Flow over a cylinder

INTRODUCTION: 

Potential flow around a circular cylinder is a classical solution for the flow of an inviscid, incompressible fluid around a cylinder that is transverse to the flow. Far from the cylinder, the flow is unidirectional and uniform.
 The flow has no vorticity and thus the velocity field is irrotational and can be modelled as a potential flow. Unlike a real fluid, this solution indicates a net-zero drag on the body.


Analysis done on ansys shows how flow will look like.

we will be replicating such analysis on solidworks.

Here Reynolds number(Re) is the main variable parameter that we have to consider while taking into consideration the variation in the velocity of the fluid flowing over the cylinder.

OBJECTIVE:

This study aims to simulate the flow over a cylinder considering velocity and pressure depending on the variation in Reynolds number(Re) with the use of cut plots using Solidworks.

Reynolds number, `Re=(ρ*v*d)/μ,

                                 Re=(v*d)/ϑ`

                       where, ρ = density of air          µ = dynamic viscosity.              v = velocity              d = diameter of the pipe  

                 
this picture covers the flow at different Reynolds number.

CALCULATIONS:
At, T = 20degC = 293K;

density of air, rho = 1.2047;

dynamic viscosity, mu = 1.8205*10^(-5);

initial inlet velocity(baseline), v = 10m/s;

therefore, Re(baseline) = 26.4698*10^3;

Re1 (20%) = 31.763*10^3;

Re2 (40%) = 37.056*10^3;

Re3 (100%) = 52.938*10^3;

Therefore, v1 at Re1 = 11.999m/s;

                  v2 at Re2 = 13.999m/s;

                  v3 at Re3 = 19.999m/s;

PROCEDURE:

To start with draw a circle using sketch command in the front plane and extrude it to certain length to construct a cylinder.

Then use the wizard to in the flow simulation to set the type fluid, fluid flow, and the inlet velocity parameters.

set it for time-dependent flow.

Now run the flow simulation to get the results.

Then using the results generate a cutplot for velocity and pressure.

Now simulate an animation for the flow over the cylinder using the simulation results and the cutplot.

Next, start a parametric study for the different velocity at respective Reynolds number and generate the cutplots for the same.

Results:

At baseline for the velocity of 10m/s:

flow-through time, t1 = 0.046s     ,         end time, te1 = 0.092s

plots (velocity and pressure):

                          
                   

Animation:  https://youtu.be/mjKYlqOku88

At the velocity of 11.999m/s(at Re1):

Animation: https://youtu.be/aQA7ll7clmo


velocity at Re2
Animation: https://youtu.be/XUabdIW5Ng4

velocity at Re3
Animation:  https://youtu.be/NMcnL-_pBnM

OBSERVATIONS:

In fluid dynamics, a von Karman street is a repeating pattern of swirling vortices caused by a process known as vortex shedding, which is responsible for the unsteady separation of flow of a fluid around blunt bodies.

vortex shedding is an oscillating flow that takes place when a fluid such as air or water flows past a bluff body at certain velocities, depending on the size and shape of the body.in this flow, vortices are created at the back of the body and detach periodically from either side of the body forming von Karman vortex street. the fluid flow past the object creates alternating low-pressure vortices on the downstream of the object. the object will tend to move toward the low-pressure zone.

When the body experiences the pressure drag during the fluid movement, then the body is said to blunt. They are said to have separated flow over a considerable portion of its layer.

PHENOMENON EXPLANATION :

Vortex shedding happens when the equilibrium flow suffers a Hopf bifurcation and flow settles down to a new equilibrium flow, which is almost time-periodic (at Strouhal frequency). The range of Re values will vary with the size and shape of the body from which the eddies are being shed, as well as with the kinematic viscosity of the fluid. Over a large Re_d range (47<Re_d<10⁵ for circular cylinders; reference length is d: diameter of the circular cylinder) eddies are shed continuously from each side of the circle boundary, forming rows of vortices in its wake. The alternation leads to the core of a vortex in one row being opposite the point midway between two vortex cores in the other row, giving rise to the distinctive pattern shown in the picture. Ultimately, the energy of the vortices is consumed by viscosity as they move further downstream, and the regular pattern disappears.

GRID INDEPEDENCY TEST:
  BASIC MESH

 MESH VALUE=6

 MESH VALUE=7


This shows that the solution has reached convergence and the values are no longer dependent on the nodes of the discretized body.