The Structural Tailoring of Advanced Turboprops (STAT) computer program was developed to perform numerical optimization on highly swept propfan blades. The optimization procedure seeks to minimize an objective function defined as either: (1) direct operating cost of full scale blade or, (2) aeroelastic differences between a blade and its scaled model, by tuning internal and external geometry variables that must satisfy realistic blade design constraints. The STAT analysis system includes an aerodynamic efficiency evaluation, a finite element stress and vibration analysis, an acoustic analysis, a flutter analysis, and a once-per-revolution forced response life prediction capability. STAT includes all relevant propfan design constraints

Brown, K. W.

Hopkins, Dale A.

English

NASA Technical Reports Server

N88-22400
STRUCTURAL TAILORING OF ADVANCED TURBOPROPS*
K.W. Brown* and Dale A. Hopkins
Structural Mechanics Branch
NASA Lewis Research Center
ABSTRACT
The Structural Tailoring of Advanced Turboprops (STAT) computer program was
developed to perform numerical optimizations on highly swept propfan blades.
The optimization procedure seeks to minimize an objective function defined as
either; (i) direct operating cost of full-scale blade or, (2) aeroelastic dif-
ferences between a blade and its scaled model, by tuning internal and external
geometry variables that must satisfy realistic blade design constraints.
The STAT analysis system includes an aerodynamic efficiency evaluation, a
finite element stress and vibration analysis, an acoustic analysis, a flutter
analysis, and a once-per-revolution forced response life prediction capabil-
ity. STAT includes all relevant propfan design constraints.
The STAT system has been applied to three large scale advanced propfan applica-
tions. The STAT program made significant improvements in all three cases and
demonstrated the great potential for design enhancements through the applica-
tion of numerical optimization to turboprop fan blades of composite construc-
tion.
p_RECF_ING PAGE BLANK NOT FILMED
*Pratt & _"nitney Aircraft, East Hartford, CT. Work performed under NASA
contract NAS-23941.
2-205
https://ntrs.nasa.gov/search.jsp?R=19880013016 2020-03-20T06:32:21+00:00Z
THE HIGHLY COMPLICATED PROCESS OF THE SWEPT PROPFAN DESIGN
The swept turboprop design process involves the application of state-of-the-art
interdisciplinary engineering technologies. Numerous design iterations are
required between several work disciplines, including aerodynamics, acoustics,
structures, and aeroelastic analysis groups. Using these current design proce-
dures, it is very difficult to arrive at a satisfactory turboprop design, much
less an optimum one, because of multi-iterative, manual intergroup design proc-
ess that is required.
The penalties of this process include less than optimum designs, long design
times, low performance, and high noise and weight levels.
MANY DISCIPLINES MUST BE TIED TOGETHER
• AERODYNAMICS
• ACOUSTICS
• STRUCTURES
• AEROELASTIC (FLUTTER)
CD-88-32924
2-206
SR-7 PROPFAN DESIGN HISTORY -- CONFLICTS BETWEEN 
FLUTTER AND STRESS CONSTRAINTS 
In the design process for the SR-7 Propfan, a satisfactory aerodynamic con- 
figuration was reached by design iteration number 40. The final, acceptable 
design, however, was not reached until design number 100. Thus, 60 configura- 
tion changes were required before all structural design constraints could be 
met. The cost and labor required to complete this process is obviously very 
high. 
For the SR-7, the increased sweep tended to improve the flutter stability mar- 
gin, at the expense of higher foil stresses. The final 20 iterations in the 
design process proved to be little more than a fine-tuning of the blade sweep. 
HIGHER SWEEP IMPROVES 
INCREASED SWEEP INCREASED 
FLUTTER MARGIN. 
AIRFOIL STRESS. 
THE FINAL SR-7 BLADE IS 
DESIGN ITERATION NUMBER 100. 
CD-88-32925 
2-20 7 
MULTIDISCIPLINARYANALYSISCAPABILITIESOF STAT
STATis a highly modular software package, consisting of an executive system,
an optimizer, a design preprocessor, a set of approximate analyses, and a set
of refined analyses. Currently, STATuses the ADSoptimization package, which
is quite versatile, and also publicly available.
STAT's design preprocessor uses design curves to define both geometric and con-
struction blade properties. Based on input from the optimizer, a new geometry
is defined, and appropriate numerical models constructed.
STAT's approximate and refined analyses include aerodynamic, acoustic, flut-
ter, finite element stress and vibrations, and I-P forced response analyses.
• OPTIMIZER:
ADS
• DESIGN PROCESSING:
BASELINE DESIGN CURVES
DESIGN CURVE PERTURBATIONS
• MODULAR APPROXIMATE, REFINED ANALYSES:
AERODYNAMICS
ACOUSTICS
FLUTTER
STRESS
VIBRATIONS
FORCED RESPONSE
CD-88-32926
2-208
THREEPROPFANAPPLICATIONSOFSTAT
The STATprogram has successfully demonstrated the potential of design optimi-
zation whenapplied to turboprop fan blades of composite construction. STAT
produced improved designs for both the SR-7 and 18-E LAPblades. Addition-
ally, the optimizer proved to be capable of constructing an improved aero-
elastic scaled model propfan.
The final SR-7 blade was design numberi00 in a long, expensive development
process. STATwas able to demonstrate further improvements available from
this finely tuned design. The 18-E Propfan was an early infeasible design
candidate in the SR-7 development program. STATshowed the capability to take
an early configuration and significantly improve it, thus greatly reducing the
expense of the design process.
By applying STATto an aeroelastic scaled model blade, STATshows the poten-
tial for increasing the relevance of wind tunnel testing, while aiding design
of these test configurations.
• SR-7 PROPFAN--CAN WE IMPROVE ON THIS DESIGN (lOOth ITERATION)?
• PROPFAN 18-E--CAN WE GET TO A FEASIBLE PROPFAN FASTER THAN HSD'S
ENGINEERS DID?
• AEROELASTIC SCALE MODEL--CAN STAT BE USED TO DESIGN
AEROELASTICALLY SIMILAR SCALE MODELS FOR WIND TUNNEL TEST?
CD-88-32927
2-209
DEMONSTRATIONS OF STAT UTILIZED TWO DIFFERENT OBJECTIVE FUNCTIONS
For conventional swept propfans, STAT uses aircraft direct operating cost as
the objective function. Thus, a weighted function including aircraft fuselage
noise level, propeller efficiency, and propeller weight is minimized, subject
to appropriate design constraints.
For economical evaluation of candidate propfan designs, wind tunnel tests of
scaled models are conducted. For effective wind tunnel testing, it is neces-
sary to have aerodynamic, aeroelastic, and modal similarities between the full
scale blade and the scaled model. In STAT, a weighted overall measure of full
scale to scaled model configurations is minimized. A properly scaled blade
will have similar flutter, resonance, efficiency, acoustic, and static and
modal deflection characteristics.
• FOR FULL SIZE PROPFANS,DIRECT OPERATINGCOSTIS MINIMIZED.
• FOR THEAEROELASTICSCALEMODEL, A WEIGHTED SIMILARITY FUNCTION
MEASURESDIFFERENCESIN VIBRATORY,MASS, MODE SHAPESAND UNTWIST
DEFLECTIONS.
CD-88-32928
2-210
STANDARD PROPFAN DESIGN CONSTRAINTS USED BY STAT
STAT includes all design constraints normally considered in the propfan design
process. Side constraints limit the movement available on the various compo-
nents of geometry. Vibratory frequencies are limited according to prescribed
resonance margins. Stresses are limited via a Goodman diagram construction
including both steady stress and once per revolution forced response stresses.
Both classical unstalled and stalled flutter are constrained. Finally, rotor
power is held constant through an equality constraint.
BLADEGEOMETRY
• THICKNESS/CHORD
• ROOTSTACKINGPOSITION
FLUTTER
• CLASSICALFLUTTER
• STALL FLUTTER
POWER
RESONANCEMARGINS
• 1st MODE 2E
• 2nd MODE 4E
• 2nd MODE 5E
• 3rd MODE 5E
STRESSES
• STEADY STRESS
• 1-P FORCEDRESPONSE
CD-ff-3292g
2-211
STAT IMPROVES DOC FOR SR-7 PROPFAN BY 3.0 PERCENT
The SR-7 Propfan utilizes a complex composite construction. A nickel sheath
edge layer protects a fiberglass outer shell. Also utilized are an internal
aluminum spar, and foam to fill the gaps between the spar and the shell.
The initial optimization pass, using 38 design variables, reduced DOC by
5.0 percent. When design space was unscaled, however, the I-P life was found
to be unacceptable.
Using just 12 design variables to optimize the blade stacking, an improvement
of 5.3 percent over the base blade was found. Subsequent refined analysis
found that all constraints were satisfied, but that the actual DOC reduction
was 3.0 percent.
• INITIAL OPTIMIZATION PASS, USING 38 DESIGN VARIABLES, REDUCED DOC BY
5.0 PERCENT, BUT THE 1-P FORCED RESPONSE LIFE CONSTRAINT WAS VIOLATED.
• USING TWELVE STACKING VARIABLES, STAT IMPROVED APPROXIMATE DOC
BY 53 PERCENT
• REFINED ANALYSIS INDICATED:
ALL CONSTRAINTS WERE SATISFIED
ACTUAL D0C IMPROVEMENT WAS 30 PERCENT
CD-88-32930
2-212
THE18-E LABDESIGNWASAN EARLY,INFEASIBLE
DESIGNIN THESR-7 HISTORY
The 18-E Propfan design was a candidate in the SR-7 design evolution that was
unacceptable because of stress considerations. An interesting study performed
with STAT was to see how this design would evolve relative to the manually
designed SR-7.
Using 12 stacking and twist variables, STAT was able to improve the approximate
DOC by 5.3 percent, which is a 4.4 percent improvement over the final SR-7
configuration.
,, STEADY, 1-P STRESSES OF THE 18-E DESIGN ARE UNACCEPTABLE.
• BY ALTERING THE BLADE STACKING AND STAGGER, STAT WAS ABLE TO FIND
AN IMPROVED DESIGN.
• TWELVE DESIGN VARIABLES EMPLOYED.
• ALL CONSTRAINTS SATISFIED.
• DOC REDUCED BY 5.3 PERCENT (OR, 4.4 PERCENT IMPROVED OVER FINAL
SR-7 DESIGN).
CD-88-32931
2-213
THESR-7AIS ANAEROELASTICPROPFANSCALEMODEL
The SR-7Ais a 2/9 size aerodynamic scaled model of the SR-7LAPblade design.
The blade is composite in construction, madeup with 12 layers. For the STAT
optimization, the exterior shape was fixed to the scaled SR-7. The composite
construction was tailored using 37 design variables to better match the aero-
structural performance of the blades, including: scaled frequencies, mode
shapes, untwist static deflections, and mass distribution.
As the objective function, a summationof squared differences for all the above
parameters wasminimized. STATwas successful at reducing this objective func-
tion by 32 percent over the existing scaled model configuration.
• 219 SIZE SCALEMODEL, LAMINATEDCOMPOSITECONSTRUCTION.
• EXTERIORGEOMETRYIS FIXED BY THE SR-7, BUT COMPOSITECONSTRUCTIONWAS
TAILOREDTO BETTERMATCH AEROSTRUCTURALSCALING REQUIREMENTS
(37 DESIGNVARIABLES).
FREQUENCIES
MODE SHAPES
DEFLECTIONS
MASS DISTRIBUTION
• COMPONENTSTRESSESWERE THE ONLY DESIGN CONSTRAINT.
• DIFFERENCESSQUAREDOBJECTIVEFUNCTIONWAS REDUCEDBY 32 PERCENT
CD-88-32932
2-21_
WORKIN PROGRESS
Currently, STAT is being expanded to allow the tailoring of counter rotation
propfans. This effort involves extensive improvements to the aerodynamic and
acoustic modules, including an upgrade of the approximate acoustic analysis,
to improve correlations with refined analysis.
Enhancements to STAT include an improved optimization scaling algorithm, and
also improved flexibility in initial design selection.
• APPLICATIONTO COUNTERROTATIONPROPFANS.
AERODYNAMICS
ACOUSTICS
• INCREASEDAIRFOIL DEFINITIONFLEXIBILITY.
• IMPROVED OPTIMIZATIONSCALINGALGORITHMS
CD-B8-32933
2-215
CONCLUSIONS
The STATpropfan optimization system has shownthat design tailoring can be
effectively applied to large, multidisciplinary systems, showing great poten-
tial for manpowerequirement reductions, relative to present, manual design
procedures.
STAThas been successfully applied to the optimization of two full scale prop-
fans, and also to an aerostructural scaled model. With the exception of the
approximate acoustic analysis, all approximate analysis modules have shown
very good accuracy.
. DESIGN OPTIMIZATIONHAS BEENSUCCESSFULLYAPPLIED TO THE COMPLEX
PROPFANDESIGN PROCESS.
• STAT HAS BEENSUCCESSFULLYAPPLIED TO THE OPTIMIZATIONOF TWO
PROPFANS,AND ALSOTO AN AEROSTRUCTURALSCALEMODEL.
• THE APPROXIMATEACOUSTICANALYSIS NEEDS IMPROVEMENT.
CD-88-32934
2-216
REFERENCES
Brown, et al., 1987, "Structural Tailoring of Advanced Turboprops," AIAA/ASME/
ASCE/AHS 28th Structures, Structural Dynamics, and Materials Conference,
Monterey, CA, April, 1987.
Sullivan, et al., "Large-Scale Advanced Prop-Fan SR-7 Blade," NASA Contract
NAS3_23051 (to be published).
Vanderplaats, et al., 1983, "ADS-I: A New General Purpose Optimization Pro-
gram," AIAA 24th Structures, Structural Dynamics and Materials Conference,
Lake Tahoe, NV, May 1983.
2-217


Structural tailoring of advanced turboprops

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server