Fabrice Falissard

Aero-mechanical optimization of a contra-rotating open rotor and assessment of its aerodynamic and acoustic characteristics:

Within the frame of the ongoing 7th Framework European Project DREAM, this article presents a synthesis of Cenaero, DLR, and Oneras joint effort to demonstrate the aerodynamic and acoustic optimization potential of a contra-rotating open rotor. Within WP 3.2 led by Snecma, the objective was to maximize the propellers efficiency at top-of-climb conditions and to minimize the noise emission at take-off focusing on interaction noise while fulfilling the thrust and torque split specifications at both operating points. These objectives were successfully met by the development and exploitation of efficient multi-objective three-dimensional Reynolds-averaged Navier–Stokes (RANS)-based surrogate-assisted optimization strategies. In order to assess the aerodynamic and acoustic characteristics of both baseline and optimized geometries, coupled unsteady RANS (URANS) simulation and farfield prediction based on an integral Ffowcs Williams–Hawkings approach were then carried out. The results demonstrate that although the acoustic criterion driving the optimization process did not lead to an improvement of the noise characteristics over the whole directivity range, it may be regarded as a cost-effective way to incorporate noise-related aspects into the design intent.

Vorticity-preserving schemes for the compressible Euler equations

The concept of vorticity-preserving scheme introduced by Morton and Roe is considered for the system wave equation and extended to the linearised and full compressible Euler equations. Useful criteria are found for a general dissipative conservative scheme to be vorticity preserving. Using them, a residual-based scheme is shown to be vorticity preserving for the Euler equations, which is confirmed by vortex flow calculations.

Influence of Torque Ratio on Counter-Rotating Open-Rotor Interaction Noise

This paper investigates the influence of the torque ratio, at constant total thrust, on the interaction noise of a generic counter-rotating open rotor in pusher configuration. It is shown that torque ratio has a small influence on the open-rotor aerodynamic performance but a strong impact on interaction noise at takeoff condition. The noise source mechanisms are investigated in detail and linked with the characteristics of the front rotor blade-tip vortices. Tip vortex characteristics are detailed and compared with analytical vortex models. It is verified that torque ratio variation has no strong impact on the open-rotor aerodynamic performance at cruise condition.

Genuinely multi-dimensional explicit and implicit generalized Shapiro filters for weather forecasting, computational fluid dynamics and aeroacoustics

This paper addresses the extension of one-dimensional filters in two and three space dimensions. A new multi-dimensional extension is proposed for explicit and implicit generalized Shapiro filters. We introduce a definition of explicit and implicit generalized Shapiro filters that leads to very simple formulas for the analyses in two and three space dimensions. We show that many filters used for weather forecasting, high-order aerodynamic and aeroacoustic computations match the proposed definition. Consequently the new multi-dimensional extension can be easily implemented in existing solvers. The new multi-dimensional extension and the two commonly used methods are compared in terms of compactness, robustness, accuracy and computational cost. Benefits of the genuinely multi-dimensional extension are assessed for various computations using the compressible Euler equations.

Computation of Airfoil-Vortex Interaction Using a Vorticity-Preserving Scheme

We recently proved that a dissipative residual-based scheme of second-order accuracy is vorticity-preserving for the compressible Euler equations. In the present paper, this scheme is extended to curvilinear grids and applied to the computation of the interaction between a Scully vortex and a NACA0012 airfoil at a Mach number of 0.5. A grid convergence study and a comparison with a conventional scheme and with experimental measurements are presented. The new scheme shows a faster grid convergence, especially for the vortex trajectories and deformations during the interaction.

Computational Fluid Dynamics as a Support to Counter-Rotating Open-Rotor Wind-Tunnel Test Analysis

The rising price of oil since the early 21st century produced a regain of interest in the counter-rotating open rotor, seen as an economic propulsive device for future transport aircraft. Although simple methods are used for design and optimization, the need for advanced methods to assess aerodynamic and acoustic performance of a counter-rotating open rotor within a complex configuration and to support wind-tunnel tests analysis is rising. In this paper, a methodology for complex counter-rotating open-rotor installations is set up to compute an actual test-rig geometry using high performance computing capabilities of ONERA computational-fluid-dynamics software elsA. Comparing the numerical results with the wind-tunnel test data enables to assess both the computational-fluid-dynamics code accuracy and the representativity of the wind-tunnel test, which relies on a somewhat intrusive test rig through a better understanding of the flowfield around the test rig.

Numerical and Analytical Investigation of Orthogonal Blade/Vortex Interaction Noise

Fast prediction methods used for preliminary design or in optimization algorithms often rely on linear analytical models based on drastic simplifications of the physical problem to be solved. To be used with a reasonable confidence level, these models must be validated over either experimental data or data coming from numerical simulations. In this context, this paper presents a cross-comparison of the aeroacoustic response of an orthogonal blade/vortex interaction computed using a high-order CFD solver and an acoustic analogy with an analytical model recently developed for this specific problem. The general framework is the acoustic prediction of Counter-Rotating Open Rotors in the preliminary design stages. This work follows two objectives. The first one is to improve the understanding of the phenomena occurring during such an interaction through the mean of CFD. The second one is to characterize the current limitations of the analytical modeling to make recommendations for their improvement.

Uneven-order decentered Shapiro filters for boundary filtering

This paper addresses the use of Shapiro filters for boundary filtering. A new class of uneven-order decentered Shapiro filters is proposed and compared to classical Shapiro filters and even-order decentered Shapiro filters. The theoretical analysis shows that the proposed boundary filters are more accurate than the centered Shapiro filters and more robust than the even-order decentered boundary filters usable at the same distance to the boundary. The benefit of the new boundary filters is assessed for computations using the compressible Euler equations.

Chebyshev-like generalized Shapiro filters for high-accuracy flow computations

This paper presents Chebyshev-like generalized Shapiro (CS) filters with improved spectral-like resolution compared to existing generalized Shapiro filters. These new filters combine the advantages of Shapiro filters, i.e. arbitrary accuracy order, no-dispersion, full damping of 2-waves, and the advantages of Chebyshev filters, i.e. purely dissipative response function with equal ripples satisfying an arbitrary Chebyshev criterion in passband. Thanks to the formalism of generalized Shapiro filters, general formulas are derived for arbitrary accuracy orders and arbitrary Chebyshev criterion. A python script is provided in appendix to compute CS filter coefficients. Computations based on the Euler equations assess the benefit of CS filters compared to the standard Shapiro filters. Since CS filters differ from Shapiro filters only by their coefficients, they can easily and advantageously be implemented in computational solvers already making use of generalized Shapiro filters.

Aeroacoustic Study of the Interaction of a Rotating Blade with a Batchelor Vortex

The aeroacoustic response of the orthogonal interaction of a rotating blade with an isolated Batchelor vortex is studied by means of numerical simulation. The relative influence of the vortex tange...