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