Experimental and computational investigation of a new solar integrated collector storage system

The paper discusses a combined experimental-numerical analysis of an innovative solar thermal device to be used as an Integrated Collector Storage (ICS) system providing domestic hot water. In this equipment the collector acts also as a storage unit, without requiring an external vessel. Due to its simple configuration, the ICS device was successfully used in several circumstances, especially in extreme situations such as in post-earthquake tent cities or to reach remote users in Africa. In order to assess the efficiency of this collector, the draw-off process was investigated measuring the value of the mean temperature of the water discharging from the tap as cold water filled the collector. In the present configuration the draw-off is not completely optimised and a detailed analysis was carried out in order to investigate the mixing of cold and hot water in the solar collector during the discharge phase. A series of thermocouples was placed in selected positions around the shield of the collector to investigate the evolution of the near wall temperature. Furthermore, a numerical analysis based on Large-Eddy Simulation (LES) of the mixing process inside the collector was carried out using an open source, in-house, finite-volume computational code. Even if some restrictive hypotheses were made on the thermal boundary conditions and the absence of stratification, the LES results gave interesting findings to improve the collector performance

A CFD-based virtual test-rig for rotating heat exchangers

Rotating heat exchangers are used in steel industry, air conditioning and thermal power plants to pre-heat air used in steam generators or for waste heat recovery. Here we focus on a rotating heat exchanger on a so-called Ljungström arrangement operated in thermal power plants to pre-heat the air fed to the steam generators. In these devices the heat exchange between two fluids is achieved through a rotating matrix that gets in contact alternatively with the two fluid streams and acts as a thermal accumulator. To increase the heat capacity and the overall exchange surface, the rotating matrix is filled by a series of folded metal sheets. In the paper we de-scribe a methodology to account for the effects of the Ljungström in a virtual test-rig implemented in a Computational Fluid Dynamics environment. To this aim, a numerical model based on the work of Molinari and Cantiano was derived and implemented in the OpenFOAM library. RANS numerical results were compared with those of a mono-dimensional tool used by ENEL to design Ljungström heat exchangers and validated against available measurements in a real configuration of a thermal power plant

Design and verification of a micro wells turbine for Mediterranean operations

In the framework of the Poseidone Project we have designed a Wells turbine for Mediterranean operations. Here we present RANS computations carried out with OpenFOAM at different operating conditions. Rotor-stator interaction was synthetized with MRF approach and RANS closure relied on the cubic eddy viscosity closure of Lien et al. The virtual test rig reproduced the ISO conditions of the laboratory and was able to correctly predict torque and efficiency at different operations. Computations moreover allowed to acquire information on the threedimensional velocity and pressure field that develops inside the Wells turbine. The aim was to have an insight on the secondary motions and on the possible stall mechanism that characterize the device at low flow rates. Results were successfully validated against experimental measures

Surrogate modeling of the aeroacoustics of an NM80 wind turbine

Wind turbines play a major role in the European Green Deal for clean energy transition. Noise is a critical aspect among open technological issues, as it determines the possibility of onshore installations near inhabited places and the possible detrimental effects on wildlife when offshore. This paper assesses the accuracy of different approaches to predicting the sound pressure level (SPL) of a wind turbine. The 2.75 MW Neg Micon NM80 horizontal axis wind turbine (HWAT) was simulated in OpenFOAM, modeling the turbine with the actuator line method (ALM) implemented in the turbinesFoam library. Two different inflow conditions were considered: a stationary inflow with a typical atmospheric boundary layer profile and a time-dependent inflow derived from a precursor channel with fully turbulent conditions. The surrogate model for noise prediction used for this work is based on the synthetic/surrogate acoustics models (SAMs) of Amiet and Brooks-Pope-Marcolini (BPM). This approach allows for blade motion modeling and the prediction of the SPL of the URANS postprocessing results. The SPL spectrum obtained was then compared to the results from the other aeroacoustic solvers of IEA Task 39 participants, showing the best performance in the fully turbulent case. The results demonstrate that coupling between the ALM and surrogate acoustics provides more accurate results than the blade element momentum (BEM) approach

predicting the performance of an industrial centrifugal fan incorporating cambered plate impeller blades

Application of computational methods to industrial fan design processes has progressed steadily over the past decade. The reducing cost of the computer hardware upon which codes run has brought the hardware within the reach of all industrial fan designers. However, the cost of commercially available codes remains high. Open source codes provide industrial fan designers with an alternative. The finite volume open-source solver OpenFOAM has been used by scholars to predict the performance of industrial centrifugal fans incorporating impeller blades constructed from cambered plate, but not by industrial fan designers. This paper presents a modelling approach which we developed for application as part of an industrial fan manufacturers order related design process. We compare numerical performance predictions with experimental results both at peak pressure and at peak efficiency conditions. As a further possible investigation, the simulated flow field is used to predict the patterns of erosion of the impeller

MULTISCALE PARTIALLY AVERAGED NAVIER STOKES APPROACH FOR THE PREDICTION OF FLOW IN LINEAR COMPRESSOR CASCADE WITH MOVING CASING

In this paper we present an innovative Partially Averaged Navier Stokes (PANS) approach for the simulation of turbomachinery flows. The elliptic relaxation k-ε-ζ-f model was used as baseline Unsteady Reynolds Averaged Navier Stokes (URANS) model for the derivation of the PANS formulation. The well established T-FlowS unstructured finite volume inhouse code was used for the computations. A preliminary assessment of the developed formulation was carried out on a 2D hill flow that represents a very demanding test case for turbulence models. The turbomachinery flow here investigated reproduces the experimental campaign carried out at Virginia Tech on a linear compressor cascade with tip leakage. Their measurements were used for comparisons with numerical results. The predictive capabilities of the model were assessed through the analysis of the flow field. Then an investigation of the blade passage, where experiments were not available, was carried out to detect the main loss sources. Copyright © 2011 by ASME