Novel Method for Evaluating Intake Unsteady Flow Distortion

Abstract

Closer integration between the airframe and the propulsion system is expected for future aircraft to reduce fuel consumption, emissions, weight and drag. The use of embedded or partially embedded propulsion systems will require the use of complex intakes. However, this can result in unsteady flow distortion which can adversely affect the propulsion system efficiency and stability. Relative to conventional measurement systems, time-resolved Particle Image Velocimetry provides sufficient spatial and temporal resolution to enable the development of new methods to assess unsteady flow distortion. This work proposes a novel analysis approach to assess the unsteady flow distortion. For an S-duct configuration, the method was successfully used to evaluate the unsteady flow distortion in terms of idealized incidence angle perturbations. This example showed peaks up to ± 30° incidence and a duration equivalent to the passing time of 3 blades. The introduction of a non-uniform total pressure profile at the S-duct inlet increased the probability of peak distortion events with higher magnitude. The method provides an estimate of the likelihood, magnitude and duration of distortion events and is a new way to evaluate flow distortion that could induce instabilities for the propulsion system.

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

“…al. [8] introduced a novel method to evaluate the distortion in the relative frame of reference of compressor blades. This represents a notable step forward for the dynamic distortion characterization, as suggesting that the characteristic signature of the flow distortion perceived by the propulsion system would also depend on the rotational speed of the blades through the unsteady distorted flow field.…”

“…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.…”

“…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]. The velocity maps measured at the aerodynamic interface plane were converted into the relative frame of reference of a representative transonic compressor fan (NASA Rotor 67).…”

“…al. [8] focused on the signature of the incidence angle fluctuations at only discrete radial locations. Nevertheless, it was shown that distortion events affected the full blade span and, consequently, the distribution of the incidence perturbation on the blade could generate a synchronous positive or negative change of incidence across the full blade or instead, it could generate distortions with positive incidence perturbation at the root while negative at the tip of the blade.…”

Design of a high-speed intake distortion simulator for propulsion integration research

“…These measurement techniques would also be difficult to apply to full-scale engine tests without previous substantial derisking of the measurement techniques. Such techniques include non-intrusive, optical velocimetry methods such as Particle Image Velocimetry which are already demonstrated in sub-sonic configurations for dynamic distortion measurements (McLelland et al [7], Migliorini et al [8] and Doll et al [9]). In addition, a scaled-down rig configuration would also enable the application of methods that can eventually offer high-resolution, rich datasets to characterise the supersonic intake entry such as dynamic pressure sensitive paint or high-speed shadowgraph techniques.…”