A. Oliva

Detailed Experimental Validation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors

A detailed experimental analysis of the thermal and fluid dynamic behavior of hermetic reciprocating compressors is presented. A hermetic compressor for household appliances has been experimentally tested. The fluid and solid thermal map evolution has been logged in several strategic points. The absolute instantaneous pressure has been determined in three specific zones: suction muffler, compression chamber, and cylinder head. The pV diagram inside the compressor chamber has also been experimentally obtained for the different working conditions studied without any previous hypothesis to determine the absolute pressure level. A complete description of the experimental equipment and its instrumentation is included. This experimental approach has allowed validating a mathematical model developed for the numerical simulation of the thermal and fluid dynamic behavior of hermetic reciprocating compressors. Good agreement between the detailed numerical results and the experimental data has been obtained, allowing a better understanding of the thermal and fluid dynamic behavior of these compressors.

Effect of contaminant properties and temperature gradients on the efficiency of transient gaseous contaminant removal from an enclosure : a numerical study

Abstract This paper reports the results of a numerical study on the transient removal of a contaminant from a two-dimensional enclosure with one inlet and one outlet. The influence of buoyancy forces due to thermal and concentration gradients, contaminant diffusivity, inlet velocity and outlet disposition over the cleaning-time are studied. The governing equations of the laminar flow (continuity, momentum, energy and contaminant concentration) are solved by means of the SIMPLEC algorithm. Several simulations of the same test case have been made, using two numerical schemes : PLDS and SMART, in order to determinate which one provides better performances. For isothermal situations, the time required to remove the contaminant is studied parametrically as a function of the outlet position and the governing dimensionless numbers (Reynolds number, Schmidt number and solutal Rayleigh number) , while the effect of horizontal temperature differences is studied in several situations in which it plays an important role. Buoyancy forces are found to have a strong influence over the flows and, in consequence, over the cleaning times.

Modeling and Numerical Simulation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors—Part 2: Experimental Investigation

An experimental validation of a mathematical model developed for the numerical simulation of the thermal and fluid dynamic behavior of hermetic reciprocating compressors is presented. Details of the physical model and a critical analysis of the quality of the numerical solutions are presented in a companion paper (Part 1). Different compressor geometries have been tested considering a wide range of working conditions and refrigerant fluids. A complete description of the experimental equipment and its instrumentation is included here. Good agreement between numerical and experimental data has been obtained, generating a better understanding of the thermal and fluid dynamic behavior of these compressors.

Modeling and Numerical Simulation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors—Part 1: Theoretical Basis

A detailed numerical simulation of the thermal and fluid dynamic behavior of reciprocating compressors, commonly used in household refrigerators and freezers, has been developed. The model is based on the integration of the transient fluid conservation equations (continuity, momentum, and energy) in the whole compressor domain (compression chamber, valves, manifolds, mufflers, shell, piston, connecting tubes, parallel paths, etc.) using instantaneous local mean values for different variables. Effective flow areas are evaluated considering a multidimensional model based on modal analysis of fluid interaction in the valve. In order to evaluate the instantaneous compression chamber volume, force balances in the crankshaft connecting rod mechanical system are simultaneously solved at each time-step. The thermal analysis of the solid elements is based on global energy balances at each macro-volume considered (shell, muffler, tubes, cylinder head, crankcase, motor, etc.). The resulting governing equations (fluid flow, valve dynamics, conductive heat transfer in solids, etc.) are discretized by means of a fully implicit control volume formulation. The complete set of algebraic equations is coupled using the segregated pressure-based algorithm Semi-Implicit Method for Pressure-Linked Equations (SIMPLEC) extended to compressible flow. A detailed numerical analysis is presented with the aim of verifying the quality of the numerical solution. A comparison between numerical simulation results and experimental data is presented in the companion paper (Part 2).

Optimising the Termofluids CFD code for petascale simulations

ABSTRACT This paper presents some recent efforts carried out on the expansion of the scalability of TermoFluids multi-physics Computational Fluid Dynamics (CFD) code, aiming to achieve petascale capacity for a single simulation. We describe different aspects that we have improved in our code in order to efficiently run it on 131,072 CPU-cores. This work has been developed using the BlueGene/Q Mira supercomputer of the Argonne Leadership Computing Facility, where we have obtained feedback at the targeted scale. In summary, this is a practical paper showing our experience at reaching the petascale paradigm for a single simulation with TermoFluids.

Large-Eddy Simulations of Wind Turbine Dedicated Airfoils at High Reynolds Numbers

This work aims at modelling the flow behaviour past airfoils used for wind turbine blades at high Reynolds number and large AoA. Three profiles have been selected: DU-93-W-210, DU-91-W2-250 and FX-77-W-500. To do this, a parallel unstructured conservative formulation has been used together with walladapting local-eddy viscosity model within a variational multi-scale framework (VMS-WALE). A methodology based on unstructured meshes has been developed in order to optimize the performance of the grid for LES calculations. Numerical results are presented in comparison with experimental ones for each airfoil. A good agreement between them can be observed.

Numerical simulations of conjugate convection combined with surface thermal radiation using an Immersed-Boundary Method

Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Numerical solutions for the fluid flow and the heat transfer of viscoplastic-type non-Newtonian fluids

The aim of this work is to provide numerical solutions for the fluid flow and the heat transfer generated in closed systems containing viscoplastic-type non-Newtonian fluids. A lid driven cavity (LDC) and a differentially heated cavity (DHC) are used as test cases. These numerical solutions can be an appropriate tool for verifying CFD codes which have been developed or adapted to deal with this kind of non-Newtonian fluids. In order to achieve this objective, an in-house CFD code has been implemented and correctly verified by the method of manufactured solutions and by some numerical solutions too. Furthermore, a high-performance CFD code (Termo Fluids S.L.) has been adapted and properly verified, by the corresponding numerical solutions, to deal with this kind of non-Newtonian fluids. The viscoplastic behaviour of certain non-Newtonian fluids will be generated from a viscous stress which has been defined by a potential-type rheological law. The pseudoplastic and dilatant behaviours will be studied. On this matter, the influence of different physical aspects on the numerical simulations will be analysed, e.g. different exponent values in the potential-type rheological law and different values of the non-dimensional numbers. Moreover, the influence of different numerical aspects on the numerical simulations will also be analysed, e.g. unstructured meshes, conservative numerical schemes and more efficient and parallel algorithms and solvers.

DNS of the Rising Motion of a Swarm of Bubbles in a Confined Vertical Channel

The motion of bubbles and droplets is ubiquitous in a variety of natural processes and technological applications, such as boiling heat transfer, steam generators of nuclear power plants, unit operations of the chemical engineering (e.g. distillation, absorption columns, bubble reactors), micro-devices, among others [8].

Coherent Structures in a Flow Past a Circular Cylinder at Critical and Super-Critical Reynolds Numbers

It is well known that the wake topology in the flow past a circular cylinder remains almost unchanged up to Reynolds number \(\sim 10^5\) Williamson (Annu Rev Fluid Mech 28(1), 477–539 (1996)) [1]. Then, at \(Re\sim 2\times 10^5\) major changes take place entailing flow separation, turbulence transition in the detached shear layers, reattachment of the flow and further separation of the boundary layer. In the present work, large-eddy simulations of the flow past a cylinder at Reynolds numbers in the range \(2.5\times 10^5{-}10^6\) are performed. This range includes both critical and super-critical Reynolds numbers (J Fluid Mech 10(3), 345–356 (1961)) [2]. Contradicting results about the wake configuration and structures are found in the literature.