Flow over a cylinder

Aim: To study the flow over a cylinder using the Solidworks simulation feature for a baseline simulation & with a varying Reynolds number by a factor of 20%,40% & 100%.

objective :

• calculate the Reynolds number for a baseline simulation.
• Run a baseline simulation.
• Run the transient simulation feature by varying the Reynolds number by Factor of 20%,40%& 100% with a baseline simulation.
• Create animations for pressure-velocity for all the three Reynolds numbers.
  
  

Theory:

Transient Flow Simulation

Transient flow is a flow where the flow velocity and pressure are changing with time. when changes occur to fluid systems such as starting or stopping a pump, closing or opening a valve, or changing a tank level then transit flow conditions exist. otherwise, the system is in a steady state.

The transient flow conditions persist as oscillating pressure and velocity waves for some time after the initial event that caused it.

Explanation:

Reynolds Number

=reynolds number

=density of fluid

=flow speed

=chraterstic linear dimension

=dynamic viscosity of the fluid.

Step 1- Draw a cylinder as per dimension for a simulation.

Diameter, D= 0.04m Length,L =0.05m

characteristics of fluid flowing over a cylinder,fluid type - Air

=1.81 × 10^-5 kg/(m·s)

= 1.125 kg/m³

simulate the flow over a cylinder as per shown in video.

calculate the baseline case reynolds number.

calculations:

For a basline simulation

v= 10m/s

Re = ( ρ x v x D)/(`μ`)

= (1.125x 10x 0.04)/(1.81 × 10^-5 )

= 27012.13

similarly , for a reynolds numbers increase by factor of a 20,40 & 100 percent.

At 20% - 32414.55

40% - 37817

100% - 54024.26

Total Analysis time

The Physical time period until the simulation will be run from its initial instant of time (t=0 sec by dependent)

T = 2t

for Re= 120% of 27012 .13 = 32414.55

v= 12m/s

flow throgh time = domain length / velocity

flow through time = 0.04166 sec

simulation end time = (2t)= 2x 0.04166=0.0833 sec

similarly ,

Re =27012.13	120%	140%	200%
velocity (m/s)	12	14	20
Re	32414.55	37817	5402.26
time (t) sec	0.833	0.0714	0.05

Results:- Simulation

velocity = 10m/s Pressure

v1= 12m/s Pressure 1

V2 = 14m/s Pressure 2

V3 = 20m/s Pressure 3

conclusion:

• as per the above assignment, we can conclude that the max velocity variation over a cylinder, maximum at the surface of cylinder contact, at the inlet velocity becomes zero observed.
• The relative pressure variation does not vary due to the large Reynolds number. There is no pressure variation over a cylinder.
• from the above calculation, we can say the Reynolds number directly to velocity, as velocity increases the Reynolds number also increases.