NASA Technical Memorandum 87231
Computational Engine Structural Analysis
(NASA-T_]-87231) CG_!PUTIL_.iCNAL _NGINE
,_RU_.TU_AL ANAL_SiS (NASA) 2i.% p[C A02/M_ AOi CSCL 20t<
G 3/39
N86-I 9663
Christos C. Chamis and Robert H. Johns
Lewis Research Center
Cleveland, Ohio
Prepared for the
31st International Gas Turbine Conference and Exhibit
sponsored by the American Society of Mechanical Engineers
Dusseldorf, West Germany, June 8-12, 1986
https://ntrs.nasa.gov/search.jsp?R=19860010192 2018-06-12T21:36:15+00:00Z
t
TABLE OF CONTENTSPage
SUMMARY ...................... L ........... l
INTRODUCTION - LEWIS'S RESEARCH ACTIVITIES ON
COMPUTATIONAL ENGINE STRUCTURAL ANALYSIS ................ l
AEROELASTICITY OF BLADES ROTORS ..................... 2
HIGH VELOCITY IMPACT OF FAN BLADES .................... 2
BLADE LOSS TRANSIENTS .......................... 2
ROTOR/STATOR/SQUEEZE-FILM-BEARING INTERACTION .............. 3
BLADE-FRAGMENT/ROTOR-BURST CONTAINMENT .................. 4
ADVANCED TURBOPROP STRUCTURAL BEHAVIOR .................. 4
SUMMARY OF RESULTS ............................ 5
REFERENCES ................................ 5
COMPUTATIONALENGINESTRUCTURALANALYSIS
Chrlstos C. Chamlsand Robert H. JohnsNational Aeronautics and SpaceAdministration
Lewis Research CenterCleveland, Ohio 44135, U.S.A.
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SUMMARY
A significant research activity at the NASA Lewis Research Center is the
computational simulation of complex multldlsclplinary engine structural prob-
lems. This simulation is performed using computational engine structural
analysis (CESA) which consists of integrated multldlsclpllnary computer codes
in conjunction with computer post-processlng for "problem-speclflc" applica-
tion. A variety of the computational simulations of specific cases aredescribed in some detail in this paper. These case studies include (1) aero-
elastic behavior of bladed rotors, (2) high velocity impact of fan blades, (3)
blade-loss transient response, (4) rotor/stator/squeeze-film/bearlng interac-tion, (5) blade-fragment/rotor-burst containment, and (6) structural behavior
of advanced swept turboprops. These representative case studies were selected
to demonstrate the breadth of the problems analyzed and the role of the com-
puter including post-processlng and graphical display of voluminous outputdata.
INTRODUCIION
The need for lightweight, durable, fuel-efflcient, cost-competltlve air-craft requires engine structures which are made from advanced materials
including composites, and which resist higher temperatures, maintain tighterclearances and reduce maintenance costs. These requirements tend to increase
the complexity of aircraft engines which are already intricate structural
systems consisting of dynamically interacting components. Prediction of the
integrated response of these systems requires complex analytical models (finite
element, for example) as well as complex static, periodic, transient, and
impact analyses. A major engine structures program (fig. l) is currently beingconducted by NASA Lewis, with emphasis on computational engine structural
analysis (CESA). Several independent computer codes for specific aspects of
engine structures modeling and/or structural analysis are being developed as
part of this program. These codes include: (1) interactive finite elements
for bearlng/shaft interaction, (2) engine structural component modeling, (3)
automatic finite element generators, (4) nonlinear analysis with various levels
of sophistication, (5) nonlinear constitutive relationships, (6) automatic
thermal load transfer, (7) blade-loss transient analysis, (8)aeroelastIc
analysis of bladed disks, (9) multimode impact analysis, and (lO) structuraltailoring of engine blades.
Several of these computer codes were briefly described in a previous paper
(ref. l). The objective of this paper is to illustrate typical computational
results obtained from these codes for: (1) aeroelastlc behavior, (2) high-
velocity impact, (3) blade-loss transients, (4) rotor/stator/squeeze film/-
bearing interaction, (5) blade fragment containment, and (6) advanced turbo-
prop structural behavior. The role of the computer in the solution of these
complex multldlscipllnary problems, the post-processlng, and the graphic
display of voluminous results obtained therefrom are emphasized.
AEROELASTICITY
The multldlscipllnary analysis required for predicting aeroelastlcbehavior including flutter is performed by a speclal-purpose code (ref. 2).
This code couples appropriate aerodynamics with the structural response ofbladed, shrouded disks. Flutter is an important aeroelastlc design consider-
ation for fan blades. When it occurs it subjects a blade to hlgh-amplltude
cyclic loading which can rapidly degrade its structural integrity and lead toblade failure.
Blade failure induces rotor imbalance which, if of sufficient magnitude
can cause rotor stage failure and/or bearing failures, both of which can leadto catastrophic engine failure, if only very infrequently.
The computer code predicts the flutter speed and the blade motion near or
at this speed. The code uses cyclic symmetry substructurlng concepts and the
wldely-used NASTRAN structural analysis computer code. A computer plot of a
typical sector of a bladed shrouded disk analyzed is shown in figure 2. Com-
puted graphical results of the motion of this sector near flutter speed are
shown exaggerated in figure 3. The character of the motion and location of
high bending (fatigue) stresses are readily observable in this figure.
HIGH VELOCITY IMPACT OF FAN BLADES
High-veloclty impact which can result in foreign object damage (FOD) is an
important design consideration in aircraft turbine engine fan blades. Some
research activities at NASA Lewis focused on developing technology for impact-
resistant fan blades using advanced design concepts and several computer codes
(ref. l).
A computer-produced three-dlmenslonal finite element model for one of theseadvanced blade concepts is shown in figure 4. Stress contour plots obtained
using thls flnlte element model are shown in figure 5 for several blade depth
locations or "surfaces." Impact location and blade root stresses obtained
using modal synthesis for transient analysis are summarized in figure 6.
The amount of information associated wlth hlgh-veloclty impact analysis is
very voluminous. Computer post-processlng and computer graphics including
computer-produced movies is the practical way to handle it. Furthermore,
computer color graphics enhance the interpretation of the output relative to
displacement magnitudes, stress distributions and magnitudes, and transient
motion of the impacted blade.
BLADE-LOSS TRANSIENTS
Partial or full blade loss due to impact, for example, causes stage
_mbalance which can induce rotor transient whirling. This type of imbalance
and the resulting transient and steady-state motion must be predictable sothat appropriate tolerances and operating restrictions can be provided. Pre-diction of blade loss transient response requires an integrated structuraldynamic analysis where the bladed rotor, shaft, and bearings are all modeledin the analysis. A computer code (Turbine Engine Transient ResponseAnalysis[TETRA]ref. l) was developed for such an integrated analysis.
TETRAuses the componentelement analysis method with progressively reducedmodel complexity as shownin figure 7. TETRA output is also voluminous. Com-
puter graphics is the practical way to display this type of output. Typically
TETRA produces dlsplacement/tlme history plots as shown in figure B, or cor-
responding frequency-domain plots as shown in figure 9. Both of these plots
are valuable and necessary in interpreting the blade loss transient responseand in assessing the adequacy of the design.
ROTOR/STATOR/SQUEEZE-FILM/BEARING INTERACTION
Squeeze-film damper bearings are designed for specified blade-loss transi-
ents and rotor imbalance and vibration. Rotor/squeeze-film/bearlng/ stator
interactions are inherently nonlinear because of: (1) the inherent behavior
characteristics of squeeze films, particularly during transient situations,and (2) potential structural interactions wherein either large deformation
kinematics or material nonlinearity (plastlcity) are excited.
Because of such behavior, the overall rotor-bearlng-stator computational
simulation must be able to incorporate the various sources of nonlinearity.Additionally, to enable efficient solutions in situations wherein the behavior
of the model components is linear, the overall simulation scheme must incorpo-
rate substructurlng capabilities. Furthermore, since transient problems need
to be considered, such features must be accommodated by the various integration
algorithms used to solve the governing model equations.
A general purpose squeeze-film-damper/Interactlve-force finite element
model has been developed as part of the NASA Lewis program (refs. 3 to 4).This finite element model was implanted in a general purpose finite element
computer code. Three different numerical integration methods were also incor-
porated to solve the governing structural dynamics equations of the interactive
finite element. The general purpose code is used subsequently to predict the
structural dynamic response of the rotor/stator coupled structure subjected toimbalance and impulse type excitations. The structural dynamic responses pre-
dicted include: (1) bearlng/rotor trajectories, (2) stator trajectory, (3)
rotor orbit, and (4) force, velocity and acceleration histories at a given
location in the coupled structure. Three-dimenslonal post-processors are used
to graphically display the predicted results in isometric views. Typical com-
puter post-processlng results are shown in figure lO for a shaft/slngle bearing
interaction, and in figure II for a shaft/multlbearlng interaction. These
graphical results clearly indicate squeeze film pressures, orbit motion, orbit
stability, clearances, and respective margins.
BLADE-FRAGMENT/ROTOR-BURSTCONTAINMENT
Blade-fragment containment and rotor-burst containment are critical designrequirements for turbine engines for commercial aircraft. The computationalsimulation of blade-fragment and/or rotor-burst containment require complexanalyses including fragment tracking, nonlinear material behavior, and predic-tion of finite strains, large rotations and large displacements. These complexanalyses were developed as part of the NASALewis program and incorporatedinto an integrated computer code using nonlinear finite element theory (ref. 5).
The containment computational simulation using thls code starts with the
initial configuration of the containment ring, rotor speed, fragment size, and
fragment location. The simulation proceeds to determine the fragment kinetic
energy, momentum, direction, and impact point on the containment ring. The
transient structural response of the rlng from this contact point Is tracked
as a function of time. The transient structural response generally includes
displacements, strains and stresses.
Because of the importance of fragment containment, extensive experimental
studies have been conducted on specific rotors and containment rings. Thecomputational simulation results for one of these cases are included herein.
The containment ring geometry and properties and the rotor characteristics are
shown In figure 12. A computer plot of the shape of the deformed ring at about
its maximum deformation is shown in figure 13. Computer plots for the stresses
at the corresponding time are shown in figure 14 for the outer surface and in
figure 15 for the inner surface.
ADVANCED PROPELLER STRUCTURAL BEHAVIOR
The use of thin, highly swept, twisted propeller blades is important to
the development of fuel-efflclent and quiet advanced aircraft. Hlgh sweep
angles produce significant reductions in noise and are therefore a desirable
design feature. However, blades of thls type (thin, highly swept, twisted)
exhibit complex structural response under a centrifugal force field, which
requires special analysis techniques for accurate characterlzatlon. These
techniques are required to establish the structural dynamic response of the
turboprop blades at operating rotor speeds including the avoidance of possible
leading edge buckling under centrifugal loads. Computational simulation
studies (refs. 6 to B) were performed at NASA Lewis to determine analytically
the structural behavior and possible leading edge buckling of advanced, highly
swept turboprop airfoils In centrifugal force fields. Computational simulation
studies were also performed in order to identify any advantages of using "high
performance" composites in order to change the regions of instability. The
theoretical studies were performed using an In-house program (COBSTRAN, ref. l)
designed for composite blade analysis. Schematics of the rotor, the propeller
and the finite element model used in the analyses are shown in figure 16.
Computer output results for rotor speed effects on the vibration mode
shape and potential for leading edge buckling are shown in figure 17. Computer-
plotted mode shapes of the propeller blade superimposed on a Campbell Diagram
are shown in figure 18. Display of the amount of computer output information
summarized In figure 18 would be impractical without computer post-processlng
and graphical display. The availability of all this information in one figure
makes it convenient to assess the adequacy of the design on a quantitativebasis.
SUMMARY OF RESULTS
The complex behavior of integrated aircraft engine structures requires the
solution of interacting multidlsclplinary problems. Some recent research
activities at NASA Lewis focus on computational engine structural analysis
(CESA). CESA is essentially the computational simulation of complex engine
structural behavior using multldlsclpllnary integrated computer programs in
Conjunction with extensive computer post-processlng and graphical display of
computer output. Representative case studies were selected and are describedin some detail to illustrate the role of the computer on the computational
simulation of complex multldlsclpllnary engine structural problems. These
case studies include: (1) aeroelastic behavior of bladed rotors, (2) high
velocity impact of fan blades, (3) blade-loss transient response, (4) rotor/
stator/squeeze-fllm/bearing interaction, (5) blade-fragment/rotor-burst con-
tainment, and (6) structural behavior of advanced swept turboprops. These
representative case studies further demonstrate the indispensable utility of
computer post-processing and graphical display of voluminous analysis results
which make it possible to readily assess the adequacy of a design on a quanti-tative basis.
REFERENCES
I. Chamls, C.C., "Integrated Analysis of Engine Structures,: NASA TM-B2713,1981.
2. Smith, G.C.C. and Elchurl, V., "Aeroleastic and Dynamic Finite Element
Analyses of a Blader Shrouded Disk," Textron Bell Aerospace Co., Buffalo,
NY, 1980. (NASA CR-159728)
3. Adams, M.L., Padovan, J., and Fertis, D.G., "Finite Element for Rotor/
Stator Interactive Forces in General Engine Dynamic Simulation,"
EDA-2OI-3A, Akron Univ., Akron, OH, 1980. (NASA CR-165214)
4. Padovan, J., et al., "Engine Dynamic Analysis, with General Nonlinear
Finite Element Codes," Akron Univ., Akron, OH, 1982. (NASA CR-167944)
5. Rodal, J.J.A. and Witmer, E.A., "Finlte-Straln Large-Deflection Elastic-
Vlscoplastlc Finlte-Element Transient Response Analysis of Structures,"
ASRL-TR-154-15, Massachusetts Institute of Technology, Cambrldge, MA,
1979. NASA CR-159874)
6. Aiello, R.A. and Chamls, C.C., "Large Displacement and Stability Analysis
of Nonlinear Propeller Structures," Tenth NASTRAN User's Colloquium, NASA
CP-2249, 1982, pp. I12-132.
7. Chamls, C.C. and Aiello, R.A., Tensile Buckling of Advanced Turboprops,"
Journal of Aircraft, Vol. 20, No. II, Nov. 1983, pp. 907-912.
8. Hirschbeln, M.S., et al., "Structural and Aeroelastlc Analysis of theSR-TL Propfan," NASA TM-86877, 1985.
FOREIGNOBJECTDAMAGE STRUCTURAL DESIGN CONCEPTS
,_ ,, ,, COMPOSITEFOLDEDBU.NE,• IMPACT ANALYSIS _,_ lg/ FRAME
• LOCAL DAMAGEANALYSIS I_[-_... __" ,_lll_
• LARGE BLADE DEFLECTION " " .-(-----_ _ _ " _II
OPTIMIZATION AND _ __-q__ I
_ _ " HIGH TEMPERATURESTRUCTURES
£.AUTO AT,C_-_: F -_" _ TURBINE BLADEMETHODS
WITH COOLING COMPLEX• OPTIMIZATION ENGINESYSTEMS BLADE
CRITERIA MODEL TO DISK• DESIGN ATTACHMENT
TAILORING• MANY DEGREESOF FREEDOM• AUTOMATIC MESH GENERATION• INTEGRATIONOF STATIC STRESS,
THERMAL, AND VIBRATIONANALYSES
PASSAGES LOADING
• COMPLEX GEOMETRIES• CREEPAND PLASTICITY• COMPLEXTHERMAL AND
MECHANICAL LOADING• NONLINEAR EFFECTS
Figure I. - Engine structural components amenable to computational simulation.
/
BLADE- 64 PLATEELS
SHROUD - 4 PLATEELS
Z
DISK - 12 SOLID ELS
NASA LEWIS ROTOR12FINITE ELEMENTMODELFOR AEROELASTICANDMODAL ANALYSIS
Figure 2. - Finite element model foraeroelastic analysis of bladedshrouded disks.
UNDEFORMED MODE I785 Hz
MODE 21830 Hz
Figure 3. - Aeroelastic finite element analysis of bladed shrouded disks(bell code).
• 3 ELEMENTS THICK
• 306 ELEMENTS
• .504NODES
LEADING
TRAILING EDGE
CS-81-1470
Figure 4. - Superhybrid composite blade finite element model.
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I 333 (Radial) - Concave Layer I - Case 2 -(Int. Sp.)
333 !Radial) - Convex Layer 3 - Case 2 -(Int. Sp.)
,¢D 3330(Radial)_ - Concave Layer 2 - Case 2 -(Int. Sp.)
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Figure 9. - Demonstrator model, 100g-in. sudden unbalance atthe fan at 12 000rpm (spectrum-log mag. versus linear fre-quency).
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STATORIROTORORBITS RELATIVEROTORORBITS
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Figure 11. - Structural dynamics analysis using rotorlstatorlsqueeze-filmlbearing interactive finite element.
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TRANSI,ATION_ - Ise,gn IN-L_
RO'rATIONAL - 144,01B IN-LB
•OTAL - 302,9_0 IN-LB
Figure 12. - Geometric, test, and modeling data for the 4130 steel containment ringsubjected to tri-hub T58 rotor burst in NAPTCtest 201.
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SMALL-STRAIN PREDICTION
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Figure 13. - Deformed configuration 1180 _sec after burst.
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PROPERLIFRSTAGE PROPELLERBLADE 423GRIDPOINTS,744ELEMENTS
Figure 16. - Turbopropstagepropellerandfinite elementmodel.
SUMMARY OF TENSILEBUCKLING ROTORSPEEDS
TURBOPROP ROTOR SPEED,rpm
UNSWEPT-COMPOSITE
600 - SWEPT-TITANIUM
600 - SWEPT-COMPOSITE
600 - SWEPT-COMPOSITE(STIFF+450 PLIES)
12 470
I0 950
Ii 370
N
>_-(..)z
O
IA-
CAMPBELL DIAGRAM 600 SWEPT-COMPOSITETURBOPROP
1800
800
600
400
VIBRATION
MODE
3RD
200
2ND
-- IST
I I0 4000 8000
ROTORSPEED, rpm
I12 000
EFFECTOF ROTOR SPEEDON THEVIBRATION MODE i NODAL LINES, 600 SWEPTCOMPOSITETURBOPROP
0 rpm 3000 rpm 6000 rpm 7500 rpm 9000 rpm
Figure 17. - Structural behavior of advanced turboprops.
X
ANALYSIS MODEL
8OO
700
600'
500'
_0 --
_0
200
100
r
• MSCINASTRANo Experimental
2000
II
L_
4000
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6000 8000Bladerotational speed, rpm
CAMPBELL DIAGRAM
Figure 18. - Composite turboprop vibration analysis.
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
NASA TM-87231
5. Report Date4. Title and Subtitle
Computational Engine Structural Analysis
7. Author(s)
Chrlstos C. Chamls and Robert H. Johns
9. Performing Organization Name and Address
National Aeronautics and Space AdministrationLewis Research Center
Cleveland, Ohio 44135
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546
6. Performing Organization Code
505-63-II
8. Performing Organization Report No.
E-2898
10. Work Unit No.
Ill. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementa_ Notes
Prepared for the 31st International Gas Turbine Conference and Exhibit,sponsored by the American Society of Mechanical Engineers, Dusseldorf, WestGermany, June 8-12, 1986. Invited paper.
_16. Abstract
A significant research activity at the NASA Lewis Research Center is the.compu-tational simulation of complex multidlsclpllnary engine structural problems.This simulation is performed using computational engine structural analysis(CESA) which consists of integrated multldlsclpllnary computer codes In conjunc-tion with computer post-processing for "problem-specific" application. A vari-ety of the computational simulations of specific cases are described in somedetail in this paper. These case studies include (l) aeroelastlc behavior ofbladed rotors, (2) high velocity impact of fan blades, (3) blade-loss translentresponse, (4) rotor/stator/squeeze-fllm/bearlng interaction, (5) blade-fragment/rotor-burst containment, and (6) structural behavior of advanced swept turbo-props. These representative case studies were selected to demonstrate thebreadth of the problems analyzed and the role of the computer including post-processing and graphical display of voluminous output data.
17. Key Words (Suggested by Author(s))
Engine structures; Structural response;Multidisplinaryanalysis;Cow,outercodes;
Aeroelasticity;High velocityimpact;Impact
containment;Squeeze-filmbearings;Advanced
turboprops
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