Flow over a cylinder
AIM
Simulate the flow over a cylinder for the conditions shown in the video.
THEORY
Transient flow simulation is the time dependent simultion where the results vary with respect to time. Flow over a cylinder is the simulation where we study how the velocity and pressure varies over the surface and also many things like boundary layer theory, no slip condition on the surface of the body etc. We can also plot the various graphs of velocity and pressure vs time to get the idea how the flow happens. Moreover, we can create the animation of the flow over the cylinder by giving the required inputs.
INITIAL FLOW PARAMETERS
Inlet velocity= 2.5 m/s
Fluid = Air
Flow type - External
Density of water- 1.23 kg/m3
Dynamic viscocity of air= 1.81 × 10-5 kg/(m·s)
Cylinder Diameter= 0.04m
Base line Reynolds number= 6795.58.
CASE 1 - 20% increase in Reynolds number
Re=8154.456
v=3 m/s
Fow length= 0.5m
Flow through time= 0.166 sec
End time= 0.5 sec
Velocity plot
Pressure plot
LINKS
pressure variation https://drive.google.com/file/d/1cy3zu-FWZcv4rb2BixMlmq4n9Tx4nu4o/view?usp=sharing
velocity variation https://drive.google.com/file/d/1cbyYC_J451ElLaDcgnEmcUSt4kBLxVJr/view?usp=sharing
CASE 2 - 40% increase in Reynolds number
Re=9513.812
v=3.5 m/s
Fow length= 0.5m
Flow through time= 0.143 sec
End time= 0.5 sec
Velocity plot
Pressure plot
LINKS
pressure variation https://drive.google.com/file/d/1bIMI0E6b_KHi0QzlnFydyx03kpC-MGZe/view?usp=sharing
velocity variation https://drive.google.com/file/d/11gIokO3-J2JUa4YtJulYXXbo5MFwpr_f/view?usp=sharing
CASE 3 - 100% increase in Reynolds number
Re=13591.16
v=5 m/s
Fow length= 0.5m
Flow through time= 0.1 sec
End time= 0.4 sec
Velocity plot
PRESSURE PLOT
LINKS
pressure variation https://drive.google.com/file/d/1KBQ9hy0zJqxZChAX-GpwMKa1Brh_1Aoy/view?usp=sharing
velocity variation https://drive.google.com/file/d/1ldyelHUPbOiWFSEUUnLKr73cOI7XTL57/view?usp=sharing
OBSERVATION AND CONCLUSIONS
VELOCITY PLOTS
- @20% increase in Reynolds number i.e Re=8154 the flow is turbulent in nature and as we increase the reynolds number to 40 % and 100% of the basic reynolds number the velocity of the flow increases.
- Hence, flow through time decreases as the Reynolds number increases with constant domain length
- The boundary layer seperation takes place large distance way from the stagnation point.
- The velocity @ stagnation point is zero and the same at other end which appears blue in colour.
- Far distance from the tail end the flow again regains its velocity
- The velocity vatiation is very fast along Y- direction since the kinematic viscocity of air is very high.
PRESSURE PLOTS
- There will be sudden increase in pressure at stagnation point i.e at leading edge which appeares red in colour. Hence, changes in pressure around the cylinder takes place.
- 50 to 60 degrees from the leading edge pressure decreases and a wake pressure region is created just after the cylinder.
- In dynamic flow as we increase the reynolds number the velocity of the flow increases. Hence, the pressure at stagnation point also increases @ leading edge
- For the delay of fluid seperation negative pressure gradient is favorable but the negative pressure is adverse.