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This paper investigates the effects of surface roughness on the flow past a circular cylinder at subcritical to transcritical Reynolds numbers. Large eddy simulations of the flow for sand grain roughness of size k/D = 0.02 are performed (D is the cylinder diameter). Results show that surface roughness triggers the transition to turbulence in the boundary layer at all Reynolds numbers, thus leading to an early separation caused by the increased momentum deficit, especially at transcritical Reynolds numbers. Even at subcritical Reynolds numbers, boundary layer instabilities are triggered in the roughness sublayer and eventually lead to the transition to turbulence. The early separation at transcritical Reynolds numbers leads to a wake topology similar to that of the subcritical regime, resulting in an increased drag coefficient and lower Strouhal number. Turbulent statistics in the wake are also affected by roughness; the Reynolds stresses are larger due to the increased turbulent kinetic energy production in the boundary layer and separated shear layers close to the cylinder shoulders., We acknowledge “Red Española de Surpercomputación” (RES) for awarding us access to the MareNostrum III machine based in Barcelona, Spain (Ref. FI-2015-2-0026 and FI-2015-3-0011). We also acknowledge PRACE for awarding us access to Fermi and Marconi Supercomputers at Cineca, Italy (Ref. 2015133120). Oriol Lehmkuhl acknowledges a PDJ 2014 Grant by AGAUR (Generalitat de Catalunya). Ugo Piomelli acknowledges the support of the Natural Sciences and Engineering Research Council (NSERC) of Canada under the Discovery Grant Programme (Grant No. RGPIN-2016-04391). Ricard Borrell acknowledges a Juan de la Cierva postdoctoral grant (IJCI-2014-21034). Ivette Rodriguez, Oriol Lehmkuhl, Ricard Borrell and Assensi Oliva acknowledge Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ref. ENE2014-60577-R)., Peer Reviewed, Postprint (author's final draft)

This paper aims at studying numerically the flow of a fluid through reed type valves, which are generally used in some reciprocating compressors and engines. The analysis and design of these valves serve not only to improve the performance of filling or discharging, but also to ensure system reliability. The valve opening-closing process involves fluid dynamics and deformation of a flat plate structure, both physics being completely coupled. To overcome this and other kind of fluid-structure interaction (FSI) problems, an in-house CFD-CSD (Computational Fluid Dynamics-Computational Structural Dynamics) coupled solver has been implemented within TermoFluids code. The CFD solver consists of a three dimensional explicit finite volume fractional step algorithm formulated in a second order, conservative and collocated unstructured grid arrangement. Since this case involves a turbulent flow, the wall adapting local eddy viscosity (WALE) model is employed. In order to save considerable effort in time and cost, the normal mode summation method is used to solve the deformation of the elastic valve. The geometric interaction between both dynamically moving media is managed with a fluid deformable mesh with moving boundaries, which belong to the solid valve. The static bodies, such as the walls, are embedded into the fluid mesh thanks to the immerse boundary method. The ‘CFD - Moving Mesh’ coupling is built by means of the space conservation law. From the point of view CFD-CSD coupling, a partitioned algorithm is used. For each time step, fluid and solid are solved consecutively until fluid pressure on the interface and displacements of the structure converge. In fact, only the Poisson equation for the fluid pressure ought to be coupled with the structure solver. Thus, grid updates and predicted fluid velocity calculation are solved only once at the beginning of the time step. First of all, the simulation platform is validated reproducing a benchmark FSI case from the lite

The aim of this paper is to present a group of numerical experiments of the fluid flow through different suction mufflers geometries to analyse pressure and velocity behaviour in addition with acoustic pressure effect. The numerical results are oriented to compare how suction muffler geometry affects mas flow rate and compressor efficiency performance on one side and pressure pulsations, transmission losses and compressor noise on the other side (1). The CFD&HT results have been obtained by means of TermoFluids code, a new unstructured and parallel object-oriented CFD&HT code for accurate and reliable solving of industrial flows (2). In all studied cases a multi-dimensional explicit finite volume fractional-step based algorithm has been used with symmetry preserving discretization scheme. When turbulence modelling is needed, an extension of the Yoshizawa non-equilibrium fixed-parameter subgrid-scale (3) model to non-structured meshes is used. The pressure equation is solved by means of parallel Fourier Schur decomposition solver, which is an efficient direct solver for loosely coupled PC clusters (4). Different CFD analysis of compressor suction mufflers has been developed (5) mainly based on k-e RANS models. The present paper is oriented on Large Eddy Simulation (LES) models. On the other hand, boundary conditions are coupled with a modular, unstructured and object oriented tool of the numerical simulation of hermetic reciprocating compressors (6)(7). (1) W. Soedel, Mechanics, simulation and design of compressor valves, gas passages and pulsation mufflers, Purdue University, 1992. (2) O. Lehmkuhl, R. Borrell, C.D.Pérez-Segarra, M. Soria, A. Oliva, A new parallel unstructured CFD code for the simulation of turbulent industrial problems on low cost PC cluster, Parallel Computational Fluid Dynamics, Ankara, Turkey, 2007. (3) W. Rodi, DNS and LES of some engineering flows, Fluid Dynamic Research, vol. 38, pp. 145-173, 2006 (4) R. Borrell, O. Lehmkuhl, M. Soria, A. Oliv