Supersonic Jet Exhaust Noise At High Subsonic Flight Speed

An empirical model to predict the effects of flight on the noise from a supersonic transport is developed. This model is based on an analysis of the exhaust jet noise from high subsonic flights of the F-15 ACTIVE Aircraft. Acoustic comparisons previously attainable only in a wind tunnel were accomplished through the control of both flight operations and exhaust nozzle exit diameter. Independent parametric variations of both flight and exhaust jet Mach numbers at given supersonic nozzle pressure ratios enabled excellent correlations to be made for both jet broadband shock noise and jet mixing noise at flight speeds up to Mach 0.8. Shock noise correlated with flight speed and emission angle through a Doppler factor exponent of about 2.6. Mixing noise at all downstream angles was found to correlate well with a jet relative velocity exponent of about 7.3, with deviations from this behavior only at supersonic eddy convection speeds and at very high flight Mach numbers. The acoustic database from the flight test is also provided.Norum, Thomas D. and Garber, Donald P. and Golub, Robert A. and Santa Maria, Odilyn L. and Orme, John S.Armstrong Flight Research Center; Langley Research CenterJET AIRCRAFT NOISE; JET EXHAUST; SUBSONIC SPEED; SUPERSONIC SPEED; MATHEMATICAL MODELS; AEROACOUSTICS; FLIGHT TESTS; SHOCK WAVES; SUPERSONIC TRANSPORTS; MACH NUMBER; JET MIXING FLOW; F-15 AIRCRAFT; PRESSURE RATIO; EXHAUST NOZZLES; VORTICES; DATA REDUCTION; DATA ACQUISITION

Inhaltsangabe:Introduction: On the 26th of August 2010 the new ultra-large-cabin ultra-long-range Gulfstream G650 business jet reached Mach 0.995 during its flight test campaign (1). This is almost the speed of sound (Mach 1) and inspires one to say, why not fly faster than the speed of sound! Reduce travelling time in the commercial business aviation segment. This is, however not a completely new vision. Many companies and research facilities have already spent a lot of time and investment in studies to investigate the feasibility of supersonic flight. Entry Into Service (EIS) for the new Gulfstream G650 is scheduled for 2012. In the following the main performance parameter of the G650 aircraft will be summarised. The parameters range, cruise speed, MTOW, etc. have been selected and serve as a basis to allow an appropriate comparison between the G650 as the latest high end Subsonic Business Jet and potential in future Supersonic Business Jets (SSBJ) within this subject Master Thesis. With the impressive maximum range of nearly 13,000 km the G650 can connect Dubai with New York or London with Buenos Aires within almost 14 hours. Maximum Range @ Normal Cruise Speed: 7,000 nm/12,964 km. Normal Cruise Speed Mach: 0.85/904 km/h. Mmo (Maximum Operating Mach Number): Mach 0.925. Maximum Cruise Altitude: 51,000 ft/15,545 m. Maximum Takeoff Weight (MTOW): 99,600 lb/45,178 kg. Maximum Fuel Weight: 44,200 lb/20,049 kg. Passengers: 11 18. Price: appr. 60-70 million USD. Gulfstream business rival Bombardier Aerospace also announced in October 2010 two new high end models, the Global 7000 and 8000 with a maximum range of 7,300 nm (13,520 km) and 7,900 nm (14,631 km) at cruise speed Mach 0.85. Entry Into Service is scheduled for 2016 (Global 7000) and 2017 (Global 8000). A comprehensive overview of business jets in service and in development is given in attachment 13.1. A Supersonic Business Jet flying at Mach 2 cruise speed could virtually halve the travelling time, which would enormously enhance the mobility and flexibility. In order to achieve this ambition a paradigm shift is required. New technologies must be established, the impact on the environment must be understood and minimised, existing regulations must be changed to permit overland flight restrictions and the product still needs to be economically viable. All of the above aspects must be considered and will be subject for discussion within this Master Thesis (See also figure [...]

The noise produced by the supersonic, high temperature jets that exhaust from military aircraft is becoming a hazard to naval personnel and a disturbance to communities near military bases. Methods to reduce the noise produced from these jets in a practical full-scale environment are difficult. The development and analysis of distributed nozzle blowing for the reduction of radiated noise from supersonic jets is described. Model scale experiments of jets that simulate the exhaust jets from typical low-bypass ratio military jet aircraft engines during takeoff are performed. Fluidic inserts are created that use distributed blowing in the divergent section of the nozzle to simulate mechanical, hardwall corrugations, while having the advantage of being an active control method. This research focuses on model scale experiments to better understand the fluidic insert noise reduction method. Distributed blowing within the divergent section of the military-style convergent divergent nozzle alters the shock structure of the jet in addition to creating streamwise vorticity for the reduction of mixing noise. Enhancements to the fluidic insert design have been performed along with experiments over a large number of injection parameters and core jet conditions. Primarily military-style round nozzles have been used, with preliminary measurements of hardwall corrugations and fluidic inserts in rectangular nozzle geometries also performed. It has been shown that the noise reduction of the fluidic inserts is most heavily dependent upon the momentum flux ratio between the injector and core jet. Maximum reductions of approximately 5.5 dB OASPL have been observed with practical mass flow rates and injection pressures. The first measurements with fluidic inserts in the presence of a forward flight stream have been performed. Optimal noise reduction occurs at similar injector parameters in the presence of forward flight. Fluidic inserts in the presence of a forward flight stream were observed to reduce the peak mixing noise below the already reduced levels by nearly 4 dB OASPL and the broadband shock-associated noise by nearly 3 dB OASPL. Unsteady velocity measurements are used to complement acoustic results of jets with fluidic inserts. Measured axial turbulence intensities and mean axial velocity are examined to illuminate the differences in the flow field from jets with fluidic inserts. Comparisons of laser Doppler measurements with RANS CFD simulations are shown with good agreement. Analysis of the effect of spatial turbulence on the measured quantities is performed. Experimental model scale measurements of jets with and without fluidic inserts over a simulated carrier deck are presented. The model carrier environment consists of a ground plane of adjustable distance below the jet, and a simulated jet blast deflector similar to those found in practice. Measurements are performed with far-field microphones, near-field microphones, and unsteady pressure sensors. The constructive and destructive interference that results from the interaction of the direct and reflected sound waves is observed and compared with results from free jets. The noise reduction of fluidic inserts in a realistic carrier deck environment with steering of the ``quiet planes'' is examined. The overall sound pressure level in heat-simulated jets is reduced by 3-5 dB depending on the specific angle and ground plane height. Jets impinging upon a modeled jet blast deflector are tested in addition to jets solely in the presence of the carrier deck. Observed modifications to the acoustic field from the presence of the jet blast deflector include downstream acoustic shielding and low frequency augmentation. The region of maximum noise radiation for heat-simulated jets from nozzles with fluidic inserts impinging on the jet blast deflector is reduced in overall sound pressure level by 4-7 dB. This region includes areas where aircraft carrier personnel are located.

The report summarizes the results obtained at General Electric during the first phase of the Air Force Supersonic Exhaust Noise - Velocity Model Program. The overall objective of the program is to develop the technology to significantly reduce supersonic aircraft propulsion system noise with minimum associated performance and weight penalties. To fulfill that objective, research is being carried out to develop the experimental techniques and the necessary theory to reveal the basic mechanisms of jet generated noise through the range of velocities and temperatures typical of present and future military and commercial supersonic aircraft propulsion systems. A comprehensive aerodynamic analytical model describing the flow mechanisms in supersonic jets is presented and compared with experimental data. A large number of theoretical models describing supersonic far field jet noise are evaluated. (Author).

This report discusses detailed accounts of major theoretical and experimental investigations directed toward obtaining better understanding and mathematical specification of supersonic turbulent jets. Complete theoretical discussions are given describing the influence of a jet's mean flow shrouding on acoustic radiation of heated and unheated jets, approximate closed form acoustic expressions for turbulent mixing noise characterized by self-noise and shear-noise are given, and theoretical aero-acoustic formulations for the orderly structure of supersonic jets are reviewed. Extensive theory/data comparisons of developed acoustic models are given. Experimental investigations aimed at studying high velocity jet refraction, and the influence of jet swirl and upstream combustion roughness on jet noise is presented. Additionally, an extensive series of laser velocimeter measurements for high velocity and high temperature simple circular jets is discussed. Results include hot-film/laser velocimeter comparisons for ambient jets, mean velocity and turbulent velocity plume surveys of heated supersonic shock-free and shocked flow nozzles, and a demonstration experiment illustrating the capability of performing in-jet turbulence to far-field acoustic cross-correlation. (Author).