Steady Vs Unsteady flow over a cylinder

Results for steady state conditions:

Residuals Plot:

Vertex Average of velocity magnitude as a function of iterations:

OBSERVATIONS:

• It is clear from the graph that the solution has been converged.
• Cannot find Strouhal number because this is taken in steady state condition.
• Difficult to find the vertex magnitude at a particular time.

RESULTS FOR TRANSIENT CONDITIONS;

Residuals Plot:

Vertex Average of velocity magnitude as a function of time:

OBSERVATIONS:

• It is clear from the graph that the solution has been converged.
• The fluctuations has became steady.
• We can find the vertex magnitude at a particular time in this case .

STROUHAL NUMBER:

The Strouhal number (St) is a dimensionless number describing oscillating flow mechanisms.

The Strouhal Number represents the ratio of inertial forces due to the unsteadiness of the flow or local acceleration to the inertial forces due to changes in velocity from one point to another in the flow field.

So we cannot find strouhal number for steady conditions.

For the unsteady or transient condition:

St=f*D/U,

Where St = stroual number, f= frequency, D= characteristic length, U= velocity of air flow.

f=7/90=0.0777;

St=0.0777*2/1;

St=0.1556