DDP-Final

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MOTIVATION

INTRODUCTION

PROBLEM STATEMENT

Contra-Rotating Compressor was designed aerodynamically using balde angle method

Design was primarily focused on aerodynamics ; less work was done on Mechanical Integrity

• A 4-stage mini axial contra-rotating compressor
• Driven by contra-rotaing gearbox

• Innovative
• Challenging Problem
• Furthering Project

• Structural Analysis

- Static Stress Analysis

- Fatigue Analysis

- Vibrational Analysis

• Investigate reasons of blade failure
• Suggest appropriate changes

Blade Specifications

Geometry

Material

• Chord Length-3 cm
• Span- 3.2 cm
• Tip Clearance- 0.96 mm
• Maximum thickness at 13% the cord length
• Uneven numbers of blades in consecutive rotors

• Accura-60
• Specific gravity-1.21 gm/cm^3
• Tensile modulus-2690 MPa
• Ultimate Tensile Strength-58 Mpa
• Yield Strength-37.36 MPa
• Melting Point ~433 K
• Solid-State Stereolithography

FEM using COMSOL

SOLVER

MESH GENERATION

METHODS

• For structural analysis study solver was used
• It uses Damped Newton Methods, Linear Solvers and Non-Linear Solver

• COMSOL provides us physics based mesh generation
• It generates free tetrahedral meshes and size parameter can be controlled by user; T.E. 2474301, Vertex:- 118

FUTURE WORK

• For fatigue analysis time-dependent solver was used
• It uses implicit Time-Dependent Solver, Backward Differentiation Formula and Generalized-alpha

• Boundary Conditions and Inputs

• For both the rotors, at hub boundary was considered as fixed it means no displacement
• Mass Flow Rate was kept constant 0.6 kg/s
• Inlet pressure, relative angle and relative velocity for rotor 101325 Pa, 13.85 degrees and 47.56 m/s respectively for rotor 1
• Inlet pressure and relative velocity for rotor 101818 Pa, 50.83 degrees and 57.40 m/s respectively for rotor 2
• Dynamic viscocity and density of fluid 1.79E-5 and 1.27 kg/m^3
• Fluid was considered incompressible
• Fatigue Ductility Coefficient and Ductility exponents values are 0.084 and -0.7 respectively

MODULES

• Three modules were used for structural analysis

Results

• Solid Mechanics Module
• Fluid-Solid Interaction Module
• Fatigue Module

• Bending and twisting can be seen in the following pictures

FEM

SOLID-MECHANICS MODULE

FLUID-SOLID INTERACTION MODULE

FATIGUE MODULE

• It takes count for gravity and loads due to rotational frame

• This models calculates the loads generated by fluid-solid interaction
• Illustrates deformation of solid using arbitrary Lagrangian-Eulerian Technique

• This module provides us four options to predict the life to structure for given load

• Stress-Based
• Strain-Based
• Energy-Based
• Cumulative Damage Analysis

Standard Blade Model: Beam Analysis

• Strain-based method was chosen for our problem since our problem involves high load and stress concentrators
• In strain-based Coffin-Manson model was selected

• Solution of coupled equations

• Selection of continuum body followed by displacement model
• Derive the stiffness and global load vector
• Force-displacement and stress-strain relationships helps in calculating unknown values
• Faster calculations with accurate prediction

Advanced Beam Model

3D-Photoelastic Model

Results

• Fatigue Life Prediction

Results

• Maximum Deformation vs RPM

• Maximum von-Mises stress was found at the T.E. of rotor 1 blade and L.E. of rotor 2 blade

Results

• Cross sectional views of both airfoil and along the blade length are given below

• Maximum von-Mises Stress vs RPM

• This involves 2-dimensional cross-sectional analysis and geometrically one-dimensional analysis
• Calculation of stiffness and mass properties using VABS
• Exact beam analysis is carried out to find the internal forces and moments
• The variational formulation

• Experimental technique for stress and strain analysis
• Heat the object till stress-annealing temperature while loading a dead load
• Cool slowly with the weights still applied
• The elastic state of stress remains fixed in the model together with the deformation
• Slice the object normally to the surface and measure isochromatic fringe order with secondary principal differenece
• Subslice the above part normally and do the same
• Sublice the above part parallel to the the surface and measure the angle of principal stress w.r.t. either of the side
• Calculate principal stresses

• Replacement of integration with summations for calculating section properties
• Runge-Kutta method to integrate differential equations
• Bending stress calculation using stored values

• Finite element analysis gives high accuracy
• External aerodynamics forces can be calculated using airfoil design program
• Internal forces and moments can be calculated using external aerodynamics forces
• Strain recovery analysis using 2D-model

• Above data is sufficient to calculate maximum shear stress and its direction at any point

Conclusion

• Attachment region will face the maximum load
• From the L.E. of the bottom airfoil, failure will start
• Stress decreases radially from hub to tip in both the rotors
• There is a slight reduction in von-Mises stress close to designing speed 3600 RPM. It might be because of maximum flow interaction
• According to von-Mises failure criteria operational speed of the compressor should be 3750 RPM
• Deformation in every direction varies parabolically with RPM
• Aerodynamic constraint allows only rotating speed till 2200 RPM
• Hence, critical speed of the compressor will be 2200 rpm
• Fatigue Load-Life Graph allows user to trade between life and RPM of the compressor
• For future compressor design, one should consider both aerodynamic and structural aspects together to get optimum results

Designing of New Compressor

Dynamic Analysis

Multiphysics Modelings

All 4 Rotors Simulation

3. 3D-Photoelastic Stress Analysis

4- Advanced Beam Model

1. Finite Element Analysis

2. Beam Model

Feb'14

Mar'14

May'14

April'14

Structural Analysis of Contra-Rotating Compressor

-A Demonstrator

DDP Final Stage

Nishant Khanduja

09001013

UNDER THE SUPERVISION OF

Prof. P.J. Guruprasad