Flow Simulation Project 2 : Flow over a cylinder
AIM:
Simulate the flow over a cylinder for various conditions.
Problem Statement :
Simulate the flow over a cylinder for the conditions. Run a baseline simulation and then calculate the Reynolds number. Then increase the Reynolds number by a factor of 20%, 40%, and 100% then run the transient flow simulation.
Theory :
A flow over a cylinder is considered as a model problem for a range of bluff body flow problems. A study of a flow past cylindrical bodies provides a general picture of the phenomenon of flow separation and bluff body wakes.
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulent flows. Initial validation of such software is typically performed using experimental apparatus such as wind tunnels. In addition, previously performed analytical or empirical analysis of a particular problem can be used for comparison. A final validation is often performed using full-scale testing, such as flight tests.
CFD is applied to a wide range of research and engineering problems in many fields of study and industries, including aerodynamics and aerospace analysis, weather simulation, natural science and environmental engineering, industrial system design and analysis, biological engineering, fluid flows and heat transfer, and engine and combustion analysis.
Reynolds number :
The Reynolds number (Re) is an important dimensionless quantity in fluid mechanics used to help predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents). These eddy currents begin to churn the flow, using up energy in the process, which for liquids increases the chances of cavitation. The Reynolds number has wide applications, ranging from liquid flow in a pipe to the passage of air over an aircraft wing. It is used to predict the transition from laminar to turbulent flow, and is used in the scaling of similar but different-sized flow situations, such as between an aircraft model in a wind tunnel and the full size version. The predictions of the onset of turbulence and the ability to calculate scaling effects can be used to help predict fluid behaviour on a larger scale, such as in local or global air or water movement and thereby the associated meteorological and climatological effects.
The Reynolds number is defined as
ρ is the density of the fluid (SI units: kg/m3)
u is the flow speed (m/s)
D is the diameter of the tube (m)
μ is the dynamic viscosity of the fluid (Pa·s or N·s/m2 or kg/(m·s))
ν is the kinematic viscosity of the fluid (m2/s).
Flow over a Cylinder for Various Reynolds Number
Calculations :
Diameter of cylinder (D) = 0.05m
Length of Computational domain L = 0.45m
Case 1 Baseline Case
Assumed air velocity = 10 m/s
Reynolds number
`Re = {(10) *(0.05)}/{(1.516 )*(10^{− 5})}`
Re = 32981
Flow through time = `L/V = 0.45/10 = 0.045s`
Simulation time is taken as 2 times of the flow through time.
Simulation time T = 2 x 0.045 =0.09s
Case 2 Increasing value of baseline reynolds number by 20%
New values
`Re = (1 + 0.2) ⋅ 32981` = 39578
Now air velocity
`39578 = {V *(0.05)}/{(1.516 )*(10^{− 5})}`
V = 12m/s
Flow through time = `L/V = 0.45/12 = 0.0375s`
Simulation time T = 2 x 0.0375 =0.075s
Case 3 Increasing value of baseline reynolds number by 40%
New values
`Re = (1 + 0.4) ⋅ 32981` = 46173`
Now air velocity
`46173 = {V *(0.05)}/{(1.516 )*(10^{− 5})}`
V = 14m/s
Flow through time = `L/V = 0.45/14 = 0.032s`
Simulation time T = 2 x 0.032 =0.064s
Case 4 Increasing value of baseline reynolds number by 100%
New values
`Re = (1 + 1) ⋅ 32981` = 65962`
Now air velocity
`65962 = {V *(0.05)}/{(1.516 )*(10^{− 5})}`
V = 20m/s
Flow through time = `L/V = 0.45/20 = 0.0225s`
Simulation time T = 2 x 0.0225 =0.045s
Design and Analysis in SolidWorks:
1. Cylinder model
2. Wizard Setup
3. Mesh Generation :
Output And Result :
1. Case 1
A. Velocity Contours
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B. Pressure Contours
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2. Case 2
A. Velocity Contours
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B. Pressure Contours
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3. Case 3
A. Velocity Contours
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B. Pressure Contours
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4. Case 4
A. Velocity Contours
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B. Pressure Contours
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Conclusion :
From this simulation it is gain that how the flow over cylinder is varing with the changes in the Reynold Number.