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Project Number : PS 7.1 Rotorcraft Fuselage Drag Study using OVERFLOW-D2 on a Linux Cluster PI: Associate Professor E PowerPoint Presentation
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Project Number : PS 7.1 Rotorcraft Fuselage Drag Study using OVERFLOW-D2 on a Linux Cluster PI: Associate Professor EPN Duque tel : 928-523-5842 www.cet.nau.edu/~end2 Northern Arizona University Graduate Assistant/Research Engineer: Nathan Scott

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slide1

Project Number : PS 7.1

Rotorcraft Fuselage Drag Study using

OVERFLOW-D2 on a Linux Cluster

PI:

Associate Professor EPN Duque

tel : 928-523-5842

www.cet.nau.edu/~end2

Northern Arizona University

Graduate Assistant/Research Engineer:

Nathan Scott

2004 RCOE Program Review

May 4, 2004

background problem statement
Background/ Problem Statement:
  • Evaluate fuselage force and moment prediction capability of the OVERFLOW2 and OVERFLOW-D
  • Utilize cost effective computer systems
technical barriers or physical mechanisms to solve
Technical Barriers orPhysical Mechanisms to Solve :
  • Appropriate grid generation over specific aircraft
  • Lift and drag forces over simplified shapes such as prolate spheroid
  • Grid sensitivity studies required
  • Unsteady flow capturing on bluff bodies
task objectives
Task Objectives:

Using the OVERFLOW code

  • Evaluate drag prediction on a prolate spheroid
  • Evaluate drag prediction on a helicopter fuselage
  • Evaluate and document effects of grid resolution
  • Evaluate turbulence models upon predictions.
    • 1-eqn, 2-eqn, DES
  • Compare results with Penn State Methods
approaches
Approaches:

• OVERFLOW2 Code

• Grid Generation

  • Near body grid refinement in boundary layer
  • Grid adaptation in the field for vortical flow

• Turbulence models

  • Baldwin-Barth
  • Spalart-Almaras
  • k-w
  • Mentor-SST
  • include Detached Eddy Simulation (DES)
overview
Overview
  • Explain S-A and SST Detached Eddy simulation
  • Discuss DES Implementation in OVERFLOW
  • Circular Cylinder results
  • 6:1 Prolate Spheroid results
experimental data
Experimental Data
  • Virginia Tech Stability Wind Tunnel
    • Wetzel, Simpson, Ahn
  • 1.37 m 6:1 Prolate Spheroid
  • Free stream conditions
    • α=20º, Re=4.2E6, Ma=0.16
  • Coefficient of Pressure (Cp), Skin Friction (Cf)from Wetzel Dissertation
  • U/u*, y+ from Simpson’s Website
cfd methodology
CFD Methodology
  • Reynolds Averaged Navier-Stokes Equations
    • OVERFLOW-D code developed at NASA and Army
    • Uses detailed overset grids
    • Allows for detailed geometry definition
    • Captures viscous effects such as unsteady flow separation
  • OVERFLOW2 used for turbulence model study and Implementation of DES
    • Scalar penta-diagonal scheme
    • 1st order difference in time
    • 2nd or 4th order RHS (OVERFLOW2)
    • 2nd and 4th order central difference dissipation terms
detached eddy simulation
Detached Eddy Simulation
  • First Formulated by Spalart as a modification to S-A model in 1997.
  • Later generalized to any model by Strelets in 2001.
  • First step was to modify the S-A model
s a des formulation
S-A-DES formulation
  • Change distance to wall in S-A model dw to
    • Ĩ=min(dw,CDES∆)
    • ∆ is the maximum of the grid spacing in three dimensions- ∆=max(δX, δY, δZ)
    • CDES=0.65
k w sst des formulation
k-w-SST-DES Formulation
  • Change k-transport source term: ρβ*kω=ρk3/2/Ĩ
    • Ĩ=min(lk-ω,CDES∆)
    • lk-ω=k1/2/(β*ω)
    • ∆ is the maximum of the grid spacing in three dimensions- ∆=max(δX, δY, δZ)
    • CDES=(1-F1) Ck-ε+F1Ck-ω
    • Ck-ε=0.61, Ck-ω=0.78
  • At equilibrium reduces to an algebraic mixing-length Smagorinski type model.
implementation in overflow
Implementation in OVERFLOW
  • Determine grid cell edge lengths in J,K,L directions
    • One sided difference at boundaries
    • Central difference otherwise
  • Background Cartesian Grids - DES always enabled
circular cylinder test case
Circular Cylinder Test Case
  • Re=140,000, Ma=0.2
  • Fully Turbulent
  • S-A, S-A-DES, SST-DES turbulence models
  • 7.6 million grid points
    • Near body 181 by 60 by 99
    • Background 426 by 61 by 252
    • Off Body grid resolution 0.05 the diameter
    • H type block grid extends 10 diameters
    • 2 total grids
  • Methods
    • 4th central difference in space
    • 1st order Beam-Warming in time
  • Inviscid wall Boundary Conditions
other des work with cylinder
Other DES work with Cylinder
  • Travin, A, Shur, M, Strelets, M, Spalart, P
    • Re = 50,000 and 140,000
    • Laminar Separation
      • Laminar Separation
      • LES in Background
    • Turbulent Separation
      • Run Fully Turbulent
      • Compares to higher Re
iso surface visualization comparison circular cylinder
Iso-surface visualization comparison Circular Cylinder

OVERFLOW S-A-DES

Travin-DES

OVERFLOW URANS (Not Unsteady Yet)

OVERFLOW k-w-SST-DES

conclusions from circular cylinder
Conclusions from Circular Cylinder
  • S-A DES in OVERFLOW looks promising
    • More fine scale resolution
    • Cross Flow on “2-D” cases
    • Comparable comparisons to Experimental Data
  • k-w-SST DES in OVERFLOW also looks promising
    • SST has been shown to approximate separation better so more desirable in shear layer
    • More verification needs to be done
6 1 prolate spheroid test case
6:1 Prolate Spheroid Test Case
  • Re=4,200,000, Ma=0.16
  • Trip to Turbulence at x/L=0.2
  • S-A, S-A-DES, SST-DES turbulence models
  • 7 million grid points
    • Near body 361 by 310 by 45
    • First off body Grid spacing 0.08 the length
    • Remaining off body grids reduce in resolution by half
    • Off body grids extent to 10 times the length
    • 61 Total grids
    • Grid shown to be convergent in Previous Study
  • Methods
    • 4th central difference in space
    • 1st order Beam-Warming in time
other des work with 6 1 prolate spheroid
Other DES work with 6:1 Prolate Spheroid
  • Rhee, S. H. and Hino,T.
    • Re = 4,200,000 Ma=0,16
    • Run Steady and Unsteady
    • Showed under prediction of Lift
comparison of lift and pitching moment for 6 1 spheroid
Comparison Of Lift and Pitching Moment for 6:1 Spheroid
  • All of the models fall with error for Pitching Moment
  • All of the models under predict lift
6 1 spheroid conclusions
6:1 Spheroid Conclusions
  • DES shown to work with overset grids
  • DES did not improve integrated forces
  • Skin friction remained the same
  • Surface pressure showed slight improvement
  • Velocity profiles remained the same close to surface y+<10
  • Velocity profiles improved farther away from surface y+>100
accomplishments
Accomplishments
  • Summer work with Roger Strawn and Mark Potsdam at Ames
  • Presented at AIAA 43rd Aerospace Sciences Meetings.
future work
Future Work
  • Grid Refinement Study on 6:1 Prolate spheroid and DES
  • New research engineer, explore new LES
  • Apply DES and LES to helicopter fuselage