Diese Präsentation wurde erfolgreich gemeldet.
Wir verwenden Ihre LinkedIn Profilangaben und Informationen zu Ihren Aktivitäten, um Anzeigen zu personalisieren und Ihnen relevantere Inhalte anzuzeigen. Sie können Ihre Anzeigeneinstellungen jederzeit ändern.
Nächste SlideShare
×

# SIMULATION OF VON KARMAN STREET IN A FLOW

591 Aufrufe

Veröffentlicht am

• Full Name
Comment goes here.

Are you sure you want to Yes No
• Als Erste(r) kommentieren

### SIMULATION OF VON KARMAN STREET IN A FLOW

1. 1. SIMULATION OF VON KARMAN STREET IN A FLOW OVER A CYLINDER - SALEEM MOHAMMED HAMZA (250873614)
2. 2. WHAT IS VON KARMAN STREET? • A fluid dynamics phenomenon • Repeating pattern of swirling vortices caused by the unsteady separation of flow of a fluid around blunt bodies. • Named after the engineer and fluid dynamist T. Von Karman. • Vortex formation only starts above Re>80. • Vortex Shedding is given by Strouhal number, 𝑆𝑡 = 𝑓𝑑/𝑈. • For flow over cylinder St = 0.2
3. 3. OBJECTIVE • To simulate the flow over a cylinder for Re 103 and 104 using different turbulence models and to compare the results and suggest the best model for this case. • To obtain the coefficients of lift and drag and to compare it with the theoretical data available. • To find the Strouhal number from the simulation and to compare it with the theoretical data available.
4. 4. PROBLEM SPECIFICATION • Unsteady state. • Fluid as air of 𝜌 = 1.225 kg/m3 and 𝜇 = 1.78 x 10−5 kg/ms. • Set diameter as 1 m for ease of calculation. • Obtain the velocity at the inlet in order to maintain the desired Reynolds number, i.e., 103 and 104 by using the below formula. 𝑅𝑒 = 𝜌𝑈𝐷 𝜇
5. 5. SOLUTION DOMAIN • A circular domain will be used for this simulation. • Thus, the outer boundary will be set to be 64 times as large as the diameter of the cylinder. • That is, the outer boundary will be a circle with a diameter of 64 m.
6. 6. MESH • Mesh Quality • Aspect Ratio - 2.25882 • Minimum Edge Length – 1.57m • Growth Rate – 1.20 • Mesh Size • Level – 0 • Cells – 18432 • Faces – 37056 • Nodes – 18624 • Partitions – 1
7. 7. BOUNDARY CONDITIONS • We will set the left half of the outer boundary as a velocity inlet. • Next, we will use a pressure outlet boundary condition for the right half of the outer boundary with a gauge pressure of 0 Pa. • Lastly, we will apply a no slip boundary condition to the cylinder wall.
8. 8. SOLVER SETTINGS • SIMPLE • Second Order Implicit • Time Step Size • 0.2 secs for Re = 104 • 5 secs for Re = 1000 • • No. of Time Steps • 400 for Re = 104 • 800 for Re = 1000
9. 9. NUMERICAL RESULTS Re 1000 ( k-Epsilon Model) Velocity Streamlines Velocity Magnitude
10. 10. CD & CL PLOTS -6.000 -5.000 -4.000 -3.000 -2.000 -1.000 0.000 1.000 2.000 3.000 4.000 0.000 500.000 1000.000 1500.000 2000.000 2500.000 Cd Time (s) Cd Vs Time -0.800 -0.700 -0.600 -0.500 -0.400 -0.300 -0.200 -0.100 0.000 0.100 0.200 0.000 500.000 1000.000 1500.000 2000.000 2500.000 Cl Vs Time Re 1000 ( k-Epsilon Model)
11. 11. NUMERICAL RESULTS Re 1000 (K-Omega Model) Velocity Streamlines Velocity Magnitude Cd Vs Time CL Vs Time
12. 12. NUMERICAL RESULTS Re 1000 (K-Omega SST Model) Velocity Streamlines Velocity Magnitude Cd Vs Time CL Vs Time
13. 13. NUMERICAL RESULTS Re 104 (K-Epsilon Model) Velocity Streamlines Velocity Magnitude Cd Vs Time CL Vs Time
14. 14. NUMERICAL RESULTS Re 104 (K- Omega Model) Velocity Streamlines Velocity Magnitude Cd Vs Time CL Vs Time
15. 15. NUMERICAL RESULTS Re 104 (K- Omega SST Model) Velocity Streamlines Velocity Magnitude Cd Vs Time CL Vs Time
16. 16. NUMERICAL SOLUTIONS • We can see how the lift coefficient changes with the flow time, becoming periodic due to the vortex shedding from the cylinder. • We can use this plot to calculate the Strouhal number of the flow, which is a ratio of the unsteadiness in the flow to inertial forces in the flow field. • We can calculate the Strouhal Number by calculating the frequency of the vortex shedding from our plot.
17. 17. RESULTS Re Model Cd Cd Actual Cl Time period F (Hz) St No St Actual 10000 K-Epsilon 1.28015 1.00 0.00368 2.6 0.3846 0.2634 0.2 K-Omega 1.00063 1.00 0.00256 3.00 0.3333 0.2283 0.2 K-Omega- SST 1.00002 1.00 0.00048 3.20 0.3125 0.2140 0.2 1000 K-Epsilon 1.01413 1.20 0.00263 450 0.002222 0.1522 0.2 K-Omega 1.45677 1.20 0.05266 310 0.003226 0.2209 0.2 K-Omega- SST 1.28016 1.20 0.06904 335 0.002985 0.2044 0.2
18. 18. STROUHAL VS REYNOLDS 0.0000 0.0500 0.1000 0.1500 0.2000 0.2500 0.3000 0 2000 4000 6000 8000 10000 12000 St Re Strouhal No VS Reynold No K-Epsilon k-Omega K-Omega SST Theoretical
19. 19. CD VS REYNOLDS NO 0.00000 0.20000 0.40000 0.60000 0.80000 1.00000 1.20000 1.40000 1.60000 0 2000 4000 6000 8000 10000 12000 Cd Re Drag Coefficient Vs Re No K-Epsilon K-Omega K-Omega SST Theoretical • We can see from the above comparison that the K-Omega SST model is the most accurate among the three models as its value are closer to the theoretical data available for flow over cylinder
20. 20. DISCUSSIONS • The simulation experiences some instabilities at the start and gradually stabilizes as the flow develops. • To avoid this, we can either patch the region and apply a initial condition of velocity or run the simulation under steady state and then use this case as the boundary condition for the unsteady simulation. • This results in earlier vortices shedding and thus allows us to see the oscillation in the lift coefficient vs time plot better. • This also effectively reduces the time step size & number times steps to be run and thus effectively capture the vortex shedding.
21. 21. CONCLUSION • Thus the flow over a cylinder was simulated in FLUENT 16.0 and the different turbulence models were compared. • The drag coefficient and the Strouhal no obtained from simulations were compared to the theoretical data available and were found to be inline. • It was found that the K-Omega SST Turbulence model was the most accurate and the percentage error with the theoretical data for drag coefficient and Strouhal number was 6% and 2% respectively which is acceptable.
22. 22. THANK YOU!!! 