[oj.bulmer]

Hi

I want some good literature on performance of perforated sheet with hexagonal holes. While Idelchik's "Handbook of Hydraulic Resistance" has abundant information about circular hole patterns, it has no mention of hexagonal holes.

Entire day of searching and I could stumble upon just two references. One is a published paper claiming hexagonal holes produce smaller pressure drop than circular ones, and other is a patent (yea, I have to search patents now, in the absence of literature ) which claims the velocity distribution for hex holes is smooth etc.

I want some good literature beforehand that gives resistance coefficients for different percentages of open areas and thickness to hole diameter ratio etc, or at least something. I can always do a unitary cell symmetric arrangement of hexagonal hole to understand the characteristics, but it is time consuming and it is not possible to cover all types of perf sheets in limited time.

Thanks
OJ

[evcelica]

These types of parametric analyses are what workbench is good at. You can do you unitary cell symmetric arrangement, but define your geometry parametrically, and make an expression for the pressure drop that is an output parameter. Then set up your ranges of input parameters and hit update all results.


I hate searching all day and coming up with nothing! at least if the computers running you are making some progress and feel better.

[oj.bulmer]

Thanks but such a comprehensive study is my last resort. I always insist on some literature search before I launch a serious investigation. I have already done a study of symmetrical unitary cell for circular holes and the results seem to be sensitive to meshes. I had to use close to 5 million cells to achieve a mesh independence solution. But then, I did this study just to compare the results versus Idelchik's data, to understand if my approach is reasonable, and my results were within 1% of that of Idelchik's predictions.

Since different open areas and t/d ratios will alter the geometry signifiacantly, the mesh independence for a range of these cases would be necessary, and the computational effort thus is mammoth.

It always is beneficial to have a bit of patience while combing through literature. I have (pleasantly) surprised myself for enough no. of times to believe that

OJ

[yanki]

Originally Posted by oj.bulmer

Thanks but such a comprehensive study is my last resort. I always insist on some literature search before I launch a serious investigation. I have already done a study of symmetrical unitary cell for circular holes and the results seem to be sensitive to meshes. I had to use close to 5 million cells to achieve a mesh independence solution. But then, I did this study just to compare the results versus Idelchik's data, to understand if my approach is reasonable, and my results were within 1% of that of Idelchik's predictions.

Since different open areas and t/d ratios will alter the geometry signifiacantly, the mesh independence for a range of these cases would be necessary, and the computational effort thus is mammoth.

It always is beneficial to have a bit of patience while combing through literature. I have (pleasantly) surprised myself for enough no. of times to believe that

OJ

Hey OJ,

Were you able to find out how to calculate this? I am trying to simulate a flow through perforated plate with hexagonal holes, and was wondering how to calculate pressure loss.

[ghorrocks]

There is nothing special about the flow you describe, standard CFD techniques should work fine. But as OJ says, you need to be careful with mesh resolution to get accurate results - but this is the case with any CFD simulation so is nothing special.

Or if you are having a specific problem then please ask a specific question.

[yanki]

Originally Posted by ghorrocks

There is nothing special about the flow you describe, standard CFD techniques should work fine. But as OJ says, you need to be careful with mesh resolution to get accurate results - but this is the case with any CFD simulation so is nothing special.

Or if you are having a specific problem then please ask a specific question.

Hey Glenn,

I think I quoted the wrong message, sorry for that. I was referring to the first message of OJ, asking for "....resistance coefficients for different percentages of open areas and thickness to hole diameter ratio etc,..."

I am trying to model a perforated cover as a porous jump boundary condition, but this is in Fluent, that's why I didn't get into specifics, since this is the CFX forum.

[ghorrocks]

I think I understood your question - were you trying to get resistance coefficients from a porous plate, which you are doing by running a detailed simulation to get the pressure loss across a few holes which you can then work out the resistance coefficients for the plate? Even if you are trying to model a range of hole sizes, the concept is still the same.

If this is the correct question then my response is still appropriate - this is a basic CFD simulation, but still requires validation and verification like any CFD simulation which you would like to be accurate.

[yanki]

Originally Posted by ghorrocks

I think I understood your question - were you trying to get resistance coefficients from a porous plate, which you are doing by running a detailed simulation to get the pressure loss across a few holes which you can then work out the resistance coefficients for the plate? Even if you are trying to model a range of hole sizes, the concept is still the same.

If this is the correct question then my response is still appropriate - this is a basic CFD simulation, but still requires validation and verification like any CFD simulation which you would like to be accurate.

Thanks for the answer Glenn. I am trying to model something like a server cabinet, which has a perforated cover. I am not very much interested in different covers or holes with different sizes, just wanted to include the cover in my model. But I got really confused along the way and other topics in the forum didn't help much. So, I might have asked a silly question. I thought if I know the pressure loss through the cover, I would be able to model it with one of the boundary conditions.

[ghorrocks]

Modelling it as a momentum sink is a common way of dealing with this. The best way of doing this is to use experimental data of manufacturer's data for the sheet. If you don't have that you can estimate the pressure loss versus flow rate by assuming the openings are equivalent to oriface plates of equivalent area. It is a bit crude but good enough to start off.

The momentum sink can be applied to an interface or a solid region. You will need to define this in the mesh and geometry.

[yanki]

Originally Posted by ghorrocks

Modelling it as a momentum sink is a common way of dealing with this. The best way of doing this is to use experimental data of manufacturer's data for the sheet. If you don't have that you can estimate the pressure loss versus flow rate by assuming the openings are equivalent to oriface plates of equivalent area. It is a bit crude but good enough to start off.

The momentum sink can be applied to an interface or a solid region. You will need to define this in the mesh and geometry.

OK I'll try this. Thanks for guiding.