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

Abstract

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

Boundary-Layer Development Downstream of Normal Shock in Transonic Intakes at Incidence

“…However, in a previous investigation of the baseline lip (i.e. : Figure 5b), despite the Schlieren showed no obvious sign of shock-induced separation, a small recirculating region was observed using oil flow visualisation [5]. Thus, the inability to observe a λ-shock structure does not exclude the presence of a small separation.…”

“…Thus, based on this evidence, some degree of shock-induced separation is expected over each lip for every flow condition. Furthermore, in a previous investigation [5], it was shown how, for a number of flow conditions, the distance between the onset of pressure rise and the sonic line can provide a reasonable upper bound of the separation size (i.e. : a larger separation 'spreads' the pressure rise over a greater stream-wise distance).…”

“…This provides unprecedented optical access and allows a more economical replacement of the lip geometry, facilitating parametric surveys. A total of five inlet shapes are considered in this investigation: a representative baseline inlet shape (amply discussed in a previous paper [5]) and four lip variations. Their geometry definition is discussed in §II.E.…”

Effect of Reynolds number on a normal shock wave-transitional boundary-layer interaction over a curved surface

“…This is used in a forward scatter configuration. The ellipsoidal working volume has a maximum diameter of 130 μ m. Paraffin particles, with a diameter of approximately 0.5μ m (Colliss 2014), are used to seed the flow. The laser emitting head and receiving optics are mounted on a threeaxis traverse.…”

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

“…Several studies in literature addressed the effect of distortion on the fan-performance and vice versa. In the context of intakes subjected to high-incidence, Makuni et al [8] and Coschignano et al [9] built an experimental rig based on the highly loaded two-dimensional section of the intake lip. They explored the dynamics of the shock-wave boundary layer interaction (SWBLI) and the three-dimensional flow field with increasing incidence onto the intake.…”