Silent Propulsors for Air Taxis

  Silent Propulsor Copyright: © RWTH Aachen | IST

The development of modern air taxes is intended to establish a new transport option that will take passengers to their destination quickly, safely, comfortably and with low emissions. This urban and regional air mobility is one of the most important future fields of the aviation industry and should make a decisive contribution to the mobility of the future. 

 

Audible Emission Reduction

The research and innovation strategy Flightpath 2050, jointly developed by the EU Commission and the aerospace industry, envisages a 65% reduction in perceived noise emissions from flying aircraft.

These values refer to the capabilities of typical new aircraft in the year 2000.

 

Noiseless Aviation

As regional air traffic is expected to grow by orders of magnitude, it becomes more and more essential to cut down the produced noise accordingly. To tackle this challenge, we at RWTH Aachen University’s Institute of Jet Propulsion and Turbomachinery have committed ourselves to develop a nearly noiseless propulsion system for air taxis. The result: Our virtually noiseless ducted propeller, which in combination with emission-free hydrogen fuel cell power, has the potential to enable the next revolution in regional air mobility.

 
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Technical Introduction

To meet the requirements of a fast and comfortable means of transportation, air taxis must operate in close proximity to residential areas and city centers. This can only be realized by creating a high level of acceptance among the population through virtually silent operation of the propulsor. The optimization of such a quiet propulsor includes both the reduction of sound generation within the propulsor and sound propagation toward the stationary observer, so that the transient pressure field arriving at the observer is of the lowest possible amplitude and annoyance.

While the configuration for classical passenger aircraft has reached an apparent convergence for several decades, a wide variety of configurations are being discussed for air taxis. Depending on the configuration, various aircraft parts are placed upstream of the propulsor, thus affecting the homogeneity of the flow entering the propulsor. For optimal aerodynamic and acoustic performance of the propulsor, a high inflow quality is essential.

 

Research Trends

CFD simulation of a propulsor Copyright: © RWTH Aachen | IST CFD simulation of a propulsor

Method development

The continuous development of the tool chains and methods available at the institute is the basis for the activity in the field of quiet propulsors.

Due to the large number of design variables and their pronounced interdisciplinary dependencies, physics-based prediction tools for predicting trends and design trade-offs are of crucial importance. The existing tool chain ranges from mean-square methods to high-resolution URANS simulations and is continuously being extended.

Aeroacoustic optimization

To minimize sound generation, the geometry of blade rows is optimized to maximize the mixing of pressure disturbances until they impinge on adjacent blade rows and/or cancel each other out by destructive interference.

To reduce sound propagation, the concept of a shrouded propeller is being intensively pursued at the institute. Here, with a clever choice of blade numbers, individual acoustic modes within the propulsor are not capable of propagation. The use of acoustic liners further reduces sound propagation.

Integration into novel flight taxi configurations

As part of the propulsor integration, the inflow to the propulsor induced by the flight taxi configuration is determined for the relevant operating conditions and its effect on the propulsor flow is determined. A combined use of the flow solvers TRACE and TAU leads to an optimization of propulsor position, inlet geometry and blade design.