CEAS Aeronautical Journal

, Volume 5, Issue 3, pp 305–317 | Cite as

Aerodynamic performance of an over-the-wing propeller configuration at increasing Mach number

Original Paper

Abstract

Over-the-wing propeller configurations and particularly channel wing concepts show increased climb performance, and through effective acoustic shielding, reduced noise emissions when compared to a conventional tractor configuration. The main aerodynamic mechanisms could be identified by steady flow simulations of a simplified wing geometry and actuator disk. At take-off, where the thrust coefficient is very high, the drag of the wing decreases much stronger than the thrust of the propeller. This paper investigates the cruise conditions where the thrust coefficient is by one order of magnitude lower. The numerical results give evidence that, even at a moderate flight Mach number of 0.6, the beneficial influence of the over-the-wing propeller on the drag coefficient of the wing is negligibly small. On the other hand, the amount of propeller efficiency that is lost through high inflow velocity above the wing increases with Ma due to compressibility effects. As a result, the propulsive efficiency of an over-the-wing configuration is 16 % smaller than the reference (tractor). Semi-empirical correlations show that even at very low Mach numbers a drawback of at least 5 % remains. Although repositioning the propeller at the wing trailing edge may recover 4 % of the propulsive efficiency at Ma = 0.6, it is not advisable to give up most of the noise-shielding effect at take-off which is an important advantage of the channel wing.

Keywords

Propeller Over-the-wing Channel wing Integration High-speed Aerodynamic 

List of symbols

b, s

Wing span, semispan

c

Chord length

cl, cd

Section lift, drag coefficients

cp

Pressure coefficient

CD

Drag coefficient

CL

Lift coefficient

CT

Thrust coefficient

CM

Pitching moment coefficient

Ma

Mach number

p

Static pressure

PS

Propeller shaft power

q

Dynamic pressure

Re

Reynolds number

S

Wing area

T, t/tmax

Thrust of one engine, relative local thrust

U, V, W

Velocity components

x, y, z

Cartesian coordinates

y+

Dimensionless wall coordinate

α

Angle of attack

\(\eta_{P}\), \(\eta_{Pro}\)

Propeller efficiency, overall propulsive efficiency

\(\eta_{PP}\)

Propulsive efficiency of the propeller

ρ

Density

θmax

Maximum climb angle

Subscripts

0

Propeller inflow (far upstream)

3

Propeller slipstream (far downstream)

Free-stream

ref

Reference (aircraft or cruise condition)

CW

Channel wing

IW

Isolated wing (clean wing)

TC

Tractor configuration

P

Propeller

g

Geometric influence

t

Influence of thrust

Notes

Acknowledgments

This work was funded by the German Research Funding Organisation (DFG) in the framework of the collaborative research centre SFB 880. Computational resources have been gratefully provided by the North-German Supercomputing Alliance (HLRN). The authors would like to acknowledge Carsten Lenfers, DLR Braunschweig, Institute of Aerodynamics and Flow Technology (DLR-AS) for providing the propeller data and Jochen Wild (also DLR-AS) for providing the wing airfoil geometry. Further thanks go to Wolfgang Heinze of the Institute of Aircraft Design and Lightweight Structures, TU Braunschweig, for his multidisciplinary studies on the reference aircraft.

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Copyright information

© Deutsches Zentrum für Luft- und Raumfahrt e.V. 2014

Authors and Affiliations

  1. 1.Institute of Jet Propulsion and TurbomachineryTechnische Universität BraunschweigBraunschweigGermany
  2. 2.Institute of Fluid MechanicsTechnische Universität BraunschweigBraunschweigGermany
  3. 3.Department of Automotive and Aeronautical EngineeringHamburg University of Applied SciencesHamburgGermany

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