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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.

The inducers increase the pressure available at the inlet of the impellers of centrifugal pumps. This technological solution may induce instabilities, such as prerotating flow at partial flow rates. The scientific literature offers studies on the cavitation in the inducers, as well as on the associated instabilities. However, studies describing devices that improve the behavior in these unstable regimes are rare. This is particularly true for fluids like aviation fuels or liquids with dissolved gases. In this work we expose, an experimental study for two axial inducers carried out at low flow rates in cavitating and noncavitating regimes in a closed-loop equipped with a transparent test pipe. The working liquid is water with and without dissolved CO2. We employ a camera and a high-speed camera to take the photographs of the dynamics of the cavitation structures. The experimental campaign provided results of head breakdown comparison. The added dissolved CO2 gas at a concentration of 300 mg L-1 does not change the overall inducers' performance in noncavitating regime. The paper presents also the impact of some of inducers' geometrical parameters on their cavitating performance. The authors observed prerotating flow instability, which they tried to decrease by incorporating a grooved ring into the inlet side of the inducers. It is found that prerotating structures are much less developed in the upstream when a grooved ring is employed. [ABSTRACT FROM AUTHOR]

In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modeling of the flows and heat transfers occurring in these areas. Within the framework of the European program main annulus gas path interaction (MAGPI) WP1, a two-stage axial turbine test rig provided an experimental database used to validate the computational fluid dynamics (CFD) models. The aim of this study is to setup a numerical methodology using the CFD solver ANSYSFluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature/pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A Reynolds-averaged Navier-Stokes (RANS) three-dimensional sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, disks rotor, the casing, and the nozzle guide vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data. As a baseline, the first calculations were performed with a cooling flowrate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures/pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Two other cooling configurations were conducted, one with cooling air exiting from the disk rim cavity to the main gas path and the other with the lowest cooling flowrate and so the highest ingress. Finally, the turbine performance under nonadiabatic conditions has been evaluated with an appropriate efficiency definition. [ABSTRACT FROM AUTHOR]

Inducers in centrifugal pumps are generally placed upstream to increase the pressure before the impeller and prevent cavitation occurrence. Their general goal is to obtain a positive impact on the performances of a pump in a two-phase regime. Cavitation phenomenon has been the subject of many studies; however, the influence of the presence of dissolved gas in the liquid pumped under particular operating conditions remains not sufficiently explored. To the best of our knowledge, aviation jet fuel cavitation is moderately documented. In the present work, we conducted an experimental study on two three-bladed axial inducers at partial flow rates only in cavitating and noncavitating regimes. The experimental work used aviation jet fuel, water, and water with dissolved content of CO2 at constant temperature in two closed loops with transparent test sections. In one tank, a specific device is placed to inject a controlled quantity of CO2 and to dissolve it in water. We achieved a comparison of the flow dynamics through the use of a high-speed camera with a sampling rate of 1000 Hz. The results show inducers' water-CO2 cavitation performances to be in good agreement with aviation jet fuel cavitation results. [ABSTRACT FROM AUTHOR]

This study deals with a low pressure-ratio centrifugal compressor consisting of two counter-rotating rotors called a counter-rotating centrifugal compressor (CRCC). The design method based on the loss model was presented to determine the geometric parameters of the two counter-rotating rotors. According to this method, the rotor of a selected single rotor centrifugal compressor (SRCC) has been redesigned into two counter-rotating rotors (upstream and downstream rotors) by choosing the value of meridional length ratio (LR). The meridional view, the volute shape, and the operating parameters of SRCC are preserved during the design process. In a first step, the counter-rotating mode at a constant rotor speed of 11k rpm has been carried out. The overall characteristics of CRCC are compared to those of SRCC. In a second step, the map characteristic of CRCC is established for seven speed ratios. The results show that CRCC increases up to 4.6% for the pressure ratio and 3.5% for the efficiency compared to SRCC at the same tip-speed. In addition, CRCC can operate at a lower tip-speed by about 2k rpm to produce the same characteristics as SRCC, with better efficiency over a wide range of flow rates. However, the surge margin of the CRCC is shifted to higher flow rates. This disadvantage of the CRCC was solved by choosing the adequate pair of the rotational speeds of the two rotors that will be presented in other publication. [ABSTRACT FROM AUTHOR]