Flow past a cylinder

vishnuambali@gmail.com · January 8, 2016, 12:58

while simulating unsteady flow past a cylinder I always get the value of CL to be near to zero though drag values fall within limit ?? Why does this happen even after i wait for 100s of flow?

shereez234 · January 9, 2016, 18:06

You should post more details to get proper help. What is the flow conditions you are using? Velocity? Reynolds number? Laminar? Turbulent? Viscous model? Reference Values you use? Coupled or Segregated Solver?

AHF · January 10, 2016, 02:20

Quote:

Originally Posted by vishnuambali@gmail.com

while simulating unsteady flow past a cylinder I always get the value of CL to be near to zero though drag values fall within limit ?? Why does this happen even after i wait for 100s of flow?

major problem in your case is that you not set references value

vishnuambali@gmail.com · January 16, 2016, 11:15

The above problem was solved but has the below mentioned trouble now.

With Re=100,v=1m/s,density=100.When i simulate an unsteady flow I always get the Cl to be greater than 0.3 eventhough the frequency is .16(St=.16).

Why I am not getting the value of CL<0.26??

Please help..My cylinder dia is 1m

AHF · January 19, 2016, 03:37

Quote:

Originally Posted by vishnuambali@gmail.com

The above problem was solved but has the below mentioned trouble now.

With Re=100,v=1m/s,density=100.When i simulate an unsteady flow I always get the Cl to be greater than 0.3 eventhough the frequency is .16(St=.16).

Why I am not getting the value of CL<0.26??

Please help..My cylinder dia is 1m

what about dynamic viscosity ?
is it set to 1 ?
cause Reynolds number need it too
and another thing , what is your solver ?

vishnuambali@gmail.com · January 20, 2016, 03:42

Dynamic viscosity is set to one...I have tried with both simple and coupled solvers(QUICK SCHEME) 2nd order implicit with standard initialization

AHF · January 20, 2016, 12:05

Quote:

Originally Posted by vishnuambali@gmail.com

Dynamic viscosity is set to one...I have tried with both simple and coupled solvers(QUICK SCHEME) 2nd order implicit with standard initialization

so , its laminar if Reynolds be 100
what about your mesh ?
its fine enough ?

vishnuambali@gmail.com · January 21, 2016, 05:53

Mesh is very fine..No of elements is around 40,000.Flow domain is 16mx32m

AHF · January 21, 2016, 06:08

Quote:

Originally Posted by vishnuambali@gmail.com

Mesh is very fine..No of elements is around 40,000.Flow domain is 16mx32m

well, you can't figure out fine mesh just by number
you should check grid dependencies , increase your grid especially at boundary
and compare data

vishnuambali@gmail.com · January 21, 2016, 11:18

I tried with different biasing and no of elements..But still Cl value exceeds .3.

vishnuambali@gmail.com · February 18, 2016, 05:19

Could you please tell me how to call a particular Boundary condition after a certain no of time step is reached using UDF?

January 8, 2016, 12:58	Flow past a cylinder	#1
vishnuambali@gmail.com New Member VISHNU Join Date: Jan 2016 Posts: 13 Rep Power: 10	while simulating unsteady flow past a cylinder I always get the value of CL to be near to zero though drag values fall within limit ?? Why does this happen even after i wait for 100s of flow?

January 9, 2016, 18:06		#2
shereez234 Senior Member M Sereez Join Date: Jan 2014 Location: England Posts: 352 Blog Entries: 1 Rep Power: 13	You should post more details to get proper help. What is the flow conditions you are using? Velocity? Reynolds number? Laminar? Turbulent? Viscous model? Reference Values you use? Coupled or Segregated Solver? AHF likes this.

February 18, 2016, 05:19	Implement boundary condition	#11
vishnuambali@gmail.com New Member VISHNU Join Date: Jan 2016 Posts: 13 Rep Power: 10	Could you please tell me how to call a particular Boundary condition after a certain no of time step is reached using UDF?

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January 16, 2016, 11:15		#4
vishnuambali@gmail.com New Member VISHNU Join Date: Jan 2016 Posts: 13 Rep Power: 10	The above problem was solved but has the below mentioned trouble now. With Re=100,v=1m/s,density=100.When i simulate an unsteady flow I always get the Cl to be greater than 0.3 eventhough the frequency is .16(St=.16). Why I am not getting the value of CL<0.26?? Please help..My cylinder dia is 1m

January 20, 2016, 03:42		#6
vishnuambali@gmail.com New Member VISHNU Join Date: Jan 2016 Posts: 13 Rep Power: 10	Dynamic viscosity is set to one...I have tried with both simple and coupled solvers(QUICK SCHEME) 2nd order implicit with standard initialization

January 21, 2016, 05:53		#8
vishnuambali@gmail.com New Member VISHNU Join Date: Jan 2016 Posts: 13 Rep Power: 10	Mesh is very fine..No of elements is around 40,000.Flow domain is 16mx32m

January 21, 2016, 11:18		#10
vishnuambali@gmail.com New Member VISHNU Join Date: Jan 2016 Posts: 13 Rep Power: 10	I tried with different biasing and no of elements..But still Cl value exceeds .3.