PPT-Aeroacoustic

Aeroacoustic and Aerodynamic Modeling

Theoritical Prediction of tonal contribution to acoustic pressure by Ffowcs-Williams/Hawkings equation. Discretizing the blades in N finite elements along the span

For aerodynamics modeling, one of most popular and simple Momentum/Blade Element Theory was used

where

UAV Propulsive System

• 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

To evaluate induced angle, momentum theory applied to the circular annuls corresponding to the blade elements

Results

• 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.

Propeller Random Noise

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.

Marine Propeller

Results

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

Noise generated by propeller can be generally classified into

• Cavitating noise
• Non-Cavitating noise

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

Research on Propeller Noise in Various Areas

Rotar Interaction Noise in Counter-Rotating Propeller

What are Propeller and Propfan?

CRP Noise Vaidation

In order to validate it, CRP method data was compared with data provided by Industry

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

Resons for CRP noise

A few of the areas are mentioned below

• Small UAVs

Features like quiteness and efficiency are demanded for the success of any UAV mission by military

• Marines

Try to escape from underwater detection

• Counter-Rotating Propellers

Due to their inherent noise challenge and potential for significant reductions in fuel burn, counter-rotating propfans noise study is important

Types of Propeller Noise

Propfan

Propeller

Japanese Radio

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.

• 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

Propeller Noise

Classified into three categories:-

Japanese Music

• Harmonic Noise
• Brodband Noise
• Narrowband Random Noise

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.

Noise Genration Mechanism

Steady Sources

• Linear Thickness
• Linear Loading
• Nonlinear (Quadrupole)

Unsteady Sources (Time Dependent)

• Periodic Loading
• Random Loading

Random Sources

• Operating Conditions
• Propeller Design

Harmonic Noise

Characteristics

Counter-Rotating Propeller

Integrated Aircraft Performance and Noise Assessment Framework

• 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

The overal goal is to define advance CRP configuration with improved noise characteristics while mainting the required aerodynamics

• Hence, Integrated Aircraft Performance and Noise Assessment Framework was designed by Andreas Peters

BroadBand Noise

Characteristics

• 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

Framework

Narrowband Random Noise

Characteristics

Propeller and Propfan Noise

Nishant Khanduja (09001013)

Thank You