The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Erik D. Olson - One of the best experts on this subject based on the ideXlab platform.
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Hybrid Wing Body Aircraft System Noise Assessment with Propulsion Airframe Aeroacoustic Experiments
International Journal of Aeroacoustics, 2020Co-Authors: Russell H. Thomas, Casey L. Burley, Erik D. OlsonAbstract:A system noise assessment of a hybrid wing body configuration was performed using NASA's best available Aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and Aircraft system models were created to define the hybrid wing body Aircraft concept as a twin engine Aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology, in production, bypass ratio seven turbofans. The baseline hybrid wing body Aircraft was assessed at 26.4 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the ...
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Propulsion Airframe Aeroacoustic Experiments
16th AIAA CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010Co-Authors: Russell H. Thomas, Casey L. Burley, Erik D. OlsonAbstract:A system noise assessment of a hybrid wing body configuration was performed using NASA’s best available Aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and Aircraft system models were created to define the hybrid wing body Aircraft concept as a twin engine Aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology high bypass ratio turbofans. The baseline hybrid wing body Aircraft was assessed at 22 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the highest noise sources. Aft radiated noise was expected to be the most challenging to reduce and, therefore, the experimental database focused on jet nozzle and pylon configurations that could reduce jet noise through a combination of source reduction and shielding effectiveness. The best configuration for reduction of jet noise used state-of- the-art technology chevrons with a pylon above the engine in the crown position. This configuration resulted in jet source noise reduction, favorable azimuthal directivity, and noise source relocation upstream where it is more effectively shielded by the limited airframe surface, and additional fan noise attenuation from acoustic liner on the crown pylon internal surfaces. Vertical and elevon surfaces were also assessed to add shielding area. The elevon deflection above the trailing edge showed some small additional noise reduction whereas vertical surfaces resulted in a slight noise increase. With the effects of the configurations from the database included, the best available noise reduction was 40 dB cumulative. Projected effects from additional technologies were assessed for an advanced noise reduction configuration including landing gear fairings and advanced pylon and chevron nozzles. Incorporating the three additional technology improvements, an Aircraft noise is projected of 42.4 dB cumulative below the Stage 4 level.
Chris K. Mechefske - One of the best experts on this subject based on the ideXlab platform.
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Effect of Bulkhead Pressurization on the Vibro-Acoustic Properties of an Aft-Fuselage-Mounted Twin-Engine Aircraft
Journal of Vibration and Acoustics, 2019Co-Authors: Braden T. Warwick, Chris K. MechefskeAbstract:Abstract Despite widespread use of an aft-fuselage-mounted Twin-Engine Aircraft in the business jet industry, a thorough investigation into the vibro-acoustic properties of this Aircraft type has yet to be undertaken. Additionally, the effect of bulkhead pressurization on the vibro-acoustic properties of this Aircraft fuselage has yet to be investigated in isolation. This work investigates the effect of bulkhead pressurization on two different designs of an aft-fuselage-mounted Twin-Engine Aircraft: a single and a double bulkhead designs. A modal analysis, a harmonic frequency response analysis, and an acoustic response analysis were performed. A split bulkhead pressurization methodology was introduced as a means of improving structural performance without impacting passenger comfort levels in a double bulkhead Aircraft. Modal coupling between components was seen to be the primary cause of increased cabin noise, peaking above 80 Hz. The bulkhead frequency response was highly dependent upon bulkhead pressurization, as the modal participation factors were significantly impacted by bulkhead pressurization. Therefore, the importance of understanding all bulkhead natural frequencies was highlighted, as the response changed as a function of bulkhead pressurization. Bulkhead resonance conditions generated a tone in the acoustic frequency response inside the passenger cabin, highlighting the importance of this component to passenger comfort levels.
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Substructuring verification of a rear fuselage mounted Twin-Engine Aircraft
Aerospace Science and Technology, 2019Co-Authors: Braden T. Warwick, Chris K. MechefskeAbstract:Abstract Dynamic substructuring allows for the reduction of large complex structures into substructures to increase computational efficiency and to isolate the local dynamic behaviors of concern. However, errors such as truncation, continuity and rigid body mode errors still limit the applicability of this method experimentally. Additionally, the feasibility of implementing substructuring techniques on finite element models of multi-component fuselage structures has yet to be shown in the literature. The objective of this paper is twofold: first to introduce a feasible substructuring methodology that mitigates the experimental and multi-component limitations with current methods; and secondly, to investigate the modal properties and applicability of substructuring analysis on a rear fuselage mounted Twin-Engine Aircraft. This configuration is not well understood in the literature despite having been shown to have increased interior cabin noise and vibration levels. Experimental validation of the computational model was first performed. A substructuring analysis of the validated computational model produced natural frequencies of the local and global modes that agreed within 6.47% on average, and pseudo-orthogonality terms greater than 0.89 for all modes considered. This methodology proved to be useful for generating an accurate representation of local modes within a global structure for the Aircraft configuration studied. This will allow for future work to more thoroughly investigate the local modes using innovative design methods with confidence that the local modes will correlate with the global modes.
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Experimental Modal Analysis of a Half-Scale Model Twin-Engine Aircraft Rear Fuselage Engine Mount Support Frame
Volume 8: 29th Conference on Mechanical Vibration and Noise, 2017Co-Authors: Diego A. Chamberlain, Chris K. MechefskeAbstract:Experimental modal testing using an impact hammer is a commonly used method for obtaining the modal parameters of any structure for which the vibrational behavior is of interest. Natural frequencies and associated mode shapes of the structure can be extracted directly from measured FRFs (Frequency Response Functions) through various curve fitting procedures. This paper provides an overview of the modal testing conducted on an aerospace component. Testing set-up, experimental equipment and the methodology employed are all described in detail. Further validation of the testing procedure was done by ensuring that the experimental results satisfy the requirements of repeatability, reciprocity and linearity. The relevant ISO standard has been referenced and important concepts to modal analysis are expanded upon. Recorded natural frequencies, coherence and a description of the observed mode shapes are presented along with notable trends.
Russell H. Thomas - One of the best experts on this subject based on the ideXlab platform.
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Hybrid Wing Body Aircraft System Noise Assessment with Propulsion Airframe Aeroacoustic Experiments
International Journal of Aeroacoustics, 2020Co-Authors: Russell H. Thomas, Casey L. Burley, Erik D. OlsonAbstract:A system noise assessment of a hybrid wing body configuration was performed using NASA's best available Aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and Aircraft system models were created to define the hybrid wing body Aircraft concept as a twin engine Aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology, in production, bypass ratio seven turbofans. The baseline hybrid wing body Aircraft was assessed at 26.4 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the ...
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Experimental Studies of Open Rotor Installation Effects
Russell The Journal Of The Bertrand Russell Archives, 2011Co-Authors: Michael J. Czech, Russell H. Thomas, The Boeing Company, Nasa LangleyAbstract:Open rotor propulsion technologies offer an opportunity for reducing fuel burn due to the very high effective bypass ratio that results in increased propulsive efficiency. Open rotor effective bypass ratio can be 25 or higher and represents a potential advantage over even advanced ultra high bypass ratio turbofan engines. At the same time, great challenges arise from this radically different engine architecture in terms of Aircraft system integration. The propulsion airframe aeroacoustic (PAA) effects of integration are one of those key challenges. Total installed noise, open rotor noise including integration effects, can be impacted by angle of attack, spacing between rotors and airframe elements, flow effects from wake ingestion or distortion from the airframe elements and several other parameters that generally depend on the Aircraft configuration. In general, these effects increase noise compared to that of an isolated open rotor. This inter-relationship of the aerodynamic and aeroacoustic system integration effects is particularly important to enable future application. Furthermore, innovative integration and advanced technology may also offer the possibility of mitigating these usually negative aeroacoustic effects for a total Aircraft system noise reduction. Understanding of these installation effects is essential to be able to assess the Aircraft system benefits and to develop technology and approaches to achieve the best Aircraft system benefits possible. An extensive model scale test campaign was conducted to investigate a broad range of these open rotor installation effects for both a conventional and an unconventional airframe. The conventional airframe was patterned after a modern Twin-Engine Aircraft configuration. The unconventional airframe was a hybrid wing body Aircraft concept. The contra-rotating, eight by eight, open rotor used in this experiment was legacy technology from the 1980s flight test project. The experimental campaign was conducted in the Boeing Low Speed Aeroacoustic Facility (LSAF), shown in Figure 1. A 9 by 12 ft open jet is used to produce the forward flight simulation with a maximum Mach number of 0.25 for this experimental setup. Figure 1 shows the basic setup for this campaign with the airframe attached from the overhead structure and the open rotor rig attached on a strut from below the open jet. LSAF installed specially designed modifications for efficient positioning of the airframe relative to the open rotor. The airframe was traversed remotely relative to the fixed open rotor rig providing for the investigation of a large number of installation positions. Eight positions around the main wing of the conventional airframe and eleven positions above the hybrid wing body airframe were documented. Figure 2 shows a typical spectrum of the open rotor. In this case, the forward and aft blade rows were run intentionally at slightly different speeds. This allows the engine
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Propulsion Airframe Aeroacoustic Experiments
16th AIAA CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference), 2010Co-Authors: Russell H. Thomas, Casey L. Burley, Erik D. OlsonAbstract:A system noise assessment of a hybrid wing body configuration was performed using NASA’s best available Aircraft models, engine model, and system noise assessment method. A propulsion airframe aeroacoustic effects experimental database for key noise sources and interaction effects was used to provide data directly in the noise assessment where prediction methods are inadequate. NASA engine and Aircraft system models were created to define the hybrid wing body Aircraft concept as a twin engine Aircraft with a 7500 nautical mile mission. The engines were modeled as existing technology high bypass ratio turbofans. The baseline hybrid wing body Aircraft was assessed at 22 dB cumulative below the FAA Stage 4 certification level. To determine the potential for noise reduction with relatively near term technologies, seven other configurations were assessed beginning with moving the engines two fan nozzle diameters upstream of the trailing edge and then adding technologies for reduction of the highest noise sources. Aft radiated noise was expected to be the most challenging to reduce and, therefore, the experimental database focused on jet nozzle and pylon configurations that could reduce jet noise through a combination of source reduction and shielding effectiveness. The best configuration for reduction of jet noise used state-of- the-art technology chevrons with a pylon above the engine in the crown position. This configuration resulted in jet source noise reduction, favorable azimuthal directivity, and noise source relocation upstream where it is more effectively shielded by the limited airframe surface, and additional fan noise attenuation from acoustic liner on the crown pylon internal surfaces. Vertical and elevon surfaces were also assessed to add shielding area. The elevon deflection above the trailing edge showed some small additional noise reduction whereas vertical surfaces resulted in a slight noise increase. With the effects of the configurations from the database included, the best available noise reduction was 40 dB cumulative. Projected effects from additional technologies were assessed for an advanced noise reduction configuration including landing gear fairings and advanced pylon and chevron nozzles. Incorporating the three additional technology improvements, an Aircraft noise is projected of 42.4 dB cumulative below the Stage 4 level.
J. P. Fielding - One of the best experts on this subject based on the ideXlab platform.
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Flight Operational Assessment of Hybrid Laminar Flow Control (HLFC) Aircraft
Aerodynamic Drag Reduction Technologies, 2020Co-Authors: T. M. Young, J. P. FieldingAbstract:Hybrid Laminar Flow. Control (HLFC) offers the potential for significant fuel burn reductions. However the system is likely to have a lower operational reliability than other Aircraft systems. The “failure modes” which will result in a loss of laminar flow, are mechanical (i.e. system failure) and environmental (i.e. rain, ice or insect contamination). The typical contingency fuel taken onboard to accommodate unplanned contingencies is 3 to 5% of the trip fuel. This is inadequate to cover a complete loss of laminar flow for an extended period during the cruise. The probability of an in-flight diversion decreases as the planned contingency fuel is increased; however this leads to a reduced fleet efficiency due to increased take off weights. A computer performance model of a twin engine Aircraft in the class of the Boeing 757, has been used to study the change in block fuel for alternative fuel planning assumptions based on a loss in laminar flow due to cloud encounters in the cruise.
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Potential fuel savings due to hybrid laminar flow control under operational conditions
Aeronautical Journal, 2020Co-Authors: T. M. Young, J. P. FieldingAbstract:Hybrid laminar flow control (HLFC) is an active drag reduction technique that permits extended laminar flow on an Aircraft surface and thus offers the potential for significant fuel savings. This is at the expense of an increase in system weight and specific fuel consumption. An overview of HLFC system failure types and consequences is presented as an introduction to this study, which investigated the impact of a potential loss of laminar flow due to flight in cirrus clouds. At typical cruising altitudes, the ice crystals are of a sufficient size and may result in sufficient particle flux to cause a temporary transition of the boundary layer. A computer performance model of a twin engine Aircraft in the class of the Boeing 757 has been used to study the impact of alternative fuel planning scenarios on the fuel consumed by a HLFC Aircraft, taking into account a model of probable cloud encounter. Based on the models, the study showed that if the fuel planning assumed 25% time-in-cloud (TIC) during the cruise, then in the extreme case of 55% TIC during the cruise, the contingency fuel (taken as 3% of the trip fuel), would be sufficient for the Aircraft to complete the mission (including the alternate leg and hold).
Barry J Dempsey - One of the best experts on this subject based on the ideXlab platform.
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From Yesterday’s Three- and Four-Engine Airliners to Twin-Engine Airliners: Are Bird Strikes More Hazardous for Today’s Twin-Engine Aircraft?
2020Co-Authors: Kivanc A Avrenli, Barry J DempseyAbstract:Bird strikes are hazardous for turbofan Aircraft engines because of: i) continuous increase in large bird populations, ii) modern-day turbofan engines are not tested for large birds, iii) birds are less likely to detect and avoid turbofan engines. The trend towards Twin-Engine Aircraft renders bird strikes all the more hazardous. With the engine redundancy being cut from three or four to two, bird strikes can more likely cause damage to all engines of the struck Aircraft. Damage to all engines of the struck Aircraft is one of the most perilous possible consequences of a bird strike because the Aircraft may lose all engine redundancy and undergo total loss of power. In view of the growing threat of bird strikes, the objective of this study is to test whether bird strikes are significantly more hazardous for today’s commercial Aircraft that has “typically” two under-wing-mounted engines. A large sample of over 70,000 U.S. bird strikes is used to test for the research hypothesis. The goal is to find out the factors that are significantly associated with the probability that a bird strike will cause damage to all engines of the struck Aircraft. Prior to statistical analysis, the missing data in the sample are multiply imputed using a robust Approximate Bayesian Bootstrap method. Based on the multiply imputed data, fifteen different predictor variables are analyzed. Five of those variables are found to be significantly associated with the probability that a bird strike will result in damage to all engines of the struck Aircraft. These are bird size, number of birds struck, engine position on Aircraft, number of engines, and flight phase. A logistic regression model is developed and a detailed probabilistic interpretation of the model is given for practitioners. The results show that today’s “typical” commercial Aircraft is significantly more prone to sustaining damage to all engines in the event of a bird strike. Using the findings: i) aviation authorities can improve bird strike hazard mitigation strategies; ii) flight crews can take measures to reduce the potential of bird strikes resulting in damage to all engines; and iii) researchers can better understand the nature of bird strikes and develop a scientific approach to minimize the likelihood of damage to all engines in the event of a bird strike.
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Statistical Analysis of Aircraft–Bird Strikes Resulting in Engine Failure
Transportation Research Record, 2014Co-Authors: Kivanc A Avrenli, Barry J DempseyAbstract:Engine failure caused by bird strikes can be particularly perilous for today's typical Twin-Engine Aircraft. Although large-bird populations have increased substantially since the 1970s, modern-day turbofan engines are not tested for large birds. Instead, it is acceptable for contemporary turbofan engines to lose all power because of large-bird ingestion. With the increasing use of turbofan engines and air traffic, not only are more bird strikes expected in the near future, but also more bird strikes are anticipated to result in engine failure. This study identified the factors that were statistically associated with the probability of engine failure in the event of a bird strike. A large sample of more than 42,000 U.S. bird strikes was used. The missing data in the sample were multiply imputed by using an approximate Bayesian bootstrap method. With the multiply imputed data, 15 factors were statistically analyzed. Six of those factors were found to be significantly associated with the probability of engi...
