Inspired by bird feather structures that enable the resistance of powerful aerodynamic forces in addition to their lower weight to provide stable flight, a biomimetic composite turbine blade was proposed for a low-temperature organic Rankine cycle (ORC) turboexpander that is capable of producing lower weight expanders than that of stainless steel expanders, in addition to reduce its manufacturing cost, and hence it may contribute in spreading ORC across nonconventional power systems. For that purpose, the fluid–structure interaction (FSI) was numerically investigated for a composite turbine blade with bird-inspired fiber orientations. The aerodynamic forces were evaluated by computational fluid dynamics (CFD) using the commercial package ANSYS-CFX (version 16.0) and then these aerodynamic forces were transferred to the solid model of the proposed blade. The structural integrity of the bird-mimetic composite blade was investigated by performing finite element analysis (FEA) of composite materials with different fiber orientations using ANSYS Composite PrepPost (ACP). Furthermore, the obtained mechanical performance of the composite turbine blades was compared with that of the stainless steel turbine blades. The obtained results indicated that fiber orientation has a greater effect on the deformation of the rotor blades and the minimum value can be achieved by the same barb angle inspired from the flight feather. In addition to a significant effect in the weight reduction of 80% was obtained by using composite rotor blades instead of stainless steel rotor blades.

Abstract:The present paper provides a numerical study that leads to the proper selection of a working fluid for use in low-temperature organic Rankine cycle (ORC) applications. This selection is not only based on the provision of best efficiency but also to comply with global warming potential (GWP) regulations. For that purpose, different pure organic working fluids, including R245fa, R236fa, R123, R600a, R134a, and R1234yf as well as zeotropic mixture R245fa/R600a, are selected. The investigation is conducted on a single stage radial inflow turbo-expander, which was originally used in the Sundstrand Power Systems T-100 Multipurpose Small Power Unit. The commercial package ANSYS-CFX (version 16.0) was used to perform the numerical study using 3D Reynolds-Averaged Navier-Stokes (RANS) simulations. Peng-Robinson equation of state is adopted in the finite-volume solver ANSYS-CFX to determine the real-gas properties. The obtained results show that, while the use of R134a and R1234yf provides the best efficiency of all the working fluids under investigation, the latter is best selected for its comparatively low global warming effects.

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This study pertains to an experimental analysis on the effects of the transverse jet flow geometry on the stability of a 6 × 6 square rod bundle. The experimental work represents a reduced scale fuel assembly subjected to localized cross flow conditions. This type of complex system is typically found in the nuclear industry (pressurized water reactor cores). The goal of the experimental study is to investigate the onset and characterize rod instability as it relates to the intensity and diameter of the jet cross-flow. The rod response was recorded using a high-speed camera in the vibration plane. From image processing, rod vibration amplitudes, and power spectral densities are acquired in both stream-wise and transverse directions. The results indicate that by increasing the jet nozzle diameter ratio, the critical flow velocity is reduced, however, the maximum vibration amplitude in the bundle decreases as the jet diameter ratio increases. The experimental datasets produced by all three sets of experiments were analyzed by Principal Component Analysis (PCA). The method obtained the orbit plots of the rod bundle undergoing fluid-elastic instability due to the transverse jet flow penetration for each set of experiments. A significant outcome of this research is the relation of acceleration ratio when the nozzle diameter is increased.

Flow-induced vibration (FIV) is a constant concern in nuclear power plants. Demand for better thermal performance challenges the mechanical and flow characteristics of fuel designs. In the hypothetical case of a loss of coolant (LOCA) event in a reactor, the hydrodynamic pressure would increase significantly across the baffle plates. PWRs include safety features such as Loss-of-Coolant-Accident (LOCA) holes and slots in the core periphery baffles surrounding the fuel assemblies to release the pressure build up during a LOCA event. Accordingly, these fuel assemblies are subjected to combined axial and jet cross-flow at certain axial locations along their spans due to their proximity to the LOCA holes. The jet flow could induce vibrations for fuel assemblies located near LOCA holes, which might lead to grid-to-rod fretting and thus potential fuel failure. Research on circular jet induced vibrations of rod bundles is limited. Thus, it is required to investigate the dynamical behavior of rod bundle subjected to jet flow to define the critical velocity at which the fuel rods may undergo instability. This article presents an experimental study of jet flow induced vibrations for a 6 × 6 closely packed normal square rod bundle with a pitch-to-diameter ratio of 1.32 simulating the actual PWR fuel rod dimensions. A specialized test apparatus was designed to investigate the stability effect of jet centerline offset from array centerline (jet eccentricity). From the test results the instability threshold of the rod bundle subjected to jet cross-flow is determined. The results show that the rod array vibration is affected by the jet eccentricity. Two excitation mechanisms are identified. The first is an apparent lock-in type mechanism that maybe related to shear layer or jet oscillation. The second, more important excitation, is an apparent fluidelastic instability induced by the jet flow.