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Propulsion System Design with VSP
Russ Denney Jon Gladin
August 9, 2013
Project Objectives
• Improved conceptual design of engine flowpath and improved propulsion-airframe integration – To enable analysis of alternatives for advanced concepts
• Effective communication and illustration of design ideas • Stepping-stone to higher-order analyses
– Bring higher-order analyses forward to conceptual design – Empirical design rules from conventional designs do not apply
• System level view – Propulsion Airframe Integration
• Cycle & architecture choices installation issues
– Internal engine flowpath • Component zooming
– From cycle to 3-D definition • Establish basic geometric outline
– Later export to higher order CAD/analysis
2
Outline
• NASA NRA Overview • Engine Flowpath Design • WATE-VSP Sockets • VSP Components • Interfaces with Higher-Order Analysis Codes
3
Approach
• It is not practical to draw an engine flowpath “freehand” in VSP the same way one might draw an airplane
• The engine flowpath is largely determined by the thermodynamic cycle along with mechanical and aerodynamic constraints
4
Tool Set
• NPSS provides the engine thermodynamic cycle calculations required to initiate the design process
• WATE++ provides the initial parameterizations and constitutive relations to introduce aerodynamic and mechanical considerations into the design – WATE was originally intended primarily for weight estimation
• OpenVSP provides 3D visualization and initial geometry for higher-order analyses – Aircraft design tool
• Our specific objectives then are to: – Identify improvements to the WATE parameterizations and constitutive relations – Extend the 2D flowpath geometry to 3D component geometry at the WATE/VSP
interface – Identify the interface requirements for higher-order analyses
NPSS WATE++ OpenVSP Higher-
Order
Analyses
5
0-D 2-D 3-D
Roadmap
6
NPSS WATE++ OpenVSP Higher-Order
Analyses
Flowpath analysis to determine
inputs to WATE++
WATE++ sockets to output 3D
geometry to VSP
Component meta-geometry to
interface with analysis codes
Identify potential improvements to
WATE++
New VSP components for
engine parts
Analyses to determine inputs
to VSP sockets
First Year
7
NPSS WATE++ OpenVSP Higher-Order
Analyses
WATE++ sockets to output 3D
geometry to VSP
Component meta-geometry to
interface with analysis codes
The first year focused primarily on the WATE-VSP sockets and preliminary work with higher-order analysis codes
Second Year
8
NPSS WATE++ OpenVSP Higher-Order
Analyses
Flowpath analysis to determine
inputs to WATE++
WATE++ sockets to output 3D
geometry to VSP
Component meta-geometry to
interface with analysis codes
Identify potential improvements to
WATE++
New VSP components for
engine parts
The second year completed most of the 2D geometry, extended work on higher-order analysis codes, and began developing custom VSP components
Third Year Plan
9
NPSS WATE++ OpenVSP Higher-Order
Analyses
Flowpath analysis to determine
inputs to WATE++
WATE++ sockets to output 3D
geometry to VSP
Component meta-geometry to
interface with analysis codes
Identify potential improvements to
WATE++
New VSP components for
engine parts
Analyses to determine inputs
to VSP sockets
The third year will complete development of the 2D and 3D geometry tools and the evaluation of higher-order analysis tools
Engine Flowpath Design
10
NPSS WATE++ OpenVSP Higher-Order
Analyses
Flowpath analysis to determine
inputs to WATE++
Identify potential improvements to
WATE++
Rolls-Royce Demo Problem
• Sample flow-path design problem: – Evaluate current engine design
methods – Test influence of improved methods
• Rolls-Royce supplied thermodynamic cycle data for a notional mixed-flow turbofan (MFTF) – GT created initial calibrated
NPSS/WATE++ MFTF model to match cycle data
– WATE++ inputs varied to match MFTF drawing (fixed shaft speeds)
• Some modifications to WATE++: – Inclusion of stratified fan model – New mixer drawing routines – GT 1-D combustor designs
• Initial flowpath parameters estimated
11
• Component design relies on good initial flowpath choices
• Use physics-based design procedure to determine flowpath parameters
Example WATE++ Compressor
• Specified inlet and exit Mach numbers determine the inlet and exit areas
• Inlet hub/tip radius ratio determines the inlet passage height
• Specify constant hub, mean, or tip radius to set the exit passage height
• Assume equal stage loading to determine stage count
• Assume linear variation in rotor and stator aspect ratio to set chord lengths and compressor length
• Specified solidity determines the blade counts on each blade row
• Calculate individual blade weights, inner and outer casing weights, disk weights, etc.
12
Many geometric inputs must be specified by the designer
Flowpath Setup Process
13
• Stage Loading
• First Stage Hub/Tip Ratio
• First Stage Pressure Ratio
• Spool RPM/Tip speed
Design Process
• Collect thermodynamic engine cycle data
• Compressor Constraint Analysis
– Identify bounds on the constraints
– Compute the distribution of flow angle (α1) and
shaft speed (ω) for each constraint
– Identify a feasible design space of α1 and ω and
choose design point
– Compute hub/tip, stage loading, flow coefficient
• Turbine Constraint Analysis
– Identify bounds on the constraints
– Compute the distribution of mean radius (Rm) and
shaft speed (ω) for each constraint
– Identify a feasible design space of Rm and ω and
choose design point
– Compute stage loading, flow coefficient
Engine Cycle
Data
Constraint
Analysis
WATE++
Inputs
Compressor
Turbine
• Mass Flow
• Temperature
• Pressure
• Mach Number
Compressor
• Tip Velocity
• Hub/Tip Ratio
• AN2
• Stage Loading
• Flow Coefficient
Turbine
• Stator Turning
Angle
• Mach Number
• AN2
Constraints
Methodology based on:
Byerley, Boyer & Halliwell, Using Design
Envelopes to Aid in the Preliminary Design
of Rotating Machinery, GT2004-53952
HPC Constraint Analysis
• Applicable Constraints: Hub/Tip, Vtip, AN2, Flow Coefficient (ϕ = u1/U), Stage Loading (ψ = gccp∆Tt/U2)
• First Stage Analysis
Available Design Space
Max Ψ = 0.35 Min Φ = 0.45
Min Ψ = 0.3 Max Φ = 0.55
Min HtoT = 0.38
Max HtoT = 0.7
Max Vtip = 1500
Max AN2 = 6 e10
14
HPT Constraint Analysis
• Applicable Constraints: Stator Turning Angle (α2), AN2, Rotor Exit Relative
Mach Number (M3R) • First Stage Analysis
Available Design Space
Max α2 = 70○
Min α2 = 57○
M3R
15
Compressor-Turbine Matching
Figures adapted from Byerley, Boyer & Halliwell, Using Design Envelopes to
Aid in the Preliminary Design of Rotating Turbomachinery, ASME Paper
GT2004-53952
16
Engine Flowpath Design – Summary
• Ga Tech is collaborating with Rolls-Royce on 2D flowpath definition • In the process of implementing Rolls-Royce recommendations
– Some implementation may require re-coding of the WATE++ components – Will be done if level of effort required isn’t too large – Others will be implemented through pre-processing WATE++ inputs – All recommendations will be documented and provided to NASA for
consideration
• Preliminary NPSS/WATE++ study model created – Model is continually updated as new design recommendations are received
from Rolls-Royce
• Conceptual flow path constraint analysis “element” coded in NPSS – Working on convergence issues and verification of results – Expanding to include additional constraints and degrees of freedom
17
Roadmap
18
NPSS WATE++ OpenVSP Higher-Order
Analyses
Flowpath analysis to determine
inputs to WATE++
WATE++ sockets to output 3D
geometry to VSP
Component meta-geometry to
interface with analysis codes
Identify potential improvements to
WATE++
New VSP components for
engine parts
Analyses to determine inputs
to VSP sockets
3D Geometry Design
NPSS WATE++ OpenVSP
Higher-
Order
Analyses
Identify potential
improvements to
WATE++
New VSP
components for
engine parts
Flowpath
analysis to
determine inputs
to WATE++
WATE++ sockets
to output 3D
geometry to VSP
Component
meta-geometry
to interface with
analysis codes
19
How to draw an engine with a “Vehicle” Sketch Pad?
• Existing Engine Model
– Only thing in VSP “intended” to be an engine or engine component
– Useful “picture” tool
– Need higher degrees of freedom
• Translate from a conceptual component parameterization into VSP parameterization
• Use 3 types of geometry in VSP used for engine flow path modeling
• Nacelles/Ducts/Nozzles/Mixers – Fuse2
– Longitudinal xsec stack up
– Multiple xsec options (circular, elliptical, input file, etc.)
• Turbomachinery blades/stators– Propeller
– Turbines/compressors, etc
– Fuel swirlers
• Disk – MSWing
– Body of rotation
Fuse2 Element for Nacelle Creation
• Using 2 Fuse2 instantiations to create the “Nacelle” element
• 3 Cross sections for ”inlet“
– Fan face
– Throat
– Highlight
• 3 Cross Sections for “cowl”
– Highlight
– Max Nacelle Area
– Nozzle exit (either bypass or core depending on engine type)
• Note that approach is similar to existing Engine
– Advantage is that we can inherit the cross sectional parameters from Fuse2
– Shape parameters at the top, bottom, left, right
Cowl/Nozzle/Engine Parameters
Lmax
Fore cowl Tan Str1 and 2 Aft Tan Str1 and 2
Rexit
Aft Length
Rmax
• 3 hard cross sections
Rhl
Inlet Parameters
Rfan Rhl
L
Rth
Lip Fineness x (Rhl-Rth)
Lip Tan Str1 and 2 Diffuser Tan Str1 and 2
• 3 hard cross sections
Nozzle Parameters
Inner and Outer Radii
3rd Cross Section
L/D
Inner and Outer Radii
Inner Tan Str 1-4 OuterTan Str 1-4
Interp xsec %
Can add 4th cross section for cowl or plug
Example: Turbofan Outer Geometry
• Composed using all fuse2 geometries – Can add “Pucks” for CFD if desired
Inlet
Cowl Inner duct connects nozzle and fan case
Outer Bypass Nozzle
Inner Bypass Nozzle
Outer core nozzle
Plug
Cross Sectional Geometry
Width offset allows for “fat” nacelles
Asymmetric “Height”
• Ellipse allows different width and height
• Might want a different radius from the centerline for top and bottom or left and right
• Use offset and height or width
Fuse2 Rotation Angles
• Added angular rotation to the fuse2 for each cross-section – Enables scarfing for the inlet
– Also enables different location of max nacelle areas
– Makes 2-D/supersonic inlets much easier
Turbomachinery in VSP
• “PROP” Component • Turbines and Compressors • Blade cross-sectional stack up
– Arbitrary number of sections – Specify cross section span-wise
location – Multiple types of airfoil
specifications (NACA 6 series, 4 series, etc)
– Parameters for thickness, camber, etc
• Parameters: – lean/sweep/twist, etc – Hub/tip ratio
• Use “FUSE2” component for turbomachinery ducts
Example: Compressors in OpenVSP
• Component Parameters – Inport location and Radii
– Outport Radii
– Total compressor length
– IGV length
– Front frame length
• Stage Parameters – Blade axial length (each stage)
– Stator axial length (each stage)
– Spacing length (or % of stage length)
– Num blades (each stage)
– Tip Radius
– Hub radius (or HtoT ratio)
• Blade Parameters – Twist distribution
– Airfoil shape
– Taper
– Etc.
150Pax HPC
150Pax Booster
Disk Parameterization
• Disks are relatively non-complex shapes when compared to other parts of the engine
• Currently there are 4 possible profiles being considered for disk shapes
• These include: – Continuous Slope*
– Hyperbolic
– Web
– Ring
*Gutzwiller , D.P. and Turner, M.G., Rapid low fidelity turbomachinery disk optimization, Advances in Engineering Software 41 (2010) 779–791
Example: Disks
• Can create disks with MSWING using “dihedral” and custom “.af” files
• Really just a body of revolution
• Generic enough to allow arbitrary cross section inputs
Hyperbolic Design Web Design
Courtesy of Jon Seidel (NASA Glenn)
Compressor Transition Duct
Example: Transition Duct Element
• Two FUSE2 with 3 cross sections
• L/D ratio
• InPort and OutPort Radii
• Use of tangent strength and angles to vary the shape and slope of the duct
• Can vary the location of the intermediate cross section(s) if you want…..again, be careful!
• Can also stand as a placeholder for the combustor
Example: Hi-Bypass Fan • Extension of the axial compressor
element in WATE++
• Inherits the basic properties of the axial compressor element except:
– Add a splitter
– Have fan hub spinner which needs to be parameterized
– Fan stator in the bypass
– Have a rear-frame present in the bypass duct as well
• Frame has additional parameters (numBlades, length ratios, etc)
Rear frame
Fan stator
Fan Rotor
Spinner
Example: Fan Hub Spinner Parameterization
• The WATE distribution version just draws a fixed curvature arc
– Changed to be parameterized
• Many modern designs have “conical” spinners
• Both can modeled using the FUSELAGE2
– Xsecs at nose, fan face, and fan outport (core flow interface)
– Nose is a “point” type
– Appropriate tan strengths and angles to modify shape of the flow path
– Conical shape controlled by angle at the nose
– Set the angle to vertical for the rounded shape
Example: Mixers
Uses the fuselage xsec “edit” capability
Cubic Bezier • Each segment has 4 control
points
Symmetry requires number of lobes is a multiple of (2n+2) for n = 0, 1, 2, ….
Simple 2-D Mixer Xsec Parameterization
hlobe
Rinner
Center
θ
Parameters: • Lobe height • Inner Radius • Number of lobes • Two “tangent strengths” (control
point degree of freedom)
1
3 4
2
Control Point 1:
Control Point 2:
Control Point 3:
Control Point 4:
Geometry
reflected about
line 0-4 and
rotated by 2θ
Control Points
calculated for
each lobe and
can be input into
vsp input file
Mixer Xsec Stack-up
• Standard Fuse 2 parameterizations:
– List of xsecs with shape parameters defining the curve connecting the xsecs
– Xsecs have varying lobe height (generally a varying xsec definition)
WateVSP Socket Concept
WATE++ 2D Parameterization
Component 3D Parameterization
VSP Component Parameterization
WATE Socket
• 3-D parameters defined within the socket
• WATE doesn’t set them
• Default values • Higher order
analyses
VSP File
• Sometimes WATE++ different than VSP
WATE++ OpenVSP “Sockets”
40
Element Compressor CmpFan { #include <CmpFan.map> Fl_O.MN = 0.45; S_map.NcDes = 1.0; S_map.PRdes = 1.65; S_map.effDes = 0.875;
NPSS Model Component Instantiation
WATEhiBypassFan WATE_CmpFan { componentRef = "CmpFan"; geometryType = "ConstTipRadius"; numContainedStages = 1; MNin = 0.667; MNout = 0.4155; stg1MaxPR = 1.8; hubTipRatioIn = 0.337; maxSpdRatio_in = 1; bladeSolidity = 1.27; stg1BladeAR = 1.76; stg1StatorAR = 1.333; stg1NcTip = 1600;
WATE Model Component Instantiation
Subelement WATEvsphiBypassFan S_VSPGeom { } void postexecute() { S_VSPGeom.update(); }
WATE-VSP Socket Instantiation
• Each WATE++ component element includes an associated “WATEvsp Socket”
• This socket translates WATE data and a user specified set of additional 3-D parameters into a VSP file
• Can call the VSP model creation after WATE++ converges on a design
• Object oriented, so not engine specific: • Code one socket and then
plug into different engine models
Current Sockets
• Focused on engine flowpath elements:
– Duct
– Inlet/Low-drag Nacelle (WATE nacelle)
– Hi-bypass Fan (you can do low bypass too)
– Forced 2-D Mixer
– Core nozzle
– Bypass nozzle
– Axial Compressor
– Axial Turbine
41
• Structure of a socket: – Same as a normal NPSS
element
– Input parameters
– Calculate function • Update function
• Writes each xml line to an entry in a string array
• Output data at the end of the NPSS run file
• Engine has many components – Added controls for
num_pnts/blades etc.
Example Engines
Mixer
• Mixed flow turbofan • Based off Rolls-
Royce thermo data
• Separate flow turbofan • 150 passenger model • Based off CFM56 cycle
• Simple Turbojet Model
New VSP Components
NPSS WATE++ OpenVSP
Higher-
Order
Analyses
New VSP
components for
engine parts
43
Motivation for “Engine VSP Components”
WATE++ 2D Parameterization
Component 3D Parameterization
VSP Component Parameterization
WATE Socket
VSP File
• Goal is to create new VSP components • E.g. nacelle, disks, blades
etc. • New VSP components
think the way engine designers do
• Want similar level of simplicity (keep the VSP way)
• Resolve some meta-geometry generation issues
New Components
Tube Component
• Intended to be a replacement for the copy/paste method
• Allows a set of cross-sections from 0-1 and from 1-0
• Forms a closed surface and works with the mesher
Disk/Blades Component
• New xsec definitions that vehicle people wouldn’t want – Add new driver groups
• Blades is a re-design of the propeller – Naming conventions
– Default values
Advantages of New Components
46
<Airfoil_List> <Airfoil> <Type>4</Type> <Inverted_Flag>0</Inverted_Flag> <Camber>0.000000</Camber> <Camber_Loc>0.500000</Camber_Loc> <Thickness>0.500000</Thickness> <Thickness_Loc>0.500000</Thickness_Loc> <Radius_Le>0.000000</Radius_Le> <Radius_Te>0.001000</Radius_Te> <Six_Series>63</Six_Series> <Ideal_Cl>0.000000</Ideal_Cl> <A>0.000000</A> <Name>Disk attempt5 WEB</Name> <Original_AF_Thickness> 0.500000 </Original_AF_Thickness> <Radius_LE_Correction_Factor> -1.000000 </Radius_LE_Correction_Factor> <Radius_TE_Correction_Factor> 0.000000 </Radius_TE_Correction_Factor> <Upper_Pnts>0.000000,…,1.000000,</Upper_Pnts> <Lower_Pnts>0.000000,…,1.000000,</Lower_Pnts> <Slat_Flag>0</Slat_Flag> <Slat_Shear_Flag>0</Slat_Shear_Flag> <Slat_Chord>0.250000</Slat_Chord> <Slat_Angle>10.000000</Slat_Angle> <Flap_Flag>0</Flap_Flag> <Flap_Shear_Flag>0</Flap_Shear_Flag> <Flap_Chord>0.250000</Flap_Chord> <Flap_Angle>10.000000</Flap_Angle> </Airfoil> <Airfoil> … </Airfoil> <Airfoil> … </Airfoil> </Airfoil_List>
<Component> <Type>Disk</Type> <General_Parms> ... </General_Parms> <Disk_Parms> <Profile_Type>2</Profile_Type> <Bore_Radius>1.800000</Bore_Radius> <Rim_Radius>4.500000</Rim_Radius> <Bore_Height>0.250000</Bore_Height> <Rim_Height>0.250000</Rim_Height> <Bore_Width>2.000000</Bore_Width> <Rim_Width>2.000000</Rim_Width> <Web_Thickness>0.100000</Web_Thickness> </Disk_Parms> </Component>
<Component> <Type>Mswing</Type> <General_Parms> ... </General_Parms> <Mswing_Parms> <Total_Area>0.000200</Total_Area> <Total_Span>0.000200</Total_Span> <Total_Proj_Span>0.000100</Total_Proj_Span> <Avg_Chord>18.000000</Avg_Chord> <Sweep_Off>0.000000</Sweep_Off> <Deg_Per_Seg>10</Deg_Per_Seg> <Max_Num_Seg>18</Max_Num_Seg> <Rel_Dihedral_Flag>0</Rel_Dihedral_Flag> <Rel_Twist_Flag>0</Rel_Twist_Flag> <Round_End_Cap_Flag>0</Round_End_Cap_Flag> </Mswing_Parms>
<Section_List> <Section> <Driver>4</Driver> <AR>0.001000</AR> <TR>1.000000</TR> <Area>0.000100</Area> <Span>0.000100</Span> <TC>18.000000</TC> <RC>18.000000</RC> <Sweep>0.000000</Sweep> <SweepLoc>0.000000</SweepLoc> <Twist>0.000000</Twist> <TwistLoc>0.000000</TwistLoc> <Dihedral>0.000000</Dihedral> <Dihed_Crv1>0.500000</Dihed_Crv1> <Dihed_Crv2>0.500000</Dihed_Crv2> <Dihed_Crv1_Str>0.750000</Dihed_Crv1_Str> <Dihed_Crv2_Str>0.750000</Dihed_Crv2_Str> <DihedRotFlag>1</DihedRotFlag> <SmoothBlendFlag>0</SmoothBlendFlag> <NumInterpXsecs>1</NumInterpXsecs> </Section> <Section> ... </Section> </Section_List> </Component>
New Component Demo
• Demo
Tube Re-design
• Could separate parameters into “inner” and “outer”
– Pros: User wouldn’t have to know the trick
– Cons: Slightly more complicated/larger GUI and more parameter names
• Needs better defaults for the GUI
• Separate the inner and outer surfaces into different “pieces”
– Allows proper variation of leading and trailing angles
– Essentially the same thing as using FUSE2
• Need ways to flag inner and outer surfaces for separation of force integrals in CART3D
Meta-Geometry Generation and Analysis
NPSS WATE++ OpenVSP
Higher-
Order
Analyses
Component
meta-geometry
to interface with
analysis codes
49
Cart3D Progress
• TUBE component works for flow-through and powered
• Separate flow nacelle analysis – Successful water-tight mesh
generation
• Nacelle “powered” analysis – The nacelle was modeled with the
FUSE2 components – Based on CFM56 design – FUSE2 elements created to fit within
the engine envelope for powered BC – BC’s pulled from NPSS models
• Issues: – Solutions convergence sensitive to AIP
placement
50
VSP to Calculix
51
NPSS/WATE++
VSP “Viewer” Blades (VSP:PROP)
Disk Profiles (VSP:MSWING)
FEA PYTHON SCRIPT
VSP
Solid Model (Step, IGES)
Finite Element Model (Calculix) (Mesh Only – STL)
VSP/XML File
Courtesy of Dan Trowbridge
WATE-VSP
Sockets
VSP Disk and Blade
Components
VSP to SWIFT
• SWIFT may be used for higher-order analysis of turbomachinery airfoils – Thin layer Navier-Stokes code
• CCGEOM
– Input: Parametric blade geometry – Output: Blade data in MERIDL format
• TCGRID – Input the hub & tip geometry and the blade geometry from
the MERIDL file – Include grid size and inlet condition parameters – Output: 3-Dimensional multiblock grids
• SWIFT – Input 3-Dimensional grids
– Include inlet flow conditions and iteration parameters
– Output: CFD solution files (PLOT3D format)
• Current plan is to replace CCGEOM with a Python script
which will accept the parametric blade geometry from the VSP XML file and convert it to TCGRID format
52
Iyengar, A First Principles Based Methodology for Design of Axial Compressor Configurations, PhD Dissertation, Georgia Tech, August 2007
Future VSP Developments
PAI Development – Resolve TUBE issues
(significant re-design) – Surface flagging issues – Center-body issues – New Engine2 component
• Combines old engine and fuselage capability
• Include powered boundary conditions
• Optional separate flow derivative
– CART3D testing – Model PAI problem
Flowpath Development – Disk/Blades
• New xsec driver groups
– Mixer
– Duct
– Combustor (simplified) • May be useful for volume
calculations
• Emission predictions modules
– Swift and Calculix wrappers
Plan is to have new component for each socket