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Williams eric paper_mec_e200


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This is my first crack at writing a technical report for an assignment in a mechanical engineering course at the University of Alberta. How was the clarity? Any feedback on how I can improve?

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Williams eric paper_mec_e200

  1. 1. Nacelle Design for a Low-Boom Supersonic Aircraft Eric Williams 2nd Year Mechanical Engineering Student Prepared: June 2012 1
  2. 2. Abstract Although supersonic aircraft is a well-established technology, its use in the publicdomain is effectively banned by aviation regulators. The primary concern that preventscivil supersonic flights is the loudness of the sonic booms these aircraftscreate.Gulfstream, an aerospace company, has done much research into the designingof supersonic jets that will satisfy regulators’ noise requirements. To achieve this, theyhave designed and tested a new type of engine which is enclosed by a high-flow bypassnacelle. Through heavy-computation tools and wind tunnel experiments, Gulfstream hasshown thatthis new nacelle can reduce drag, and can lower the sonic boom of theaircraft. 2
  3. 3. IntroductionThe aviation industry is striving to make supersonic transportation available to thepublic. This would accommodate the business market that would be willing to pay morefor faster transportation. However, for overland flight to be permitted by regulators, thenoise level and the sonic boom of supersonic aircraft must be reduced. Sonic boomsare fluctuations of pressure caused by aircraft reaching speeds that exceed the speedof sound. In an attempt to satisfy regulators, Gulfstream Aerospace Corporation hasdesignedseveral new components forsupersonic aircraft that would produce lowerbooms and quieter noise levels.As well, they also insure that their new designs wouldnot compromise the aircraft’s functionality.[1]Among the most challenging parts to design was the nacelle: the cover housing for anengine. Gulfstream’s solution was a high-flow bypass nacelle, in which a portion of theincoming airflow would be directed around the engine itself in a separate flowpath. (seeFigure 1) Without this type of nacelle, the gearbox attached to the engine would have beenclosed in a bulge which would increase the boom and drag of the aircraft significantly.(see Figure 2) The bypass airway of this nacelle also reduces inlet spillage. [1] Inletspillage occurs when the intake of air supplied exceeds the intake of air required by theengine. Excess air is then “spilled over” the edge of the nacelle which increases dragand sonic boom. However, in a high-flow bypass nacelle, the air is simply redirected tothe bypassairway.MethodsThroughexperimentation in wind tunnels and through airflow analysis using CFD(computation fluid dynamics), Gulfstream has made several tests on its nacelle concept.Initial testing was done in 2009 in the subsonic wind testing facility at the University ofIllinois where they studied the airflow of the bypass airway. [2] They used rapid-prototyped material to simulate the components of the engine at 1/6th scale.Thesecomponents represented the main body of the engine, a gearbox fairing, and two 3
  4. 4. supporting crane beams. (see Figure 3) A gearbox fairing is an aerodynamic structuresurrounding the gearbox which reduces drag from airflow. In their experiment, theystudied the airflow on each of following configurations: 1) the empty circular wind tunnel;2) the engine model within the wind tunnel; 3) the engine model with the gearbox fairing;4) the engine model with the gearbox fairing and supporting crane beams. [2]In 2010, Gulfstream went to the NASA Glenn Research Center, where they couldconduct tests inthe 8-x6-foot Supersonic Wind Tunnel. [3] There, they tested twodifferent models. (see Figure 4) One was a dual stream inlet, which would model as theengine hardware and the surrounding bypass layer. Secondly, they used a singlestream model which allowed room for a camera to visually capture the effects of vortexgenerators on the boundary layer. When a boundary is separated from a surface, veryhigh drag occurs. The vortex generators are micro-ramp structures which were tested tosee if they could prevent a separation of the boundary layer with the surface. Bothmodels were tested at various angles from the air flow, known as angles of attack.Results and DiscussionGulfstream’s wind tunnel experiment at the University of Illinois provided useful data onthe effect of the components on dynamic pressure and velocity of the flow. Mostnotably, the fairing caused a major reduction in dynamic pressure and velocity of thedownstream air of the lower side of the model. Conversely, the fairing increased thedynamic pressure of the velocity of the downstream air on the upper side of the model.(see Figure 5) This indicated that a better flowpath channels would need to beconsidered in future designs. In addition, the data accumulated in this experiment wasused to develop more accurate CFD (computational fluid dynamics) models. [2]The wind tunnel experiment at the NASA Glenn research centre yielded very positiveresults. The models performed well and a maximum pressure recovery of 96%, even athigh angles of attack.Also, it was shown that a near-zero inlet spillage is possible. 4
  5. 5. Figure 6 shows the relationship between the pressure recovery and the mass flow ratio.The mass flow ratio is the ratio between the air intake of the inlet and the total airsupplied. In addition, the shock on the lip of the cowl, the casing of the nacelle, was alsovery low at supersonic wind speeds. The vortex generators were observed to have verylittle effect on overall inlet performance. [3]ConclusionGulfstream’s goal was to design a turbofan engine that would produce a relatively lowboom. They decided the best way to do this was to design a streamlined nacelle with abypass flowpath. After creating some prototypes and models, they tested the concept atwind tunnel research facilities. After gathering data and using CDF analysis theyconcluded that the high-flow bypass nacelle design for had good pressure recovery,good performance, low shocks and reduced drag. All these factors indicate that theconcept is functional and will produce a lower sonic boom. In conclusion, the concept ofa low boom aircraft is feasible and merits more research. 5
  6. 6. Figure 1 – Comparison of a traditionalnacelle with a high-flow bypass nacelle. [2]Figure 2 – Comparison of engines withand without a nacelle bypass [2] 6
  7. 7. Figure 3 – Computer-modeled rendering of the componentsused in the wind tunnel test at the University of Illinois [2] Figure 4 – Single stream and dual stream models used in the Glenn Research Centre [3] 7
  8. 8. Figure 5 – Normalized dynamic pressure mapping of engine modelwith gearbox fairing. (Downstream) [2]Figure 6 – Pressure Recovery vs. Mass Flow Ratio at various anglesof attack (AOA) and at Mach 1.7 wind speed. [3] 8
  9. 9. References[1] (Last accessed July 2, 2012)[2] (Last accessedJuly 2, 2012)[3] accessed July 2, 2012) 9