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Nowadays, axial fans participate in the most important areas of industry and research, including aviation, navy, wind tunnels, cooling towers, and even automobiles. Thus, more emphasis has been placed on improving their aerodynamic performances. It is important to notice that the parameters involved in designing a fan are mainly concerned with aeraulic power, torque and efficiency. This study investigates the utilization of flow control techniques to improve performances of an axial fan equipped with hollow blades, shroud, and hub. These features grant the fan crucial characteristics, namely, its lightweight and facilitate the blowing action by taking advantage on its hollow parts. The fan's performance is evaluated using a steady RANS numerical model with a k-ω SST turbulence closure, which was validated with experimental data. An active control air blowing through a slot was introduced with various positions and dimensions. The results demonstrate a significant improvement in the fan's performance, with an up to 56% increase in aeraulic power gain, accompanied by changes in the overall flow topology, noticed by closely analyzing the flow structure near the tip clearance. [ABSTRACT FROM AUTHOR]

Reactive rotational molding (RAM) is a process to manufacture hollow plastic articles. Comparing to rotational molding of thermoplastics, it decreases the process cycle time due to the reactivity of the system. However, the number of influent parameters is relatively high and optimization of the process is complex. During RRM, the viscosity is one of the key parameters and varies according to the polymer molecular weight due to chemical reactions. Simulation is a way to optimize this process. Prediction of the reactive flow is of great interest to optimize process conditions and wall thickness distribution of the molded part. We developed a solver based on smoothed particle hydrodynamics method. This Lagrangian meshfree method is well adapted to simulate free surface flows like those occurring in ARM. First, we validated the code comparing the simulation results to analytical Couette flow solution and experimental measurements of dam break problem. Then, we performed two-dimensional (2D) and 3D simulations to observe the influence of the change of viscosity on the flow, due to the chemical reactions. Adhesion of the polymer on the mold surface is modeled by new boundary conditions. POLYM. ENG. SCI., 53:2509-2518, 2013. 0 2013 Society of Plastics Engineers, INTRODUCTION Rotational molding is a process for manufacturing the hollow plastic parts from few centimeter to several meters (1), (2). The main advantages of this method are no residual stresses [...]

The aim of this paper is to analyze, from experimental results, the influence of the shape of the leading edge and its sharpening on the cavitating behavior of an inducer. The studied inducer is designed according to a methodology developed at LEMFI. Successive cutting and sharpening (four cuts, which modify up to 20 percent of the blade chord at the tip), were made to modify the shape of the leading edge. For the various geometries, the experimental results obtained on the LEMFI test rig are presented as follows. Noncavitating Regime: Overall performances at 1450 rpm. Cavitating Regime: (1) The development of the cavitation versus the cavitation number, (2) the description of the various cavitation pictures, and (3) the pressure fluctuations measured at the wall at 150 mm downstream of the trailing edge for various flow rates and inlet pressures. The CFD simulations carried out under CFX-Blade Gen + on this range of inducers are presented to explain certain aspects observed.

Several applications were carried out in order to validate the method presented in Part I. In Part II, two examples of these applications are presented; one relating to the aeroacoustics of the axial fans and the other one to the interaction impeller-volute tongue in a centrifugal pump. The test benches used to study the behavior of these machines are presented. The study of the fan was capable of quantifying the discrete noise associated with the fluctuations in pressure linked to the potential flow. The analysis of the centrifugal pump permitted comparing the theoretical pressure fluctuations with experimental ones measured by various unsteady pressure sensors placed on the impeller shroud and in the volute. The qualitative and quantitative results obtained confirm the interest and the range of the developed algorithm. [DOI: 10.1115/1.1399287]

An algorithm using the singularity method was developed. It allows taking into account the interaction between fixed and mobile cascades. Its principle is based on the summation of discrete vortices distributed periodically on the rotor and stator profiles. The overall matrix, obtained by applying the boundary conditions, takes into account the complexity of the studied cascade geometry (presence or not of splitter blades, possibly variable pitch of the profiles, etc...) To illustrate the interest and the impact of the algorithm, two parametric studies on turbomachines cascade are presented: Planes cascade made up of a rotor and a stator (at the mean radius of an axial fan). Circular cascade made up of impeller and a volute (peripheral cascade of a centrifugal pump). [DOI: 10.1115/1.1399286]

Recommendations are offered in using the singularities method in studying the flow through turbomachinery. The trailing edge geometry should be studied. Smoothing is necessary if the geometry indicates instability. Circulation smoothing is sometimes necessary after trailing edge smoothing has been performed particularly in profiles with a cusped trailing edge. Sophisticated compliers can be utilized to increase the number of discretization points.

It is a known fact that incorporating textures in the contact surfaces can significantly enhance bearing performances. The purpose of this paper is to outline the effects of texture bottom profiles and contour geometries on the performances of hydrodynamic textured journal bearings. The analysis was conducted using computational approach to test eight texture shapes: rectangular, cylindrical, spherical, triangular (TR, T1, T2, T3) and chevron. The steady-state Reynolds equation for modelling the hydrodynamic behaviour of thin viscous film was solved using finite difference technique and mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. The comparison with the benchmark data shows good consistency and an enhancement in bearing performances (load carrying capacity and friction). The results clearly show that the mechanisms of wedge effect and micro-step bearing for the full/partial texturing feature are the main crucial parameters, where the convergent wedge effect present in T2 triangular texture shape can significantly enhance the load-carrying capacity, while the divergent wedge action causes a net load loss. Considering the right arrangement of textures on the contact surface, their surface contours can have a significant impact on the performance of hydrodynamic journal bearings at high eccentricity ratios. [ABSTRACT FROM AUTHOR]

Byline: D. Fedala, S. Kouidri, F. Bakir, R. Rey In this paper, a modelling of the broadband noise radiated by an axial subsonic fan is presented and validated. It is an extension of Amiet's model predicting the broadband noise generated by an isolated airfoil. Two sources are analysed, incident turbulence interaction noise and trailing edge noise. It shows the dominance of the leading edge noise. The broadband noise directivity for axial fans presents a main radiation lobe along the fan axis for both mechanisms. It was observed that the leading edge acoustic spectra feature is very sensitive to the turbulence length scale of the incident flow.

Byline: T. Bouquet, S. Kouidri, F. Bakir, R. Rey The study presented in this paper is part of the research work on forward-curved blades centrifugal fans carried out over the last few years by the 'Laboratoire d.Energetique et de Mecanique des Fluides Interne' (Lemfi - Site Paris). The objective of this study is to better understand the internal flow in this type of machine in order to be able to correlate the aeraulic and acoustic behaviours with the geometrical characteristics of the machine. Two impellers with different profiles were manufactured and tested. The aeraulic and acoustic tests were carried out on a test bench standardised ISO 5801. The 3D CFD of the flow was carried out with a commercial code based on the resolution of the Navier-Stokes equations in finite volumes. The analysis of these results confirms that a more organised flow field leads to a better acoustic performance.