MESH DEPENDENCY

Ivan Dario Arroyave Zuluaga Automotive Engineering Research Center

(CIMA) Tecnológico de Monterrey Campus Toluca

México

Opportunity Statement / Expected Outcome

Current State In a OEM, Cabin & Thermal models are meshed for analysis using tetrahedral mesh with generic requirements recommended by the Software Vendor. CFD engineers have encountered significant differences in the simulations when the grow rate and type of element is changed.

Desired State

Find the required mesh type and mesh requirements for each analysis creating Best practices.

Robust Design

• We are looking for a new general methodology to build grids for CFD problems; we would like to do our mesh design robust for different types of elements. Hence we selected robust design to carry out our analysis.

• This is the first approach to mesh dependency problems; we want to understand not only how to optimize the mesh construction, but also figure out if Robust Design is a good tool to do this optimization.

Background

Background

Background

Background

Opportunity Statement / Expected Outcome

Defroster Windshield Physical

test patterns

Defroster Side Windows

Physical test patterns

Expected Outcome (Specific physics test):

• Understand sensitivity of meshing characteristics of the determined factors in the event

of thermal analysis

Constrains:

• Software capability, computational cost

Opportunity Statement / Expected Outcome

Develop Concept: Current Best Practices

Develop Concept The following parameters were considered critical for mesh construction

using Hypermesh

4 1

1mm 0.6mm

A. Tetra Number of uniform layers

D. First layer thickness

B. Tetra Growth rate

1.4 1

F. BL Growth rate:

C. Number of BL layers

• YES • NO

1.6 1.1

6 0

Noise/Tetra to Polyhedral

A

B

C,D,F

Parameter Diagram

System

Fluid Mesh process

Control Factors:

Tetra Number of uniform layers

Tetra Growth rate

Number of BL layers

First layer thickness

BL Growth rate

Noise Factors:

(e.g.) Tetra to polyhedral

Noise Factor 1

Noise Factor 2

Noise Factor 3

Outputs:

fit against

physical test

results multiple

response

(R1,R2,R3)

Symptoms:

Meshing time

Solve time

Quality Mesh

Input:

2D Mesh, Boundary

condition

Control Factor Strategy

A - Tetra Number of uniform layers TNUL1 1 Layers

TNUL2 2 Layers

TNUL3 3 Layers

TNUL4 4 Layers

B -Tetra Growth rate TGR1 1.1 rate

TGR2 1.2 rate

TGR3 1.4 rate

TGR4 1.6 rate

C -Number of BL layers NBL1 0 Layers

NBL2 2 Layers

NBL3 4 Layers

NBL4 6 Layers

D– First layer thickness FLT1 0.6 mm

FLT2 0.8 mm

FLT3 0.9 mm

FLT4 1 mm

F - BL Growth rate BGR1 1. rate

BGR2 1.2 rate

BGR3 1.3 rate

BGR4 1.4 rate

• Tetra Number of uniform layers

levels comprehend benchmark

observed typical values

• Tetra Growth rate levels is

selected for its current best

practices and the lower limit that

allows software.

• Number of BL layers , First layer

thickness And BL Growth rate is

chosen to explore different ways to

achieve fill out space without

interference between one surface

and its opposite.

Noise Factor Strategy Full factorial, two cases • First case one factor:

– Tetra to Polyhedral (2 levels)

• Second case Three Factors – Noise factor 1 (2 levels) – Noise factor 2 (3 levels) – Noise factor 3 (3 levels)

Response Strategy Separated Analysis • R1. Numerical-fit physical results

– % Defroster area 25 minutes. – % Defroster area 35 minutes.

• R2. Qualitative-fit physical results • R3. Solving time

Due to the parameters and parameters levels, an L16 orthogonal array was

chose. The objective is to fit the response to experimental value, the

nominal is best formulation is selected.

Optimization Details response 1

Noise factor polyhedral

Response Plots for Means

Response Plots for S/N

Results for one Response

• Optimal levels and factors for Means

– Factor A Level 3

– Factor B Level 4

– Factor C Level 1

• Optimal level and factors for S/N

– Factor A level 2

– Factor B level 2

– Factor C level 1

Conclusions • Hypermesh is versatile enough to carry out an experimental mesh

dependency for CFD Thermal Analysis.

• This analysis should be carried out for each phenomena.

• Variables (e.g. iteration convergence) from the specific solver should

be considered as a response, in order to get general mesh

construction rules.

• This study is the first step to create rules for optimal mesh

generation process.

• Robust Design could be a useful tool to analysis Mesh Dependency

when the quality of mesh does not interfere with the convergence

speed.

Thank you