Experimental and computational analysis of separation bubble behavior for compressible, steady and oscillatory flows over a NACA 0012 airfoil at M=0.3 and a reynolds number of 540,000.

206 Pages·3.6 MB·en_US

by  Van Dyken, Robert D.

NPS ARCHIVE
1997. 03
VAN DYKEN, R.
NAVAL POSTGRADUATE SCHOOL
Monterey, California
DISSERTATION
EXPERIMENTAL AND COMPUTATIONAL ANALYSIS
OF SEPARATION BUBBLE BEHAVIOR FOR
COMPRESSIBLE, STEADY AND OSCILLATORY
FLOWS OVER A NACA 0012 AIRFOIL
(M = 0.3, Re = 540,000)
co c
by
Robert D. Van Dyken
March 1997
Max
Dissertation Advisor: F. Platzer
Thesis Co-Advisor: M. S. Chandrasekhara
V16335
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March 1997 PhD. Dissertation
4. TITLEANDSUBTITLE 5. FUNDINGNUMBERS
EXPERIMENTALANDCOMPUTATIONALANALYSISOFSEPARATIONBUBBLE
BEHAVIORFORCOMPRESSIBLE,STEADYANDOSCILLATORYFLOWSOVERA
NACA0012AIRFOIL(M^ = 0.3, Re = 540,000)
c
6. AUTHOR(S)
Robert D. Van Dyken
7. PERFORMINGORGANIZATIONNAME(S)ANDADDRESS(ES) 8. RPEEPROFROTRMNIUNMGBOERRGANIZATION
Naval Postgraduate School
Monterey, CA 93943-5000
9. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES) 10. ASGPOENNSCOYRIRNEGP/OMROTNNITUOMRBIENRG
11. SUPPLEMENTARYNOTES
The views expressed in this thesis are thoseofthe author and do not reflect the official policy orposition ofthe Departmentof
DefenseortheU.S. Government.
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Approved forpublic release; distribution is unlimited.
13. ABSTRACT (Maximum200words)
In this thesis, the separation bubble behavior and its effect on the steady and dynamic stall
characteristics of a thin airfoil in a compressible flow at a transitional Reynolds number was studied.
For such flows, laminar separation occurs near the airfoil leading edge, but turbulent reattachment
occurs within a short distance downstream, forming a separation bubble in the underlying region.
Two experimental techniques, point diffraction interferometry (PDI) and laser doppler velocimetry
(LDV), were used to acquire detailed flowfield information that showed the development of the
leading-edge separation bubble and its subsequent bursting at higher angles of attack. The initiation
of the stall process from the leading-edge separation bubble as opposed to trailing-edge flow reversal
pointed to the need for transitional flow analysis. Both in the boundary layer and Reynolds-
averaged, Navier-Stokes (N-S) analysis methods, transition models were incorporated to determine the
location and extent of the transition zone that best modeled the measured separation bubble behavior.
Computed results for steady flow gave remarkable agreement with the measurements. The
computations compared favorably with the measurements for an airfoil oscillating in pitch about the
quarter-chord point during the airfoil upstroke. However, the computations did not predict the light
stall and vorticity-shedding process that was measured during the airfoil downstroke.
14. SUBJECTTERMS 15. NUMBEROFPAGES
Airfoil Flows, Separation Bubbles, Light Dynamic Stall, Transition Modeling, 203
Vorticity Shedding Processes
16. PRICECODE
17. SECURITYCLASSIFICATION 18. SECURITYCLASSIFICATION 19. SECURITYCLASSIFICATION 20. LIMITATIONOFABSTRACT
OFREPORT OFTHISPAGE OFABSTRACT
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Approved for public releasedistribution is unlimited.
EXPERIMENTAL AND COMPUTATIONAL ANALYSIS OF
SEPARATION BUBBLE BEHAVIOR FOR COMPRESSIBLE,
STEADY AND OSCILLATORY FLOWS OVER A NACA 0012
AIRFOIL AT M=0.3 AND A REYNOLDS NUMBER OF 540,000
Robert D. van Dyken
Aeronautical Engineer, Naval Air Warfare Center, Weapons Division
B.S., Montana State University, 1971
M.S., California State University at Northridge, 1988
Submitted in partial fulfillment ofthe requirements for the degree of
DOCTOR OF PHILOSOPHY IN AERONAUTICAL ENGINEERING
from the
NAVAL POSTGRADUATE SCHOOL
WPS
(
/
tf/L Wi-
DUDLEYKNOXLIBRARY
NAVAL POSTGRADUATE SCHOOL
MONTEREY CA 9394*5101
ABSTRACT
In this thesis, the separation bubble behavior and its effect on the steady
and dynamic stall characteristics of a thin airfoil in a compressible flow at a
transitional Reynolds number was studied. For such flows, laminar separation
occurs near the airfoil leading edge, but turbulent reattachment occurs within a
short distance downstream, forming a separation bubble in the underlying region.
Two experimental techniques, point diffraction interferometry (PDI) and laser
doppler velocimetry (LDV), were used to acquire detailed flowfield information
that showed the development of the leading-edge separation bubble and its
subsequent bursting at higher angles of attack. The initiation of the stall process
from the leading-edge separation bubble as opposed to trailing-edge flow reversal
pointed to the need for transitional flow analysis. Both in the boundary layer and
Reynolds-averaged, Navier-Stokes (N-S) analysis methods, transition models were
incorporated to determine the location and extent of the transition zone that best
modeled the measured separation bubble behavior. Computed results for steady
flow gave remarkable agreement with the measurements. The computations
compared favorably with the measurements for an airfoil oscillating in pitch about
the quarter-chord point during the airfoil upstroke. However, the computations
did not predict the light stall and vorticity-shedding process that was measured
during the airfoil downstroke.
VI
... 1
TABLE OF CONTENTS
INTRODUCTION
I. 1
H. REVIEW OF LOW-SPEED AIRFOIL FLOWS WITH LEADING-EDGE
SEPARATION BUBBLES
5
INTRODUCTION
A. 5
B. FUNDAMENTAL FLOW PHYSICS OF LEADING-EDGE
SEPARATION BUBBLES
5
C. TRANSITION ONSET PREDICTION 10
D. TRANSITION LENGTH PREDICTION 10
EFFECT OF AIRFOIL OSCILLATION ON LEADING-EDGE
E.
SEPARATION BUBBLES
1
ANALYSIS METHODS FOR AIRFOIL FLOWS WITH SEPARATION
F.
BUBBLES
12
m. EXPERIMENTAL SETUP AND MEASUREMENT TECHNIQUES
15
INTRODUCTION
A. 15
B. EXPERIMENTAL TEST FACILITY 15
UNSTEADY LDV MEASUREMENTTECHNIQUE
C. 17
D. STROBOSCOPIC PDI MEASUREMENT TECHNIQUE 20
1. Implementation 20
2. Fringe Counting To Determine Mach Number 22
E. MEASUREMENT UNCERTAINTIES 23
F. DATAVALIDATION (LDV SYSTEM) 24
IV. DESCRIPTION OF COMPUTATIONAL ANALYSIS METHODS 31
A. UNSTEADY POTENTIAL FLOW CODE (UPOT) 31
1 Introduction 31
2. Theory and Numerical Method 32
STEADY BOUNDARY LAYER FLOW CODE
B. 35
1 Introduction 35
2. Theory and Models 36
3. Numerical Implementation 38
C. NAVIER-STOKES (N-S) CODE METHODOLOGY 44
1 Introduction 44
2. Numerical Method 45
3. Numerical Implementation 46
vii
. )
4. Transition Modeling 48
5. Boundary Conditions and Gridding 51
D. COMPUTATIONAL UNCERTAINTIEr 52
EXPERIMENTAL RESULTS
V. 55
A. FLOW OVER STEADY NACA 0012 AIRFOIL 55
1. Pressure Distributions From the PDI Interferograms 60
2. Mach Number From PDI Density Ratio 62
3. U-Component (LDV) Velocity Contours 63
B. UNSTEADY/OSCILLATING NACA 0012 AIRFOIL 66
1 Deep Dynamic Stall ( a = 10° - 10°sinco t 66
2. Light Dynamic Stall Flow (a = 10° -2° sinco t) 74
a. PDI Images 74
b. Pressure Distribution From PDI Images 76
LDV
c. Phase Distribution of Velocities at (X/C) Locations 78
LDV (U/UJ
d. Velocity Profiles 82
LDV
e. Velocity Magnitude Contours 89
LDV
Vorticity Magnitude Contours 89
f.
VI. COMPUTED RESULTS 97
A. FLOW OVER STEADY NACA 0012 AIRFOIL 97
1. Pressure Distributions 97
2. Skin-Friction Coefficient Distribution on Suction Surface 100
3. Displacement Thickness Distribution on Suction Surface 105
4. Boundary-Layer Velocity Profiles on Suction Surface 106
B. OSCILLATORY FLOW OVER NACA 0012 AIRFOIL 117
1. UPOT Pressure Distributions ( a = 10° -10°sincot) 117
2. UPOT Pressure Distributions (a = 10° -2°sinco t) 120
3. N-S Pressure Distributions (a = 10° -2°sincot) 124
4. N-S Skin-Friction Coefficients 127
5. N-S Velocity Profiles 128
6. N-S Lift, Drag, and Moment 131
VH. COMPARISONS OF MEASURED AND COMPUTED RESULTS 135
A. INTRODUCTION 136
B. STEADY FLOW RESULTS 137
1. Transition Onset and Length Effects 137
2. Density Contour Comparisons 140
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