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Transcript of PPT-Aeroacoustic
What are Propeller and Propfan?
Types of Propeller Noise
Research on Propeller Noise in Various Areas
A few of the areas are mentioned below
Features like quiteness and efficiency are demanded for the success of any UAV mission by military
Try to escape from underwater detection
Due to their inherent noise challenge and potential for significant reductions in fuel burn, counter-rotating propfans noise study is important
Propeller and Propfan Noise
Noise Genration Mechanism
Aeroacoustic and Aerodynamic Modeling
UAV Propulsive System
Propeller Random Noise
Classified into three categories:-
The Japanese played American and British music on the radio during world war II. They did this to promote the allies to listen to their radio broadcasts. Since music was played before and after the propaganda the European and American soldiers would be subjected to Japanese ideas and morals.
Japanese radio stations did not only target Japanese listeners but the allied soldiers as well. The Japanese use allied music to get more allied listeners. The Japanese used very indirect and discreet propaganda to undermine the American and European ideals.
To get a quiet propeller for UAV, researchers has carried many numerical optimizations under structural and aerodynamics constraints
Here, conventional means aerodynamically efficient
Represented comparison between opitimized propeller and conventional propeller
Rotar Interaction Noise in Counter-Rotating Propeller
Noise generated by propeller can be generally classified into
Nishant Khanduja (09001013)
Narrowband Random Noise
Narrowband Random Noise
Unsteady Sources (Time Dependent)
To evaluate induced angle, momentum theory applied to the circular annuls corresponding to the blade elements
Theoritical Prediction of tonal contribution to acoustic pressure by Ffowcs-Williams/Hawkings equation. Discretizing the blades in N finite elements along the span
These random noises basically give rise to broadband noise. The power spectral density of the trailing edge noise can be written as
The power spectral density of the flow sepration on the broadband noise can be relevant
The extention of broadband theory of the airfoil to the propeller blade is by means of integration of above two equations over the blade elements, as for the tonal analysis. The total broadband noise is then obtained by averaging over the the angular position of the blades and by introducing a correction factor for the doppler shift.
The results of the optimization, mainly the distributions of the chord, the pitch and thickness to reduce the acoustic signature
Comparison between optimized and conventional propeller
At pi/2 location the optimized propeller is actually quiter than the conventional one, but this difference falls to almost zero when obsever is in the wake of the propeller.
Cavitation of the marine propeller is the most prevalent source of underwater sound in oceans and is often the dominant noise source of a single marine vehicle. However, submarines and torpedoes are usually operated deep enough under the sea to avoid cavitation
Hence non-caviting noise methodologies are being researched now days
For underwater propeller, non-uniformity of inflow is a primary source of noise
Modelling of Aeroacoustic
The formulation is same as was in the same last case. Instead of discretization. Here it is coninuous
The noise generated by a propeller working in a non-uniform inflow is caused by incoming turbulence and non-uniformities. Hence, the distribution of inflow significantly impacts the corresponding sound radiation
Unsteady thrust and torque predicted by Detached Eddy Simulation were harmonically analyzed
Propeler Noise Spectra in uniform and non-uniform inflow.
Observer locations at spherical angle is 75 degree
The harmonic spikes at the blade passing frequency and its multiples can be seen clearly on the spectrum curves with the non-uniform inflow
Rear-rotor upstream influence interacting with the front rotor,
Tip-vortices shed from the front rotor interfering with the rear rotor,
Front-rotor viscous wakes affecting the rear-rotor loading, and
Front-rotor hub wake and hub boundary layer influencing the rear-rotor hub loading
Resons for CRP noise
In order to explore the fuel burn benefits and acoustic performance of CRP configurations, a multidisciplinary integrated noise and performance assessment capability is required
Low computatiom time is required as compared to hybrid methods and CAA methods
Hence, Integrated Aircraft Performance and Noise Assessment Framework was designed by Andreas Peters
Integrated Aircraft Performance and Noise Assessment Framework
The overal goal is to define advance CRP configuration with improved noise characteristics while mainting the required aerodynamics
Dissect and quantify the impact of the mechanisms responsible for interaction tone noise,
Explore and define necessary CRP noise reduction technologies, and
Quantify the potential noise reductions on a consistent aircraft mission basis
Noise Estimation of CRP
It is based on Goldstein's formulation of the acoustic analogy of moving media and Hanson's frequency Domain single rotor noise method
CRP Noise Vaidation
In order to validate it, CRP method data was compared with data provided by Industry