Propellers are louder over ground

Date:
May 24, 2023
Source:
University of Bristol
Summary:
The effects of the ground on propeller noise have now been measured
experimentally.


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FULL STORY ==========================================================================
The effects of the ground on propeller noise have been measured
experimentally for the very first time by researchers in the Aeroacoustics research team at the University of Bristol.

In findings, published in the Journal of Sound and Vibration,the team
found clear differences in the noise characteristics of propellers
when over ground, known as 'Ground Effect', compared to when operated
normally. They noted an overall noise increase when measuring at angles
above the ground, with hydrodynamic and acoustic interaction effects
being a key factor to the overall noise trends.

It is hoped this research, tested in the National Aeroacoustic Wind
Tunnel facility, can inform strategies to reduce the noise of aircraft
while taking off or landing, by either changing the design of the landing
pads or by changing the design of proposed aircraft architectures.

Lead author Liam Hanson explained: "In light of the need for greener
aviation, there has been a push in the aviation industry to develop
electrified aircraft.

"There is a lot of potential benefits from electric aircraft which have
been identified by a variety of companies worldwide, including all of the
major aircraft manufacturers." However, if urban air services such as
on demand air taxis are to become a reality within city limits, engineers
must tackle the issue of sound pollution, generated by propellers.

An important subset of electric aircraft being developed recently are
for the purposes of Advanced Air Mobility (AAM). These aircraft can be
broadly considered to fit in three different categories.

The first is Electric Vertical Take-Off and Landing (eVTOL) aircraft
which is focussing on Urban Air Mobility (UAM) applications such as air
taxis, patient transfers, rooftop-to-rooftop trips within cities and
airport transfers.

The second category is Electric Conventional Take-Off and Landing (eCTOL) aircraft which is being developed for Regional Air Mobility (RAM). RAM
focusses on cargo deliveries, short-range flights and passenger transfers
from rural regions.

The most commonly recognisable electric aircraft, small Unmanned Aircraft Systems (sUAS) or drones, can be considered the third category which
focusses on videography, small package delivery and medical supply
transfer.

Each of these categories of electric aircraft often uses propellers or
rotors to generate thrust to take off and land. Crucially, eVTOL aircraft
are operating in urban areas with large populations and as a result the
noise generated by the aircraft is critical to understand and reduce if
UAM is to be possible.

The propellers used by the aircraft are smaller than helicopters which
have been in use for years, usually being far smaller in diameter and
rotating at higher speeds. As a result the noise characteristics are very different to the existing knowledge, and so further research is required.

While eVTOL and sUAS aircraft are taking off or landing from a rooftop
or landing pad, the propellers are likely to experience Ground Effect,
an aerodynamic phenomenon which changes the performance of propellers.

This change in the propeller aerodynamics within Ground Effect changes the acoustic performance of the propellers and causes complex interactions.

Liam said: "Until now, no literature existed for the problem of isolated propeller noise in ground effect.

"Our research sought to answer for the first time what happens to
propeller noise while it operates in Ground Effect and what are the
key acoustic and aerodynamic interactions which are most important
to understand.

"For the first time we have comprehensively measured the noise of
small-scale propellers during take-off and landing while interacting
with the ground. It is clear we can expect louder eVTOL aircraft during take-off and landing if the complex interactions with the ground are
not considered." Based off their new understanding of propeller noise
in Ground Effect, they are now conducting additional tests on different
methods to potentially reduce the noise of the entire system.

The research was sponsored by Embraer S.A. and the Horizon 2020 SilentProp project (agreement number 882842).

* RELATED_TOPICS
o Matter_&_Energy
# Aviation # Vehicles # Aerospace #
Automotive_and_Transportation
o Earth_&_Climate
# Environmental_Issues # Pollution # Air_Pollution #
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* RELATED_TERMS
o Jet_aircraft o Inversion_(meteorology) o Altitude o
Sound_effect o Tornado o Fog o Infiltration_(hydrology)
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========================================================================== Story Source: Materials provided by University_of_Bristol. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Liam Hanson, Hasan Kamliya Jawahar, SH. S. Vemuri, Mahdi
Azarpeyvand.

Experimental investigation of propeller noise in ground
effect. Journal of Sound and Vibration, 2023; 559: 117751 DOI:
10.1016/j.jsv.2023.117751 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230524182045.htm

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