S-duct flow distortion with non-uniform inlet conditions

Abstract

Convoluted aero-engine intakes are often required to enable closer integration between engine and airframe. Although the majority of previous research focused on the distortion of S-duct intakes with undistorted inlet conditions, there is a need to investigate the impact of more challenging inlet conditions at which the intake duct is expected to operate. The impact of inlet vortices and total pressure profiles on the inherent unsteady flow distortion of an S-duct intake was assessed with stereo particle image velocimetry. Inlet vortices disrupted the characteristic flow switching mode but had a modest impact on the peak levels and unsteady fluctuations. Non-uniform inlet total pressure profiles increased the peak swirl intensity and its unsteadiness. The frequency of swirl angle fluctuations was sensitive to the azimuthal orientation of the non-uniform total pressure distribution. The modelling of peak distortion with the extreme value theory revealed that although for some inlet configurations the measured peak swirl intensity was similar, the growth rate of the peak values beyond the experimental observations was substantially different and it was related with the measured flow unsteadiness. This highlights the need of unsteady swirl distortion measurements and the use of statistical models to assess the time-invariant peak distortion levels. Overall, the work shows it is vital to include the effect of the inlet flow conditions as it substantially alters the characteristics of the complex intake flow distortion.

Characterization of unsteady distortion events for S-duct intakes under non-uniform inlet conditions

“…1. This S-duct geometry was thoroughly investigated with experimental and computational studies [18,19], which include evaluation of steady and unsteady total pressure distortion [20], swirl distortion [9], sensitivity to inlet Mach number [17], as well as the effectiveness of passive and active flow control methods [21], and, more recently, the operation under non-uniform inlet conditions [11]. Downstream of the intake, a constant area duct provides optical access for measurements at the Aerodynamic Interface Plane (AIP), and a diffuser duct drives the flow to the suction fan (Fig.…”

“…2). Previous research demonstrated that AoA = -12° generates a vortex whose strength can alter the flow distortion characteristics at a noticeable level [11], thus this setup has been considered in the current study. Given the negative incidence of the delta wing with reference to the incoming flow, the vortex rotates anti-clockwise when viewed from downstream.…”

“…Fig. 2: Semi-span delta wing dimensions and definition of the angle of attack (AoA) relative to the incoming flow (top view) [11].…”

“…Recently, a new technique to evaluate the unsteady flow distortion in the relative frame of reference of a notional compressor system was introduced [8]. The exploitation of the high temporal and spatial resolution of the unsteady 3D velocities measured with high-bandwidth Particle Image Velocimetry [9][10][11] enabled the classification of distortion events based on the magnitude, on the duration relative to the blade rotation, and the relative probability. This method accounts for synchronous spatial and temporal non-uniformities due to the unsteady flow field as well as the relative position and exposure of a set of notional rotor blades located at a given position downstream of the measurement plane [8].…”

Comparative evaluation of the efficiency of the ring-type and bucket inlet devicesfor a power plant with a turbopropfan engine

“…In [8], the influence of inlet conditions on the non-stationary aerodynamics of complex inlet devices by the method of a full-scale experiment was evaluated. That factor plays an important role in assessing the actual operation of the inlet device.…”