seen on the velocity and pressure contours, and after a certain value of valve lift both these parameters becomes constant just as mass flow rate.

Matlab Program for the above graph is as shown below

%PLOT VERSUS MASS FLOW RATE AND VALVE LIFT .

% INPUTS 
valve_lift =  linspace(2,8,4);
mass_flow_rate = [-7.8808 -.0478 -.0455 -.0438];



plot(mass_flow_rate,valve_lift,'color','b','linewidth',3)
axis([-8 2 0 10])
xlabel('mass flow rate(Kg/s)')
ylabel('Valve lift(mm)')
title('Mass flow rate v/s Valve lift')

Negative sign of the mass flow rate indicates that the fluid is moving out of the flow bench ,so for calculation purpose take magnitude only.

Applications of flow bench: