Influence of Upstream Total Pressure Profiles on S-Duct Intake Flow Distortion

Abstract

For some embedded engine arrangements, the nature of the inlet distortion is influenced by the boundary layer characteristics at the inlet plane of the intake. This research presents the first quantitative assessment on the influence of inlet boundary layer thickness and asymmetry on the swirl distortion at the exit of an S-shaped intake. Measurements of high spatial and temporal resolution have been acquired at the outlet plane of the S-duct using time-resolved particle image velocimetry. When boundary layer profiles typical of embedded engines are introduced, the characteristic secondary flows at the outlet plane are intensified. Overall, the peak swirl intensity increases by 40% for a boundary layer which is 7 times thicker than the reference case. The unsteady modes of the S-duct remain, although the dominant fluctuations in the flow arise at a frequency 50% lower. When the inlet boundary layer profile becomes asymmetric about the intake centerline the peak swirl events at the hub are reduced by up to 40%. At the tip the peak swirl intensity increases by 29%. The results demonstrate that the effects of inlet boundary layer thickness and asymmetry must be carefully considered as part of engine compatibility tests for complex intakes. Nomenclature ai(t) = Temporal coefficient for i th mode in Proper Orthogonal Decomposition [ms -1 ] Ain = S-duct inlet plane area [m 2 ] Aout = S-duct outlet plane area [m 2 ] Din = S-duct inlet plane diameter [m]

Novel Method for Evaluating Intake Unsteady Flow Distortion

“…11a). A more in-depth analysis has been presented by McLelland et al [24] in which unsteadiness and spectral analysis have been assessed for this thicker inlet profile configuration. The distribution of the relative velocity remains broadly unaltered (Fig.…”

“…These inlet conditions are expected when the duct axis is not aligned with the main fuselage body. One example is when the intake is located in a region of upper surface and spanwise flow causes skew in the airframe boundary layer or when the intake is operating at notable yaw angles for a top-mounted S-duct, or at notable pitch angles for a side-mounted S-duct [24,41].…”

“…The frequencies of these coherent structures are contained within St < 1.2; and therefore, they are within the range of the critical frequencies for a typical propulsion system. The S-duct aerodynamics were also investigated for non-uniform inlet conditions representative of possible approaching conditions of boundary layer ingestion airframe or intake operation under angles of yaw and pitch [24]. An intensification of the vortical structures and an increase of the swirl angle unsteadiness were observed with thicker inlet total pressure profiles.…”

Effects of Splitting Airfoil’s Aspect Ratio on the Control of Separation and Loss Distribution in a Distortion Generator

“…Calculating these effects on a combat aircraft equipped with embedded engine subjected to varying degrees of distortion during maneuver flight at high flight angles is a critical step in the design process [5]. High levels of pressure distortion are present due to the combined influence of the ingestion of the airframe boundary layer and the generation of secondary flows by the intake [6].…”

Quantification of Swirl Distortions Caused by S-shape Inlet Ducts

“…Although the steady and unsteady simulations can achieve abundant flow details, relevant experiments are still necessary to verify the numerical results due to the complex secondary flow and boundary seperation. Recently, Zachos et al, Gil-Prieto et al and McLelland et al used stereoscopic particle image velocimetry (SPIV) to provide a clear view of the swirl flow field generated by two different S-shaped aero-engine intakes, and obtained the steady and unsteady flow characteristics inside these S-ducts (Zachos et al, 2016;Gil-Prieto et al, 2017;McLelland et al, 2020).…”