Flow over a cylinder
AIM: To run external flow simulation over a cylinder with increment in Reynolds number by 20%,40%,60%,100%.
Objective:
1. Running a baseline simulation and calculating the Reynolds number.
2. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
Introduction:
Flow Simulation is an intuitive Computational Fluid Dynamics (CFD) solution embedded within SOLIDWORKS 3D CAD that enables you to quickly and easily simulate liquid and gas flow through and around your designs to calculate product performance and capabilities.
TYPES OF STUDY FLOWS:
External and internal flow,
External flow studies concerns flow not bounded by outer surfaces, but rather only by the fluid domain boundaries. In this case, the solid part is surrounded by the flow, this type of analysis is most commonly associated with aerodynamic studies. Internal flow studies concern flow bounded by outer solid surfaces. In this case, the fluid only circulates on the interior of your part, this type of analysis is most commonly associated with pipe or valve studies.
TYPES OF FLOW:
There are three flow regimes. When a flow moves on in a tranquil fashion it is said to be streamlined or laminar flow, because the various axial layers in the fluid remain intact as the flow proceeds. The so-called turbulent flow is chaotic because layers in the flow conduit do not remain intact but are constantly being mixed due to turbulence, that is, 10 chaotic motions in the flow. Transitional flow is a mixture of laminar and turbulent
flows.
REYNOLDS NUMBER:
Reynolds number can reveal whether the flow is laminar or turbulent. The transition from laminar to turbulent flow depends on the surface roughness, flow velocity, geometry, surface temperature, and type of fluid, among others. Flow regime mainly depends on the ratio of inertial forces to viscous forces in the fluid. This ratio is called the Reynolds number and is expressed as.
Under most practical conditions, the flow in a circular pipe is:
• Laminar when Re ≤ 2300
• Transitional when 2300 ≤ Re ≤ 4000
• Turbulent when Re ≥ 4000
Calculation:
1. First, we assume inlet velocity and using Reynolds calculator we find Reynolds number.
2. From there we multiply the Reynolds number by 1.,1.4,1.6,1.8,2 and Create animations for pressure-velocity for all the Reynolds numbers.
TRANSIENT FLOW SIMULATION:
Parameters that are changing with time and position in the coordinate system.
MESH:
The initial mesh of a Flow Simulation is the first mesh used for performing actual calculations. The software starts with the basic mesh, then refines area with certain geometrical features based on the different settings in the software.
We can get a converged solution from a coarse mesh and a completely different converged solution for the same study using a fine mesh. Convergence alone doesn’t tell us we’ve reached a good solution - we need to do a bit more work here.
PROCEDURE:
1. Build a solid body of the cylinder.
2. Go to the Solidworks add on and go to flow simulation.
3. Open the wizard and make the required arrangements for the simulation i.e.,
i)Set up CFD problem
ii)Next unit system
iii) Set as External flow along with transient flow with time limits as:
Total analysis time:0.1s; Output time step:0.01s.
iv)Defined fluid(gas), flow characteristic, flow type
v)Surface roughness(if required)
vi)The thermodynamic property, velocity parameter, turbulence property(if required)
4. The computational domain is created where we can edit acc to our requirements.
5. Run the simulation
6. Creating cut plots of velocity and pressure
7. Using the animate option saving the avi file.
Observations:
1. As velocity increases Reynolds number increases which inturn reduces flow through time.
2. Laminar flow occurs at low Reynolds number and Turbulent flow occurs at high Reynolds number.
3. The separation point is different from different cases.
4. As the Reynolds number increases the red region of velocity converges but we couldn't found a measurable change in the pressure.