MSGID: 1:317/3 646ee46b   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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 #   
                   Air_Quality   
       * RELATED_TERMS   
             o Jet_aircraft o Inversion_(meteorology) o Altitude o   
             Sound_effect o Tornado o Fog o Infiltration_(hydrology)   
             o Environmental_impact_assessment   
      
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   Story Source: Materials provided by University_of_Bristol. Note: Content   
   may be edited for style and length.   
      
      
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   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   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230524182045.htm   
      
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