Transient Flow Analysis over a Cylinder using SolidWorks Flow Simulation

Aim: To simulate a transient flow over a cylinder for different Reynolds number

Objectives:

1. Simulating a baseline flow with inlet velocity (X-axis) as 10m/s with the associated Reynolds number
2. Performing flow simulations for Reynolds number increased by factors of 20%, 40%, and 100%
3. Creating Animations for pressure and velocity distribution for each case.

Introduction:

There are two types of flows with respect to time. The flow where the flow parameters (velocity and pressure) only change with the position is known as a steady-state flow. On the other hand, the flow in which the parameters are dependent on time along with the position in the coordinate system is known as a transient or unsteady flow.

The Reynolds number in fluid mechanics is a unitless number defined by the ratio of inertial forces to viscous forces. This number is characterized by the density of the fluid `rho` in kg/m^3, the flow speed u in m/s, the diameter of the tube D in m, and the dynamic viscosity `mu` of the fluid in Pa-s.

Re = `(rho * u*D)/mu`

Problem Overview:

The Geometry of over which the analysis is done is a cylinder. The velocity flow is taking over the circumferential surface of the cylinder. The Computational Domain is a box under our consideration and is 0.36m in length along the flow axis. The simulation is performed for 4 different Reynolds numbers using a parametric study where the inlet velocity parameter is the input. The pressure inside the domain is assumed to be 1 atm. For visualization purposes, Cut Plots are generated for pressure and velocity distribution. In addition, animations are generated to see the transient flow behavior of the fluid over the cylinder with respect to time.

Problem Specifications:

• Cylinder dimensions: 0.05m x 0.04m (L x D)
• Fluid Material: Air
• Density: 1.225 kg/m^3
• Viscosity: 1.81e-5 Pa-s
• Total time: 0.1s
• Time steps: 10 (0.01s each)

	Baseline	20% Increase	40% Increase	100% Increase
Reynolds number	2707	3248.4	3789.8	5414
X - Velocity (m/s)	1	1.2	1.4	2

RESULTS:

Pressure-Velocity Animations for baseline Re:

Pressure-Velocity Animations for a 20% increase in Re:

Pressure-Velocity Animations for a 40% increase in Re:

Pressure-Velocity Animations for a 100% increase in Re:

Conclusions:

1. As we increase the Reynolds number, the velocity flow parameter over the cylinder gets increased.
2. The velocity is greatest at the top and bottom surfaces where it hits tangentially to the cylinder. The corresponding pressure in the same region is at its minimum value. This satisfies the condition that pressure and velocities are inversely proportional to keep the algebraic sum of potential energy, kinetic energy, and pressure constant.
3. The pressure is maximum on the left surface region of the cylinder where it hits normally to the surface. This is true in a real sense as velocity will reduce if there is obstruction and the pressure will rise in the same region.
4. The absolute pressure change seems to be negligible as there is not enough deviation as compared to the 101325 Pa (1 atm) pressure. Having said that, if we change the pressure scale to gauge pressure (1 atm = 0 for reference) and measure the pressure change, we can see a significant pressure change.
5. Looking at the velocity animations, the region of maximum velocity (red in color) increases with an increase in Reynolds number.