Modelling and simulation of flow through a flowbench
OBJECTIVE :- Modelling and Simulation of flow through the Flowbench and Obtain a plot of Lift vs Mass flow rate.
COMPUTATIONAL FLUID DYNAMICS (CFD) :-
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulent flows. Initial validation of such software is typically performed using experimental apparatus such as wind tunnels. In addition, previously performed analytical or empirical analysis of a particular problem can be used for comparison. A final validation is often performed using full-scale testing, such as flight tests.
CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation, natural science and environmental engineering, industrial system design and analysis, biological engineering, fluid flows and heat transfer, and engine and combustion analysis.
Methodology:-
In all of these approaches the same basic procedure is followed.
During preprocessing
- The geometry and physical bounds of the problem can be defined using computer aided design (CAD). From there, data can be suitably processed (cleaned-up) and the fluid volume (or fluid domain) is extracted.
- The volume occupied by the fluid is divided into discrete cells (the mesh). The mesh may be uniform or non-uniform, structured or unstructured, consisting of a combination of hexahedral, tetrahedral, prismatic, pyramidal or polyhedral elements.
- The physical modeling is defined – for example, the equations of fluid motion + enthalpy + radiation + species conservation
- Boundary conditions are defined. This involves specifying the fluid behaviour and properties at all bounding surfaces of the fluid domain. For transient problems, the initial conditions are also defined.
- The simulation is started and the equations are solved iteratively as a steady-state or transient.
- Finally a postprocessor is used for the analysis and visualization of the resulting solution.
AIR FLOW BENCH :-
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 is one of the primary tools of high performance engine builders, and porting cylinder heads would be strictly hit or miss without it.
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.
- Daimeter of the cylinder = 100mm
- Length of the cylinder = 100mm
- Now create the axis lines of the inlet for swepting purpose.
- Now, create an Plane in the Inlet valve.
- Then sketch the circle with diameter 0.025m.
- Then use the swept feature for creating Inlet.
- Create an axis at the Inlet and Cylinder oriface.
- Now Select Front Plane > Sketch Tool.
- Then Sketch Lifting mechanism around the created axis plane with specific dimensions as shown below.
- Specify the Lift Position.
- Then use Revolve base feature.
- Create Lids @ Inlet Valve and @ Outer Cylindrical Surface.
- Now go to Flow Simulation > wizard > General Settings.
- Internal Flow @ Air(gases) @ Laminar and Turbulent.
- Now Create Boundry Conditions
- Velocity @ Inlet Valve.
- Static pressure @ Outer Cylindrical outlet.
- And create the Global mesh with Advanced channel Refinement.
- At Lifting mechanism create Refined Local mesh.
BASELINE SIMULATION :-
Analyse type: Internal
Working Fluid: Air
Boundry Conditions
- Velocity @ Inlet Valve = 100m/sec.
- Static pressure @ Outer Cylindrical outlet.
Add Goals
Global Mass Flow Rate
Surface mass Flow rate @ Outer Cylindrical outlet.
Valve Lift = 1mm
Global Mesh level = 3 with Advanced channel Refinement.
OUTPUT:
Velocity-
Pressure-
GRID DEPENDENCY TEST :-
Scaling (Grid Independence) 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.
With same Baseline simulation parameters, we will initiate this study.
- Valve lift = 1mm
- Input Parameters
- Global Mesh > Automatic mesh > Level of Refinement
- Output Variables
- Goals @ SG Mass flow rate
- Results @ Cut Plots
- Global Mesh Levels scienerio @ 3,4,5
- Run the Paramatric Study and Study the Plots
RESULTS :-
Velocity Plots-
Level of refinement = 3 :-
Level of refinement = 4 :-
Level of refinement = 5 :-
Result of Simulation-
## Negative value of the Surface mass flow rate indicates about the fact that fluid is leaving out of the domain in Flow Simulation inside the Flow bench. Only magnitude can be considered.
Higher Refinement of the Mesh level give better Simulation results, hence we will choose 5th order refinement of the mesh level.
VALVE LIFT 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.
With same Baseline simulation parameters, we will initiate this study.
- Input Parameters
- Global Mesh > Automatic mesh > Level of Refinement = 4
- Add Dimension @ Select Lift Demension in the valve.
- Range of Valve lift Dimention > (0.001-0.007) = 7 values
- Output Variables
- Add Goals @ SG Mass flow rate
- Add Results @ Cut Plots and Flow trajectory
- Number of scienerio @ 7
- Run the Paramatric Study and Study the Plots
RESULTS :-
Valve Lift = 1mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
Valve Lift = 2mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
Valve Lift = 3mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
Valve Lift = 4mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
Valve Lift = 5mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
Valve Lift = 6mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
Valve Lift = 6mm :-
Velocity Plot and Flow Trajectory-
Pressure Plot and Flow Trajectory-
COMPARING MASS FLOW RATE :-
CODE :-
% COMPARING SG MASS FLOW RATE
% Input Parameters
% Valve lift
lift = [1:7];
% SG Mass flow rate
SG = [-4.1335 -7.8808 -0.0597 -0.0478 -0.0457 -0.0445 -0.0438];
%Plotting
plot(lift, SG,'*-')
axis([-2 8 -9 2])
xlabel('Valve lift(mm)')
ylabel('SG mass flow rate(kg/s)')
title('Comparing mass flow rate for different valve lift')
Observation:-
CONCLUSION :-
- At lowest valve lift i.e. 1mm the Velocity is less than the second lower valve lift due to high hindrance for the gases.
- Then Velocity decreaes with the increase in the Valve lift.
- Pressure at the valve lift decreases with the increase in valve lift due to less hindrances for the gases.
- Mass flow rate gets constant at the absolute level of valve lift.
- Mass flow rate at the Inlet of the valve and Outlet of the cylinder lid increases with the increase in the Valve lift.