Development of an Inertial Particle Separator Test Facility for Air-breathing Aircraft Systems
Creators: name:  J.L. HEE 
name:   N. BOJDO 
name:   M. QUINN 
name:   A. FILIPPONE 
name:   O. OZER 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLOW CONTROL
AEROSPACE

description: An inertial particle separator is a device fitted to the intakes of air-breathing engines to remove foreign object debris, dust particles, and water droplets. Their primary aim is to clean the inbound air in order to protect the rotating turbo-machinery from premature damage. They are commonly found on helicopters and short take-off military turboprop aircraft, and work by forcing particle-laden air around a bend before bifurcating the flow into clean (core) and dirty (scavenge) channels [1]. An EU Horizon 2020 innovative project called A New Technology Innovation for Foreign Object Debris removal (ANTIFOD) has been established to develop a prototype of an intake protection system for the turbo-compressor of a more-electric aircraft air management system. In such an architecture, the air used for cabin pressurisation is taken directly from the atmosphere external to the aircraft, mitigating the need to bleed air off the turbofan engine compressor stage; hence improving the overall efficiency and reducing fuel burn. However, removing the turbofan and several stages of compressor from the pathway of fresh air to the cabin, leaves the replacement compression system vulnerable to erosion, corrosion, and structural damage by ingested particulates, water and foreign object debris, severely shortening its working life. The major challenge of this project is to develop a protection system that extends the turbo-compressor maintenance intervals to reasonable levels within a strict pressure loss budget, and across a wide range of atmospheric conditions. The design requirements are quite unique in comparison to prior art, thereby necessitating a fresh approach to particle separator design. To enable the necessary investigations, we have developed a new facility for testing particle separators of this scale and application. The paper discusses the design of an experimental rig whose test section is a scaled two-dimensional planar particle separator geometry which was designed to permit full optical access for flow visualisation and two-phase particle image velocimetry studies. The 1:2 scale rig, shown in Figure 1, has been sized to replicate duct Reynolds numbers of the full-scale geometry at the key operating points. The test section housing is designed to accommodate other multi-channel IPS configurations, and facilitate investigations of span-wise flow on particle separation through the use of an aluminium-perspex layered configuration. We discuss the reasoning for geometric scaling, sizing of centrifugal pumps and filters, flow control and metering as well as data acquisition systems. Within this contribution we present the capabilities of the facility, demonstrated using a well-characterised geometry from the literature [2] (inset, Figure 1). Rig characteristic data, shown in Figure 2, shows the range of inlet Reynolds numbers and scavenge mass flow proportions that the rig is capable of achieving. The dataset was created by systematically adjusting a set of sleeves to alter the amount of air bled into the perforated pipe. This causes a change in the suction in each leg of the separator, thereby modifying the share of inlet mass flow into the core and scavenge channels (known as the split flow parameter, ?), and the inlet Reynolds number as characterised by hydraulic diameter. In Figure 2a we show the range of attainable ? values, which narrows with increasing flow rate, as ? tends towards the area ratio of the scavenge and core outlet areas (1:4) at the suction source. At a corrected mass flow rate of 0.17 kg/s, the split flow parameter rapidly increases. This indicates a breakdown of the flow within the separator, caused by an adverse pressure gradient around the surface of the separation hump, leading to a greater proportion of flow entering the scavenge leg, rather than the core. This is demonstrated in Figure 2b, which shows a large rise in core pressure loss at an inlet Reynolds number of around 110,000, followed by a plateauing of the core pressure drop and a greater sensitivity to ?. We conclude the paper with some examples of the flow diagnostic techniques available for validating numerical simulations, including Particle Image Velocimetry (PIV). We demonstrate the benefit of the layered configuration in capturing 3-dimensional flow features, but also discuss practical drawbacks we encountered. Finally, we shown preliminary results of a particle shadow-based imaging system capable of capturing particle velocity, size and shape at primary bounce locations, which may be used to obtain restitution coefficient data for implementation in numerical simulations.