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Aircraft Noise Prediction

My blog post is on Analytics Designer Hackathon. I have written this blog on”Prediction of Aircraft noise” which is my use case for #Analytics Designer Hackathon.

This blog post is about Prediction of Aircraft noise by using some computer codes and comparison on noise level of both Baseline and model with possible methods to reduce engine noise. I have taken High Bypass Turbofan Engine for my use-case.

Vision: Making Aircraft models for testing is cost as well as time consuming process. If noise level is predicted before we can use our results directly for creating Prototype and can minimize model making cost.

The reduction of noise around airports is one of the most urgent and crucial matters for aircraft and engines. In general Aircraft noise is classified into two types,

  1. Engine noise (Fan, Combustor and Nozzle).
  2. Air-frame noise (Landing gear and Flap).

Aircraft Noise

Noise level will differ from place to place. Comparison of noise level at different places is required when we want to control noise level. Aircraft noise is just closer to the EPNL (Effective Perceived Noise Level) which can cause Eardrum rupture. It’s necessary to know the sources of the Aircraft noise so that noise can be reduced in an effective way. Engine is more contributing in noise than Air-frame especially Fan.

In Turbofan Engine Fan, Nozzle and Combustor are the main noise producing parts contributing 31%,29% and 23% respectively whereas Airframe contributes 17% in total. The names of computer codes used for prediction methods and for Simulation has been mentioned in every page.

Engine-Fan noise prediction

  1. Fan noise is a strong function of the rotational tip speed and fan pressure ratio. The surest way to reduce fan noise is to reduce the tip speed and pressure ratio. Fan Sharp leading edge reduces fan speed and noise.
  2. Discrete-frequency noise generated by unsteady blade row interactions between rotor and stator blades. Using fan sweep near tip we can reduce aerodynamic losses associated with shocks considerably.
  3. Swept stators reduce fan noise in two ways,
    • By increasing the phase changes from hub-to-tip which producing sound.
    • By increasing effective distance from the fan to the stator vanes.

Engine-Nozzle noise prediction

Jet noise comprises turbulent mixing noise which is very difficult to control. Jet noise can be reduced by developing high bypass flows. Today the most successful technique for reducing jet noise from high-bypass engines involves the installation of chevron mixers on the exhaust nozzles.

Chevrons are saw-tooth shapes at the end of the nacelle protrude into the flow and generate axial vorticity and therefore enhance the mixing of core, fan and ambient air streams. The nozzles allowed the core and by-pass flows to mix in a way that reduced low frequency mixing noise from highly turbulent flows.

Noise evaluation is obtained by using pressure fluctuations computed from (u-RANS) unsteady Reynolds-Averaged Naiver-Stokes turbulent model based on CFD solver and Broadband noise with (LES) Large Eddy Simulations.

 

 

Engine-Combustor noise prediction

Combustor is noise source lean burning involves highly unsteady flames. There are two components of combustion noise

  • The direct noise is due to pressure fluctuations
  • The indirect noise is produced by entropy fluctuations

By reducing the level of entropy and pressure fluctuations noise level inside combustor could be reduced to a certain level.The prediction of combustion noise spectrum is obtained by evaluating the volume integral over the flame brush (Green’s function). The CFD results indicates that the predominant combustion occurs close to the combustor inlet. Combustor contributes more noise level than plenum and premixer which are the engine parts.

 

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