Abstract
To fulfill the objective of a predictive tool for rotorcraft, comprehensive analysis (CA) needs to be capable of providing both accurate and time-efficient predictions of rotor air loads and structural loads. The more recent methodology based on comprehensive analysis coupled with high-fidelity computational fluid dynamics (CFD) has shown improved predictions of air loads, but it has not the strength of computational efficiency and the versatility of stand-alone CA. The present article is concerned with modeling aerodynamics about helicopter rotors for CA. The aerodynamics about rotors are very complex, encompassing subsonic to transonic flow with unsteady, stalled behavior and 3D effects. CA treats aerodynamics as separated into local and global flows. Semi-empirical models of dynamic stall were created in the 1970s–1990s for modeling unsteady local aerodynamics, including stalled flow. Most of them fail to provide good predictions of experimental results and also suffer problems of numerical convergence. The main effort in this study is about modeling local aerodynamics based on the revised “ONERA–Hopf bifurcation model”. It is implemented in the comprehensive analysis code of ONERA according to a scheme that ensures numerical convergence. The experimental results obtained in the Wind Tunnel S1 of Modane (France) in 1991 on the Rotor 7A are considered for validation of the analysis under three flight test conditions: high-speed test, high-thrust tests with light stall and deep stall, respectively. There is a reasonable agreement between the predictions of CA with experimental results. The distinct features of the stall model are the modeling of the boundary-layer effects and the vortex-shedding phenomenon.
Highlights
To fulfill the objective of a predictive tool for rotorcraft, comprehensive analysis (CA) needs to be capable of providing both accurate and time-efficient predictions of rotor air loads
The detailed aspects of the dynamic stall model are not described in this article; they can be found in the previous publication [9]; only the revised part is discussed thoroughly
To attain reasonable agreement of the predictions of the comprehensive analysis with experiments on the Rotor 7A, various issues have been solved at two different levels, physics modeling of aerodynamics for capturing the dynamic stall phenomenon and 3D effects and code implementation for ensuring numerical convergence: 1
Summary
To fulfill the objective of a predictive tool for rotorcraft, comprehensive analysis (CA) needs to be capable of providing both accurate and time-efficient predictions of rotor air loads. Aerospace 2017, 4, 21 the case of the UH-60A in the stalled regime [10] Applied to another stalled test in a wind tunnel [11], most dynamic stall models suffered problems of numerical convergence. There are two levels of difficulties for semi-empirical models: providing good physics description of aerodynamics and ensuring numerical convergence when implemented in comprehensive analysis codes. The computations are done mainly with the comprehensive analysis code ROTOR of ONERA [12] equipped with the revised dynamic stall model. The numerical implementation of the dynamic stall model in the comprehensive analysis code of ONERA is described. The application of the comprehensive analysis code equipped with the dynamic stall model is made for three different test points of the Rotor 7A.
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