On the Aerodynamic Design of the Boxprop
Doktorsavhandling, 2018

Economic factors and environmental awareness are driving the evolution of aircraft engines towards increasingly lower fuel consumption and emissions. The Counter-Rotating Open Rotor (CROR) is actively being researched around the world, promising a significantly increased propulsion efficiency relative to existing turbofans by employing two, unducted, counter-rotating propeller blade rows, thereby increasing the bypass ratio of the engine and decreasing nacelle drag. Historically, these engines have been plagued by high noise levels, mainly due to the impingement of the front rotor tip vortices on the rear rotor. In modern designs, the noise levels have been decreased by clipping the rear, counter-rotating propeller. This comes at a cost of decreased efficiency.

An alternative, potential solution lies with the Boxprop, which was invented by Richard Avellán and Anders Lundbladh. The Boxprop consists of blade pairs joined at the tip, and is conceptually similar to a box wing. This type of propeller could weaken or eliminate the tip vortex found in conventional blades, thereby reducing the acoustic signature.

This thesis summarizes advances done in the research regarding the aerodynamics of the Boxprop. Aerodynamic optimization of the Boxprop has shown that it features higher propeller efficiency than conventional propellers with the same number of blades, but lower propeller efficiency than conventional propellers with twice as many blades. A key design feature of optimal Boxprop designs is the sweeping of the blade halves in opposite directions. This reduces the interference between the blades and allows the Boxprop to achieve aerodynamic loading where it is most efficient - close to the tip.

A Wake Analysis Method (WAM) is presented in this work which provides a detailed breakdown and quantification of the aerodynamic losses in the flow. It also has the ability to distinguish and quantify the kinetic energy of the tip vortices and wakes. The Wake Analysis Method has been used to analyse both Boxprop blades and conventional propeller blades, and insights from it led to a geometric parametrization and an optimization effort which increased the Boxprop propeller efficiency by 7 percentage points.

Early Boxprop blades did not feature a tip vortex since aerodynamic loading near the tip was relatively low. The optimized Boxprop blades have increased the aerodynamic loading near the tip and this has resulted in a vortex-like structure downstream of the Boxprop at cruise conditions. This vortex is significantly weaker and of different origin than the tip vortex of a conventional propeller.

A CROR featuring the Boxprop as its front rotor (BPOR) has been designed and its performance at cruise is competitive with other published CRORs, paving the way for future work regarding take-off performance and acoustics.

CROR

Wake Analysis Method

Propeller Design

Tip vortex

Propellers

Optimization

CFD

Open Rotors

Propfans

EA
Opponent: Professor Fernando Martini Catalano, Universidade de São Paulo, Brazil

Författare

Alexandre Capitao Patrao

Chalmers, Mekanik och maritima vetenskaper, Strömningslära

Wake Energy Analysis Method Applied to the Boxprop Propeller Concept

Aerospace Science and Technology,; Vol. 79(2018)p. 689-700

Artikel i vetenskaplig tidskrift

Energy balance analysis of a propeller in open water

Ocean Engineering,; Vol. 158(2018)p. 162-170

Artikel i vetenskaplig tidskrift

Numerical Simulation of Nacelle Flowfield for Counter-Rotating Open Rotor Propellers

International Society of Air-breathing Engines (ISABE),; (2017)

Paper i proceeding

An Optimization Platform for High Speed Propellers

Konferensbidrag (offentliggjort, men ej förlagsutgivet)

Wake and Loss Analysis for a Double Bladed Swept Propeller

Proceedings of ASME Turbo Expo 2016: Turbine Technical Conference and Exposition, Seoul, South Korea, Jun 13-17, 2016,; Vol. 1(2016)

Paper i proceeding

A. Capitao Patrao, T. Gronstedt, A. Lundbladh, and G. Montero Villar. "Wake Analysis of an Aerodynamically Optimized Boxprop High Speed Propeller", Submitted to Journal of Turbomachinery on the 16th of August 2018

Economic factors and environmental awareness are driving the evolution of aircraft engines towards decreased fuel consumption and emissions. One idea for designing more efficient engines is to increase the bypass ratio of the engine, effectively increasing the diameter of the fan. Unfortunately, a larger fan also results in a larger nacelle, which increases weight and aerodynamic drag. There is an alternative approach however, called the Counter-Rotating Open Rotor (CROR), consisting of two, unducted, counter-rotating propellers, which increases the bypass ratio of the engine without the increase in aerodynamic drag. Historically, these engines have been plagued by high noise levels due to the impingement of the front propeller tip vortices onto the rear counter-rotating propeller. These engines lack the outer nacelle found in conventional turbofans, so in modern designs the noise levels have been decreased by shortening the rear, counter-rotating propeller. This comes at a cost of decreased efficiency.

An alternative, potential solution lies with the Boxprop, which was invented by Richard Avellán and Anders Lundbladh. The Boxprop consists of blade pairs joined at the tip, and is conceptually similar to a box wing. This type of propeller could weaken or eliminate the tip vortex found in conventional propellers, thereby reducing the noise of a CROR.

This thesis summarizes advances done in the research regarding the aerodynamics of the Boxprop. Aerodynamic optimization of the Boxprop has shown that it features higher propeller efficiency than conventional propellers with the same number of blades, but lower propeller efficiency than conventional propellers with twice as many blades. It is also shown that optimal Boxprop designs share a common design attribute, namely that the blade halves are swept in opposite directions.

The thesis also derives a method to keep track of the energy transferred from the propeller blade to the flow, which can be used for estimating how much of the energy has been used for propulsion and how much has been lost to different aerodynamic and thermodynamic losses. It can also quantify the amount of energy used to create tip vortices and other non-uniformities in the flow.

Finally, a CROR has been designed which incorporates the Boxprop and its performance at cruise is competitive with other published CRORs, paving the way for future research regarding noise.

Innovativ Framdrivning och Motorinstallation

VINNOVA, 2013-07-01 -- 2017-06-30.

Ämneskategorier

Annan maskinteknik

Rymd- och flygteknik

Energiteknik

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Infrastruktur

C3SE (Chalmers Centre for Computational Science and Engineering)

ISBN

978-91-7597-795-9

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4476

Utgivare

Chalmers tekniska högskola

EA

Opponent: Professor Fernando Martini Catalano, Universidade de São Paulo, Brazil

Mer information

Senast uppdaterat

2018-09-06