Effect of a rotating propeller on the separation angle of attack

Boldman, D. R.; Iek, Chanthy; Hwang, Danny P.; Larkin, Michael J.; Schweiger, P.

doi:10.2514/6.1993-17

Cited by 12 publications

(9 citation statements)

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“…The inlet flow is separated in the flow-through nacelle, whereas the boundary layer remained attached in the powered nacelle simulation due the favorable pressure gradient induced by the rotor suction near the shroud. The results of flow-through nacelle calculations with reduced AoA indicate that the presence of the rotor increases the separation-free AoA by 4° relative to the flow-through nacelle, which is in agreement with the observations in past numerical investigations [15,16] and experimental studies [19]. The results underline the importance of capturing the influence of the rotor on the inlet flow in short-inlet designs and demonstrate the capability of the developed body force method to deal with the fan-inlet coupling.…”

Section: Capabilities and Validationsupporting

confidence: 80%

“…Conventional methods that determine whether the inlet flow is separated are based on through-flow nacelle models which do not account for the effects induced by the rotor including blockage, swirl, and suction [17]. Including the influence of the rotor and stator in the design of the inlet and nozzle is important as the favorable pressure gradients in the inlet, induced by the rotor suction, can increase the separation-free AoA [18][19][20]. Also, determining the distortion transfer and stability margin requires modeling the complete fan stage.…”

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confidence: 99%

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Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

Peters

Spakovszky

Lord

et al. 2014

Journal of Turbomachinery

106

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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: Capabilities and Validationsupporting

confidence: 80%

mentioning

confidence: 99%

Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

Peters

Spakovszky

Lord

et al. 2014

Journal of Turbomachinery

106

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“…The size of the separation determines the distortion at the fan face which will influence the performance of the fan and its compatibility. studies can be broadly classified into the following categories, which explored the effect of the: (a) Off-design conditions like high-incidence and crosswinds on the intake-only configuration [1] and the hysteresis phenomena associated with flow separation and reattachment [2]; (b) Inlet distortion on the stability of the fan [3] ; (c) Fan-intake interaction on the incidence tolerance [4], [5] and the subsequent optimization of the intake shape [6].…”

Section: Fig 1: Schematic Showing the Flow Physics Around An Intakementioning

confidence: 99%

“…This delay of the onset of flow separation observed in a powered inlet operation was also duplicated by placing struts (which create blockage) at the fan face. Boldman et al [5] presented a comprehensive experimental work investigating the effect of rotating propeller on the intake separation angle of attack. It was demonstrated the propeller has increased the separationfree angle of attack by 2.7-4°, when compared to a clean inlet without fan, depending on the operating mass flow.…”

Section: Fig 1: Schematic Showing the Flow Physics Around An Intakementioning

confidence: 99%

Fan–Intake Interaction Under High Incidence

Cao

Vadlamani

Tucker

et al. 2016

Journal of Engineering for Gas Turbines and Power

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In this paper, we present an extensive numerical study on the interaction between the downstream fan and the flow separating over an intake under high incidence. The objectives of this investigation are twofold: (a) to gain qualitative insight into the mechanism of fan-intake interaction and (b) to quantitatively examine the effect of the proximity of the fan on the inlet distortion. The fan proximity is altered using the key design parameter, L/D, where D is the diameter of the intake and L is the distance of the fan from the intake lip.Both steady and unsteady Reynolds Averaged Numerical Simulations (RANS) were carried out. For the steady calculations, a low order fan model has been used while a full 3D geometry has been used for the unsteady RANS. The numerical methodology is also thoroughly validated against the measurements for the intake-only and fan-only configurations on a high bypass ratio turbofan intake and fan respectively. To systematically study the effect of fan on the intake separation and explore the design criteria, a simplified intake-fan configuration has been considered. In this fan-intake model, the proximity of the fan to the intake separation (L/D) can be conveniently altered without affecting other parameters.The key results indicate that, depending on L/D, the fan has either suppressed the level of the post-separation distortion or increased the separation-free operating range. At the lowest L/D (~ 0.17), around a 5° increase in the separation-free angle of incidence was achieved. This delay in the separation-free angle of incidence decreased with increasing L/D. At the largest L/D (~ 0.44), the fan was effective in suppressing the postseparation distortion rather than entirely eliminating the separation. Isentropic Mach number distribution over the intake lip for different L/D's revealed that the fan accelerates the flow near the casing upstream of the fan face, thereby decreasing the distortion level in the immediate vicinity. However, this acceleration effect decayed rapidly with increasing upstream distance from the fan-face. Previous work:An improved understanding of the intake aerodynamics and its interaction with the fan is hence crucial in developing the modern aircraft engines. Extensive studies were carried out in the literature by various researchers to address this issue. These

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“…A coupled fan-nacelle design approach is required as the inlet length is reduced and the interaction between inlet flow and fan stage increases. Including the influence of rotor and stator in the design of inlet and nozzle is important to capture mechanisms such as the increase in separation-free angle-of-attack due to the presence of the fan [24][25][26]. In addition, determining the distortion transfer and stability margin requires modeling the complete fan stage.…”

Section: Challengesmentioning

confidence: 99%

Ultra-Short Nacelles for Low Fan Pressure Ratio Propulsors

Peters¹,

Spakovszky²,

Lord³

et al. 2014

Volume 1A: Aircraft Engine; Fans and Blowers

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This thesis addresses the uncharted inlet and nacelle design space for low pressure ratio fans for advanced aeroengines. A key feature in low fan pressure ratio (FPR) propulsors with short inlets and nacelles is the increased coupling between fan and inlet. The thesis presents an integrated fan-nacelle design framework, combining a spline-based tool for the definition of inlet and nacelle surfaces with a fast and reliable body-force-based approach for the fan rotor and stator blade rows. The new capability captures the inlet-fan and fan-exhaust interactions and the flow distortion at the fan face and enables the parametric exploration of the short-inlet design territory. The interaction of the rotor with a region of high streamwise Mach number at the fan face is identified as the key aerodynamic mechanism limiting the design of short inlets. The local increase in streamwise 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 inlet length to fan 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 baseline 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 for engine propulsive efficiency benefits is suggested to be between 0.25 and 0.4. A candidate design with L/D = 0.25 maintains the cruise propulsive efficiency of the baseline case without jeopardizing fan and LPC stability at off-design conditions. On the aircraft system level, fuel burn benefits are conjectured to be feasible due to the reductions in nacelle weight and drag compared to an aircraft powered by the long-inlet baseline propulsor.

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Effect of a rotating propeller on the separation angle of attack

Cited by 12 publications

References 1 publication

Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

Ultrashort Nacelles for Low Fan Pressure Ratio Propulsors

Fan–Intake Interaction Under High Incidence

Ultra-Short Nacelles for Low Fan Pressure Ratio Propulsors

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