Properly Calculating Lift

dryaridnod · April 1, 2011, 01:19

I am modeling a 3-D fuselage subjected to a free stream flow at sea level at various angles of attack and am attempting to find the coefficient of lift.

1. If using the conventional coordinate system, should the lift force direction be as such: [-cos(alpha),sin(alpha)] in the force coefficient report?

2. The part selected that define the input in the force coefficient report, should this be the entire body in the region?

Thanks in advance for any input!

abdul099 · April 2, 2011, 13:21

1. Drag is the force on a body parallel to the flow and lift is the force on a body perpendiculat to the flow. Yes, you will need to specify the direction according to the angle.
2. The input parts for your reports should be any boundary you want to be taken into account for that specific report. E.g. when you want to get the lift of a ship hull, you would set the input parts to be all boundaries of the ship hull, but not the inlet, outlet, sea ground or the submarine which tries to sink your ship.

dryaridnod · April 2, 2011, 13:37

Quote:

Originally Posted by abdul099

1. Drag is the force on a body parallel to the flow and lift is the force on a body perpendiculat to the flow. Yes, you will need to specify the direction according to the angle.
2. The input parts for your reports should be any boundary you want to be taken into account for that specific report. E.g. when you want to get the lift of a ship hull, you would set the input parts to be all boundaries of the ship hull, but not the inlet, outlet, sea ground or the submarine which tries to sink your ship.

Thank you for the reply. I have made both fixes appropriatly to my simulation however I don't quiet beleive the answers, for high angle of attacks I'm finding it difficult to find the stall angle of attack. The cross-sectional airfoil that essentially makes up the body of my fuselage has a 2D stall angle of attack of around 9-10 degrees, however I'm finding my cl steadily increases even up to 30 degrees! I've changed my mesh resolution and base size to smaller and larger values and finding this result to be consistant. It's somewhat baffeling.

abdul099 · April 4, 2011, 16:50

Can you give a little bit more information about your case? Maybe a picture?
There might be a problem with the domain, physics setup, turbulence model or a bag of rice falling over in China. Or it is the right result. For example, for delta wings or similar shapes, the mechanism of generating lift is different do usual airfoils.
But it's impossible to judge that without having more details about your case.

screech1987 · April 17, 2011, 08:43

What is your model setup?

Even though this should not matter to the non-stall problem, just the accuracy of the CL line, have you set correct reference values for the force coefficient report.

April 1, 2011, 01:19	Properly Calculating Lift	#1
dryaridnod New Member John Doe Join Date: Apr 2011 Posts: 3 Rep Power: 8	I am modeling a 3-D fuselage subjected to a free stream flow at sea level at various angles of attack and am attempting to find the coefficient of lift. 1. If using the conventional coordinate system, should the lift force direction be as such: [-cos(alpha),sin(alpha)] in the force coefficient report? 2. The part selected that define the input in the force coefficient report, should this be the entire body in the region? Thanks in advance for any input!

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April 2, 2011, 13:21		#2
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 637 Rep Power: 14	1. Drag is the force on a body parallel to the flow and lift is the force on a body perpendiculat to the flow. Yes, you will need to specify the direction according to the angle. 2. The input parts for your reports should be any boundary you want to be taken into account for that specific report. E.g. when you want to get the lift of a ship hull, you would set the input parts to be all boundaries of the ship hull, but not the inlet, outlet, sea ground or the submarine which tries to sink your ship.

April 4, 2011, 16:50		#4
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 637 Rep Power: 14	Can you give a little bit more information about your case? Maybe a picture? There might be a problem with the domain, physics setup, turbulence model or a bag of rice falling over in China. Or it is the right result. For example, for delta wings or similar shapes, the mechanism of generating lift is different do usual airfoils. But it's impossible to judge that without having more details about your case.

April 17, 2011, 08:43		#5
screech1987 New Member Martin Join Date: Nov 2010 Posts: 23 Rep Power: 8	What is your model setup? Even though this should not matter to the non-stall problem, just the accuracy of the CL line, have you set correct reference values for the force coefficient report.