Russell W. Powers

Experimental Comparison of Supersonic Jets Exhausting from Military Style Nozzles with Interior Corrugations and Fluidic Inserts

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.

Acoustics Measurements of Scale Models of Military Style Supersonic Beveled Nozzle Jets with Interior Corrugations

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.

Supersonic Jet Noise Reduction by Nozzle Fluidic Inserts with Simulated Forward Flight

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.

Acoustics Measurements of Scale Models of Military Style Supersonic Beveled Nozzle Jets

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.

Prediction, Experiments and Optimization of High-Speed Jet Noise Reduction Using Fluidic Inserts

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.

Mean Velocity and Turbulence Measurements of Supersonic Jets with Fluidic Inserts

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. Fluidic inserts have been developed for noise reduction using distributed nozzle blowing. Fluidic inserts are created that simulate mechanical, hardwall corrugations, while having the advantage of being an on demand noise reduction method. This research focuses on detailed measurements of the flow field modifications created by the hardwalled and fluidic corrugations to better understand how each produces noise reduction of the jet. Unsteady velocity measurements using a Laser Doppler Velocimeter are performed on jets exhausting from nozzles with fluidic inserts and hardwall corrugations. Measured mean axial velocity and axial turbulence intensity 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. The fluidic inserts produce less velocity deficit but more turbulence in the near exit region of the jet. After one jet diameter the mean flows are nearly identical, but the turbulent levels behind the fluidic inserts continue to be slightly higher than behind the hardwall corrugations.

Noise Reduction in Supersonic Jets from Rectangular Convergent-Divergent Nozzles

The design and development of noise reduction methods for rectangular supersonic, convergentdivergent nozzle jets are presented. This study focuses on the analysis of hard-wall corrugations and fluidic inserts for use in non-round rectangular nozzle jets. The baseline rectangular nozzle was tested at several operating conditions and azimuthal angles and compared to similar measurements in the literature. Hard-wall corrugations were seen to reduce the shock strength of over-expanded jets exhausting from the rectangular nozzles. This results in significant reduction of the BBSAN in the forward arc. Mixing noise reductions of over 3 dB OASPL were observed in the direction of the major axis of the rectangular hard-wall corrugation nozzle. Preliminary experiments on jets issuing from a single fluidic insert rectangular nozzle with distributed blowing were conducted. Mixing noise reductions were slightly less than for the hard-wall corrugation nozzle. For these rectangular nozzle jets, BBSAN was not significantly affected by the presence of the fluidic inserts. To exploit the fluidic insert noise reduction method for rectangular supersonic nozzle jets, a systematic parameter optimization study will be required.

Acoustics measurements of military-style supersonic beveled nozzle jets with interior corrugations

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.

Laser Doppler Velocimetry in Supersonic Round Jets

Development of a laser Doppler velocimetry (LDV) system was undertaken for supersonic aeroacoustic laboratory measurements. Initial qualification of the system was undertaken by measuring subsonic jet exhaust flows. The mean velocity of the centerline of the jet was measured and compared to previous LDV studies. The axial turbulence intensity was also estimated and compared to previous LDV studies. The LDV system was then tested by measuring a near sonic and supersonic jet exhaust at over-expanded, under-expanded, and fully expanded conditions. The centerline mean jet velocity, axial turbulence intensity, probability density function, histograms, and power spectral density were all analyzed with comparisons made to previous studies. Similar measurements were made on the jet shear layer. The importance of proper seeding of both the core and entrainment flow was highlighted.

High-performance aircraft short-takeoff and vertical-landing noise measurements on an aircraft carrier

The noise levels caused by high-performance aircraft are relatively high in the close proximity experienced by crew on board aircraft carriers, which can interfere with communications and may pose a risk for hearing loss. This paper reports on preliminary results of noise measurements of the operations of F-35B aircraft performing short-takeoff and vertical-landing (STOVL) operations on the flight deck of an LHA aircraft carrier. This noise measurement campaign was performed in late 2016, by scientists from the Air Force Research Laboratory (AFRL) in collaboration with the Naval Air Systems Command (NAVAIR) and the F-35 Integrated Task Force (ITF). The measurements were taken using hand-held noise recorder systems, and the recording engineers shadowed actual locations of crew. These data will be used to validate STOVL models of crew noise exposures on deck. [Work supported by F-35 JPO.]