Prediction of Boundary-Layer Flow Separation in V/STOL Engine Inlets

Chou, David C.; Luidens, R. W.; Stockman, N. O.

doi:10.2514/3.58393

Cited by 17 publications

(4 citation statements)

References 3 publications

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“…Previous experimental studies [3,4], analytical models and computations [5][6][7] have mostly been concerned with the onset of highlight separation at both high and low speed. At lower speed, the incidence at which lip separation occurs was found to increase with mass flow rate.…”

Section: Transonic Inlets At Incidencementioning

confidence: 99%

Normal-Shock/Boundary-Layer Interactions in Transonic Intakes at High Incidence

Coschignano¹,

Babinsky²,

Sheaf³

et al. 2019

AIAA Journal

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During high-incidence manoeuvres, shock-wave boundary layer interactions can develop over transonic inlet lower lips, significantly impacting aerodynamic performance. Here, a novel experimental rig is used to investigate the nature and severity of these interactions for a typical high incidence scenario. Furthermore, we explore the sensitivity to changes in angle of incidence and mass flow rate, as potentially experienced across off-design operations. The reference flow-field, informed by typical climb conditions, is defined by an incidence of 23 • and a free stream Mach number M=0.435. The lower lip flow is characterised by a rapid acceleration around the leading-edge and a M≈1.4 shock ahead of the intake diffuser. Overall, this flow-field is found to be relatively benign, with minimal shock-induced separation. Downstream of the interaction, the boundary layer recovers a healthy profile ahead of the nominal fan location. Increasing incidence by 2 • , the separation becomes noticeably larger and unsteadiness develops. Detrimental effects are exacerbated at an even higher incidence of 26 •. Increasing the mass flow rate over the lip by up to 15% of the initial value has minor effects on performance and is not found to inhibit the boundary layer profile recovery. Nomenclature α Angle of incidence δ Boundary layer thickness δ * Boundary layer displacement thickness θ Boundary layer momentum thickness c Intake chord length H Shape factor L * Interaction length

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Section: Transonic Inlets At Incidencementioning

confidence: 99%

Normal-Shock/Boundary-Layer Interactions in Transonic Intakes at High Incidence

Coschignano¹,

Babinsky²,

Sheaf³

et al. 2019

AIAA Journal

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“…The surface pressure fluctuations can vary between ±20% of the mean value leading to detrimental effects of lift reduction and increased structural loads. However, Coschignano and Babinsky [9] note that most of these studies are confined to the flows over aerofoils/wings while very few explored the shock formation over engine intake lip [31,32]. In particular, it is crucial to (a) quantify the pressure fluctuations as it has serious implications on the rotor's structural integrity and (b) determine the extent of the spectral gap between the frequency of the shock unsteadiness and the blade-passing frequency of the rotor.…”

Section: Effect Of Fan On Intake Distortion (Foi)mentioning

confidence: 99%

Toward Future Installations: Mutual Interactions of Short Intakes With Modern High Bypass Fans

Vadlamani

Cao

Watson

et al. 2019

Journal of Turbomachinery

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In this paper, we investigate the coupled interaction between a new short intake design with a modern fan in a high-bypass ratio civil engine, specifically under the off-design condition of high incidence. The interaction is expected to be much more significant than that on a conventional intake. The performance of both the intake-alone and rotor-alone configurations are examined under isolation. Subsequently, a comprehensive understanding on the two-way interaction between intake and fan is presented. This includes the effect of fan on intake angles of attack (AoA) tolerance (FoI) and the effect of circumferential and radial flow distortion induced by the intake on the fan performance (IoF). In the FoI scenario, the rotor effectively redistributes the mass flow at the fan-face. The AoA tolerance of the short-intake design has increased by ≈4 deg when compared with the intake-alone configuration. Dynamic nature of distortion due to shock unsteadiness has been quantified. ST plots and power spectral density (PSD) of pressure fluctuations show the existence of a spectral gap between the shock unsteadiness and blade passing, with almost an order of magnitude difference in the corresponding frequencies. In the IoF scenario, both the “large” (O(360 deg)) and “small” scale distortion (O(10–60 deg)) induced by the intake results in a non-uniform inflow to the rotor. Sector analysis reveals a substantial variation in the local operating condition of the fan as opposed to its steady characteristic. Streamline curvature, upwash, and wake thickening are identified to be the three key factors affecting the fan performance. These underlying mechanisms are discussed in detail to provide further insights into the physical understanding of the fan-intake interaction. In addition to the shock-induced separation on the intake lip, the current study shows that shorter intakes are much more prone to the upwash effect at higher AoA. Insufficient flow straightening along the engine axis is reconfirmed to be one of the limiting factors for the short-intake design.

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“…The formation of shock waves on the inside lip of engine intakes has often been overlooked and, so far, only highlight (nacelle leading edge) separation at large incidence (> 30 • ) has been investigated in detail. 2,3 However, these early experiments were characterised by poor resolution and limited measurements. The onset of separation near the throat, which precedes highlight stall, 2 has not been considered.…”

Section: Shock-boundary Layer Interactions In Subsonic Engine Intakesmentioning

confidence: 99%

Normal Shock Wave-Turbulent Boundary Layer Interactions in Transonic Intakes at Incidence

Coschignano

Babinsky

Sheaf³

et al. 2018

2018 AIAA Aerospace Sciences Meeting

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The flow field around a transonic engine inlet lip at high incidence is investigated for a variety of flow conditions around the design point. Generally, the flow on the upper surface of the lip is characterised by a supersonic region, terminated by a near-normal shock wave. At the nominal design point, the shock is not strong enough to cause significant flow separation, resulting only in marginal losses in pressure recovery. Off-design conditions were explored by altering the angle of attack as well as changing the mass flow rate over the upper lip, intended to mimic the effect of an increase in engine flow. The results suggest that angle of attack has the greatest effect on the flow field. In particular, even a relatively small increase of 2 • can lead to large and highly unsteady flow separation with an associated shock oscillation. Both qualitative and quantitative measurements suggest a noticeably reduced aerodynamic performance resulting from higher incidence operation. In contrast, an increase of up to 5.2% in mass flow over the upper part of the intake lip did not result in large separated regions or flow-field unsteadiness.

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Prediction of Boundary-Layer Flow Separation in V/STOL Engine Inlets

Cited by 17 publications

References 3 publications

Normal-Shock/Boundary-Layer Interactions in Transonic Intakes at High Incidence

Normal-Shock/Boundary-Layer Interactions in Transonic Intakes at High Incidence

Toward Future Installations: Mutual Interactions of Short Intakes With Modern High Bypass Fans

Normal Shock Wave-Turbulent Boundary Layer Interactions in Transonic Intakes at Incidence

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