Internship phase 1 - 08 07 2012

Safran Engineering Services

Pre/Post Treatment Benchmark Study

Tools compared: Solver:

PATRAN v2008r2 SAMCEF 13.1-01 vs. ANSYS Workbench Release 13.0

Prepared by: Yassine Rayad

PATRAN – Methodology & Performance

Boundary & Load Conditions/Analysis/Post-processing

PATRAN Flow Chart

Import solids from

CATIA

Modify surfaces depending on meshing

needs (regular vs. scattered, Isomesh vs.

Paver) and possible geometric

discontinuities

1

Extract surfaces from

solids and organize groups

Check

Fail

Mesh entities surface by surface according

to given mesh criteria

Extract surfaces in CATIA, import back

to PATRAN

2 3

Repeat steps 1-4 for all

remaining entities

Apply cyclic symmetry multipoint

constraint on disc entities

Apply inertial “pre-torsion”

load via fictional node

MPC

Apply pressure

loads on disc and flange

entities

Apply 2-D induced

displacements on disc flanges

Apply thermal conditions on

disc entities via interpolation

Apply aerodynamic pressure felt by the blade

Apply blade temperature

range

Generate dataset for SAMCEF

solver

Launch static

analysis iterations

Perform result post-processing

on PATRAN

5

Legend

Time Penalty

Moderate Timing

No Time Penalty

Verify Model/Project Nodes

Equivalence nodes

Manually move

remaining problematic

nodes

Verify boundaries

for free edges/faces

Verify duplicates,

jacobian ratio & zero, and

normal vectors

Lower global tolerance drastically, reorganize

nodes, save a copy of the database, and project

nodes on original surface geometry

4

Create volume

mesh

SNECMA Silvercrest The new generation business jet engine.

Specifications Type: Turbofan

Length: ~ 1.90 m

Diameter: Fan ~ 1 m

Components Compressor: Low pressure 1 axial stage

High pressure 4 axial stages + 1 centrifugal stage

Turbine: Low pressure 4 axial stages

High pressure 1 axial stage

Performances

Overall Pressure Ratio: ~ 27

Max. Thrust: 42 – 53 kN

Applications

Cessna Citation Longitude

PATRAN Flow Chart

MESHING

Triangular surface mesh (Tri 3)

Tetrahedral volume mesh (Tet 4)

PATRAN Flow Chart

Silvercrest – low pressure turbine Stage 2 (axial) – composed of three entities

Blade

Disc Stage 1 flange

Comparison Subject /1.1.1/

PATRAN Flow Chart

171 mm

1 mm in the blade and 0.5 mm in the radii

Blade tip

Disc

Blade root Scattered mesh in the disc

(2 mm)

Given Meshing Criteria /1.1.2/ (general criteria)

PATRAN Flow Chart

Given Meshing Criteria /1.1.2/ (radii)

Lower radius

Upper radius

Nodes measured

0.506 mm

0.539 mm

PATRAN Flow Chart

Given Meshing Criteria /1.1.2/ (disc socket)

Regular mesh in the disc socket (0.5 mm) 0.489 mm

Nodes measured

PATRAN Flow Chart

Given Meshing Criteria /1.1.2/ (blade root) Blade root stilt (0.7 mm)

Regular mesh in the contact zones of the blade root (0.5 mm)

Nodes measured

0.498 mm

0.685 mm

PATRAN Flow Chart

Given Meshing Criteria /1.1.2/ (blade tip)

Blade tip (~ 1 mm)

Nodes measured

1.06 mm

PATRAN Flow Chart

Geometric Discontinuities /1.1.3/ (bottom blade radius)

ISSUE: This discontinuity caused an issue early in meshing process as it rendered a time penalty in the surface extraction from the given CATIA model. SOLUTION: Run the surface extraction process for the failed entity directly CATIA and re-import surface geometry in PATRAN

PATRAN Flow Chart

Discontinuity

Geometric Discontinuities /1.1.3/ (upper surface [blade])

ISSUE: This discontinuity located near the bottom radius of the upper blade surface caused a time penalty in the surface treatment. Many other discontinuities similar to this one were present throughout the entire model. SOLUTION: Remove unnecessary vertices which can be problematic. Otherwise, take the time to create intermediate points and chain all edges within each surface to form curves and create new surfaces that will be used solely for meshing. Nodes must be projected on original geometry.

S 640

PATRAN Flow Chart

Geometric Discontinuities /1.1.3/ (upper surface [blade])

This surface is the bi-parametric surface created from chaining the edges of Surface 640. It has been used to mesh the problematic upper surface of the blade. Note that the nodes generated were then projected onto S 640, the original surface.

S 688

PATRAN Flow Chart

Element Jacobian Ratio Irrelevant – Triangular elements

Element Jacobian Zero Illustrates element disparities, must be positive but contained

Element Normals Illustrates element normal vector direction, must be either +1 or -1 throughout entire model

Boundaries via Free Faces Displays any free faces or edges depending on method. For a closed solid, the entire model must be yellow to allow volume meshing from surface mesh

Meshing Verifications /1.1.4/

PATRAN Flow Chart

Volume Mesh Creation /1.1.5/

Elements/Create/Mesh/Solid

PATRAN Flow Chart

BOUNDARY CONDITIONS

&

LOAD CASE SPECIFICATION

PATRAN Flow Chart

Prelude to L/BC /1.2.1/

Before we dive into the details of the various loads and conditions applied on this 3-D model, we must first note that many of these conditions come from an existing model. Indeed, as in most cases similar in nature to this one, the 3-D model creation was piloted by an existing 2-D model (120424_MissionVFD_mct12171.db) created by EATT (SES France). For the purpose of this benchmark, we were interested solely by the instant t= 368.39 s which represents the Take-off segment of the mission.

PATRAN Flow Chart

Cyclic Symmetry Multi-point Constraint /1.2.2/

Cyclic symmetry of disc and flange lateral faces via node

automatic liaison (MPC .LIA) with respect to cylindrical

coord. sys.

Master Surfaces: Region 1

Slave Surfaces: Region 2

Cylindrical coord. sys.

Mécanique/Conditions aux limites/Liaisons automatiques

PATRAN Flow Chart

Cyclic Symmetry Multi-point Constraint /1.2.2/

The cyclic symmetry of the disc and flange lateral faces is applied in order to maintain continuity within the turbine. There are 116 turbine blades in the second stage of this low pressure turbine. Due to a lack of computing power and in order to simplify the analysis, we break the disc into 116 equivalent sections. As we know, deformation is a function of the derivative of displacement. In order for the entire turbine analysis to be coherent, we must maintain continuity and derivability. If these are ensured, we can safely and accurately calculate and predict deformations in the turbine. Hence, all loads applied to a face of the disc must be equivalent in magnitude and in direction on the opposite face.

PATRAN Flow Chart

Pre-torsion Inertial Load /1.2.3/ (preparation)

RM2

Alpha en Degre 2.56

Alpah en Rad 0.045

L 16.087837

delta=L Tan(Alpha) 0.719

Alpha

Adjacent blade induced effect.

PATRAN Flow Chart

Blade Tip

Fictional node

Elements/Create/MPC/Explicit

Pre-torsion Inertial Load /1.2.3/ (application)

PATRAN Flow Chart

2-D Induced Displacements on Flanges /1.2.4/ (prep)

Stage 1 flange

Stage 2 flange

PATRAN Flow Chart

2-D Induced Displacements on Flanges /1.2.4/ (app)

PATRAN Flow Chart

Disc and Flange

Pressures Felt by Disc and Flange /1.2.4/

The pressure markers shown on image on the right display the pressure distribution on the disc and flange. These were collected from a 2-D model created first, which pilots the creation of our 3-D model. These pressures are felt at time (t) = 368.39 seconds which represents the Take-off instant for the mission VFD.

PATRAN Flow Chart

Aerodynamic Pressures Felt by Blade /1.2.5/ (contours)

The pressure contours shown here refer to the PS3D file: rm2.YKYL.YKYL_RM2_TO18_SC264_MAJ_VENTIL_ITE02 For a complete explanation of the preparation of these contours, please refer to the following presentation: « Formation Pression Aérodynamique pour les Aubes »

Note that, as expected, the aerodynamic pressure peak is located on the lower blade surface and represents a value of approximately 0.4 MPa.

PATRAN Flow Chart

Aerodynamic Pressures Felt by Blade /1.2.5/ (pressure resultant vector)

Lower blade surface

Upper blade surface

As expected, the resultant pressure vector is directed from the lower blade surface to the upper blade surface.

PATRAN Flow Chart

Temperatures Felt by Blade /1.2.6/

The thermal effects present on the blade are presented as a radial distribution and are applied using a pre-defined Spatial Field. These temperature values are taken from the Aero_Meca files provide by SNECMA. We then plot the temperature contours on the blade entity as shown below.

Min = 600 ° C (located in the neck of the blade) Max = 993 ° C (located in the blade tip)

PATRAN Flow Chart

Thermal Interpolation in Disc and Flange /1.2.7/ (prep)

This task is the most tedious and delicate task in the PATRAN methodology. It requires precision and patience. It is also dangerous for the database and if an incorrect interpolation is done, the whole .db file can be affected. Therefore, it is essential to save a copy before and after any interpolation is rendered in order to avoid unfortunate data losses. The interpolation file used is the following: RTBP_SC_V3_C1.MisVFD_02.mailther

It may not be evident on this snapshot, but the 2-D thermal meshing geometry doesn’t exactly correspond to the geometry of our 3-D model. In order to account for this we have had to create correction vectors with respect to nodes from both meshed models. The vectors used are the following and they are applied to mechanical model.

X Y Z

Disc (Stage 2) -0.87839 0 0

Flange (Stage 1) 0.72945 0 2.35003

PATRAN Flow Chart

Thermal Interpolation in Disc and Flange /1.2.7/ (prep)

X Y Z

Disc (Stage 2) -0.87839 0 0

Flange (Stage 1) 0.72945 0 2.35003

Apply correction vectors here

PATRAN Flow Chart

Thermal Interpolation in Disc and Flange /1.2.7/ (app)

As we can see here the correction vectors have allowed us to mitigate the effects of the geometry mismatch in the thermal interpolation of the disc and flange entities.

PATRAN Flow Chart

Thermal Interpolation in Disc and Flange /1.2.7/ (verif)

We validate our interpolated model by verifying the contours and making sure that there are no incoherent temperature peaks and that the max and min values are respectively located in the socket and in the bottom of the disc entity.

PATRAN Flow Chart

Node to Surface Contact /1.2.8/ (prep)

The graphics below show the contact zones we are interested in. The red zones represent the contact surfaces of the blade neck located at the bottom of the blade root. The blue zones represent the contact surfaces of the disc socket. In the model we can see that these zones are not directly in contact but we specify a contact condition because of the centrifugal force generated by the rotation of the turbine stage. Note that we specify Cont_SRot in the option field which is a small rotation hypothesis.

PATRAN Flow Chart

Node to Surface Contact /1.2.8/ (app)

The yellow markers shown in this graphic denotes an applied NodeSurf. contact.

PATRAN Flow Chart

.lia Multi-point Constraints /1.2.9/ (disc & blade)

This MPC creates an axial liaison between the blade and the disc to avoid having the blade move with respect to the disc in the axial direction. This can be caused by the various loads applied on the model. We simply specify the liaison on the turbine rotation axis using two nodes from each entity. These nodes must not be on the a surface.

PATRAN Flow Chart

.lia Multi-point Constraints /1.2.9/ (disc & flange)

This MPC results from an assumption and an approximation. In reality, the flanges of the turbine are fastened to the adjacent disc entities using screws of some sort. Since the given geometry did not include this feature, we assumed that this connection would behave the same way as an automatic liaison of the surfaces. Hence, we approximated the disc and the adjacent flange to be a single entity with this multi-point constraint. We applied this liaison via the inside nodes of these surfaces (avoiding the already constrained outside nodes [cyc. sym.])

PATRAN Flow Chart

Tangential Fixation of Disc and Flange /1.2.10/

The tangential fixation of the disc and flange entities allows us to void any induced tangential movement of the model that could result in incoherent results. This is done via a simple “0” displacement in the tangential direction (Y-dir) applied on two nodes: one from the disc and one from the flange as seen on the image to the left.

PATRAN Flow Chart

Pressures Felt by Blade Tip & Root /1.2.11/

Blade Root

Blade Tip

Blade Tip

As we can see the leading edge has the highest pressure associated with it in both the blade root and tip. These pressures are applied manually and are interpolated linearly to show the transition between points near the leading edge and near the trailing edge.

Leading Edge

PATRAN Flow Chart

Load Case Specification /1.2.12/

For the purpose of this study, we have decided to use a single load case for all loads applied to the model. This simplifies the generation of the data set to be used for analysis. This rendered a small issue as some of the loads applied are time dependent while others are not. In order to solve this issue we specified our single load case as a time dependent one. In order to ensure that the right instant was applied for the time dependent loads (thermal interpolation for disc and flange) we used Mecanique/Conditions aux limites/Gestion des L/BC transitoires/Action: Extraire/Objet: Temperatures. We then select the loads that we are interested in for the time specification and extract the instants directly from the load specification. This ensures that the data set includes the effects of this load despite the fact that it is the only time dependent one. The load case we have used for the final analysis on PATRAN is called IT_3 and represents the third iteration of generating the data set.

PATRAN Flow Chart

DATA SET GENERATION & DEFINITION OF ANALYSIS NATURE

PATRAN Flow Chart

Material Specification in PATRAN /1.3.1/ (explanation)

A task that must be carried out before generating a data set is the material and material property specification. For the purpose of this study we have specified the DMD 456 material for the disc & flange entities and the DS 200 material for the blade entity. The importance of this material specification lies in the nature of the material. The disc and flange entities are fabricated from an isotropic alloy whereas the blade is manufactured from an anisotropic material. Isotropy is an important material parameter as it governs the material’s dependency on direction. An isotropic material has properties which independent of direction whereas an anisotropic material has properties that depend heavily on direction. For the purpose of this study, the isotropic material was specified directly in PATRAN; on the other hand the anisotropic material had to be inputted directly within the data set (.dat).

PATRAN Flow Chart

Material Specification in PATRAN /1.3.1/ (application)

We use field inputs to specify the Modulus of Elasticity (Young’s Mod.), Poisson’s Ratio, Thermal Expansion Coefficient, and the density of the material. All these values, except for the density, are a function of the temperature of the material. As aforementioned, only the DMD 456 material has been specified in PATRAN since it is isotropic and fairly easy to deal with. NB: we also specify two degrees of material properties. Degree 1 refers to contacts, limits and boundary condition zones. Degree 2 (default) refers to all other zones.

PATRAN Flow Chart

.dat Generation /1.3.2/

We use the Analysis tool to generate the data set to be analyzed by SAMCEF.

PATRAN Flow Chart

.dat Generation /1.3.2/

PATRAN Flow Chart

.dat Modification /1.3.3/

In order to efficiently modify the data set, we must first specify a dummy material in PATRAN. We entered obsolete values for the material properties in order to easily find the SAMCEF code lines associated with the dummy material and replace them with the given properties for the DS 200 material.

PATRAN Flow Chart

READING RESULTS IN PATRAN

The static results generated by the SAMCEF solver have been plotted in PATRAN. The following slides display the deformation and stress results rendered by our mechanical model. Note that some zones required more attention than others due to the fact that we have had to remove boundary condition zones and contact zones in order to isolate the “true” theoretical deformation and stress distributions. SAMCEF analysis codes used: 1411 (stress tensor), 163 (nodal displacements).

PATRAN Flow Chart

Static Results (Global Deformation) /1.4.1/

Max Deformation = 4.95 mm

PATRAN Flow Chart

Static Results (Axis-dependent Displacement) /1.4.2/

Max Displacement = 0.975 mm

AXIAL DISPLACEMENT

PATRAN Flow Chart

Static Results (Axis-dependent Deformation) /1.4.2/

RADIAL DISPLACEMENT


PATRAN Flow Chart

Static Results (Axis-dependent Deformation) /1.4.2/

TANGENTIAL DISPLACEMENT


PATRAN Flow Chart

Static Results (Blade Stresses Global) /1.4.3/

BLADE STRESS GLOBAL

Max Stress = 707.5 MPa

PATRAN Flow Chart

Static Results (Blade Stresses Radii) /1.4.4/

BLADE STRESS BOTTOM RADIUS

Max Stress = 557.8 MPa Located on the upper blade surface side of the radius

PATRAN Flow Chart

BLADE STRESS TOP RADIUS

Max Stress = 457.1 MPa Located on the upper blade surface side of the radius

Static Results (Blade Stresses Radii) /1.4.4/

PATRAN Flow Chart

Static Results (Disc Stresses Global) /1.4.5/

DISC STRESS GLOBAL


PATRAN Flow Chart

Static Results (Disc Stresses Bore) /1.4.6/

DISC STRESS BORE


PATRAN Flow Chart

Static Results (Disc Stresses Socket) /1.4.7/

Reading results on the disc socket was a close to impossible task due to the MPC specified between the disc and blade. Removing the elements associated with the MPC rendered issues and made it hard for us to read where the “true” max stress value was located. We will attempt to read results in this region on WB and compare methodology and performance.

PATRAN Flow Chart

Conclusion To conclude PHASE 1 of this benchmark study, one can clearly see that

PATRAN is NOT a user friendly tool in any way shape or form. It is complete in the sense that it allows full control of geometry, finite element work, and loads and boundary conditions. However, it offers little or no added value in terms of time saving and efficiency. In most cases, users will be forced to treat surfaces separately in meshing the model. Applying loads and conditions, albeit a more efficient task in PATRAN, renders certain issues which we have discussed previously in this presentation. Two major issues noted with this tool: lack of a “Model Tree” (Creo, CATIA, WB), dissociation of geometry and finite element model.

As an outlook on PHASE 2 of this study and in order to shed some light on the possible alternatives to this accepted paradigm, the following slides present a predicted flow chart for Workbench as well as a demo of PATRAN 2012. When an accepted paradigm renders issues that affect efficiency, this establishes a problem. This problem can be solved by addressing every single issue or the paradigm can be shifted. “Think of a paradigm shift as a change from one way of thinking to another. It's a revolution, a transformation, a sort of metamorphosis. It just does not happen, but rather it is driven by agents of change.”

PATRAN Flow Chart

ANSYS Workbench – Methodology & Performance

PATRAN Flow Chart

Workbench Predicted Flow Chart

Treat surfaces in CATIA to avoid

discontinuities and prepare model for

boundary conditions

Regenerate solids and

import into WB

Simplify the geometry using

the Virtual Topology tool

Create named selections and specify various mesh criteria regions and boundary

condition zones

Launch mesh using criteria

specified in the named selections

Apply loads and boundary

conditions via named selections

Specify solver and analyze

locally

Generate data set and analyze via

server

Read results in WB

Boundary & Load Conditions/Analysis/Post-processing

PATRAN Flow Chart

Import solids from

CATIA

Modify surfaces depending on meshing

needs (regular vs. scattered, Isomesh vs.

Paver) and possible geometric

discontinuities

1

Extract surfaces from

solids and organize groups

Check

Fail

Mesh entities surface by surface according

to given mesh criteria

Extract surfaces in CATIA, import back

to PATRAN

2 3

Repeat steps 1-4 for all

remaining entities

Apply cyclic symmetry multipoint

constraint on disc entities

Apply inertial “pre-torsion”

load via fictional node

MPC

Apply pressure

loads on disc and flange

entities

Apply 2-D induced

displacements on disc flanges

Apply thermal conditions on

disc entities via interpolation

Apply aerodynamic pressure felt by the blade

Apply blade temperature

range

Generate dataset for SAMCEF

solver

Launch static and dynamic analysis

iterations

Perform result post-processing

on PATRAN

5

Legend

Time Penalty

Moderate Timing

No Time Penalty

Verify Model/Project Nodes

Equivalence nodes

Manually move

remaining problematic

nodes

Verify boundaries

for free edges/faces

Verify duplicates,

jacobian ratio & zero, and

normal vectors

Lower global tolerance drastically, reorganize

nodes, save a copy of the database, and project

nodes on original surface geometry

4

Create volume

mesh

PATRAN 2012 http://www.mscsoftware.com/France/Products/C

AE-Tools/Patran.aspx

http://www.mscsoftware.com/France/Products/CAE-Tools/Patran.aspx




References http://www.mscsoftware.com/training_videos/patran/reverb3/index.html#page/Geometry%2520Modeling/geometry_topics.02.4.html#

http://www.mscsoftware.com/training_videos/patran/reverb3/index.html#page/Finite%2520Element%2520Modeling/verify_forms.12.1.html#ww920120

http://www.flightglobal.com/airspace/media/nbaa/silvercrest-engine-4063.aspx

http://en.wikipedia.org/wiki/Snecma_Silvercrest#Specifications

http://www.snecma.com/-silvercrest-.html

http://www.air-cosmos.com/a-la-une/ebace-2012-cessna-devoile-un-avion-motorise-par-snecma.html

http://www.taketheleap.com/define.html

http://www.mscsoftware.com/training_videos/patran/reverb3/index.html








http://en.wikipedia.org/wiki/Snecma_Silvercrest





























http://www.taketheleap.com/define.html

Documents

Internship phase 1 - 08 07 2012