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Increasingly powerful and noisy military aircraft have generated the need for research leading to the development of supersonic jet noise reduction devices. The hot, high speed supersonic jets exhausting from military aircraft during takeoff present a most challenging problem. The present study extends prior research on two methods of noise reduction. The first is the internal nozzle corrugations pioneered by Seiner et al. and the second is the beveled exit plane explored most recently by Viswanathan. A novel research idea of creating fluidic corrugations similar to the nozzle corrugations has been initiated by Penn State. To further the understanding and analysis of the fluidic corrugations, the present study focuses on the flow field and acoustic field of nozzles with two, three, and six conventional, hardwalled corrugations. The effect of the combination of the internal corrugations with a beveled nozzle is explored. The results show that significant noise reductions of over 3 dB of the mixing noise and the broadband shock-associated noise can be achieved. The combination of the beveled nozzle and the internal nozzle corrugations showed that there is less azimuthal dependence of the acoustic field than for the purely beveled nozzle. The combination nozzle was shown to reduce the noise over a wider range of polar angles and operating conditions than either the purely beveled nozzle or the purely corrugated nozzle.

This paper describes several components of a study examining noise reduction in high speed heated jets using fluidic inserts. This noise reduction technology is based on the ideas developed by Seiner and his colleagues at NASA Langley Research Center and the University of Mississippi. That approach was based on the introduction of corrugated seals into the diverging section of a convergent divergent nozzle. These corrugations change the effective area ratio so that the jet operates closer to an on-design condition and reduces broadband shock-associated noise. In addition, the corrugations generate streamwise vorticity that breaks up the large scale structures in the jet and reduces mixing noise. The idea behind fluidic inserts, described by Morris et al. is to generate an equivalent effect with low levels of flow injection in the diverging section of the nozzle. This has the considerable advantage that the fluidic inserts can be controlled actively for maximum noise reduction and performance benefits. The present paper describes recent developments in the optimization of the fluidic insert concept. Flow and noise experiments, including the effect of forward flight are described. Numerical simulations are performed to characterize the flow features generated by the fluidic inserts as well as to develop measures of flow characteristics that can be related to the observed noise changes. These measures can be used to develop a cost function in a design optimization procedure.

The noise produced by supersonic, high temperature jets that exhaust from military aircraft is becoming more of a disturbance. Methods to reduce the noise produced from these jets in a realistic full-scale environment is difficult. This study describes the development and analysis of fluidic inserts for supersonic jet noise suppression. 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 for a large number of injection parameters and core jet conditions. It has been shown that the noise reduction of the fluidic inserts is most heavily dependent on 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 by nearly 4 dB OASPL and the broadband shock-associated noise by nearly 3 dB OASPL.

This paper describes the development and analysis of fluidic inserts for supersonic jet noise suppression. The study uses scale model experiments of jets that simulate the exhaust jets from typical lowbypass ratio military jet aircraft engines during takeoff. The fluidic inserts use distributed blowing in the divergent section of the nozzle to simulate mechanical corrugations, while having the advantage of being an active control method. Measurements with simulated forward flight are important early in the analysis of noise reduction methods. The current design of the delivery piping is not streamlined enough for forward flight measurements. Therefore, forward flight acoustic measurements were first conducted with hardwall corrugation nozzles. The noise reduction of the hardwall corrugation nozzles was not affected by simulated forward flight. Mean flow field measurements of the jet plume were conducted with both hardwall corrugation and fluidic insert nozzles. This led to the development of a newer fluidic insert nozzle fabrication technique. The new nozzles, along with supplying varying injection pressures to upstream and downstream injection ports, have produced the most noise reduction to date. Noise reduction has been optimized for two different overexpanded jet conditions and is near 5 dB in the peak noise emission direction at low polar angles and 3 dB off of the broadband shock associated noise in the sideline direction. These results were obtained with injection mass flow rates less than 4% of the core jet flow rate.

Increasingly powerful and noisy military aircraft have generated the need for research leading to the development of supersonic jet noise reduction devices. The hot high speed supersonic jets exhausting from military aircraft during takeoff present a most challenging problem. The present study extends prior research on two methods of noise reduction of supersonic jet flows. The first is the internal nozzle corrugations pioneered by Seiner et al. and the second is the beveled exit plane nozzle concept explored most recently by Viswanathan. A novel research idea of creating fluidic corrugations similar to the nozzle corrugations has been started by Penn State. To further the understanding and analysis of the fluidic corrugations, the present study focuses on the flow field and acoustic field of nozzles with two, three, and six nozzle corrugations. Additionally, the effect of the combination of the internal corrugations with a beveled nozzle is explored. The results show that significant noise reductions of over 3 dB of both the mixing noise and the broad band shock associated noise can be achieved. The combination of the beveled nozzle and the internal nozzle corrugations showed that there is less azimuthal dependence of the acoustic field than for the purely beveled nozzle. Additionally, the combination nozzle was shown to reduce the noise over a wider range of polar angles and operating conditions than either the purely beveled nozzle or the nozzle with only hard walled nozzle corrugations.

The emergence of louder, more powerful fighter aircraft has caused the research of supersonic jet noise reduction devices. Noise emitted towards the ground is most important during the takeoff segment of the flight profile (when the jet exhaust flow is typically over expanded). Small scale measurements are important so that noise reduction concepts can be evaluated early in the design process. In the past, acoustic measurements from the heat simulated small-scale anechoic facility at PSU have been compared to acoustic measurements from larger scale heated anechoic facilities with excellent results. Beveled exits for subsonic nozzles rotate the jet plume and primarily reduce noise through the subsequent rotation of the acoustic field. Until recently, this was believed to be the case for beveled exits on supersonic convergingdiverging nozzles. The jet plume from such nozzles was examined and shown to deflect less than 6 degrees for both over-expanded and under-expanded flows. Therefore any measured noise reduction is due to the alteration of the noise generation mechanisms and not the deflection of the jet plume. Beveled nozzles with the exit plane rotated 24 and 35 degrees were tested along with a baseline nozzle. Results show that for heated jets, noise in the peak emission direction was reduced by 3-4 dB on the long lip side of the nozzle, with very little altercation to the short lip side. For over expanded flows there was very little gain or reduction in the sideline broadband shock associated noise (BBSAN). However, for nearly perfectly expanded heated jets there was a noticeable increase in the sideline noise for the high frequency BBSAN.

The noise levels generated by tactical fighter aircraft can result in Noise Induced Hearing Loss for Navy personnel, particularly those involved in carrier deck operations. Reductions in noise source levels are clearly necessary, but these must be achieved without a loss in aircraft performance. This paper describes an innovative noise reduction technique that has been shown in laboratory scale measurements to provide significant reductions in both mixing as well as broadband shock-associated noise. The device uses the injection of relatively low pressure and low mass flow rate air into the diverging section of the military-style nozzle. This injection generates “fluidic inserts” that change the effective nozzle area ratio and generate streamwise vorticity that breaks up the large scale turbulent structures in the jet exhaust that are responsible for the dominant mixing noise. The paper describes noise measurements with and without forward flight that demonstrate the noise reduction effectiveness of the inserts. The experiments are supported by computations that help to understand the flow field generated by the inserts as well as help to optimize the distribution and strength of the flow injection.

Experimental research has shown how the addition of properly designed chevrons to model scale supersonic nozzles reduces the noise of the high speed jets issuing from such nozzles. It has also been shown that, to reasonable accuracy, this noise benefit scales between small‐ and moderate‐scale nozzle geometries. The new advanced acoustic model (AAM) developed by Wyle Laboratories has the capability to use noise source data to produce dynamic acoustic footprints showing noise exposure in the vicinity of airfields: especially for landing and take‐off operations. AAM uses information on aircraft engine jet exhaust noise sources for specific aircraft engine operating parameters and given flight conditions. This presentation describes the measurement and modeling of jet noise reduction using chevrons in both small and moderate scale nozzles. Then the AAM is used to demonstrate the expected change in acoustic footprint size for a full‐scale jet aircraft, where it equipped with chevrons. The effects of the chevrons are described as a decibel correction to the noise source spheres used by the model. The AAM is run for a simulated trajectory of a typical operation for a jet aircraft with and without chevrons to show the effects on the acoustic footprint.