Hybrid Wing Body Aircraft System Noise Assessment with Propulsion Airframe Aeroacoustic Experiments

TLDR: 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, which resulted in jet source noise reduction, favorable azimuthal directivity, and noise source relocation upstream.

Abstract: 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 ...

Figures

Figure 2. PAA Classification Tree

Figure 17. Aircraft system noise levels at the cutback, sideline, and approach points separated by airframe and engine noise with the effects of added PAA technologies.

Figure 1. Boeing Blended Wing Body Concept.

Figure 18. Tone-corrected perceived noise level, PNLT, as a function of flyover angle (observer at 90 degrees) for a) sideline, b) cutback, and c) approach conditions.

Table 3. Summary of noise reduction HWB configurations for system noise assessment. Engine position in fan nozzle diameters (D) is measured from the core nozzle exit plane relative to the aircraft trailing edge (positive upstream).

Figure 10. Approach (negative distance toward zero) and takeoff (positive distance away from zero) speed profiles for the SOA, NASA HWB Best, Heavy, and 2009 aircraft models. Note, HWB Heavy and 2009 are virtually identical.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Hybrid wing body aircraft system noise assessment with propulsion airframe aeroacoustic experiments" ?

Incorporating the three additional technology improvements, an aircraft noise is projected of 42. 

Q2. What was the design intent for the chevrons in Czech, Thomas, and Elko?

The design intent for the chevrons in Czech, Thomas, and Elkoby10 considered the potential impact of shielding through altering the location of jet noise sources. 

Q3. What is the way to reduce the noise from the aft radiated sources?

To maximize the HWB’s shielding potential, the aft radiating sources, fan exit, core, and jet, must be reduced and shielded more effectively through a combination of changing the baseline configuration of the HWB and through additional technology. 

Q4. What is the effect of the chevron design on the jet source?

The total installation of the jet and combining of the pylon orientation at the crown with the aggressive chevron design was very effective at reducing the jet source level and increasing shielding effectiveness. 

Q5. What was the first objective of the NASA pathfinding study?

The second objective was to understand the implications for noise of the hybrid wing body configuration and assess the potential noise reduction achievable by using fewer and relatively near termAmerican Institute of Aeronautics and Astronautics5technologies. 

Q6. What is the ability to conduct additional trade studies for low noise, efficient HWB configurations?

The ability to conduct additional trade studies for low noise, efficient HWB configurations is growing given the prior knowledge base from other disciplines, the high quality experimental data and system noise assessment methodology assembled for this study, and the identified advanced airframe, acoustic liner, and PAA technologies. 

Q7. What is the effect of moving the engines upstream on the body during cruise?

there are performance impacts of moving the engines upstream on the body closer to the high Mach number region during cruise. 

Q8. What was the next step for obtaining the correct relation between the engine noise components?

Once the calibration for obtaining the correct relation was determined, the next step was to adjust all the engine component levels by the same amount in order to match the EPNL noise levels for this aircraft (Approach: 98.1, Sideline: 95.0, Cutback: 92.0)50.