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Power effects aerodynamics for a regional turboprop

Periodic Reporting for period 2 - PERTURB (Power effects aerodynamics for a regional turboprop)

Reporting period: 2020-02-01 to 2020-12-31

Load Control Alleviation (LCA) in future regional turboprop aircraft designs will allow excessive gust and manoeuvre loads to be avoided, therefore enabling enhanced structural wing designs, eventually leading to considerable weight savings, lower fuel burn and reduced environmental impact. The PERTURB project is one of a series of projects in Clean Sky 2 which inform the flight demonstrator FTB2 in the Regional Aircraft domain. This demonstrator will evaluate new aerodynamic devices and concepts for LCA, which might appear on a future regional turboprop. PERTURB will use a combination of CFD and wind-tunnel testing to generate a trusted high-fidelity aerodynamic characterisation of both the propeller aerodynamics and the aircraft configuration aerodynamics in terms of propeller slipstream influence on wings, nacelles and flaps. As well as providing data to inform the flight trials of FTB2, PERTURB will also develop a methodology for determining accurate aerodynamic data in the future using combined CFD and wind-tunnel test data.
CFD-ready geometry has been created for the POLITE model for the cruise case. Meshes have been generated for the low-fidelity CFD simulations for both power-off and power-on (i.e. with actuator disk) for three Reynolds numbers, two relating to model scale at alternative wind-tunnel pressures and one relating to full scale. Actuator disk databases have been created using 2D RANS CFD applied to blade sections for both the full scale and model scale propeller. Blade setting angle to deliver a given propeller thrust has been calibrated using an isolated propeller setup for both model scale and full scale propellers. Using these blade setting angles, steady RANS CFD results have been computed for all cruise cases at M0.2.

CFD-ready geometry has been created for the POLITE model for the landing case, i.e. with double-slotted flap extended. A mesh for the low-fidelity CFD simulations for power-off is nearing completion.

A local mesh block for the full scale (aircraft) propeller has been generated. This has been embedded in the background airframe mesh (from the low-fidelity CFD) to form a Chimera/overlapping mesh. Automatic hole cutting of the background mesh by the propeller mesh block has been successfully tested for a complete propeller rotation. This mesh has been supplied to Bristol University for the URANS simulations.

The POLITE model has been tested in the ONERA F1 facility power-off. The full run matrix was completed. Wind-tunnel data was corrected for both strut tare and strut deformation effects, as planned. Post-test analysis has indicted that corrections are also necessary for strut blockage/interference and this was not expected. A correction process utilising historical data from a different test but with an almost identical strut is being investigated.
There are three main innovations in PERTURB:
> The coupling of a RANS capability with a Vortex Particle Method (VPM). This overall methodology, which gives superior modelling of vortices in a RANS context at little extra cost, was only conceived in the last three years and has only been demonstrated to date on very simple test cases. PERTURB will allow the methodology to be demonstrated on propeller tip vortices and flap-end vortices. It is judged that PERTURB will elevate the capability to TRL5-6.
> VFM for propeller modelling using CFD. Although Variable Fidelity Modelling has been used in simpler settings, it has not been used for installed propeller modelling. As using unsteady RANS for propeller simulation is very expensive, VFM will allow high-fidelity data at the URANS level to be generated at reduced cost, due to its combination with low-fidelity modelling using steady RANS with an actuator disk. There are good prospects for this type of process being integrated into future design studies.
> VFM for merging CFD and WTT data. The use of VFM as a tool for fusing together CFD and wind-tunnel test data will be demonstrated in the more complex setting of propeller aerodynamics. Prospects are for reduced costs of aerodynamic data generation and reduced uncertainty, and hence risk, in using data.
CFD cruise geometry for POLITE wind-tunnel model