[venkat_aero2007]

Is there any way to avoid the clustering of mesh near the leading edge of the blade. I tried to split the block near the leading edge of the blade but no change in the mesh distribution. It will be great if you give some suggestion.

[zainab]

Hi Far
Please, can you help me? I wont to mesh a horizontal cylinder of 5.83m length and 25.4mm diameter with (O Grid) by using Gambit 2.3 thanks.

[venkat_aero2007]

Hi far,
I have changed the domain shape. I had inserted Y-block at the tip of the propeller blade. In the region of Y-block, i have low angle quality as shown in figure1. Is there any way to improve the angle at the tip of the propeller.

Files can be downloaded form the following link.
https://www.dropbox.com/sh/c6e3l1hh0o1f32a/pxjVod6pAW

[venkat_aero2007]

Hi Far,
I did a simulation in fluent. The residuals oscillates. i think it is due to low angle quality. Can you suggest me idea to increase the minimum angle quality.

[Far]

Congratulation for your work and thumsup for persistence




unfortunately it is due to geometry and blocking is perfect. So it is impossible to improve the quality (angle is 9 deg) with Y-block.

You have three options

1. Use wedge block (I prefer this). For this just leave the block as it is i.e. don't insert Yblock.

2. Inset swept block

3. Change the trailing edge shape by trimming the sharp corner.

[venkat_aero2007]

Thanks for your support.

1. Use wedge block (I prefer this). For this just leave the block as it is i.e. don't insert Yblock.
I think, Because of sharp corner I will have low quality if I leave the bock without inserting Y block.

2.Insert swept block.
Could you please explain a bit more about inserting swept block.

3. Change the trailing edge shape by trimming the sharp corner.
Will trimming the sharp corner affects the flow behavior at the trailing edge.

[Far]

1. Use wedge block (I prefer this). For this just leave the block as it is i.e. don't insert Yblock.
I think, Because of sharp corner I will have low quality if I leave the bock without inserting Y block.

No. Wedge blocks are blocks with prism elements with good quality. If one recall the prism is the shape with 3 rectangles on three sides with base and top of triangle shaped.

2.Insert swept block.
Could you please explain a bit more about inserting swept block.
In the menu, where you chose the Y-block option, you can see the swept block option there. It just change the elements from structured to unstructured and you have option either use tetra or quadrilateral.


3. Change the trailing edge shape by trimming the sharp corner.
Will trimming the sharp corner affects the flow behavior at the trailing edge.

It is common practice. Moreover from manufacturing point of view it is not possible to manufacture the wing this feature. Therefore may be (or may not be ) trimming the sharp corner affects the flow, but you will be close to practical design.

[Far]

We should call it Triangular prism

[venkat_aero2007]

thanks far. final question. should i want to insert the swept block in the y-grid or i should directly insert swept block without creating y-grid.

[Far]

Directly. Check also in ICEM help

From ICEM Help

Swept

converts a mapped block to a swept block. The face selected is converted to a free face and swept across the block and any parallel blocks. While mapped blocks must have the same nodes on opposite sides of the block in the I, J and K directions, a swept block is free to have varying nodes in two directions (across the selected face) and is mapped in the third (perpendicular to the selected face).

Free

converts a block to a free (unstructured) block. In 2D, this will result in a paved surface which can be all triangles, quad dominant, quad with one tri, or all quad. In 3D, the free block mesh type can be Tetra (Delaunay, TGrid or Advancing Front), Hexa Core or Hexa Dominant mesh. In 2D, this is most often used to solve issues with poor internal angles after mapping to curves or to prevent node counts from propagating across a face.

Sorry I mixed up the swept block with free block. Anyhow please check both options and educate us as I am also not clear about swept block.

[venkat_aero2007]

I converted the Y-block to a free block. The minimum angle has improved to 19. I will also try the wedge block and post the mesh.

[venkat_aero2007]

Hi Far,
I tried wedge block without inserting Y-block at the trailing edge. There is a clustering of elements at the trailling edge as you can see in the figure1. the Determinant (3x3x3) is very low and the minimum angle is just 9.
https://www.dropbox.com/sh/c6e3l1hh0o1f32a/pxjVod6pAW

methode2: free block

I converted the Y-block to a free block. I was able to improve the minimum angle to 24 with a Determinant (3x3x3) quality 5.5. Have a look in Figure3. You can see the unstructured elements at the tip block.

[Far]

Any update please

[venkat_aero2007]

Hi far,
I had a problem in the simulation in fluent. FLUENT gave me an error saying that mixing-plane is not in the acceptable tolerance limit. I think the periodic domain boundary that i changed has created some problem.

I think the periodic domain boundary that i changed is not correct. Can you please tell me how to change the periodic boundary that follow the shape of the blade near the hub.

[Far]

could you please post some pics

[venkat_aero2007]

Actually it is a contra rotating rotor. I have meshed each rotor separately and merged in ICEM. In the figure (top view), you can see the misalignment of interface between the two rotor domain.

I have just offset the hub curve to 15.5 in the farfield and then rotated the farfield curve to a periodic angle of 32.72727.

Could you please tell me where I am going wrong.

Actually I am able to launch the calculation in fluent, but the residuals oscillates due to the problem in mixing plane (interface between the two rotor domain)

https://www.dropbox.com/sh/7r01gwggwzd78ig/veHVVDfrVc

[Far]

are you giving both rotors motion with +ve and -ve rpms? Is it possible to give the one rotor rpm1+rpm2 and other one as stationary? or this problem is related to meshing? can you post more pics with different views?

why are you merging meshes in ICEM?

[Far]

By definition, mixing plane should have same radial extent on both sides. But there is no limit on rotational / circumferential offset. For example rotor1 may be placed at 0-90 deg and rotor 2 may be placed within 90-270. And these values are arbitrary and make no difference into computation of mixing plane.

Fig1. View of rotor 1 and rotor 2 at hub
Fig2. View of rotor 1 and rotor 2 at shroud
Fig3. Overall view of rotor 1 and rotor 2

[venkat_aero2007]

yes I am giving both rotors motion with +ve and -ve rpms. It is not possible to give the one rotor rpm1+rpm2 and other one as stationary because in contra rotaing rotor, the front rotor rotates in clockwise and rear in anti clockwise direction. I am sure it is not because of meshing problem because I ran a simulation with unstructured mesh which worked perfectly fine. I also ran a simulation with structured mesh without changing the boundary shape of the domain near the hub ( with poor quality mesh). it also worked fine. So I am sure it is not because of mesh. It is due to change in the boundary shape. In the figure you can see the interaction of interface between front rotor domain and rear rotor domain. this interaction has to be avoided. I think I went somewhere wrong in changing the domain boundary shape.

"why are you merging meshes in ICEM?"

Actually the front rotor consist of 11 bades with peridic angle 32.72727 and the rear rotor with 9 blades (peridic angle 40). So meshes them seperately and merged it.

Could please tell me how to change the domain geomentry shape.

[venkat_aero2007]

Far you are too quick

I seen your reply after posting my last message. so do you mean that I have to keep same shroud height for both the rotors.