SAROD 2003 1 Aerodynamic Design Optimization Studies at CASDE Amitay Isaacs, D Ghate, A G Marathe, Nikhil Nigam, Vijay Mali, K Sudhakar, P M Mujumdar Centre for Aerospace Systems Design and Engineering Department of Aerospace Engineering, IIT Bombay http://www.casde.iitb.ac.in
50
Embed
SAROD 20031 Aerodynamic Design Optimization Studies at CASDE Amitay Isaacs, D Ghate, A G Marathe, Nikhil Nigam, Vijay Mali, K Sudhakar, P M Mujumdar Centre.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
SAROD 2003 1
Aerodynamic Design Optimization Studies at CASDE
Amitay Isaacs, D Ghate, A G Marathe,
Nikhil Nigam, Vijay Mali,
K Sudhakar, P M Mujumdar
Centre for Aerospace Systems Design and Engineering
Department of Aerospace Engineering, IIT Bombay
http://www.casde.iitb.ac.in
SAROD 2003 2
About CASDE
5 years old Master’s program in Systems Design & Engineering MDO MAV Modeling & Simulation Workshops/CEPs/Conferences
SAROD 2003 3
Optimization Studies –Overview
Concurrent aerodynamic shape & structural sizing of wing FEM based aeroelastic design MDO architectures WingOpt software
Propulsion system Engine sizing & cycle design Intake duct design using CFD
SAROD 2003 4
Intake Design - Background
Duct design practice of late 80s – based on empirical rules
Problem Revisited – using formal optimization and high fidelity analysis
Study evolved with active participation of ADA (Dr. T.G. Pai & R.K.Jolly)
SAROD 2003 5
Problem Formulation
Entry Exit Location and shape (Given)
Optimum geometry of duct from Entry to Exit ?
Objective/Constraints
• Pressure Recovery• Distortion• Swirl
SAROD 2003 6
Design Using CFD - Issues
Simulation Time CFD takes huge amounts of time for real life problems Design requires repetitive runs of disciplinary
where, PA0 - average total pressure at the section,
P60min- minimum total pressure in a 600 sector, q - dynamic pressure at the cross section.User Defined Functions (UDF) and scheme files were used to generate this information from the FLUENT case and data file.Iterations may be stopped when the distortion values stabilize at the exit section with reasonable convergence levels.
SAROD 2003 21
Huge benefits as compared to the efforts involved!!!
Methodology Store the solution in
case & data files Open the new case (new grid)
with the old data file Setup the problem Solution of (0.61 0.31 1 1) duct slapped on (0.1 0.31 0.1 0.1)
3-decade-fall 6-decade-fall
Without continuation 4996 9462
With continuation 1493 6588
Percentage time saving 70% 30%
Continuation Method
Generate new case file
FLUENT Solution
Duct Parameters
OldData
file
Journal
file
SAROD 2003 22
Simulation Time
Strategies Continuation Method Parallel execution of FLUENT on a 4-
noded Linux cluster
Time for simulation has been reduced to around 20%.
• Total Pressure: 34500 Pa• Total Temperature: 261.4o K• Hydraulic Diameter: 0.394m• Turbulence Intensity: 5%
• Outlet Boundary Conditions• Static Pressure: 31051 Pa (Calculated for the desired mass flow rate)• Hydraulic Diameter: 0.4702m• Turbulence Intensity: 5%
SAROD 2003 41
Duct Parameterization
Geometry of the duct is derived from the Mean Flow Line (MFL) MFL is the line joining centroids of
cross-sections along the duct Any cross-section along length of the
duct is normal to MFL
Cross-section area is varied parametrically Cross-section shape in merging area is same as the exit section
SAROD 2003 42
MFL Design Variables - 1Mean flow line (MFL) is considered as a piecewise cubic curve along the length of the duct between the entry section and merging section
x
y(x), z(x)
0 LmLm/2
y(Lm/2), z(Lm/2) specified
Centry
Cmerger
y1, z1
y2, z2
Lm : x-distance between the entry and merger section
y1, y2, z1, z2 : cubic polynomials for y(x) and z(x)
Baldwin-Lomax model (Algebraic model) Computationally inexpensive than more sophisticated models Known to give non-accurate results for boundary layer separation etc.
Devaki Ravi Kumar & Sujata Bandyopadhyay (FLUENT Inc.) k- realizable turbulence model
Two equation model
SAROD 2003 47
Turbulence Modeling (contd.)
Standard k- model Turbulence Viscosity Ratio
exceeding 1,00,000 in 2/3 cells
Realizable k- model Shih et. al. (1994) Cμ is not assumed to be
constant A formulation suggested
for calculating values of C1 & Cμ
Computationally little more expensive than the standard k- model
Total Pressure profile at the exit section (Standard k- model)
SAROD 2003 48
Results
Mass imbalance: 0.17%Energy imbalance: 0.06%Total pressure drop: 1.42%Various turbulence related quantities of interest at entry and exit sections:
Entry Exit
Turbulent Kinetic Energy (m2/s2)
124.24 45.65
Turbulent Viscosity Ratio 5201.54 3288.45
y+ at the cell center of the cells adjacent to boundary throughout the domain is around 18.