Dynamic Flow Distortion Investigation in an S-duct using DDES and SPIV data

Abstract

The dynamic flow distortion generated within convoluted aero-engine intakes can affect the performance and operability of the engine. There is a need for a better understanding of the main flow mechanisms which promote flow distortion at the exit of S-shaped intakes. This paper presents a detailed analysis of the main coherent structures in an S-duct flow field based on a Delayed Detached Eddy Simulation. The capability of this numerical approach to capture the characteristics of the highly unsteady flow field is demonstrated against high resolution, synchronous Stereoscopic Particle Image Velocimetry measurements at the Aerodynamic Interface Plane. The flow field mechanisms responsible for the main perturbations at the duct outlet are identified. Clockwise and counterclockwise stream-wise vortices are alternately generated around the separation region at a frequency of St=0.53, which promote the swirl switching at the duct outlet. Spanwise vortices are also shed from the separation region at a frequency of St=1.06, and convect downstream along the separated centreline shear layer. This results in a vertical modulation of the main loss region and a fluctuation of the velocity gradient between the high and low velocity flow at the Aerodynamic Interface Plane.

The impact of inlet boundary layer thickness on the unsteady aerodynamics of S-duct intakes

“…Few published research assessed the flow distortion for intakes under yaw and pitch angles [15]. Previous studies [23][24][25] used Time-Resolved Particle Image Velocimetry (TR-PIV) to measure the unsteady flow distortion characteristics at the exit plane of S-shaped aero-engine intakes. This non-intrusive experimental technique enables synchronous measurement of the 3-component velocity vector across a plane with spatial resolution up to two orders of magnitude higher than standard intrusive distortion measurement techniques [25].…”

An assessment on the unsteady flow distortion generated by an S-duct intake

“…The cameras featured a frame resolution of 1280 x 800 px (1MP) and a maximum straddle frame rate of 16,600 fps. The acquisition frequency is set at 4kHz, which is 10 times greater than dominant flow frequency that is around = 1.0 as predicted by the DDES simulations conducted by Gil-Prieto et al [21]. Each TR-PIV dataset consists of 20,000 instantaneous velocity snapshots, which are sufficient for the convergence of the out-of-plane velocity component and its standard deviation to within 0.2% and 0.4% respectively [17].…”

Unsteady flow phenomena in a highly bend engine intake with passive and active flow control

“…The simulations showed an unsteady vortex pattern in the side region of the duct. In the present literature Shear Layer Instabilities in S-ducts are assigned to Strouhal numbers between 0.6 ≤ Sr ≤ 1.06 (Gil-Prieto et al (2016). Differences are presented by the investigations of Garnier (2015), who assigns a relatively broadband Strouhal number range of 0.25 ≤ Sr ≤ 0.625 to the Shear Layer Instabilities in S-ducts.…”

“…The mechanism of this phenomenon was explained by the asymmetry of the separation area. Gil-Prieto et al (2016) presented the change from one dominant vortex to another in a time-resolved representation and analyzed the phenomenon of Swirl Switching in detail. Kalpakli Vester et al (2015) and Hellström et al (2013) investigated the phenomenon of Swirl-Switching on pipe elbows.…”