Ultra-Short Nacelles for Low Fan Pressure Ratio Propulsors

Peters, A.; Spakovszky, Z. S.; Lord, Wesley K.; Rose, Becky

doi:10.1115/gt2014-26369

Cited by 29 publications

(33 citation statements)

References 65 publications

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“…In general, about 100,000 iterations were required to reach a settled unsteady flow solution. Details on the nacelle design framework, the meshing strategy, the computational setup of the URANS calculations, and the results of grid convergence studies can be found in [14].…”

Section: Inlet and Nacelle Design Methodsmentioning

confidence: 99%

“…However, that same outward shift in the stagnation point exacerbates the over-speed along the inlet internal surface at low-speed conditions, resulting in increased rotor incidence distortion levels. A detailed assessment of unconventional spinner shapes is given in [14]. The short-inlet propulsors discussed in this paper feature conventional spinner designs similar to the shape included in the baseline configuration, as shown for example at the top in Fig.…”

Section: Short-inlet Design Strategymentioning

confidence: 99%

“…Consequently, the design strategy and guidelines presented in this section are focused on inlet L/Ds of 0.2 and above. The details of the preliminary parametric inlet length study are presented in [14].…”

Section: Short-inlet Design Strategymentioning

confidence: 99%

“…However, short inlets have reduced internal diffusion capability, and inlet flow distortion effects can be exacerbated leading to reduced rotor performance. A sensitivity analysis for a candidate secondgeneration geared low-FPR propulsor suggests a 1 % reduction in fan efficiency corresponds to a 0.85 % reduction in engine propulsive efficiency, whereas a 1 % reduction in total nacelle drag results in a 0.07 % increase in propulsive efficiency [14]. Shorter inlets can also lead to fan and LPC stability challenges and aero-mechanical issues, and yield reduced fan noise attenuation and shielding opportunities.…”

mentioning

confidence: 99%

“…The large computational resources associated with Copyright © 2014 by ASME full-annulus URANS calculations render the direct CFD approach unsuitable in the design phase or the parametric exploration of coupled inlet-fan systems. In this work, a body force method is developed to assess the performance of novel nacelle configurations [14]. In this approach, the fan rotor blade row is replaced with a force field, which produces the same pressure rise and flow turning.…”

mentioning

confidence: 99%

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Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

Peters

Spakovszky

Lord

et al. 2014

Journal of Turbomachinery

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101

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As the propulsor fan pressure ratio (FPR) is decreased for improved fuel burn, reduced emissions and noise, the fan diameter grows and innovative nacelle concepts with short inlets are required to reduce their weight and drag. This paper addresses the uncharted inlet and nacelle design space for low-FPR propulsors where fan and nacelle are more closely coupled than in current turbofan engines. The paper presents an integrated fan-nacelle design framework, combining a splinebased inlet design tool with a fast and reliable body-force-based approach for the fan rotor and stator blade rows to capture the inlet-fan and fan-exhaust interactions and flow distortion at the fan face. The new capability enables parametric studies of characteristic inlet and nacelle design parameters with a short turn-around time. The interaction of the rotor with a region of high streamwise Mach number at the fan face is identified as the key mechanism limiting the design of short inlets. The local increase in Mach number is due to flow acceleration along the inlet internal surface coupled with a reduction in effective flow area. For a candidate short-inlet design with length over diameter ratio L/D = 0.19, the streamwise Mach number at the fan face near the shroud increases by up to 0.16 at cruise and by up to 0.36 at off-design conditions relative to a long-inlet propulsor with L/D = 0.5. As a consequence, the rotor locally operates close to choke resulting in fan efficiency penalties of up to 1.6 % at cruise and 3.9 % at off-design. For inlets with L/D < 0.25, the benefit from reduced nacelle drag is offset by the reduction in fan efficiency, resulting in propulsive efficiency penalties. Based on a parametric inlet study, the recommended inlet L/D is suggested to be between 0.25 and 0.4. The performance of a candidate short inlet with L/D = 0.25 was assessed using full-annulus unsteady RANS simulations at critical design and off-design operating conditions. The candidate design maintains the propulsive efficiency of the baseline case and fuel burn benefits are conjectured due to reductions in nacelle weight and drag compared to an aircraft powered by the baseline propulsor. This document has been publicly released 2 NOMENCLATURECopyright © 2014 by ASME BACKGROUND & INTRODUCTIONNext-generation turbofan engine designs for commercial transport aircraft seek higher bypass ratios (BPR) and lower fan pressure ratios (FPR) for improved fuel burn and reduced emissions and noise [1][2][3][4], increasing fan bypass stream propulsive efficiencies and enabling higher overall pressure ratios and turbine inlet temperatures [4]. In addition, significant cabin and far-field noise benefits can be achieved by potentially avoiding buzz-saw noise, reducing fan broadband and rotorstator interaction noise, and enabling steeper take-off profiles due to excess thrust capability [5][6][7].Reductions in fan pressure ratio can be realized for example through geared low-speed fans. First-generation geared turbofan engines with BPR = 12 and FPR ≈ 1.4 for s...

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Section: Inlet and Nacelle Design Methodsmentioning

confidence: 99%

Section: Short-inlet Design Strategymentioning

confidence: 99%

Section: Short-inlet Design Strategymentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

Peters

Spakovszky

Lord

et al. 2014

Journal of Turbomachinery

Self Cite

101

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Advances in Turbofan Engines: AUSPerspective

Zante

2016

Encyclopedia of Aerospace Engineering

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Turbofan engines have been the mainstay of large aircraft propulsion systems since the first turbofan‐powered commercial airliner was introduced in the late 1960s, replacing the less efficient and noisier turbojets. Engine manufacturers have continually improved the overall engine efficiency by both increasing the propulsive efficiency of the fan system and increasing the thermal efficiency of the core. Combustor technologies have also advanced, resulting in significantly lower emissions even as the overall pressure ratio of the cores has increased. Low operating costs improve aircraft economic competitiveness and motivate the efforts for fuel efficiency/noise reduction, while emissions reduction tends to be regulation driven. The historical improvements in turbofan efficiency, noise, and emissions are reviewed. Current‐generation turbofan systems can still achieve both propulsive and thermal efficiency gains. However, the engine cycle and configuration changes that benefit efficiency can potentially have negative consequences for emissions and noise. Complementary efforts in combustion technology and noise reduction are needed for a balanced approach to engine development. The current development efforts within the United States for next‐generation engines with lower fuel burn, noise, and emissions are summarized. Additionally, research efforts are discussed for generation‐after‐next systems that are typically more electric and/or hybrid.

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