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Please use this identifier to cite or link to this item: http://dspace.dsto.defence.gov.au/dspace/handle/dsto/10520

Title: Development of Virtual Blade Model for Modelling Helicopter Rotor Downwash in OpenFOAM.
Report number: DSTO-TR-2931
AR number: AR-015-836
Classification: Unclassified
Report type: Technical Report
Authors: Wahono, S.
Issue Date: 2013-12
Division: Aerospace Division
Abbreviation: AD
Release authority: Chief, Aerospace Division
Task sponsor: Commander AOSG
Task number: 07/225
File number: 2013/1020983/1
Pages or format: 188
References: 26
DSTORL/DEFTEST terms: Computational fluid dynamics
Helicopter rotors
Infrared signatures
Other descriptors: CFD
Rotor downwash
Blade element
OpenFOAM
ANSYS Fluent
Abstract: This report documents the development of a computational model to simulate the complex flow induced by helicopter rotors, using an open-source computational fluid dynamics (CFD) code, OpenFOAM™. This computational code is now being used to perform large-scale multiphysics simulations of the flow field around helicopters including exhaust plumes and their airframe impingement. The rotor downwash model was validated against available experimental data on rotor-fuselage interactions published by the Georgia Institute of Technology. The OpenFOAM predicted result was also shown to compare favourably with ANSYS Fluent predictions.
Executive summary: The Infrared Signatures and Aerothermodynamics (IRSA) group within DSTO is tasked with providing measurement-validated infrared signature models of air vehicles to the Australian Defence Force (ADF).
In general, both fixed and rotary-wing aircraft will exhibit a significant area of unobscured hot exhaust surface. For such aircraft, the infrared signature is dominated by direct emissions from these unobscured hot surfaces, while the signature contribution from surface reflections and plume emissions can largely be neglected without great loss of accuracy. However, for low-observable aircraft, like helicopters fitted with infrared suppressors, a lack of observable exhaust surfaces means that this simplification does not apply. Infrared-suppressed helicopters are becoming increasingly important to the ADF and an understanding of their infrared signature requires a much more comprehensive understanding of their associated air and exhaust flows.
Infrared suppression systems principally function by denying direct line-of-sight to hot engine exhaust surfaces at tactically critical viewing aspects. Consequently, aircraft fitted with infrared suppression systems have signatures which are dominated by exhaust plume emissions, emissions from airframe surfaces incidentally heated by exhaust impingement and indirect reflections of directly obscured hot surfaces on rotor blades, wings, cavities, etc. In the case of a suppressed helicopter, the ability to model the complex interaction between the hot engine exhaust plume and the rotor downwash is essential to the prediction of its infrared signature. Downwash-plumecrosswind interaction determines the magnitude and disposition of volumetric exhaust gas emission and localised surface emission due to plume impingement.
This report documents the development of a computational model to simulate the complex flow induced by helicopter rotors, using an open-source computational fluid dynamics (CFD) code, OpenFOAM™. This computational code is now being used to perform large-scale multi-physics simulations of the flow field around helicopters including exhaust plumes and their airframe impingement. These simulations exploit the benefit of combining free open-source software with historically inexpensive computer cluster hardware performance to accurately model the signatures of lowobservable aircraft.
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