design of propeller blades for high...

MAAT – Multibody Advanced Airship for Transport Project ID 285602 / FP7-AAT-2011-RTD-1

Design of Propeller Blades For

High Altitude

Silvestre1, M. A. R., Morgado2 1,2 - Department of Aerospace Sciences

University of Beira Interior

MAAT 2nd Annual Meeting M24, 18-20 of September, Montreal, Canada


• Introduction • JBLADE: Propeller Design and Analysis Software

• Theoretical Formulation • Classical Blade Element Momentum Theory

• 3D Corrections

• 3D Equilibrium

• Post Stall Model

• Propeller Simulation

• Validation

• Cruiser Propeller Design • Initial requirements

• 1st design iteration

• Requirements review

• Concluding Remarks

Outline

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3


Oil peak

Fuel conservation

Propellers: the outdated inovation! Silent Unducted Fan (UDF)

Introduction /24

4


Introduction

/24

W

FTSFC

5


Multibody Concept for Advanced Airship for Transport (MAAT) project

Cruiser and Feeder

Cruiser will be at cruising at 15km most of the time (design point)

Other operating points (static thrust for required control aceleration accounting added masses effect)

Solar/electric propulsion

Altitude, Thrust, Reynolds and Mach

Aircraft => constant L/D with altitude => constant thrust

Airship => constant speed with altitude => reduced thrust with altitude

Thrust per unit weight and power

The Weight Spiral

Introduction - Motivation /24

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The Weight Spiral:

higher drag kgf

increased envelope sized + ? kg

bigger control actuator +? kg

stronger/more motors + ? kg

more solar panels +? kg

more structure+ ? kg

+ ?? kg

larger/more propellers + ? kg

increased added masses effect + ? kg

7



The inverted Weight Spiral:

reduced drag kgf

increased envelope sized - ? kg

smaller control actuator -? kg

weaker/less motors - ? kg

smaller solar panels -? kg

less structure- ? kg

- ?? kg

smaller/less propellers - ? kg

reduced added masses effect - ? kg

8



Same engine!

Different weight and size!

Different performance

9



The bicycle has almost 200 years old!

An example of inverted weight spiral,

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The success of a system/device is dictated by its

conception not by the quality of the theoretical

modelation or the optimization algorithms!

Introduction /24

A bad concept means failure!

Bad theoretical models or bad tools mean more

iterations (numerical or experimental)!

11


Introduction /24

MAAT should be about finding and equating concepts

that would make the base high altitude solar

airship cruise – feeder concept a viable one

not

carry on efforts on impossible solutions!

12


Introduction /24

In any case, any concept that might offer

weight reduction should be looked at!

Examples:

• A streamlined shape => low drag coefficient, teardrop shape

• A aerodynamically passive stable configuration =>

centre of pressure AFTER the center of mass, conventional stabilizers

• Carbon materials, unidirectional pultruded carbon fibre composite

• Active drag reduction, Goldschmied body

• Low power per unit thrust, CSIRO motor

• Ironless permanent magnet motors,

Low disk loading Propellers/Rotors


JBLADE: Propeller Design and

Analysis Software

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Open source

David Marten’s QBLADE

André Deperrois’s XFLR5

Mark Drela’s XFOIL

Introduction – JBLADE’s Concept

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Code Structure

360º Polar Object

-Lift and drag coefficients;

-Reynolds number;

-Full angle of attack range.

Extrapolated Data

Blade Object

-Geometric parameters;

-Number of stations;

-Number of blades;

360º Polar Objects

Propeller Object

-Propeller Parameters;

Blade Object

Propeller Simulation Object

-Simulation Parameters.

Propeller Object

Blade Data Object

Blade Data Object

-Simulation Results Data along

the blade.

-Induction Factors;

-Inflow Angles;

-Circulation;

-Advance Ratio;

-Speed. BEM Simulation

-Advance Ratio;

-Speed Range.

360º Polar

Extrapolation

Airfoil Object

-Airfoil

Coordinates;

-Airfoi l Camber;

-Airfoil Thickness;

Polar Object

-Lift and drag

coefficients;

-Reynolds number;

-Angle of attack range.

Airfoil Object

Simulation Results

Panel

Simulation

- Angle of attack

Range

XFOIL

BEM CODE

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sincos DLa CCC

cossin DLw CCC xx cCWF 2

2

1

tip

root

R

R

adrFBT

tip

root

R

R

trdrFBQ

Theoretical Formulation

Classical Blade Element Momentum Theory

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To find an W, the iteration variables of the classical BEM for each blade element are

the axial and tangential induction factors:

V

VWa a

a

r

rWa tt

these are derived from momentum theory as:

12

1sin4

aa

c

Fa

1

1cossin4

tt

c

Fa

Where is the local rotor solidity ratio

r

cB

2

and F is the Prandtl’s correction factor that allows the blades 3D correction

Theoretical Formulation /24

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3D Corrections

feF arccos2

gr

RBf rootroot

11

2

tanr

Rg root

root

gR

rBf

tiptip

11

2

tantip

tipR

rg

Prandtl’s correction factor:

where:


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3D Equilibrium

02

r

W

r

WW

r

WW tt

ta

a

The case where Wa is maintained constant across the propeller annulus, is reduced to:

.constrWr

W

dr

dWt

tt

Neglecting the radial velocity component in the disk, 3D equilibrium translates to:

the total propeller torque will be the result of a free vortex induced tangential velocity profile

with an average axial velocity, Ra WW 75.0 across the propeller disk


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3D Equilibrium - Implementation

In first iteration the forces coefficients are computed assuming no tangential induction factor.

The element i annulus mass flow rate is calculated as, , so, rdrWm ai 2 itotal mm

To satisfy the momentum conservation, the total propeller torque,

will be the result of a free vortex induced tangential velocity profile,

with

and an average axial velocity, 2R

mW total

a

r

RVV

tt

7575.0

rdrVWQ ta4

roottipat

RRRW

QV

375

The radial induction factor is updated and iterated: r

Va t

t


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Post Stall Model

According to the work of Corrigan and Schillings the stall delay is related to the ratio of the

local blade chord to radial position

d

dccc l

rotnonrot )(

0max

1136.0 LL CC

n

r

cK

where the separation point is related with the velocity gradient, with K

084.11517.0

K

r

c

and maximum lift coefficient of the rotating blade increased by


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Airfoil Sub-Module

Results and Discussion /24

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Results and Discussion

XFOIL Sub-Module

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360 Polar Sub-Module

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Blade Sub-Module

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Simulation Sub-Module

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NACA TR 594


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NACA TR 594 – 15 at 0.75R


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NACA TR 594 – 30 at 0.75R


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NACA TR 594 – 45 at 0.75R


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3D equilibrium shows better results than the classical BEM formulation but could be improved further for actual Wa distribution.

With the present formulation, JBLADE gets closer to the experimental data than the other available open source codes.

The post stall model plays a significant role in the low advance ratio region and may well be the main source of the remaining differences relative to the actual propeller performance.

The main future work is aimed at incorporating a blade structure module as well as an electrical motor module in the code such that the thrust per unit weight for constant power of the complete propulsion set can be optimized as a whole.

About the code validation /24

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Initial requirements for 33 propellers*:

Thrust: 60 kN @ 55m/s cruise

15 km of altitude operation

Diameter: 7.1 m

Tip Mach Number: 0.5

Cruiser Propeller Design

*according to UBI report from 07/03/2013

“Evaluation of the Number of Propellers for the

Cruiser”

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Operational environment:

Air density: 0.194 kg.m-3

Absolute viscosity: 1.43226x10-5kg/(m.s)

Speed of sound: 295.1 m.s-1


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Concepts:

Keeping the tip Mach Number fairly low

(final 0.67)

Moderate Reynolds number high performance

SG6043 airfoil

Minimim induced loss at the

design point using Drelas’ QMIL design code


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1st design iteration:

7MW each propeller

(231MW total)

high solidity (and mass)

from high disk loading with

low air density at 15km


hp= 0.5

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each propeller

year Designation F[N] Prop D[m] F/A[kgf/m^2] v_i[m/s] h_ind

1987 Egrett 2773 3.40 31.14 5.85 0.96

1988 Condor 1129 4.90 6.10 3.45 0.95

1993 Pathfinder 23 2.01 0.74 2.51 0.85

1994 Perseus 388 2.20 10.38 5.51 0.94

1995 Strato 2C 2500 6.00 9.01 4.79 0.95

1996 Theseus 409 2.74 7.05 6.97 0.84

MAAT Cruiser 60000 7.10 154.48 40.78 0.57

New MAAT Cruiser 1200 7.10 3.09 1.36 0.98

Requirement Review:

with minimized drag

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Concluding Remarks

• A new software for propeller design was developed and

validated for MAAT JBLADE: Propeller Design and

Analysis Software;

• Designing propellers for 15 km altitude requires the

use of low disk loading to maintain a moderate tip

Mach number or the result is a very high solidity and

low efficiency propeller;

• Current Requirements for the cruiser result in poor efficiency

(.50) and high propulsive system mass of 83 ton;

• Reviewing the propulsion system requirements by optimizing

the cruiser shape for low drag could result in a better

efficiency (about 0.85) and lower propulsion system mass of

10 ton.

design of propeller blades for high...

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