Effects of Diffuser Vane Geometries on Compressor Performance and Noise Characteristics in a Centrifugal Compressor

The effects of the diffuser vane geometries on the compressor performance and noise characteristics of a centrifugal compressor equipped with vaned diffusers were investigated by experiments and numerical techniques. Because we were focusing attention on the geometries of the diffuser vane’s leading edge, diffuser vanes with various leading edge geometries were installed in a vaned diffuser. A tapered diffuser vane with the tapered portion near the leading edge of the diffuser’s hub-side could remarkably reduce both the discrete frequency noise level and broadband noise level. In particular, a hub-side tapered diffuser vane with a taper on only the hub-side could suppress the development of the leading edge vortex (LEV) near the shroud side of the diffuser vane and effectively enhanced the compressor performance.

Numerical and Experimental Investigation of Tip Leakage Vortex Trajectory in an Axial Flow Pump

In this paper, the tip leakage vortex (TLV) structures in an axial flow pump were investigated by numerical and experimental methods. Based on the comparisons of different blade tip clearance size (i.e., 0.5 mm, 1mm and 1.5mm) and different flow rate conditions, TLV trajectories were obtained by Swirling Strength method, and simulated by modified SST k-ω turbulence model with refined high-quality structured grids. A high-speed photography test was carried out to capture the tip leakage vortex cavitation in an axial flow pump with transparent casing. Numerical results were compared with the experimental leakage vortex trajectories, and a good agreement is presented. The detailed trajectories show that the start point of tip leakage vortex appears near the leading edge at small flow rate, and it moves from trailing edge to about 30% chord span at rated flow rate. At the larger flow rate condition, the starting point of TLV shifts to the middle of chord, and the direction of TLV moves parallel to the blade hydrofoil. As the increasing of the tip size, the start point of TLV trajectories moves to the central of chord and the minimum pressure in vortex core is gradually reduced.

Optimized Chaotic Heat Exchanger Configurations for Process Industry: A Numerical Study

A numerical investigation of chaotic laminar flow and heat transfer in isothermal-wall square-channel configurations is presented. The computations, based on a finite-volume method with the SIMPLEC algorithm, are conducted in terms of Péclet numbers ranging from 7 to 7×105. The geometries, based on the split-and-recombine (SAR) principle, are first proposed for micromixing purposes, and are then optimized and scaled up to three-dimensional minichannels with 3-mm sides that are capable of handling industrial fluid manipulation processes. The aim is to assess the feasibility of this mass- and heat-transfer technique for out-of-laboratory commercial applications and to compare different configurations from a process intensification point of view. The effects of the geometry on heat transfer and flow characteristics are examined. Results show that the flux recombination phenomenon mimicking the baker’s transform in the SAR-1 and SAR-2 configurations produces chaotic structures and promotes mass transfer. This phenomenon also accounts for higher convective heat transfer exemplified by increased values of the Nusselt number compared to the chaotic continuous-flow configuration and the baseline plain square-duct geometry. Energy expenditures are explored and the overall heat transfer enhancement factor for equal pumping power is calculated. The SAR-2 configuration reveals superior heat-transfer characteristics, enhancing the global gain by up to 17-fold over the plain duct heat exchanger.

Numerical Study of Winglet at Low Reynolds Numbers

A numerical study has been performed to evaluate the aerodynamics coefficients of a winglet in the range of Reynolds numbers below 30,000. In this study some parameters on winglet design have been considered. The effect of winglet-tip airfoil thickness has been investigated on aerodynamics coefficients. In order to explore this effect, two different airfoils (NACA0002 and NACA0012) were employed at the winglet-tip. The influence of varying the winglet connection angle to the wing on aerodynamics coefficients and flow field characteristics in the vortex flow zone such as; circulation magnitude and vorticity magnitude in the vortex core have been studied. Six connection angles including 20°, 30°, 40°, 50°, 60° and 70° have been studied. Negative values of these angles have also been considered. In addition, the effect of changing wing aspect ratio on aerodynamics coefficients has been investigated. To solve the flow field around the studied geometry a fully structured grid was used which consists of 84 blocks.

Performance and Internal Flow of Contra-Rotating Small Hydro Turbine

Small hydropower generation is one of important alternative energy, and potential of small hydropower is great. Efficiency of small hydro turbines is lower than that of large one, and these small hydro turbine’s common problems are out of operation by foreign materials. Then, there are demands for small hydro turbines to keep high performance and wide flow passage. Therefore, we adopted contra-rotating rotors, which can be expected to achieve high performance and enable to use low-solidity rotors with wide flow passage, in order to accomplish high performance and stable operation. Final goal of this study is development of a small hydro turbine like electrical goods, which has high portability and makes an effective use of unused small hydro power energy source. In this research, experimental apparatus of the contra-rotating small hydro turbine with 60mm casing diameter was manufactured and performance of it was investigated by an experiment. Efficiency of the contra-rotating small hydro turbine was high in pico-hydro turbine and high efficiency could be kept in wide flow rate range. Internal flow condition, which was difficult to measure experimentally, was shown by the numerical flow analysis. Further, influence of spokes to support the rotor was clarified. Then, a relation between the performance and internal flow condition was considered by the experimental and numerical analysis results.

Experimental Study of Aerodynamic Noise From the Trailing Edge and Leading Edge of Blades in a Coaxial-Double Shaft Fan

Proactive acoustic noise control technologies in wind turbines and blowers have in recent years been the focus of intensive research to integrate wind turbines in residential building and to address public concerns on noise pollution. However efforts to understand the mechanics has been inconclusive, mainly due to the complexity and commercial confidentiality of the topic. The paper reports on the experimental investigation on two methods in controlling aerodynamic noise. A counter-rotating-double-row-turbine with variable gap/spacing (s) was designed, built and tested. Serrations were designed and attached on the leading edge and the trailing edge of the blades to proactively control aerodynamic noise. The model was operated in fan-mode and air velocity, shaft-revolution; electric-fan-power, acoustic noise amplitude (dB) and Centre frequency (CF in Hz) were measured for a number of spacing and serrations. Coefficients of Performance (COP), dB, CF were plotted against tip speed (TS). It was noticed that: • The double-shaft-fan has operated quieter than the single shaft fan especially as TS decreases. Acoustic noise (dB) dropped 20% at TS = 4m/s to less than 2% at TS = 10m/s. Efficiency and CF increased in the double-shaft fan as TS increased. Spacing variation between blade-rows had insignificant effect on the dB, Cf, and efficiency. • Serrations on single-shaft fan have also reduced dB (up to 10%), increased efficiency and CF with more positive effects with the serrations on the leading edge than the trailing edge. Serrations are more effective at higher TS range. • Serrations on a double-shaft fan with an optimum spacing, reduced acoustic noise (dB) only allow speeds [at TS <4m/s]. However minor improvement was noticed in efficiency or noise frequency.

Hydroelastic Stability and Vibration of a Large Reactor Pendulum Structure

Parallel-flow induced vibrations of both large and small reactor internal structures have been analyzed in the past for multiple reactor types. In parallel flows relating to annular and leakage flows, the possibility for significant wear issues can arise and need to be assessed as has been shown throughout the literature. With parallel flow induced vibration, a particular fluid-structure interaction known as hydroelastic instability can arise. If hydroelastic instability occurs, damage to components can be severe and/or catastrophic. This particular phenomenon has been studied in the literature and a few empirically derived methodologies have been published to evaluate the potential for hydroelastic instability to occur in both a limited number of specific geometries and some generic geometries. However, as structural components and their associated flow field characteristics can vary significantly and because of the potential for catastrophic damage to reactor components and the associated costs, a more detailed first principles approach may be warranted to further determine if hydroelastic instability is not only possible, but probable. A potential design for a reactor internals test in which part of the upper internals would exhibit significant annular parallel flow velocities is analyzed for the potential onset of hydroelastic instability. In particular, the upper core plate, which is attached to the rest of the upper internals via support columns in a pendulum setup with the attachment/pivot point at the upper pressure vessel head flange, is temporarily designed to carry a significant non-prototypic pressure drop causing significant upper core plate to core barrel gap flow velocities and potential instability issues. Due to the different geometry of this hardware configuration compared to those found in the literature, both an empirically-based stability analysis from the literature and a first-principles based hydroelastic stability analysis are conducted. The first-principles analysis derives and solves the time-dependent equations of motion and mass conservation for both the fluid and structure and compares the results proximity to stability limits found in the literature. A comparison of the empirically based stability assessment with the first-principles stability analysis is made. Furthermore, an assessment of the probability for the onset of hydroelastic instability of the upper internals assembly is made via a Monte Carlo simulation using the first-principles analysis methodology.

Experimental Investigation of Wellhead PCP for Gas Well Deliquification

A Progressive Cavity Pump (PCP) was evaluated for use as a multiphase pump. The pump is a 576 gpm, constant wall thickness PCP operating with an air/water mixture. Thermocouples were installed along the length of the pump to monitor the elastomer temperature to determine when excessive temperatures were present. Inlet pressures of 15, 30, and 45 psig were considered with pressure rises of 30, 60, 90, 120, and 150 psig. The GVF’s considered were 20, 40, 60, 90, and 98%. It was determined that with the water and air mixture, 98% was the maximum GVF at which the pump could operate continuously. The volumetric efficiency, pump effectiveness, and mechanical efficiency were calculated. The temperature rise across the pump was small, so an isothermal flow was assumed. The PCP investigated has a steel rotor and an elastomer stator that were manufactured with an interference fit. This resulted in volumetric efficiencies above 95% for all test conditions at full speed. This interference fit produces a significant drag on the rotor which is relatively constant at a given speed over the entire operating range considered. This results in the mechanical efficiency being low, 15 to 20%, for ΔP = 30 psig but approaching 60% at ΔP = 150 psi for 0% GVF. The mechanical efficiency decreased with increasing GVF to a low of 28% at ΔP = 150 psi for 98% GVF. The GVF specified here is the actual GVF passing through the pump. If a liquid recirculation system were added to the pump reducing the GVF in the pump, higher efficiencies and the ability to operate at 100% GVF for the process fluid entering the pump system can be obtained.

The Growth of Vortices in the Vicinity of a Wall of Elastic Moving Airfoils

There have been a number of studies on the flow field around a pitching airfoil and a heaving airfoil. Especially, the relationship between the wake structure and the characteristics of dynamic thrust has been clarified. Recently, the flow field around an elastic body has been attracted significant attention and the flow field is treated as a coupled problem between the fluid and structure. The flow field around an elastic body has been investigated primarily by numerical means, and there have been experimental studies. However, the details of the impact of elastic deformation effects on the growth process of vortices generated in the vicinity of the wall have not been clarified. In this study, we investigate the growth process of vortices generated in the vicinity of the wall of elastic moving airfoils experimentally. The elastic NACA0010 generates vortices in a large region of a wall and rolls up vortices, with the vortices growing gradually toward the trailing edge as a result of elastic deformation. The elastic NACA0010 has a characteristic whereby vortices having a rotational component that is stronger than the shear-strain component due to the vorticities in the vicinity of a wall of the elastic NACA0010 change not only spatial change of x- and y-components.

CFD Simulation of Water Flow Mixing With Discrete Phase in a Pump

The mixing process is very common in many industrial applications. In some cases, two or more liquids or discrete phase (DP) set on the pump inlet. Liquid mixture is often occurred in sanitation and agriculture applications and mixture of water with DP (such as sand) are met in the case of water transportation from natural sources (rivers, wells, etc.). DP distribution in the centrifugal pump is the subject of this study. Full pump geometry is considered, due to unsymmetrical nature of volute of the pump. Turbulence k-ε closure model and Lagrangian discrete phase model has been used for most simulations. It was found that smaller particles trap inside the pump for longer time than larger ones. The distribution of the bigger diameter particles on the outlet is more asymmetrical in comparison with particles of smaller diameter. Relatively large areas with very small particle concentrations can be observed. Particle distribution on the outlet for lighter particles demonstrates more uniformity.