Design of Propeller Blades For High Altitude Silvestre 1, M. A. R., Morgado 2 1,2 - Department of Aerospace Sciences University of Beira Interior MAAT 2nd Annual Meeting M24, 18-20 of September, Montreal, Canada
Outline 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 1 st design iteration Requirements review Concluding Remarks
Introduction 3 Oil peak Fuel conservation Propellers: the outdated inovation! Silent Unducted Fan (UDF)
Introduction 4 F TSFC W
Introduction - Motivation 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 6 The Weight Spiral: +?? kg more solar panels +? kg more structure+? kg bigger control actuator +? kg increased added masses effect +? kg increased envelope sized +? kg stronger/more motors +? kg larger/more propellers +? kg higher drag kgf
Introduction - Motivation 7 The inverted Weight Spiral: -?? kg smaller solar panels -? kg less structure-? kg smaller control actuator -? kg reduced added masses effect -? kg increased envelope sized -? kg weaker/less motors -? kg smaller/less propellers -? kg reduced drag kgf
Introduction - Motivation 8 Same engine! Different weight and size! Different performance
An example of inverted weight spiral, Introduction - Motivation 9 The bicycle has almost 200 years old!
Introduction 10 The success of a system/device is dictated by its conception not by the quality of the theoretical modelation or the optimization algorithms! A bad concept means failure! Bad theoretical models or bad tools mean more iterations (numerical or experimental)!
Introduction 11 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!
Introduction 12 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
Introduction JBLADE s Concept 14 Open source David Marten s QBLADE André Deperrois s XFLR5 Mark Drela s XFOIL
Code Structure 15 Airfoil Object Polar Object 360º Polar Object Blade Object Propeller Object -Airfoil Coordinates; -Airfoi l Camber; -Airfoil Thickness; -Lift and drag coefficients; -Reynolds number; -Angle of attack range. Airfoil Object 360º Polar Extrapolation -Lift and drag coefficients; -Reynolds number; -Full angle of attack range. Extrapolated Data -Geometric parameters; -Number of stations; -Number of blades; 360º Polar Objects -Propeller Parameters; Blade Object Simulation Results XFOIL Panel Simulation - Angle of attack Range Blade Data Object -Simulation Results Data along the blade. -Induction Factors; -Inflow Angles; -Circulation; -Advance Ratio; -Speed. Propeller Simulation Object -Simulation Parameters. Propeller Object Blade Data Object BEM Simulation BEM CODE -Advance Ratio; -Speed Range.
Theoretical Formulation 16 Classical Blade Element Momentum Theory C C w a CL cos CD sin C L sin C cos D x 2 W cc x F 1 2 T B Q B R R tip root Rtip Rroot F a dr F t rdr
Theoretical Formulation 17 To find an W, the iteration variables of the classical BEM for each blade element are the axial and tangential induction factors: a a Wa V V these are derived from momentum theory as: a a 4Fsin ca 2 1 1 Where is the local rotor solidity ratio cb 2 r a a t t Wt r r 4F sin cos 1 ct 1 and F is the Prandtl s correction factor that allows the blades 3D correction
Theoretical Formulation 18 Prandtl s correction factor: 3D Corrections F 2 arccos e f where: f tip B r 1 2 R tip 1 g f root B 1 2 R r root 1 g g tip r R tip tan g root R r root tan
Theoretical Formulation 19 3D Equilibrium Neglecting the radial velocity component in the disk, 3D equilibrium translates to: W a W r a W t W r t W r 2 t 0 The case where W a is maintained constant across the propeller annulus, is reduced to: dwt dr W r t W r t const. the total propeller torque will be the result of a free vortex induced tangential velocity profile with an average axial velocity, Wa W0. 75R across the propeller disk
Theoretical Formulation 20 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, To satisfy the momentum conservation, the total propeller torque, will be the result of a free vortex induced tangential velocity profile, with V t75 Q 3 W R R and an average axial velocity, a tip R root W a m R total 2 The radial induction factor is updated and iterated: m a t i 2W rdr Vt r a Q V t, so, m 0.75RVt r total 75 4W V rdr a t m i
Theoretical Formulation 21 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 n c K r 1 C 0.136 L C max L0 where the separation point is related with the velocity gradient, c r 0.1517 K 1.084 and maximum lift coefficient of the rotating blade increased by K with c rot ( ) c nonrot dcl d
Results and Discussion 22 Airfoil Sub-Module
Results and Discussion XFOIL Sub-Module 23
Results and Discussion 360 Polar Sub-Module 24
Results and Discussion 25 Blade Sub-Module
Results and Discussion 26 Simulation Sub-Module
Results and Discussion 27 NACA TR 594
Results and Discussion 28 NACA TR 594 15 at 0.75R
Results and Discussion 29 NACA TR 594 30 at 0.75R
Results and Discussion 30 NACA TR 594 45 at 0.75R
About the code validation 31 3D equilibrium shows better results than the classical BEM formulation but could be improved further for actual W a 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.
Cruiser Propeller Design 32 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 *according to UBI report from 07/03/2013 Evaluation of the Number of Propellers for the Cruiser
Cruiser Propeller Design 33 Operational environment: Air density: 0.194 kg.m -3 Absolute viscosity: 1.43226x10-5kg/(m.s) Speed of sound: 295.1 m.s -1
Cruiser Propeller Design Concepts: Keeping the tip Mach Number fairly low (final 0.67) 34 Moderate Reynolds number high performance SG6043 airfoil Minimim induced loss at the design point using Drelas QMIL design code
Cruiser Propeller Design 35 1st design iteration: 7MW each propeller (231MW total) high solidity (and mass) from high disk loading with low air density at 15km h p = 0.5
Cruiser Propeller Design 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 Requirement Review: with minimized drag MAAT Cruiser 60000 7.10 154.48 40.78 0.57 New MAAT Cruiser 1200 7.10 3.09 1.36 0.98 36
Concluding Remarks 37 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.