S. Kouidri

Experimental Analysis of an Axial Inducer Influence of the Shape of the Blade Leading Edge on the Performances in Cavitating Regime

We 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

Flow Study in the Impeller–Diffuser Interface of a Vaned Centrifugal Fan

In order to better understand the behavior of the fluid flow in vaned centrifugal fans, theoretical and experimental work has been carried out on unsteady three-dimensional (3D) flows. Particular attention is given to the flows located at the rotor-stator interface. This zone is the seat of strong interactions between the moving part and the fixed part. This phenomenon has as consequences: Strongly unsteady flow, fluctuating forces on the stator blades, and an efficiency decrease. This work is part of a project which main objective is the aeroacoustic optimization of high speed centrifugal fans. We present in this paper the first results, mainly aerodynamic ones, which will be used thereafter as an input data to aeroacoustic modeling. A numerical simulation tool was used in order to determine the kinematics and the dynamics of these flows. The measurements of the steady and unsteady flow characteristics allowed a comparison of the theoretical and experimental results.

Effect of inlet duct contour and lack thereof on the noise generated of an axial flow fan

Abstract This study concerns the unsteady flows in turbomachines in general, and the aeroacoustics of fans in particular. The principal objective of this paper is the determination of the influence of the upstream environment on the acoustic and aerodynamic behavior of axial fans. After analysis of the various sources of noise present in turbomachines, interest is focused on the influence of the disturbances of the velocity field at the suction. Accordingly, the effect of the presence of a contoured duct and a lack thereof at the inlet of an axial flow fan is analyzed . The results show the strong involvement of the upstream turbulence level in the generation of the noise, and in particular, of broadband noise.

On a General Method of Unsteady Potential Calculation Applied to the Compression Stages of a Turbomachine—Part I: Theoretical Approach

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)

On a General Method of Unsteady Potential Calculation Applied to the Compression Stages of a Turbomachine—Part II: Experimental Comparison

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

3D Structure of the Rotor Wake of a Three Different Sweep Axial Fan

This experimental study, applied to a three different sweep axial fan (backward, radial and forward), aims at determining the 3D structure of the rotor wake from unsteady velocity measurements. The hot-film anemometry is used to measure the 3D unsteady velocity components in nearfield, downstream the fan. The data analysis leading to averaged and turbulent velocities, the components of the Reynolds’ stress tensor and the turbulent kinetic energy is presented, in order to illustrate the influence of the sweep. A spectral analysis is also performed.Copyright

Comparative Study of the Aeroacoustic Behavior of Two Axial Flow Fans With Different Sweep Angles

The purpose of this study is to determine the effect of the sweep angle used in axial flow fans on their aerodynamic and acoustic behavior. To do so, two fans, having the same aerodynamic characteristics, were designed with forward and radial sweep angles. The 3D numerical simulation allowed obtaining steady and unsteady loading on the blades. Instantaneous velocity profiles, located downstream of the fans, will be presented and compared to the experimental data. The Ffowcs Williams & Hawkings formulation was used to model the acoustic spectra. The results from CFD simulation (acoustic rotating dipole) were used as input data for the acoustic modeling. Predicted and measured acoustic spectra will be presented. It was found that the forward fan has a uniform radial distribution of kinetic turbulence. Also, the three downstream velocity components have better radial distributions. This result was confirmed by the experimental and predicted aeroacoustic results.Copyright

Mass flow rate measurement in heterogeneous diphasic flows by using the slurry pumps behavior

Abstract This study lies within the scope of a European project, with the objective of studying and designing a tunnel boring machine able to function in continuous mode. This operating mode allows reduction of discontinuities of excavation in order to obtain greater efficiency by reducing the excavation time. The extraction of rubble is carried out by means of a hydraulic circuit composed of a set of special pumps for slurry and of a horizontal hydraulic pipe. The optimal control of the whole installation, pumps included, requires continuous assessment of the mass flow rate of the solid–liquid mixture. During this study, we aimed to develop a methodology of mass flow rate measurement to replace the existing limited method of gamma-densitometer, as the irregularities noticed during various phase measurement reduce the reliability of this technique. This paper presents a theoretical and experimental study which will make it possible to improve the accuracy of measurement carried out by the gamma-densitometer and the development of a method based on the power consumed by the engines driving the pumps.

A Numerical Study on the Aeroacoustic of a Vaned Centrifugal Fan

High speed vaned centrifugal fans are widely used in several manufacturing and home appliances. For the designers the noise generated by these machines is one of the most important parameters to be reduced. The centrifugal fan used for this study is made up of an impeller, a diffuser and a return channel. The impeller turns at a relatively high speed about 35000 rpm. The objective of this study is to understand the mechanism of the noise generation within this type of machines. The contribution of the tangential and radial forces is highlighted. These fluctuating forces are due to the unsteady flow at the impeller-diffuser interface. The obtained result shows the effect of monopole and dipole sources on the overall noise.Copyright