Yves Detandt

A comparison between the effects of Turbulent and Acoustic wall pressure fluctuations inside a car

The turbulent ow outside a rolling car induces acoustic and turbulent wall pressure uctuations on the windows, doors, windshield and roof. By combining a Computational Fluid Dynamics (CFD) with a speci c computational vibro-acoustic strategy, it is possible to predict the transmission of this noise into the car compartment. In this paper, a side window of a production car is considered. The vibro-acoustic model contains the details of the window including the sealing, the glass and a realistic representation of the trimmed car cavity. Existing unsteady CFD results are used to feed the vibro-acoustic computations. The nal acoustic results are compared with measured data up to 4 kHz, and the relative importance of the turbulent and acoustic wall pressure sources is assessed.

Analysis of the noise source interpolation within a hybrid CAA method: application to the case of the Helmholtz resonator

This contribution reports on investigations to validate a computational aeroacoustics methodology. An acoustic analogy is adopted in which the Cenaero flow solver Argo is coupled to the commercial acoustic solver Actran/LA that uses a variational formulation of the Lighthill analogy. Two approaches to transfer noise sources from the fluid dynamics mesh to the acoustic mesh are studied. The first approach is based on a linear interpolation of the acoustic sources. Although this method ensures a second order accuracy, the conservation of the source term integral from one mesh to another is not fulfilled. Previous work shows that this leads to requirements on the acoustic mesh resolution in the source region that are more severe than those to properly propagate the acoustic waves. The second approach, newly developed by Free Field Technologies, is designed to enforce the conservation of the integral of the source term so that no particular mesh refinement is required in the source region, leaving the propagation as the only criterion to design the acoustic mesh. Both approaches are compared for the computation of the noise radiated by a Helmholtz resonator placed in a duct.

Performance improvements and new solution strategies of Actran/TM for nacelle simulations

Following two papers , new advances now allow reaching higher frequencies within a smaller amount of time. The Finite Element Code whose performance is benchmarked in this paper is a specific software dedicated to solve the acoustic propagation and radiation of turbo machinery noise. The code allows the injection of duct modes representing the turbo machinery noise, and computes their propagation and free field radiation in presence of a non-uniform mean flow. The modal duct basis enables the handling of reflected modes. In addition, acoustic treatments in the presence of a mean flow are accurately accounted for using the classical Myers Boundary Condition. Such treatments can be represented using admittance boundary conditions, or alternatively using transfer admittances to couple with treated back cavities as done for non-locally reacting acoustic treatments. The code has been already presented and validated against theoretical results , and against measurements acquired in fan rigs or detected on a real engine during ground tests. This paper presents the improvements and different acoustic solution strategies improving the performance of such computations. All improvements and solution strategies are demonstrated on a representative model of a nacelle intake including acoustic treatment and in realistic flow conditions (approach). All improvements are shown while insuring a constant or comparable accuracy. The performance improvements concern both the code and the computational input (mesh type, interpolation order, ). This paper is divided into 3 sections. The first section reviews the influence on the existing solution of different meshing strategies (linear versus quadratic elements, usage of hybrid meshes). Both the influences on the accuracy of the results as on the performance improvements are assessed. The second section reviews different performance improvements brought to the computational software without affecting the accuracy of the results. The last section reviews the new implemented solution strategies and their influence both on accuracy and performance. During the last 3 years and in particular in the context of the development of Actran 15, many different alternatives have been implemented in order to improve the global efficiency of the computations. The integration of the MKL PARDISO solver offers an interesting alternative to the MUMPS solver. The difference in terms of memory consumption, scalability and performance between the two solvers will be assessed. This MKL PARDISO solver is currently not available using MPI parallelism, but offers an interesting multithreading capability that is compared with the matrix parallelism capability of the MUMPS solver. The efficiency of the matrix parallelism available with the MUMPS implementation will be compared using different strategies, such as centralized versus distributed matrix analysis or using different reordering tools. The influence of the different reordering tools used by both algebraic solvers on memory consumption and efficiency will be compared. The integration of new BLAS libraries used by the different algebraic solvers and their efficiency in multithreaded computations on different architectures will be evaluated. Finally, different performance improvements brought on matrix assembly will be evaluated in comparison with previous revisions.

Direct numerical simulation of bubbly Taylor-Couette flow

Taylor-Couette flow is a typical research target for investigating the fluid mechanical phenomena in shear flows. It features the flow of an incompressible, viscous fluid contained in the gap between two concentric cylinders at low Reynolds numbers (see references [1] and [2]). The Couette apparatus has originally been developed for measuring the viscosity of a fluid at small imposed angular velocities of the cylinders. A simple sketch of the test case geometry is shown in figure 1.

A kinetic energy-preserving P1 iso P2/P1 finite-element method for computing unsteady incompressible flows

Numerical experience with Direct Numerical and Large Eddy Simulations (DNS, LES) of incompressible turbulenth flows consistently shows that central schemes are to be preferred to stabilized methods [1, 2, 3, 4]. The turbulence community has therefore put forth considerable effort to develop central schemes that preserve the discrete kinetic energy (KE) in the inviscid limit, which guarantees numerical stability. Designing KE preserving finitedifference and finite-volume (FD,FV) schemes is not trivial, in particular for higher orders and on irregular meshes [5, 6].

Direct numerical simulation of Taylor-Couette flows in the fully turbulent regime

In the present paper, we perform a numerical analysis of the turbulent flow between co-axial cylinders. We consider that only the inner cylinder rotates (angular velocity ω) while the outer one is at rest.

Jet flow aeroacoustics at Re=14000 Comparison between experimental and numerical simulations

For low Mach numbers, far field noise can be computed using an hybrid method. The equivalent sound source terms are computed using an unsteady incompressible flow solution supplied by a code dedicated to flow in axisymmetric geometries. Turbulence model’s influence are evaluated on hydrodynamic and sound source by comparison with experimental data. The numerical solution do not satisfy conservation principles like kinetic energy or impulse preservation. The present paper evaluates the importance of these defects on the predicted sound source and reports the robustness of dierent analgies against nonconservation of kinetic energy and impulse. The results illustrate the influence of numerical solution’s defects on sound predictions.

Aero‐acoustic predictions of automotive dashboard HVAC (heating, ventilating, and air‐conditioning ducts).

The flow‐induced noise generated by automotive climate control systems is today emerging as one of the main noise sources in a vehicle interior. Numerical simulation offers a good way to analyze these mechanisms and to identify the aerodynamic noise sources in an industrial context driven by permanent reduction in programs timing and development costs, implying no physical prototype of ducts before serial tooling. This paper focuses on a numerical aeroacoustic study of automotive instrument panel ducts to estimate the sound produced by the turbulent flow. The methodology is the following: the unsteady‐flow field is first computed using a CFD solver—here FLUENT. Then, the acoustic finite element solver ACTRAN computes the acoustic sound sources from these time domain CFD results. The sources are finally propagated into the vehicle interior in the frequency domain. One advantage of the technique is that the CFD computations are completely separated from the acoustic computations. This allows reusing one CFD...