Miguel Angel Rodriguez

EPJ Web of Conferences, open-access proceedings in physics and related sciences

Assessment of LES models of confined coaxial swirling jets is the aim of this paper. Despite the simple geometrical set-up of the benchmark, the flow pattern shows complex aerodynamic behavior. The case considers two coaxial jets: one axial and another annular swirling jet. The expansion when entering the chamber will produce the Outer Recirculation Zone (ORZ). If swirl number is large enough, an Inner Recirculation Zone (IRZ) is formed. The region between both recirculation zones with high shear is where mixture occurs. Post-process in space and frequency domain supplies useful information of this benchmark. Kernel cores are identified based on the lambda2 parameter. The mesh must be fine enough to capture the inertial regime of the turbulent energy spectrum. Proper Orthogonal Decomposition let identify main flow structures. To sum up, LES models provide more information than conventional RANS models and it is a step forward in any research team to gain an insight of any transitional or fully turbulent process. Özet: Bu çalışmanın amacı, kapalı ortak eksenli swirl jetlerin LES modellerini değerlendirmektir. Karşılaştırmanın basit geometrik kurulumuna rağmen akış modeli kompleks aerodinamik davranış göstermektedir. Bu durumda, düz ve dairesel dönen olarak iki ortak eksenli jet göz önüne alınmıştır. Giriş odası genişlediğinde, dış resürkilasyon bölgesi (Outer Recirculation Zone (ORZ)) meydana gelir. Eğer swirl sayısı gereğinden fazla olursa iç resürkilasyon bölgesi (Inner Recirculation Zone (IRZ)) oluşur. Yüksek kesişme ile her iki resürkilasyon bölgesi arasındaki bölgede karışım meydana gelir. Boş ve frekans alanındaki ön proses bu karşılaştırmanın kullanılabilir bilgisini sağlar. İç çekirdek lambda2 parametresine bağlı olarak belirlenir. Ağ, türbülans enerji spektumunun iç rejimine dağılmak için yeri kadar iyi olmalıdır. Uygun ortogonal ayrışma ana akış yapısının belirlenmesine izin verir. Özetle, LES modeller geleneksel RANS modellerden daha çok bilgi sağlar ve herhangi bir geçiş yada tam türbülanslı sürecin adım adım anlaşılmasını sağlar.

This paper aims to predict the performance of Vertical Axis Wind Turbine (VAWT), hence the modeling of kinetic energy extraction from wind and its conversion to mechanical energy at the rotor axis, is carried out. The H-type Darrieus turbine consists of three straight blades with shape of aerofoil attached to a rotating vertical shaft. The criterion on the selection of this kind of turbines, despite its reduced efficiency, is the easy manufacture in workshops. A parametric study has been carried out to analyze the camber effect on the non dimensional curves of power coefficient so that the self starting features as well as the range of tip speed ratio of operation could be predicted.

Oscillating Water Column (OWC) systems are one of the most popular technologies for wave energy conversion. Their main elements are the chamber with the water column and the air turbine. When studying the performance of an OWC system both elements should be considered together, for they are effectively coupled: the damping exerted by the air turbine affects the efficiency of the conversion from wave power to pneumatic power in the OWC chamber, which in turn affects the air flow driving the turbine. The optimum level of damping is that which maximizes the efficiency of the conversion from wave to pneumatic power. In this work the turbine-chamber coupling is studied through a combination of physical and numerical modeling.

Turbines for wave energy conversion have a special feature to be taken into account in the study of the tip leakage flow: These turbines are self-rectifying, which work inside a cyclically bidirectional flow alternatively as an inflow/outflow turbine. The phenomena at the blade tip will be different in these two situations. Moreover, it is necessary to take into account the tip clearance of the guide vanes because it has a significant influence on the rotor performance. A previously developed numerical model has been used for this study. The geometry proposed by Setoguchi et al. (2002, “A Performance Study of a Radial Impulse Turbine for Wave Energy Conversion,” Journal of Power and Energy, 216, pp. 15–22) is used in the model. Three different tip clearance sizes have been simulated to compare the influence of the tip clearance size on the performance. Results show that changing the size of the tip clearance from 0% to 4% of the blade span reduces the turbine maximum efficiency by up to 8%. However, the efficiency reduction is more pronounced when the turbine works as an inflow turbine because the tip clearance effect is more important in the inner part of the rotor, since flow velocities are higher and the relative casing motion is lower. This study achieves its main aim, which is to improve knowledge about the phenomena related to the tip clearance and its influence on the performance of radial impulse turbines.

This work is focused on radial impulse turbines for an Oscillating Water Column (OWC) which is one of the alternatives to the Wells turbines traditionally installed in the OWC systems. All self-rectifying turbines work under special conditions due to the bi-directional flow caused by OWC. But a radial impulse turbine has another special point: it works alternatively as an inflow/outflow turbine, so that its behavior is not symmetrical as is expected in axial turbines for OWC (Wells and axial impulse turbines). The complete CFD analysis we have made of a radial impulse turbine is described. The model was created for a specific turbine but can be adapted for any self-rectifying turbine. We have studied the turbine by means of a one-dimensional study and a 3-D model solved with FLUENT® software, and the results were validated with experimental data extracted from the bibliography. This model allowed us to analyse both the classical dimensionless parameters and the flow pattern. Moreover, we have introduced a special definition for the reaction degree in order to analyse the process of the energy conversion.