Lid Thickness and Edge Effects in FloWorks

D.Castle · June 17, 2009, 12:23

Hi,

I'm using Flow Simulation 2009 (formerly FloWorks) to model airflow through a grate. I'm using the lid generation tool to create lids for the holes in the grate, but since they are created flush with the side exposed to the airflow, I'm wondering if the computer is able to calculate the edge effects. Should I be creating lids manually and recessing them to expose the edges of the material that will be in contact with the fluid? I'm using static pressure boundary conditions and a fine local mesh at all the openings.

I'm new to this, but we don't have anyone else in our company who knows the software. This seems like a helpful group of knowledgeable people.

Thanks a lot.

Ive · June 18, 2009, 04:44

The lids are considered as a solid material and the flow originates from the surface of a lid selected for boundary condition, not inside the lid. So in your case, the raised lids do not allow to analyze the flow around the edges, because the inlet is above the edges. The recessed lids will suit better, however, if the grade is "thin" and the length of holes is not much longer than their diameter, the flow around corners may be unrealistic due to the close proximity of the edges to the inlet. You can try the external analysis - it may better suit your case.

D.Castle · June 18, 2009, 16:21

Ivan, it looks like you're the one man answer team here. Thank you.

In this model I have the flow originating from a designated fan lid further up the duct. The airflow has to leave through the grate to ambient conditions. It is thin, so I'm optimizing thin wall resolution and creating local meshes there trying to get the most accurate results. Would an external analysis allow me to disable the lids and use them for volume goals through the grate as flow exits the duct without setting an external airflow? The breakdown of Volume Flow Rate though different grate designs is the goal of the analysis here, and the edges are important.

Thank you again. I know I'm new here, but you've already confirmed more ideas of mine than I could find answers for in any of the help sections.

Ive · June 19, 2009, 04:51

I thought that the lids in grate are inlet. At the outlet you will get more correct results, I think, but the flow will still be different from what you can get in an external analysis. Yes, you can disable the lids, and I also recommend you to specify the surface goals at their surfaces. This will allow you to measure parameters such as mass or volume flow rate through the holes and provide more accurate determination of Surface Parameters on these surfaces in postprocessor. To avoid external analysis, you may attach a virtual outlet volume to the grate by creating a hollow cube or cylinder or other geometry that suits your model and specifying outlet boundary conditions on its inner walls.
Regarding "optimize thin walls resolution" option - you should always keep this option selected, in any analysis. It should be disabled in some very special cases only, such as to resolve compatibilty issues when loading projects from very old versions.

June 17, 2009, 12:23	Lid Thickness and Edge Effects in FloWorks	#1
D.Castle New Member Join Date: Jun 2009 Posts: 7 Rep Power: 16	Hi, I'm using Flow Simulation 2009 (formerly FloWorks) to model airflow through a grate. I'm using the lid generation tool to create lids for the holes in the grate, but since they are created flush with the side exposed to the airflow, I'm wondering if the computer is able to calculate the edge effects. Should I be creating lids manually and recessing them to expose the edges of the material that will be in contact with the fluid? I'm using static pressure boundary conditions and a fine local mesh at all the openings. I'm new to this, but we don't have anyone else in our company who knows the software. This seems like a helpful group of knowledgeable people. Thanks a lot.

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June 18, 2009, 04:44		#2
Ive New Member Ivan Andronov Join Date: Jun 2009 Posts: 25 Rep Power: 16	The lids are considered as a solid material and the flow originates from the surface of a lid selected for boundary condition, not inside the lid. So in your case, the raised lids do not allow to analyze the flow around the edges, because the inlet is above the edges. The recessed lids will suit better, however, if the grade is "thin" and the length of holes is not much longer than their diameter, the flow around corners may be unrealistic due to the close proximity of the edges to the inlet. You can try the external analysis - it may better suit your case.

June 18, 2009, 16:21		#3
D.Castle New Member Join Date: Jun 2009 Posts: 7 Rep Power: 16	Ivan, it looks like you're the one man answer team here. Thank you. In this model I have the flow originating from a designated fan lid further up the duct. The airflow has to leave through the grate to ambient conditions. It is thin, so I'm optimizing thin wall resolution and creating local meshes there trying to get the most accurate results. Would an external analysis allow me to disable the lids and use them for volume goals through the grate as flow exits the duct without setting an external airflow? The breakdown of Volume Flow Rate though different grate designs is the goal of the analysis here, and the edges are important. Thank you again. I know I'm new here, but you've already confirmed more ideas of mine than I could find answers for in any of the help sections.

June 19, 2009, 04:51		#4
Ive New Member Ivan Andronov Join Date: Jun 2009 Posts: 25 Rep Power: 16	I thought that the lids in grate are inlet. At the outlet you will get more correct results, I think, but the flow will still be different from what you can get in an external analysis. Yes, you can disable the lids, and I also recommend you to specify the surface goals at their surfaces. This will allow you to measure parameters such as mass or volume flow rate through the holes and provide more accurate determination of Surface Parameters on these surfaces in postprocessor. To avoid external analysis, you may attach a virtual outlet volume to the grate by creating a hollow cube or cylinder or other geometry that suits your model and specifying outlet boundary conditions on its inner walls. Regarding "optimize thin walls resolution" option - you should always keep this option selected, in any analysis. It should be disabled in some very special cases only, such as to resolve compatibilty issues when loading projects from very old versions.