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Inlet PArticle Separator Numerical ExperiMental Assessment

Periodic Reporting for period 3 - IPANEMA (Inlet PArticle Separator Numerical ExperiMental Assessment)

Reporting period: 2020-06-01 to 2022-02-28

IPANEMA aims at developing numerical and experimental techniques for the design of inertial particle separators (IPS) in turboprop engine intakes. IPS aim at removing dust, rain, hail, ... from the main air flow by deviating it abruptly before entering the engine, such that heavier ingested particles are expelled from the main flow to a small bypass duct as they cannot follow the flow. IPS have a lower impact on engine efficiency, and can moreover be deactivated during the flight. Therefore, IPS contribute to the efficiency of the aircraft. The experimental and numerical tools for analysis of and design for separation efficiency are to date still lacking in precision, in particular for accounting for the variability in particle size. To ensure the industrial applicability of the techniques, an actual IPS will be studied during the project.

On the experimental side, the difficulties concern the injection of particles in the rig and measuring separation performance in terms of particle size. One can mention also the combination of particle measurements with measuring aerodynamic performance due to the vulnerability of the probes. A last difficulty concerns the combined detailed measurement of particle tracks and flow field in a complex geometry. On the numerical side, no methods exist that combine sufficient accuracy to an acceptable cost. Highly versatile methods based upon Lagrange particle tracking and LES, are too expensive, while Eulerian RANS based methods used in industry typically do not account well for size variability, and/or are not calibrated for flow configurations prevalent in IPS. The aim is to develop a simulation approach which offers the best compromise between geometrical flexibility, precision and cost.

Although IPS have been studied before, research was mainly targeted at assessing performance of specific geometries, whereas no significant effort is dedicated to improving models. The experimental data is typically limited to global performance, while low-cost/precision simulation approaches are used. In order to alleviate the lack of high-quality and relevant reference data for model development and physical comprehension of flow conditions prevalent in IPS, IPANEMA will publish high-resolution experimental and numerical validation data on canonical geometries.

The main conclusions are
- novel experimental and numerical capabilities have been developed that allow for a detailed analysis of the flow and aerodynamic and particle separation efficiency for both industrial and academic configurations.
- the trajectory of the larger particles, which supposedly can be evacuated easily, is mainly governed by the collision with the walls. Their ingestion depends then on the presence of dead water regions and complex recirculations, which can pick up a stationary particle.
** Tool development **

Cenaero extended the solver ArgoDG to track particles in Large Eddy Simulations. The code was validated and tested up to scale, and provides a unique capability to perform fundamental and consultancy studies.

A dedicated test bench was developed at VKI. The bench features independent control of the mass flow over two outlets, corresponding to the main engine outlet and bypass. A particle injection system was developed to control finely particle injection rate, momentum and position. Finally, a specific outlet settling chamber was constructed for monitoring particle repartition according to particle size. This test bench has optical access for PIV and PTV.

Both activities were presented during the dedicated VKI Lecture Series “Particulate flows and separation technologies in industrial applications”, in May 2021

** Aerodynamic and separation efficiency assessment of the IPS **

A first focus concerned studies of the actual IPS. Initially two campaigns were foreseen: a first concerned a simple performance assessment, and the second a detailed study including flow visualization in a scaled down version with optical access. Finally, both campaigns were combined in order to allow a larger test matrix.

Extensive numerical studies were undertaken. A first activity aimed at designing a replacement for the confidential engine intake; this was finally abandoned. A second study was dedicated to a detailed investigation of the unsteady flow patterns in the current IPS, to improving post-processing routines, and to establish sensitivity to boundary conditions and turbulence model.

Due to these iterations, the definition of the test bench and the campaign has taken some time. After the finalization of a first test section in fall 2020, tests started. Unfortunately, the first test section was damaged during the campaign. As a result, a new model had to be constructed. In January 2021 the test campaign resumed, with a further reduced test matrix and finalized in december 2022.

** Reference database on a generic test section **

A second activity was the generation of a reference database for model development on a generic open test section, which reproduces typical flow patterns of an actual IPS. Its extruded geometry allows to reduce computational cost and simplify flow visualization. This section has been introduced in the same rig.

Due to the delays in the test campaign on the real geometry, these studies were only recently started. First separation efficiency tests have been undertaken at VKI, and LES studies by Cenaero. Both will continue beyond the project to complete and publish the open access database.

** Achievements **

An experimental test bed was developed for detailed studies of the flow in and characterization of global performance of IPS. It will allow both fundamental scientific research and industrial product development and assessment.

A Lagrangian particle tracking capability was added to a high order CFD, allowing very precise Large Eddy Simulations on industrial geometries, for both consultancy studies as well as fundamental research.

A detailed assessment of the aerodynamic performance and separation efficiency of an actual inertial particle separator was performed and numerical procedures revised;

An open academic test case, representing the main flow features in an industrial IPS, was designed and a test bench constructed. Currently detailed studies are underway to construct an open database.
During the project, the following novel and unique capabilities and data were developed:
- a particle injection device for precisely controlled particle injection in the duct of an IPS test bench. This is a prerequisite to provide detailed reference data, in casu trajectories in function of injection location and particle size.
- a test bench which allows to independently control the mass flow rate in the main exhaust (engine outlet) and the bypass, provides optical access to the separator section for PIV and PTV, and allows to quantify particle repartition over the outlets as function of particle size.
- a particle tracking capability in state of the art LES Code Argo, based upon the high order discontinuous Galerkin discretisation, allowing very accurate LES on industrial geometries.
- an open test case which is representative for the flow field and particle motion in an actual inertial particle separator.
- an open database of numerical and experimental reference data is currently being composed.
Velocity field in the generic test section computed by LES
Testbench layout for the 1:1 real engine component configuration