High-Fidelity Computational Aeroacoustics Through CE/SE Based Transient Viscous Solver (original) (raw)
Related papers
Computers & Fluids, 2022
In this work, we address the finite element computation of flow noise in the presence of arbitrarily slowly moving rigid bodies at low Mach numbers, by means of hybrid and direct computational aeroacoustics (CAA) strategies. As regards the former, the problem could be dealt with by means of the Ffowcs Williams-Hawkings acoustic analogy. That reduces to Curle's analogy for a static body, which is analogous to a problem of diffraction of sound waves generated by flow eddies in the vicinity of the body. Acoustic analogies in CAA first demand computing the flow motion to extract an acoustic source term from it and then use the latter to calculate the acoustic pressure field. However, in the case of low Mach number flows, the Ffowcs Williams-Hawkings and Curle analogies present a problem as they require knowing the total pressure distribution on the body's boundary (i.e. the aerodynamic pressure plus the acoustic one). As incompressible computational fluid dynamics (CFD) simulations are usually performed to determine the flow motion, the acoustic pressure distribution on the body surface is unavoidably missing, which can yield acoustic analogies inaccurate. In a recent work, it was proposed to tackle that problem for static and rigid surfaces, by keeping the incompressible CFD and then splitting the acoustic pressure into direct and diffracted components. Two separate wave equations were solved for them, in the framework of the finite element method (FEM). In this article, we extend that work to compute the aerodynamic sound generated by a flow interacting with a slowly moving rigid body. The incompressible Navier-Stokes equations are first solved in an arbitrary Lagrangian-Eulerian (ALE) frame of reference to obtain the acoustic source term. Advantage is then taken from the same computational run to separately solve two acoustic ALE wave equations in mixed form for the incident and diffracted acoustic pressure components. For validation of the total acoustic pressure field, an ALE formulation of a direct CAA approach consisting of a unified solver for a compressible isentropic flow in primitive variables is considered. The performance of the exposed methods is illustrated for the aeroacoustics of flow past a slowly oscillating two-dimensional NACA airfoil and for flow exiting a duct with a moving teeth-shaped obstacle at its termination.
Challenges for Time and Frequency Domain Aeroacoustic Solvers
The linearized Euler equations (LEE) model acoustic propagation in the presence of rotational mean flows. They can be solved in time [1-3] or in frequency [4-6] domain, with both approaches having advantages and disadvantages. Here, those pros and cons are detailed, both from a modeling and a numerical/computational perspective. Furthermore, a performance comparison and cross-validation between two frequency and time domain state-of-the-art solvers is performed. The frequency domain solutions are obtained with the hybridizable discontinuous Galerkin (HDG) [7-12] and the embedded discontinuous Galerkin (EDG) [13-15] method, while the time domain solver is an explicit discontinuous-Galerkin based solver [1]. The performance comparison and cross-validation is performed on a problem of industrial interest, namely acoustic propagation from a duct exhaust in the presence of realistic mean flow.
Advances in computational aeroacoustics: challenges and issues
Needs of accurate and efficient numerical solvers in computational aeroacoustics have motivated the development of low-dispersion and low-dissipation schemes as an alternative to more classical methods of applied mathematics for computational fluid mechanics over the last two decades. These numerical methods have now reached maturity, even if progress is still necessary to take account of specific physics. The paper provides a short overview of some recent developments and applications involving these topics, and is organized as follows. Motivations and numerical advances are considered, but the main part of this synthesis focuses on the use of these simulations to improve our understanding of noise generation by turbulent flows. Applications to subsonic and supersonic jet noise, cavity noise and self-excited internal flows are thus presented.
Computational aeroacoustics: progress on nonlinear problems of sound generation
Progress in Aerospace Sciences, 2004
Computational approaches are being developed to study a range of problems in aeroacoustics. These aeroacoustic problems may be classified based on the physical processes responsible for the sound radiation, and range from linear problems of radiation, refraction, and scattering in known base flows or by solid bodies, to sound generation by turbulence. In this article, we focus mainly on the challenges and successes associated with numerically simulating sound generation by turbulent flows.
Comparison of outflow boundary conditions for subsonic aeroacoustic simulations
2012
Aeroacoustics simulations require much more precise boundary conditions than classical aerodynamics. Two classes of non-reflecting boundary conditions for aeroacoustics are compared in the present work: characteristic analysis based methods and Tam and Dong approach. In characteristic methods, waves are identified and manipulated at the boundaries while Tam and Dong use modified linearized Euler equations in a buffer zone near outlets to mimic a non-reflecting boundary. The principles of both approaches are recalled and recent characteristic methods incorporating the treatment of transverse terms are discussed. Three characteristic techniques (the original NSCBC formulation of Poinsot and Lele and two versions of the modified method of Yoo and Im) are compared to the Tam and Dong method for four typical aeroacoustics problems: vortex convection on a uniform flow, vortex convection on a shear flow, acoustic propagation from a monopole and from a dipole. Results demonstrate that the Tam and Dong method generally provides the best results and is a serious alternative solution to characteristic methods even though its implementation might require more care than usual NSCBC approaches.
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
Computing sound directly from unsteady flows featuring large-scale instabilities requires numerical methods that can resolve the small amplitude perturbations of sound embedded in the large-amplitude hydrodynamic flow unsteadiness. The perturbations due to sound need to be propagated with an acceptable dispersion and dissipation over significant distances to adequately resolve in space the noise near field. In this paper, a high-order compact scheme is detailed that promise to deliver the small dispersion and dissipation characteristics to directly model the noise and the unsteadiness in low Mach number flows. The performance of the scheme is assessed by cross-comparison against selected benchmark problems from the first workshop on benchmark problems in Computational Aeroacoustics (CAA) and additional test cases, including the reflection of an acoustic pulse into a corner, which is a challenging application due to the confluence of two wall conditions at the corner. Analytical solutions for the test cases are also produced to validate the predictions. The numerical results show that the scheme achieves comparable performances in computing these relatively simple two-dimensional test problems, with levels of dispersion and dissipation comparable to that in the published literature from similar computational aeroacoustic schemes. The results give confidence in developing these scheme to tackle more complex, three-dimensional noise producing flows, of interest for practical engineering applications.
Computational aeroacoustics: issues and methods
AIAA journal, 1995
Computational fluid dynamics (CFD) has made tremendous progress especially in aerodynamics and aircraft design over the past 20 years. An obvious question to ask is "why not use CFD methods to solve aeroacoustics problems?" Most aerodynamics problems are time independent, whereas aeroacoustics problems are, by definition, time dependent. The nature, characteristics, and objectives of aeroacoustics problems are also quite different from the commonly encountered CFD problems. There are computational issues that are unique to aeroacoustics. For these reasons computational aeroacoustics requires somewhat independent thinking and development. The objectives of this paper are twofold. First, issues pertinent to aeroacoustics that may or may not be relevant to computational aerodynamics are discussed. The second objective is to review computational methods developed recently that are designed especially for computational aeroacoustics applications. Some of the computational methods to be reviewed are quite different from traditional CFD methods. They should be of interest to the CFD and fluid dynamics communities.
Large Eddy Simulations of Supersonic Jet Flows for Aeroacoustic Applications
33rd AIAA Applied Aerodynamics Conference, 2015
Current design constraints have encouraged the studies of aeroacoustics fields around compressible jet flows. The present work addresses the numerical study of unsteady turbulent jet flows for aeroacoustic analyses of main engine rocket plumes. A novel large eddy simulation (LES) tool is developed in order to reproduce high fidelity results of compressible jet flows which could be used for aeroacoustic studies with the Ffowcs Williams and Hawkings approach. The numerical solver is an upgrade of an existing Reynolds-averaged Navier-Stokes solver previously developed in the group. The original framework is rewritten in a modern fashion and intensive parallel computation capabilities have been added to the code. The LES formulation is written using the finite difference approach. The energy equation is carefully discretized in order to model the energy equation of the filtered Navier-Stokes formulation. The classical Smagorinsky model is the chosen subgrid scale closure for the present work. Numerical simulations of perfectly expanded jets are performed and compared with the literature in order to validate the new solver. Moreover, speedup and the computational performance of the code are evaluated and discussed. Flow results are used for an initial evaluation of the noise radiated from the rocket plume.
ICASE/LaRC Workshop on Benchmark Problems in Computational Aeroacoustics (CAA)
1995
This volume contains the proceedings of the ICASE/LaRC Workshop on Benchmark Problems in Computational Aeroacoustics (CAA). CAA is a relatively new area of research addressing issues relevant to the acoustic propagation of sound generated by fluid flow. Advances in computer technology make addressing these issues in a more detailed manner a possibility. Such advances allow the treatment of the fully nonlinear propagation problem as well as the direct computation of the acoustic sources, the sound generation problem. These possibilities are expected to benefit both the validation of models that have been developed as well as help develop better models for more complex flows. In situations where calculations are not prohibitively expensive a direct computation of the acoustic and source fields becomes possible. When research in this area was first considered several technical challenges were apparent. The intention of these proceedings is to more fully investigate a subset of these numerical issues and make some progress in their resolution. These issues include: 1. The small magnitude of the acoustical quantities of interest and the need to distinguish and extract them from the larger background fields. 2. The sensitive dependence of the acoustical field on phase, dissipation and dispersion when propagated over large spatial distances. 3. The potentially higher frequencies of the quantities of interest in comparison to those of interest in the problems more typically addressed in unsteady aerodynamics or structural vibrations. 4. For the computation of acoustical spectra long time solutions are necessary for computing averages; numerical codes are required to be stable and accurate for long time integrations. 5. Many codes are designed for stationary problems in which the path of approach to the asymptotic solution is not important (except from the viewpoint of cost). These schemes are potentially inadequate for aeroacoustical problems in which time accurate computations are required. The dissipation, dispersion, and anisotropic biases in these schemes are now very relevant to the aeroacoustical problems of interest. 6. Time dependent boundary conditions are also required which will not reflect acoustic waves from imposed computational boundaries yet reflect acoustic waves properly from real physical boundaries. 0 5 x 5 100, 0 < r < 100. The wall and the piston are at x = 0. The cylindrical coordinate system is centered at the center of the piston. With axisymmetry, the linearized Euler equations are The initial conditions are: t = O p = u = v = p = O 1 1 3 Give the time harmonic pressure distribution at the beginning,-andof a period of 4 ' 2 4 piston oscillation. Category 5 Problem to test the suitability of a numerical scheme for direct numerical simulation of very small amplitude acoustic waves superimposed on a non-uniform mean flows in a semi-infinite duct. Use nondimensional variables with the following scales Ax = length scale a, (sound speed far upstream) = velocity scale Ax-= time scale a00 p, (density of gas upstream) = density scale ,o,a2, = pressure scale A small amplitude sound wave is incident on a convergent-divergent nozzle as shown c M=0.5
The Technique of MIEELDLD in Computational Aeroacoustics
Journal of Applied Mathematics, 2012
The numerical simulation of aeroacoustic phenomena requires high-order accurate numerical schemes with low dispersion and low dissipation errors. A technique has recently been devised in a Computational Fluid Dynamics framework which enables optimal parameters to be chosen so as to better control the grade and balance of dispersion and dissipation in numerical schemes (Appadu and Dauhoo, 2011; Appadu, 2012a; Appadu, 2012b; Appadu, 2012c). This technique has been baptised as the Minimized Integrated Exponential Error for Low Dispersion and Low Dissipation (MIEELDLD) and has successfully been applied to numerical schemes discretising the 1-D, 2-D, and 3-D advection equations. In this paper, we extend the technique of MIEELDLD to the field of computational aeroacoustics and have been able to construct high-order methods with Low Dispersion and Low Dissipation properties which approximate the 1-D linear advection equation. Modifications to the spatial discretization schemes designed by ...