Simulation of Flow over a cylinder

AIM

To simulate the Flow over a cylinder

OBJECTIVES

• To run a simulation for flow over a cylinder and calculate Reynolds Number
• To increase Reynolds number by a factor of 20%, 40% and 100% and then run the transient flow simulation.
• To calculate simulation end time
• To create animations for Pressure and Velocity

INTRODUCTION

Computational Fluid Dynamics or CFD is a technique that deals with the solution of fluid flow fields through numerical analysis. SOLIDWORKS Flow Simulation is a CFD software designed for the everyday SOLIDWORKS user and analyst. It provides dynamic feedback on the fluid flow and Thermal performance of their products. With Parametric optimization capabilities, users can automate the design and analysis process to discover the best iteration of their design within the familiar SOLIDWORKS environment.

The proper and clear understanding of aerodynamics on different bodies such as aeroplanes, ships, automobiles, turbines and propeller's blades, tall towers, hydraulic structures, buildings etc. are of great importance in technology and betterment of day to day affairs. This enables efficient, economical and improved designs. The proper shaping of the automobiles results in increases speed at low fuel consumption with ease of comfort. Flow past a stationary circular cylinder at different Reynolds number is studied.

THEORY

Geometry:

CAD model of a cylinder having the dimension as follows:

Diameter of the cylinder: 0.0m

Length of the cylinder: 0.01m

The dimensions of the computational domain for an external flow should be decided as follows:

Reynolds number equation:

`R_e=(rhovD)/(mu)`

where:

`R_e` is the Reynolds number, which is unitless

ρ is the fluid density in kilograms-per-cubic-meter (kg/m^3)

v is the velocity in meters-per-second (m/s)

D is the diameter of the pipe in meters (m)

μ is the viscosity of the fluid in Pascal-seconds (Pa⋅s)

CASE SETUP

1. The model is created using the following dimensions mentioned above.
2. Then using the ‘Wizard’ option in‘Flow Simulation’, features and required conditions are set
3. The Analysis type is set to External and Fluid is chosen as Air. Taking the animation time of 1 sec with a step count of 0.1 sec, the velocity along X-axis is set as 10 m/s.
4. Then the dimensions of computational domain so created is varied as required.
5. Using the equation for Reynolds number, the Reynolds number is calculated for velocity = 10m/s.Taking density of air=1.225 kg/m^3, velocity = 10m/s, diameter of the cylinder = 0.05 m, dynamic viscosity = 18.14 * 10^-6 Ns/m^2, the value of Re = 33765.15.
6. Similarly,increasing Reynolds number by20, 40 and 100 % , is calculated to be 405181.91, 47271.22 and 67530.31 respectively.
7. For these Reynolds number, the velocities will be 12,14 and 20 m/s respectively.
8. The Global Mesh level is chosen to be 3.
9. Cut Plots are made for displaying the Pressure and Velocity variations.
10. After this a Parametric study is made. The Input parameter is selected as the Inlet Velocity, Output parameter is the Cut Plots.
11. Four different scenarios are set up for the velocities corresponding to those Reynolds numbers i.e. 12m/s, 14m/s, 20m/s and the simulation is Run.
12. Then the Cut Plots were obtained and the animations were made.

CALCULATION OF SIMULATION END TIME

Velocity = Distance / time

Time = Distance / velocity

i.e. Time = 1.8/10 = 0.18 sec

The length of the domain along the X axis is (1.2+0.6)= 1.8 m

When the Velocity is 10 m/s for Re = 33765.15 then

Flow through time = 0.18 sec

Given that the end time should be 2 times the flow through time

At Baseline for v = 10 m/s, Re = 33765.15, Simulation end time = 0.36 sec

At 20% For v = 12 m/s, Re = 405181.91, Simulation end time = 0.3 sec

At 40% For v = 14 m/s, Re = 47271.22 , Simulation end time = 0.257 sec

At 100% For v = 20 m/s, Re = 67530.31, Simulation end time = 0.18 sec

RESULTS

Flow over a cylinder at Velocity 10m/s:

Cut Plot of Velocity contour:

Cut Plot for Pressure:

Flow over a cylinder at Velocity 12m/s:

Cut Plot of Velocity contour:

Cut Plot for Pressure:

Flow over a cylinder at Velocity 14m/s:

Cut Plot of Velocity contour:

Cut Plot for Pressure:

Flow over a cylinder at Velocity 20m/s:

Cut Plot of Velocity contour:

Cut Plot for Pressure:

OBSERVATIONS

• It was observed from the contours of velocity that maximum velocity regions are above and below he curved surface of the cylinder.
• Also at the inflow. just ,near the surface of cylinder maximum Presssure region is found.

CONCLUSION

Therefore, the simulation for Flow over the Cylinder is successfully completed and the results are studied