Flow Simulation through a Flow Bench using Solidworks Flow Simulation
OBJECTIVE:
To perform flow simulation through a flow bench, analyse the effect of valve lift on the mass flow rate for the best grid using Solidworks Flow Simulation.
ABSTRACT:
In this project, flow simulation through a flow bench was performed having air as a fluid using SolidWorks Flow Simulation. An initial study was performed to verify the setup from the study results. In order to determine the best mesh parameter, a grid dependency test was performed. Additionally, a parametric study i.e. what if analysis was performed to analyse the effect of valve lift on the exit mass flow rate. In the parametric study, the valve lift ranges from 1 mm to 9 mm with a step increase of 1 mm. Velocity contour, pressure contour, flow trajectory and valve lift vs mass flow rate plot was generated to analyse the effect on exit mass flow rate. Later a conclusion was made accordingly to the analysis results.
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CONTENTS:
1. Introduction
- Computational Fluid Dynamics (CFD)
- Grid Dependency Test
- Parametric Study: What If Analysis
- Flow Bench
- Valve & Valve Lift
- Mass Flow Rate
2. Initial Flow Motion Analysis
- Geometry Model
- Setup
- Boundary Condition
- Mesh Parameter
- Goals & Results
3. Grid Dependency Test
- Input Variables
- Output Parameters
- Scenario
- Goals & Result
4. Parametric Study – What if Analysis
- Input Variables
- Output Parameters
- Scenario
- Result
5. Observation
6. Conclusion
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1. INTRODUCTION:
Computational Fluid Dynamics (CFD)
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyse 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.
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.
Grid Dependency Test
The most common and important question is ‘How can one know if the mesh is good enough for the analysis?’ Mesh density is a significant metric used to control accuracy. Assuming no singularities are present, a high-density mesh will produce results with high accuracy. However, if a mesh is too dense, it will require a large amount of computer memory and long run times. The most fundamental method of checking the mesh quality is to refine a mesh until a result converges. In grid dependency test, the analysis begins with a coarse mesh and it is refined to finer mesh for each run until the results do not change significantly and depend of the grid size anymore. As the grid or mesh size approaches zero, the approximate solution is almost equal to the actual solution. The aim of this test is to find the optimum mesh size for the solution, where it is neither to coarse to produce inaccurate results, neither too fine, where it will consume a lot of computing effort and time.
Parametric Study: What If Analysis
Parametric studies allow you to nominate parameters for evaluation, define the parameter range, specify the design constraints, and analyse the results for each parameter variation.
Flow Bench
Figure 1: Schematic Diagram of 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, carburettors, 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.
Valve & Valve Lift
A valve is a device that regulates, directs or controls the flow of a fluid (or gas) by opening, closing, or partially obstructing various passageways. (Source: Wikipedia)
Valves form an integral component of an internal combustion engine and every cylinder in an engine atleast has two of them, i.e. an intake (intake of fuel-air mixture) and an exhaust valve (exhaust gases). A multi-valve engine can have three, four and sometimes five valves.
The valve lift is the distance by which the valve is raised from its seated position when it is fully opened. The camshaft controls the speed of valve opening, valve lift off the valve seat, and how long the valve stays open. The valve lift height and duration correspond to the height and shape of the cam lobes.
Mass Flow Rate
In physics and engineering, mass flow rate is the mass of a substance which passes per unit of time. Its unit is kilogram per second in SI units, and slug per second or pound per second in US customary units. Since mass is a scalar quantity, the mass flow rate (the time derivative of mass) is also a scalar quantity. The change in mass is the amount that flows after crossing the boundary for some time duration, not the initial amount of mass at the boundary minus the final amount at the boundary, since the change in mass flowing through the area would be zero for steady flow.
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FLOW MOTION ANALYSIS
1. Geometry Model
A flow bench was modelled. The dimensional parameters are as follows-
Cylinder Bore Diameter: 50 mm
Cylinder Height: 75 mm
Inlet Port Diameter: 15 mm
Figure 2.1: Flow Bench geometry
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2. Setup
- Add the lids on both open ends to from a closed geometry.
- Setup of the new study
- Project name: Flow_Through_Flowbench
- Type of fluid: Air (Gas)
- Type of flow: Laminar & Turbulent
- Wall Condition: Adiabatic Wall with 0 micro-meter roughness
- Initial Condition: Pressure (101325 Pa), Temperature (293.2K)
- Adjust the computational domain as per the geometry.
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3. Boundary Condition
- Inlet Total Pressure Boundary Condition: Inner lid face of inlet port
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- Outlet Static Pressure Boundary Condition: Inner lid face of cylinder
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- Wall Boundary Condition: Inner faces of port & cylinder (Real Wall)
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- Wall Boundary Condition: Outer surfaces of the valve (Real Wall)
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4. Mesh Parameter
Global Mesh: Automatic mesh with mesh level 7 and advanced channel refinement.
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Local Mesh:
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5. Goals & Results
Add the global goal & surface goal to view mass flow rate. Add cut plots on the front plane for velocity contour & pressure contour.
Figure 2.5.a : Goals
Figure 2.5.b : Velocity Contour
Figure 2.5.c : Pressure Contour
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3. Grid Dependency Test
1. Input Variables
Simulation parameter to vary: Automatic Mesh Level for discrete values of 5, 6 & 7.
Figure 3.1 : Input Variable
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2. Output Parameters
Global goal, surface goal and the velocity cut plot.
Figure 3.2 : Output Variable
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3. Scenario
Total 3 Design Points created which will evaluate the goals and generate the velocity contours for three different mesh level.
Figure 3.3 : Scenario
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4. Goals & Results
Goals
Figure 3.4.a : Goals
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Velocity Contour
Figure 3.4.b : Velocity Contours
Since, as the mesh becomes finer, the calculation approaches the correct answer.
Therefore, from the plots and goals, level 7 appears to be the best mesh parameter.
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4. PARAMETRIC STUDY – WHAT IF ANALYSIS
1. Input Variables
Dimensional parameter to vary: Valve lift dimension ranging from 1.273mm to 9.273mm with a step increase of 1mm.
* The actual valve lift is 1 mm but due to dimensional placement, it is 1.273
Figure 4.1 : Input Variables
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2. Output Parameters
Global & Surface Goal, Velocity & Pressure Contour
Figure 4.2 : Output Variable
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3. Scenario
Total 9 Design Points created which evaluates the goals and generate velocity & pressure contours.
Figure 4.3 : Scenario
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4. Goals & Results
a) Global Goal: Mass Flow Rate vs Valve Lift Plot
Figure 4.4.a : Global Goal: Mass Flow Rate vs Valve Lift Plot
b) Surface Goal: Mass Flow Rate vs Valve Lift Plot
Figure 4.4.b : Surface Goal: Mass Flow Rate vs Valve Lift Plot
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c) Goals
Figure 4.4.c : Goals
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d) Velocity Contours
Figure 4.4.d : VelocityContours
Figure 4.4.d : Magnified view of Velocity Contours
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e) Pressure Contours
Figure 4.4.e : Pressure Contours
Figure 4.4.e : Magnified view of Pressure Contours
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f) Flow Trajectory
Figure 4.4.f : Flow Trajectories
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5. OBSERVATION:
From the goals and results, following observation can be made-
- The initial basic study helped to verify the analysis setup, boundary conditions etc.
- In grid dependency test, the automatic mesh level 7 came out to be the best mesh parameter. At this parameter, the solution appears to be converging.
- In parametric study, it can be observed that as the valve lift increases, the mass flow rate also increases.
- From GG Mass Flow Rate vs Valve Lift plot, it can be observed that for a set of valve lifts (i.e. 1 to 3, 4 to 5, 6 to 9), the mass flow rate decreases but during the transition of valve lift from 3mm to 4mm & 5mm to 6mm, it increases and at 7mm, the mass flow rate is maximum i.e. 3.13E-8 kg/s.
- From SG Mass Flow Rate vs Valve Lift plot, it can be observed that as the valve lift increases, the mass flow rate also increases.
- From goals table, it can be observed that as the valve moves down up to 7 mm. the mass flow rate increases but as the valve moves down beyond 7mm, the mass flow rate starts to decrease.
- Since, the pressure difference is constant throughout the parametric study. Therefore, the maximum velocity and maximum pressure is the same for all valve lifts i.e. 11.098 m/s and 101611.26 Pascals respectively.
- From the velocity contours, it can be observed that as the valve lift increases, the region containing the high velocity flow also increases in the inlet port as well as the cylinder.
- From the pressure contours, it can be observed that as the valve lift is minimum, the pressure inside the inlet port is high and as the valve moves down, the pressure is released into the cylinder. In all cases of valve lift, the maximum pressure always acts on the curve adjacent to the valve stem.
- From the flow trajectories, it can be observed that swirl is minimum at low valve lift and is maximum at the maximum valve lift.
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6. CONCLUSION:
The flow simulation analysis helps to analyse the behaviour of the fluid flow inside the inlet port and the cylinder. The optimum mesh parameter is level 7 and for maximum mass flow rate, the valve lift should be 7mm.
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