scholarly journals Efficiency Assessment for Rehabilitated Francis Turbines Using URANS Simulations

Water ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 1883
Author(s):  
Philippe Martineau Rousseau ◽  
Azzeddine Soulaïmani ◽  
Michel Sabourin
Keyword(s):  
Model Tests ◽  
Flow Modeling ◽  
Complex Flow ◽  
Simulation Methodology ◽  
Modeling Methods ◽  
Efficiency Assessment ◽  
Efficiency Increase ◽  
Hydraulic Turbines ◽  
Low Efficiency ◽  
Time Limitations

Due to the large number of aging hydraulic turbines in North America, rehabilitation is a growing market as these turbines have low efficiency compared to modern ones. Computational Fluid Dynamics identifies components with poor hydraulic performance. The models often used in industry are based on individually analyzing the sub-components of a turbine instead of full turbine simulations due to computational and time limitations. An industrial case has shown that such analyses may lead to underestimating the efficiency increases by modifying the stay vane. The unsteady full turbine simulation proposes to simulate all components simultaneously to assess this efficiency augmentation due to stay vane rehabilitation. The developed simulation methodology is used to evaluate the efficiency increase and the flow of two rehabilitated turbines with stay vane modifications. Comparison with model tests shows the accuracy of the simulations. However, the methodology used shows imprecision in predicting the efficiency increase compared to model tests. Further works should consider the use of more complex flow modeling methods to measure the efficiency increase by the stay vane modifications.

The performance of a centrifugal compressor with a tandem impeller in off-design conditions

2019 ◽  
Vol 234 (2) ◽  
pp. 156-172 ◽  
Author(s):  
Ziliang Li ◽  
Xingen Lu ◽  
Ge Han ◽  
Yanfeng Zhang ◽  
Shengfeng Zhao ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Performance Enhancement ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Complex Flow ◽  
Maximum Enhancement ◽  
Operating Range ◽  
Wide Range ◽  
Compressor Performance ◽  
Low Efficiency

Centrifugal compressors often suffer relatively low efficiency and a terrible operating range particularly due to the complex flow structure and intense impeller/diffuser interaction. Numerous studies have focused on improving the centrifugal compressor performance using many innovative ideas, such as the tandem impeller, which has become increasingly attractive due to its ability to achieve the flow control with no additional air supply configurations and control costs in compressor. However, few studies that attempted to the investigation of tandem impeller have been published until now and the results are always contradictory. To explore the potential of the tandem impeller to enhance the compressor performance and the underlying mechanism of the flow phenomena in the tandem impellers, this paper numerically investigated a high-pressure-ratio centrifugal compressor with several tandem impellers at off-design operating speeds. The results encouragingly demonstrate that the tandem impeller can achieve a performance enhancement over a wide range of operating conditions. Approximately 1.8% maximum enhancement in isentropic efficiency and 5.0% maximum enhancement in operating range are achieved with the inducer/exducer circumferential displacement of [Formula: see text] = 25% and 50%, respectively. The observed stage performance gain of the tandem impellers decreases when the operating speed increases due to the increased inducer shock, increased wake losses, and deteriorated tandem impeller discharge flow uniformity. In addition, the tandem impeller can extend the impeller operating range particularly at low rotation speeds, which is found to be a result from the suppression of the low-momentum fluid radial movement. The results also indicate that the maximum flux capacity of the tandem impeller decreases due to the restriction of the inducer airfoil Kutta–Joukowsky condition.

Dynamic modal analysis during reduced scale model tests of hydraulic turbines for hydro-acoustic characterization of cavitation flows

2019 ◽  
Vol 117 ◽  
pp. 81-96 ◽  
Author(s):  
Arthur Favrel ◽  
Joao Gomes Pereira Junior ◽  
Christian Landry ◽  
Andres Müller ◽  
Kazuhiko Yamaishi ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Model Tests ◽  
Scale Model ◽  
Acoustic Characterization ◽  
Hydraulic Turbines ◽  
Reduced Scale

scholarly journals Performance Analysis of a Photovoltaic-Thermal Integrated System

2009 ◽  
Vol 2009 ◽  
pp. 1-6 ◽  
Author(s):  
Ewa Radziemska
Keyword(s):  
Performance Analysis ◽  
Solar Energy ◽  
Integrated System ◽  
Heat Extraction ◽  
Total Efficiency ◽  
Efficiency Increase ◽  
Low Efficiency ◽  
Exergetic Analysis ◽  
Photovoltaic Solar Cells ◽  
T System

The present commercial photovoltaic solar cells (PV) converts solar energy into electricity with a relatively low efficiency, less than 20%. More than 80% of the absorbed solar energy is dumped to the surroundings again after photovoltaic conversion. Hybrid PV/T systems consist of PV modules coupled with the heat extraction devices. The PV/T collectors generate electric power and heat simultaneously. Stabilizing temperature of photovoltaic modules at low level is higly desirable to obtain efficiency increase. The total efficiency of 60–80% can be achieved with the whole PV/T system provided that the T system is operated near ambient temperature. The value of the low-T heat energy is typically much smaller than the value of the PV electricity. The PV/T systems can exist in many designs, but the most common models are with the use of water or air as a working fuid. Efficiency is the most valuable parameter for the economic analysis. It has substantial meaning in the case of installations with great nominal power, as air-cooled Building Integrated Photovoltaic Systems (BIPV). In this paper the performance analysis of a hybrid PV/T system is presented: an energetic analysis as well as an exergetic analysis. Exergy is always destroyed when a process involves a temperature change. This destruction is proportional to the entropy increase of the system together with its surroundings—the destroyed exergy has been called anergy. Exergy analysis identifies the location, the magnitude, and the sources of thermodynamic inefficiences in a system. This information, which cannot be provided by other means (e.g., an energy analysis), is very useful for the improvement and cost-effictiveness of the system. Calculations were carried out for the tested water-cooled ASE-100-DGL-SM Solarwatt module.

Numerical and Experimental Study of Impeller Diffuser Interaction

2002 ◽  
Author(s):  
Tarek Mekhail ◽  
Zhaohui Du ◽  
Willem Jansen ◽  
Hanping Chen
Keyword(s):  
Internal Flow ◽  
Leading Edge ◽  
Initial Guess ◽  
Interaction Region ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Complex Flow ◽  
Vaned Diffuser ◽  
Flow Phenomena ◽  
Low Efficiency

The unsteadiness of the flow at the leading edge of a vaned diffuser represents a source of low efficiency and instability in a centrifugal turbomachine. Furthermore, the internal flow of the impeller can be affected by asymmetric downstream conditions, which results in extra flow unsteadiness and instabilities. Numerical and experimental data are obtained. The simulation of impeller diffuser interaction is performed using CFX-Tascflow. A frozen rotor simulation is used for the steady calculation and a rotor-stator simulation is used for the unsteady calculation using the steady results as an initial guess. The unsteady simulation is done not only for one impeller and diffuser blades, but also for the whole impeller and diffuser blades using Unix workstation. For the experimental work, a transparent fan is design and tested at The Turbomachinery Laboratory of SJTU. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A particle image velocimeter (PIV) is used to measure the 2-D instantaneous velocity in the interaction region between impeller, vaned. A series of performance measurements were carried out at different speeds. The first trial of measuring the instantaneous flow field in a part of the impeller and vaned diffuser together at different relative locations between them is presented in this work at different flow rates. Obtaining detailed measurements in the interaction region between the impeller and diffuser can help in understanding the complex flow phenomena and improving centrifugal fan and compressor performance. Finally, the comparison between the unsteady measurements and unsteady calculations showed that the Rotor/Stator Model can predict the basic characteristics of unsteady flow in centrifugal fan but still need improvement to satisfy the true transient simulation for unsteady impeller diffuser interaction.

scholarly journals ALGORITHM FOR EFFICIENCY INCREASE OF HETEROGENEOUS MULTI-PROCESSOR COMPUTER SYSTEMS

2016 ◽  
Vol 2016 (2) ◽  
pp. 186-192
Author(s):  
Александр Колпаков ◽  
Aleksandr Kolpakov ◽  
Юрий Кропотов ◽  
Yuriy Kropotov
Keyword(s):  
Parallel Computation ◽  
Computer Systems ◽  
Parallel Computations ◽  
Assessment Method ◽  
Computation Efficiency ◽  
Efficiency Assessment ◽  
Pram Model ◽  
Efficiency Increase ◽  
Assessment Results

In the paper there is considered an algorithm developed on the basis of modified PRAM-model for efficiency increase of parallel computations on specialized computer modules. By means of the efficiency assessment method there were carried out comparative experimental inves-tigations of the algorithm developed. The assessment results of the algorithm for the parallel computation efficiency increase on special computer modules show efficiency increase not less than 2-4 times depending on the number of flows under investigation.

Benchmark Study on Thruster-Hull Interaction on a Semi-Submersible Crane Vessel

2011 ◽  
Author(s):  
Harald Ottens ◽  
Radboud van Dijk ◽  
Geert Meskers
Keyword(s):  
Test Data ◽  
Model Test ◽  
Numerical Study ◽  
Open Water ◽  
Model Tests ◽  
Complex Flow ◽  
Calculation Results ◽  
Thrust Efficiency ◽  
Force Components ◽  
The Individual

During offshore heavy lift or pipelay operations the station keeping capabilities of a DP-vessel have an important influence on operability limits of these operations. Heerema Marine Contractors has two DP3-class semi-submersible crane vessels for these operations; the Thialf and Balder. An assessment of the thrust efficiency of the DP thrusters of these vessels has been made by comparing CFD computations with dedicated model tests. A numerical study using CFD is performed to assess thruster-hull interaction on a semi-submersible vessel. The CFD results are validated with a series of model tests, including an open water thruster, single thruster-hull interaction without current and full thruster-hull interaction with all thrusters active without current. The CFD calculation results show good agreement with the model test data. The forces on the semi-submersible as well as on the individual floaters with active thrusters using CFD are within 10% of the model test data. The largest discrepancies are in the bow quartering conditions when the thruster-hull interaction show the most complex flow pattern due to the location and shape of the stern keel. The comparison between the CFD and model test data demonstrates that CFD is able to predict the relevant force components well within a sufficient accuracy for engineering purposes. The paper also addresses lessons learnt to improve the CFD computations as well as practical aspects and limitations of thrust efficiency modeling using CFD from an engineering perspective.

scholarly journals EFFICIENCY ASSESSMENT OF GAS MAIN PIPELINE GEOTECHNICAL MONITORING BY QUALITY OF PRODUCED DATA

2015 ◽  
pp. 81-86
Author(s):  
Z. Sh. Aleskerova ◽  
S. A. Pulnikov ◽  
Yu. S. Sysoev ◽  
N. V. Kazakova
Keyword(s):  
Dynamic Assessment ◽  
Main Pipeline ◽  
Technical Problems ◽  
Object Condition ◽  
Geotechnical Monitoring ◽  
Efficiency Assessment ◽  
Gas Main ◽  
Gas Main Pipeline ◽  
Efficiency Increase

Geotechnical monitoring results analysis of gas main pipeline’s lineal part accomplished based on JSC «Gaz-prom» data of 2011-2013 yr. Line damages classification and its evolution dynamic assessment are made taking into account reconstruction operations of sections with non-normative condition. Definition is made about geotechnical monitoring main deficiency, which is lowering the quality of produced data about object condition. It is offering to solve the row of science-technical problems for efficiency increase of geotechnical monitoring results proceeding methodic.

Detailed CFD Analysis of the Steady Flow in a Wells Turbine Under Incipient and Deep Stall Conditions

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
M. Torresi ◽  
S. M. Camporeale ◽  
G. Pascazio
Keyword(s):  
High Efficiency ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Main Stream ◽  
Tip Leakage Flow ◽  
Complex Flow ◽  
Wells Turbine ◽  
High Rotational Speed ◽  
Flow Rates ◽  
Low Efficiency

This paper presents the results of the numerical simulations carried out to evaluate the performance of a high solidity Wells turbine designed for an oscillating water column wave energy conversion device. The Wells turbine has several favorable features (e.g., simplicity and high rotational speed) but is characterized by a relatively narrow operating range with high efficiency. The aim of this work is to investigate the flow-field through the turbine blades in order to offer a description of the complex flow mechanism that originates separation and, consequently, low efficiency at high flow-rates. Simulations have been performed by solving the Reynolds-averaged Navier–Stokes equations together with three turbulence models, namely, the Spalart–Allmaras, k-ω, and Reynolds-stress models. The capability of the three models to provide an accurate prediction of the complex flow through the Wells turbine has been assessed in two ways: the comparison of the computed results with the available experimental data and the analysis of the flow by means of the anisotropy invariant maps. Then, a detailed description of the flow at different flow-rates is provided, focusing on the interaction of the tip-leakage flow with the main stream and enlightening its role on the turbine performance.

scholarly journals Numerical analysis of the thermal and fluid dynamic behavior of the flue gases in a traditional furnace for panela production

Inge CUC ◽  
2019 ◽  
Vol 15 (1) ◽  
pp. 133-141
Author(s):  
Edxon Stiven Meneses Chacón ◽  
Julián Ernesto Jaramillo-Ibarra ◽  
Elisabet Mas de les Valls
Keyword(s):  
Optical Thickness ◽  
Flue Gas ◽  
Thermal Efficiency ◽  
Fluid Dynamic ◽  
Heat Transfer Process ◽  
Flue Gases ◽  
Thickness Effect ◽  
Efficiency Increase ◽  
Real Size ◽  
Low Efficiency

Introduction: Panela is a product derived from sugar cane that is prepared using a traditional burner designed especially for this purpose. According to studies found in the literature, it was identified that the thermal efficiency of panela burners is 30% on average. Objective: The objective of this investigation is to contribute to the search for new alternatives for the improvement of the low efficiency present on these systems, mainly affecting the flue gases duct. Methodology: The development of this study is as follows: first, a research of the radiation and optical thickness effect in a simplified furnace is carried out. Afterward, a series of simulations with modifications in the design of the flue gas duct for a real size furnace are analyzed. Results: The results showed that the radiation effect must be considered and, even though the optical thickness is low, it has a relevant impact in the heat transfer process due to the high temperatures in the furnace. A chaotic movement of the gases implied more heat transferred to the heaters and high values of Nusselt with the addition of new elements in the duct were obtained. Conclusions: Arrangement 1, provides the best results with a Nusselt and thermal efficiency increase. No significant differences between the DOM and the P-1 radiation were found.

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