Mesh refinement on modified aerofoil

mr299 · March 30, 2024, 18:48

Very new to CFD and looking into using an active flow control blowing actuator to analyse flow separation, and lift/drag coefficients. Used a baseline NACA0012 aerofoil to get 2D simulation results, I generated a 2D mesh, using calculated values to set prism layer thickness, for a Y+ = 1 and the results were accurate when compare to current research and javafoil estimations.

I have created a CAD model of the modified aerofoil (i.e. with a slot cut into the surface to be used as an additional velocity inlet, imported into STAR CCM with no issues. Due to positive results with initial baseline mesh, I have tried to marry this mesh across to the new modified part, however, I lose the prism layers at the point at which the slot is cut into the surface.

I ran a simulation anyway and the lift/drag values are way off what I was expecting (CL is 1.2 at 1Deg AoD, when I was expecting 0.1 ish). Lead me to believe the loss of prism layers are causing the spurious results.

To rectify, I have tried reducing the stretch factor of the mesh, minimum thickness size, number of layers etc. and also surface mesh. I have tried using a volumetric control by pinpointing the affected area with a cylinder or a block and controlling the mesh that way, each method has failed me.

Does anybody have any ideas as to how I can refine this troublesome area?

Many thanks

Attachments -
Baseline Mesh Domain
Baseline Mesh Leading Edge Close Up
Modified NACA0012 Close Up
Modified NACA0012 Mesh

NACA0012 Modified CAD Close Up.jpg

NACA0012 Modified.jpg

Baseline Mesh 1.jpg

Baseline Mesh.jpg

cwl · March 31, 2024, 18:16

Quote:

Originally Posted by mr299

Due to positive results with initial baseline mesh, I have tried to marry this mesh across to the new modified part, however, I lose the prism layers at the point at which the slot is cut into the surface.

Prism layers are not generated on openings and symmetry by default.
You can override that with Surface Control at slot surface (check Override option and set Prism Layers parameters).

mr299 · April 2, 2024, 08:47

Many thanks for the quick response, I’ve managed to refine the gap as much as I can although whe I have assigned the surface control to the slot inlet with specified prism layer parameters, no prism layers are created, which I can’t understand wh

SESP · April 3, 2024, 11:21

If I understand correctly, you are modeling your outlet just as a surface patch. This will always result in the prism layers collapsing. I would actually model a small section of the slot in the CAD, so "into" your airfoil. By this, you would have a segment of the channel inside the airfoil resulting in the prism layers to follow the surfaces including the sharp edges.

March 30, 2024, 18:48	Mesh refinement on modified aerofoil	#1
mr299 New Member Join Date: Mar 2024 Posts: 2 Rep Power: 0	Very new to CFD and looking into using an active flow control blowing actuator to analyse flow separation, and lift/drag coefficients. Used a baseline NACA0012 aerofoil to get 2D simulation results, I generated a 2D mesh, using calculated values to set prism layer thickness, for a Y+ = 1 and the results were accurate when compare to current research and javafoil estimations. I have created a CAD model of the modified aerofoil (i.e. with a slot cut into the surface to be used as an additional velocity inlet, imported into STAR CCM with no issues. Due to positive results with initial baseline mesh, I have tried to marry this mesh across to the new modified part, however, I lose the prism layers at the point at which the slot is cut into the surface. I ran a simulation anyway and the lift/drag values are way off what I was expecting (CL is 1.2 at 1Deg AoD, when I was expecting 0.1 ish). Lead me to believe the loss of prism layers are causing the spurious results. To rectify, I have tried reducing the stretch factor of the mesh, minimum thickness size, number of layers etc. and also surface mesh. I have tried using a volumetric control by pinpointing the affected area with a cylinder or a block and controlling the mesh that way, each method has failed me. Does anybody have any ideas as to how I can refine this troublesome area? Many thanks Attachments - Baseline Mesh Domain Baseline Mesh Leading Edge Close Up Modified NACA0012 Close Up Modified NACA0012 Mesh NACA0012 Modified CAD Close Up.jpg NACA0012 Modified.jpg Baseline Mesh 1.jpg Baseline Mesh.jpg

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April 2, 2024, 08:47		#3
mr299 New Member Join Date: Mar 2024 Posts: 2 Rep Power: 0	Many thanks for the quick response, I’ve managed to refine the gap as much as I can although whe I have assigned the surface control to the slot inlet with specified prism layer parameters, no prism layers are created, which I can’t understand wh

April 3, 2024, 11:21		#4
SESP New Member Join Date: Mar 2011 Posts: 25 Rep Power: 17	If I understand correctly, you are modeling your outlet just as a surface patch. This will always result in the prism layers collapsing. I would actually model a small section of the slot in the CAD, so "into" your airfoil. By this, you would have a segment of the channel inside the airfoil resulting in the prism layers to follow the surfaces including the sharp edges.