Hybrid Approach to Nonlinear Propagation of Jet Noise in Complex Environments

2016 ◽  
Author(s):  
Vasileios Sassanis ◽  
Adrian Sescu ◽  
Eric Collins ◽  
Robert E. Harris ◽  
Edward A. Luke
Keyword(s):  
Hybrid Approach ◽  
Jet Noise ◽  
Nonlinear Propagation ◽  
Complex Environments

‘Crackle’: an annoying component of jet noise

1975 ◽  
Vol 71 (2) ◽  
pp. 251-271 ◽  
Author(s):  
J. E. Ffowcs Williams ◽  
J. Simson ◽  
V. J. Virchis
Keyword(s):  
High Speed ◽  
Angular Position ◽  
Jet Noise ◽  
Wide Frequency Range ◽  
Nonlinear Propagation ◽  
Wave Form ◽  
Long Term Effects ◽  
Recorded Sound ◽  
Recording Process

The paper describes an investigation of a subjectively distinguishable element of high speed jet noise known as ‘crackle’. ‘Crackle’ cannot be characterized by the normal spectral description of noise. It is shown to be due to intense spasmodic short-duration compressive elements of the wave form. These elements have low energy spread over a wide frequency range. The crackling of a large jet engine is caused by groups of sharp compressions in association with gradual expansions. The groups occur at random and persist for some 10−1s, each group containing about 10 compressions, typically of strength 5 × 10−3 atmos at a distance of 50 m. The skewness of the amplitude probability distribution of the recorded sound quantifies crackle, though the recording process probably changes the skewness level. Skewness values in excess of unity have been measured; noises with skewness less than 0·3 seem to be crackle free. Crackle is uninfluenced by the jet scale, but varies strongly with jet velocity and angular position. The jet temperature does not affect crackle, neither does combustion. Supersonic jets crackle strongly whether or not they are ideally expanded through convergent-divergent nozzles. Crackle is formed (we think) because of local shock formation due to nonlinear wave steepening at the source and not from long-term nonlinear propagation. Such long-term effects are important in flight, where they are additive. Some jet noise suppressors inhibit crackle.

scholarly journals Heuristic based real-time hybrid rendering with the use of rasterization and ray tracing method

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 527-544 ◽  
Author(s):  
Patryk Walewski ◽  
Tomasz Gałaj ◽  
Dominik Szajerman
Keyword(s):  
Real Time ◽  
Ray Tracing ◽  
Graphics Processing Units ◽  
Hybrid Approach ◽  
Poor Performance ◽  
Complex Environments ◽  
Secondary Effects ◽  
Hybrid Rendering ◽  
Illumination Algorithms ◽  
Graphics Processing

Abstract Nowadays, rasterization is the most common method used to achieve real-time semi-photorealistic effects in games or interactive applications. Some of those effects are not easily achievable, thus require more complicated methods and are difficult to obtain. The appearance of the presented worlds depends to a large extent on the approximation to the physical basis of light behaviour in them. The best effects in this regard are global illumination algorithms. Each of them including ray tracing give the most plausible effects, but at cost of higher computational complexity. Today’s hardware allows usage of ray tracing methods in-real time on Graphics Processing Units (GPU) thanks to its parallel nature. However, using ray tracing as a single rendering method may still result in poor performance, especially when used to create many image effects in complex environments. In this paper we present a hybrid approach for real-time rendering using both rasterization and ray tracing using heuristic, which determines whether to render secondary effects such as shadows, reflections and refractions for individual objects considering their relevancy and cost of rendering those effects for these objects in particular case.

Algorithm for the Nonlinear Propagation of Broadband Jet Noise

AIAA Journal ◽  
2009 ◽  
Vol 47 (1) ◽  
pp. 186-194 ◽  
Author(s):  
Swati Saxena ◽  
Philip J. Morris ◽  
K. Viswanathan
Keyword(s):  
Jet Noise ◽  
Nonlinear Propagation
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