Laboratory of Thermal Power Systems

Mechanics, Algeria

Laboratory of Thermal Power Systems

Mechanics, Algeria

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Ghenaiet A.,University of Science and Technology Houari Boumediene | Touil K.,Laboratory of Thermal Power Systems
Chinese Journal of Aeronautics | Year: 2016

This study concerns the characterization of both the steady and unsteady flows and the analysis of stator/rotor interactions of a two-stage axial turbine. The predicted aerodynamic performances show noticeable differences when simulating the turbine stages simultaneously or separately. By considering the multi-blade per row and the scaling technique, the Computational fluid dynamics (CFD) produced better results concerning the effect of pitchwise positions between vanes and blades. The recorded pressure fluctuations exhibit a high unsteadiness characterized by a space–time periodicity described by a double Fourier decomposition. The Fast Fourier Transform FFT analysis of the static pressure fluctuations recorded at different interfaces reveals the existence of principal harmonics and their multiples, and each lobed structure of pressure wave corresponds to the number of vane/blade count. The potential effect is seen to propagate both upstream and downstream of each blade row and becomes accentuated at low mass flow rates. Between vanes and blades, the potential effect is seen to dominate the quasi totality of blade span, while downstream the blades this effect seems to dominate from hub to mid span. Near the shroud the prevailing effect is rather linked to the blade tip flow structure. © 2016 Chinese Society of Aeronautics and Astronautics


Cerdoun M.,Laboratory of Thermal Power Systems | Ghenaiet A.,University of Science and Technology Houari Boumediene
Institution of Mechanical Engineers - 8th International Conference on Compressors and Their Systems | Year: 2013

The operating characteristics of a turbo-compressor are tightly depending on the steady and unsteady operating characteristics of its powering turbine. The present study is aimed to highlight the flow structures through the twin-entry volute and the rotor of a radial turbine. The influence of tongue wake is depicted by a low momentum toward the rotor entry, but the effect of this critical region does not extend beyond a tangential angle of 90 deg. The unsteady simulations at different operating conditions and the FFT analyses of the pressure fluctuations due components interactions have revealed a space-time periodic behaviour that may be described by the double Fourier decomposition. The time mode analysis has permitted to determine the different frequencies and the prevailing modes. Different results were obtained based on the type of computational domains; accordingly the one-blade simulation did not reveal all the flow features as was the case of full-rotor simulation. © The author(s) and/or their employer(s), 2013.


Ghenaiet A.,Laboratory of Thermal Power Systems
Proceedings of the ASME Turbo Expo | Year: 2012

Modern gas turbines operate in severe dusty environments, and because of such harsh operating conditions, their blades experience significant degradation in service. This paper presents a numerical study of particle dynamics and erosion in an hp axial turbine stage. The flow field is solved separately from the solid phase and constitutes the necessary data in the particle trajectories simulations using a Lagrangian tracking model based on the finite element method. Several parameters consider a statistical description such as particle size, shape and rebound, in addition to the turbulence effect. A semi empirical erosion correlation is used to estimate erosion contours and blades deteriorations, knowing the locations and conditions of impacts. The trajectory and erosion results show high erosion rates over the pressure side of NGV near trailing edge, in addition to extreme erosion observed toward the root corner, due to high number of particles impacting with high velocities. On the suction side, erosion is mainly over a narrow strip from leading edge. Erosion in the rotor blade is shown along the leading edge and spreading over the fore of the blade suction side, owing to a flux of particles entering at high velocities and incidence. On the pressure side, regions of dense erosion are observed near the leading edge and trailing edge as well as the tip corner. Critical erosion spots seen over NGV and rotor blade are signs of a premature failure. Copyright © 2012 by ASME.


Ghenaiet A.,Laboratory of Thermal Power Systems
Journal of Turbomachinery | Year: 2012

Aero-engines operating in dusty environments are subject to ingestion of erodent particles leading to erosion damage of blades and a permanent drop in performance. This work concerns the study of particle dynamics and erosion of the front compression stage of a commercial turbofan. Particle trajectories simulations used a stochastic Lagrangian tracking code that solves the equations of motion separately from the airflow in a stepwise manner, while the tracking of particles in different cells is based on the finite element method. As the locations of impacts and rates of erosion were predicted, the subsequent geometry deteriorations were assessed. The number of particles, sizes, and initial positions were specified conformed to sand particle distribution (MIL-E5007E, 0-1000 micrometers) and concentrations 50-700 mg/m3. The results show that the IGV blade is mainly eroded over the leading edge and near hub and shroud; also the rotor blade has a noticeable erosion of the leading and trailing edges and a rounding of the blade tip corners, whereas in the diffuser, erosion is shown to spread over the blade surfaces in addition to the leading edge and trailing edge. © 2012 American Society of Mechanical Engineers.


Ghenaiet A.,Laboratory of Thermal Power Systems
Journal of Turbomachinery | Year: 2012

Turbocompressors manipulating particle-laden airflows suffer from severe erosion damages which affect their operating performance and lifetime. This paper presents the results of a numerical investigation of the dynamics of sand particles and the subsequent erosion in a centrifugal compressor. The particle trajectories simulations used a developed code based on a stochastic Lagrangian model, which solves the equations of motion separately from the airflow, whereas the tracking of particles in different computational cells used the finite element method. The number of particles, sizes, and initial positions were specified, conformed to a sand particle size distribution AC_coarse (0-200 μm), and a given concentration profile. The obtained results show that the speed of rotation and particle size strongly affect the trajectories of particles and their locations of impact. Erosion is spreading over the pressure side of the main blade. Regions of high erosion rates are seen over the leading edge, at the inducer top corner and along the blade tip. Over the splitter pressure side erosion wear is much less than the main blade. The suction sides are almost without erosion except near the leading edge, and the casing is mainly affected over the inducer and tips of the blades. © 2012 American Society of Mechanical Engineers.


Khalfallah S.,Laboratory of Thermal Power Systems | Ghenaiet A.,Laboratory of Thermal Power Systems
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy | Year: 2010

Centrifugal compressors have reached advanced stages of their development, and it is only through a detailed understanding of their complex airflows that improvements in the overall performance will be achieved. This article presents a numerical investigation of unsteady flows through the different components of a radial compressor, emphasizing on the impeller-vaneless-diffuser-scroll interactions. A transient rotor-stator simulation model was used for the calculations carried out by means of the code CFX-TASCflow, at design point and near stall and choke operating conditions. Spectral analyses of the pressure fluctuation-related different component interactions have resulted in the amplitudes and speeds of rotation of the main energetic modes and have revealed that the flow presents a space-time periodic behaviour that may be described by the double Fourier decomposition. The spatial mode analysis was therefore introduced to describe the interaction mechanisms, whereas the time mode analysis during the working time of the machine has permitted to determine different frequencies, and hence the most prevailing modes and their originating sources. These spectral analyses have permitted a good understanding of the flow interaction mechanisms and revealed the computations limits, depending on whether one-passage or a full-rotor simulation is considered. Principally, these limitations are related to an underestimation of pressure fluctuation amplitudes and a failure in detecting all harmonics lower than the number of passages per component. Finally, this study may help in envisaging the local treatments to reduce noise levels and increase the compressor stability.


Ghenaiet A.,Laboratory of Thermal Power Systems
AIP Conference Proceedings | Year: 2010

The erosion resulting from sand ingestion into an axial turbomachinery is predicted using a Lagrangian particle tracking model. This simulation takes into account the effects of turbulence and endwalls vorticities on particles, random size distribution and rebound of particles. The governing equations of particle motion through stationary and rotating parts are solved in a stepwise manner separately from the flow field. Particles tracking and impacts are predicted in different cells of the computational domain based on the finite element method. A semi-empirical erosion correlation is used to predict erosion areas based on impacts condition. The simulations results obtained for different positions of the rotor blade revealed that the main impacted areas are found over the blade leading edge corner and an area of the pressure side extending towards and over the tip, in addition to a strip along the leading edge of the suction side. © 2010 American Institute of Physics.


Khalfallah S.,Laboratory of Thermal Power Systems | Ghenaiet A.,Laboratory of Thermal Power Systems
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy | Year: 2012

Centrifugal compressors used for turbochargers are required to achieve high performance within wide flow ranges. However, their operability is limited at low mass flow rates by the flow instabilities leading to rotating stall and surge, which could be delayed by a suitable casing treatment. This article presents a numerical investigation aimed at studying the effects of a type of casing treatment on the flow structure through a radial compressor and the subsequent improvement of aerodynamic stability. The considered casing treatment consists of an oblique slot recess inserted in the shroud near the impeller throat and a large annular cavity connecting this slot to the bell-mouth. The flow computations were carried out by means of the code ANSYS-CFX, considering the shear stress transport (k-ω) turbulence model, in order to investigate the effects of the cavity dimensions on improving the stability limit of the compressor. The analysis of flow structure near the stall limit has revealed that the large vortex appearing near the blade tip is being controlled by such a type of casing treatment; hence the stall onset is delayed. As consequence, the operating range and the stall margin are improved by reducing the aerodynamic blockage. Copyright © IMechE 2012.


Ghenaiet A.,Laboratory of Thermal Power Systems
Proceedings of the ASME Turbo Expo | Year: 2010

Under particulate environments, turbocompressors suffer from erosion which is of serious concern to both manufacturers and users of these equipments. In this paper, the results of a numerical study of particle laden air flows through a radial compressor 'Schwitzer' are presented. Particle trajectories used an updated version of our in-house code based on a stochastic Lagrangian tracking approach, where equations of particle motion are solved separately from the air-stream. This latter considers the effects of turbulence on particles, initial locations of particles and random particle size and rebound. The tracking of particles in different computational cells and theirs corresponding impacts used the finite element method. The number of particles, their sizes and initial positions were specified according to a concentration profile and an AC coarse (0-200 micron) size distribution. The simulations results are depicting that the impeller rotating speed and particle size strongly affect the trajectories, locations of impacts and erosion rates. For a high rotational speed, erosion is spreading over the pressure side of the main blade and splitter. Regions of high erosion rates are seen on the blades leading edges and towards the upper corner at blade exit. However, the main blade is highly eroded than the splitter. The suction side is almost without erosion except near the leading edge. Furthermore, the casing is mainly affected over the inducer and along the tips of blades. © 2010 by ASME.


Ghenaiet A.,Laboratory of Thermal Power Systems
Proceedings of the ASME Turbo Expo | Year: 2010

Ingestion of dust particles by aero-engines or stationary gas turbines is inevitable when operating in extremely polluted environments. The impingements of particles on the surfaces of blades cause erosion damage and permanent losses in engine performance. This paper presents a study of the particle dynamics and erosion in the first stage of a turbofan. The steady flow field through the turbomachinery components was solved separately from the solid phase. The particle trajectories computations used a stochastic Lagrangian tracking code that implements probabilistic modeling for particle size rebound and fragmentation, and considers the eddy-lifetime concept for turbulence and the complex flow features near walls. The equations of a particle motion were solved in a stepwise manner using the seventh order RK-Fehlberg technique, whereas particle tracking in different cells of the computational domain used the finite element method. Computations of particle trajectories were carried out for sand particles MIL-E5007E (0-1000 microns) at low, mid and high concentrations. As the locations of impacts were predicted, erosion contours were estimated and the subsequent blade deteriorations were assessed. The rotor blade shows a noticeable erosion of the blade leading and trailing edges almost from root to tip and a rounding of blade tip. Erosion patterns in the diffuser depict high erosion at blade leading and trailing edges and the erosion of pressure side is spreading almost from root to tip, in addition to erosion over the suction side. The actual findings may serve in improving erosion resistance of the blades in this fan stage. © 2010 by ASME.

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