scholarly journals Dynamics of a Cavitating Propeller in a Water Tunnel

2003 ◽  
Vol 125 (2) ◽  
pp. 283-292 ◽  
Author(s):  
Satoshi Watanabe ◽  
Christopher E. Brennen
Keyword(s):  
Present Model ◽  
Gain Factor ◽  
Operating Conditions ◽  
Water Tunnel ◽  
Tube Model ◽  
Cavity Model ◽  
Flow Tube ◽  
Stream Tube ◽  
Thrust Coefficient ◽  
One Dimensional

This study investigates the unsteady dynamics and inherent instabilities of a cavitating propeller operating in a water tunnel. First, the steady characteristics of the cavitating propeller such as the thrust coefficient are obtained by applying continuity and momentum equations to a simple one-dimensional flow tube model. The effects of the tunnel walls as well as those of the propeller operating conditions (advance ratio and cavitation number) are explored. Then the transfer matrix of the cavitating propeller (considered to be the most appropriate way to describe the dynamics of propeller) is obtained by combining the simple stream tube model with the conventional cavity model using the quasi-static cavitation compliance and mass flow gain factor representation. Finally, the surge instability of a cavitating propeller observed by Duttweiler and Brennen (2001) is examined by coupling the present model of the cavitation with a dynamic model for the water tunnel. This analysis shows that the effect of tunnel walls is to promote the surge instability.

Frequency Dependence of Mass Flow Gain Factor and Cavitation Compliance of Cavitating Inducers

1996 ◽  
Vol 118 (2) ◽  
pp. 400-408 ◽  
Author(s):  
S. Otsuka ◽  
Y. Tsujimoto ◽  
K. Kamijo ◽  
O. Furuya
Keyword(s):  
Mass Flow ◽  
Present Model ◽  
Cavity Length ◽  
Incidence Angle ◽  
Low Frequency ◽  
Gain Factor ◽  
Cavity Model ◽  
Frequency Limit ◽  
Closed Cavity ◽  
Reduced Frequency

Unsteady cavitation characteristics are analyzed based on a closed cavity model in which the length of the cavity is allowed to oscillate. It is shown that the present model blends smoothly into quasi-steady calculations at the low frequency limit, unlike fixed cavity length models. Effects of incidence angle and cavitation number on cavitation compliance and mass flow gain factor are shown as functions of reduced frequency. The cavity volume is evaluated by three methods and the results are used to confirm the accuracy and adequacy of the numerical calculations. By comparison with experimental data on inducers, it is shown that the present model can simulate the characteristics of unsteady-cavitation qualitatively.

scholarly journals Performance prediction of Darrieus vertical axis wind turbines using double multiple stream-tube model

2015 ◽  
Vol 18 (4) ◽  
pp. 153-161 ◽  
Author(s):  
Hieu Thi Hong Le ◽  
Cong Chi Nguyen ◽  
Trong Huu Luong
Keyword(s):  
Experimental Data ◽  
Output Power ◽  
Wind Turbines ◽  
Performance Prediction ◽  
Vertical Axis ◽  
Operating Conditions ◽  
Dynamic Stall ◽  
Tube Model ◽  
Stream Tube ◽  
Vertical Axis Wind Turbines

Horizontal and vertical axis wind turbines (HAWTs and VAWTs) are two main kinds of wind turbines, which are the most popular way to catch energy from the wind. By comparison, VAWTs have some advantages, but they also have the complexity in aerodynamics that needs a deep investigation. A code is developed based on Double multiple stream-tube and corrections of the dynamic stall for Darrieus VAWTs. It is capable of estimating the output power versus different operating conditions defined by the tipspeed- ratio. The code is also validated with experimental data of many SANDIA Darrieus VAWT turbines.

scholarly journals CFD Study of Nozzle Configurations for Ultra High Bypass Engines

1993 ◽  
Author(s):  
H. Zimmermann ◽  
R. Gumucio ◽  
K. Katheder ◽  
A. Jula
Keyword(s):  
Engine Performance ◽  
Operating Conditions ◽  
Aerodynamic Design ◽  
Thrust Coefficient ◽  
Optimum Range ◽  
Installation Effects ◽  
Wide Range ◽  
And Performance ◽  
Aircraft Aerodynamics ◽  
Bypass Ratio

Performance and aerodynamic aspects of ultra-high bypass ratio ducted engines have been investigated with an emphasis on nozzle aerodynamics. The interference with aircraft aerodynamics could not be covered. Numerical methods were used for aerodynamic investigations of geometrically different aft end configurations for bypass ratios between 12 and 18, this is the optimum range for long missions which will be important for future civil engine applications. Results are presented for a wide range of operating conditions and effects on engine performance are discussed. The limitations for higher bypass ratios than 12 to 18 do not come from nozzle aerodynamics but from installation effects. It is shown that using CFD and performance calculations an improved aerodynamic design can be achieved. Based on existing correlations, for thrust and mass-flow, or using aerodynamic tailoring by CFD and including performance investigations, it is possible to increase the thrust coefficient up to 1%.

A Numerical Model of In-Channel Pebble Bed Thermal Storage for a Solar Chimney

2012 ◽  
Author(s):  
Brandon Schulte ◽  
O. A. Plumb
Keyword(s):  
Numerical Model ◽  
Present Model ◽  
Thermal Storage ◽  
Implicit Time ◽  
Heat Transfer Characteristics ◽  
Solar Chimney ◽  
Pebble Bed ◽  
One Dimensional ◽  
Time Stepping ◽  
Daily Energy

In this study, solar chimney performance is numerically modeled. Previously published models have considered water bags and natural earth as means to store daytime thermal energy for nighttime operation of the system. The present model considers in-channel pebble bed thermal storage. A one-dimensional, implicit time stepping numerical model is developed to predict solar chimney performance throughout a 24 hour period. The model is partially verified with available experimental data. The daily energy, daily efficiency and heat transfer characteristics of the solar chimney with pebble bed thermal storage are summarized. The numerical simulation showed that by introducing a pebble bed, nightly exit velocities reach 40% of the peak daytime velocity. However, the daily kinetic energy delivered by a solar chimney with pebble bed thermal storage is much less than a traditional solar chimney, suggesting pebble bed thermal storage is more practicable in building heating applications as opposed to power generation.

A stream tube model for miscible flow

1995 ◽  
Vol 18 (3) ◽  
pp. 263-282 ◽  
Author(s):  
Roland Lenormand ◽  
Biao Wang
Keyword(s):  
Tube Model ◽  
Stream Tube ◽  
Miscible Flow

scholarly journals Reliable simple zonal method of the furnace thermal calculation

2005 ◽  
Vol 9 (2) ◽  
pp. 45-55
Author(s):  
Vladan Ivanovic
Keyword(s):  
Energy Consumption ◽  
Flue Gas ◽  
Thermal Load ◽  
Operating Conditions ◽  
Thermal Calculation ◽  
Gas Temperature ◽  
Zonal Method ◽  
One Dimensional ◽  
Furnace Performance ◽  
Steam Boilers

The calculation of the furnace in the industrial and power boilers is the most important and the most responsible part of the thermal calculation, and it has important influence on the rationalization of energy consumption. In the paper one-dimensional zonal method of the furnace thermal calculation of steam boilers is presented. It can successfully define disposition of flue gas temperature and specific thermal load of screen walls with height of the furnace in case of uneven deposits distribution which vary in size and quality. Its greatest use is for comparing furnace performance under various operating conditions.

scholarly journals Incorporation of a Non-Constant Thrust Force Coefficient to Assess Tidal-Stream Energy

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4151 ◽  
Author(s):  
Lilia Flores Mateos ◽  
Michael Hartnett
Keyword(s):  
Near Field ◽  
Regional Scale ◽  
Resource Assessment ◽  
Operating Conditions ◽  
Force Coefficient ◽  
Thrust Coefficient ◽  
Power Extraction ◽  
Energy Assessment ◽  
Tidal Stream ◽  
Tidal Stream Energy

A novel method for modelling tidal-stream energy capture at the regional scale is used to evaluate the performance of two marine turbine arrays configured as a fence and a partial fence. These configurations were used to study bounded and unbounded flow scenarios, respectively. The method implemented uses turbine operating conditions (TOC) and the parametrisation of changes produced by power extraction within the turbine near-field to compute a non-constant thrust coefficient, and it is referred to as a momentum sink TOC. Additionally, the effects of using a shock-capture capability to evaluate the resource are studied by comparing the performance of a gradually varying flow (GVF) and a rapidly varying flow (RVF) solver. Tidal-stream energy assessment of bounded flow scenarios through a full fence configuration is better performed using a GVF solver, because the head drop is more accurately simulated; however, the solver underestimates velocity reductions due to power extraction. On the other hand, assessment of unbounded flow scenarios through a partial fence was better performed by the RVF solver. This scheme approximated the head drop and velocity reduction more accurately, thus suggesting that resource assessment with realistic turbine configurations requires the correct solution of the discontinuities produced in the tidal-stream by power extraction.

scholarly journals A zonal approach for estimating pressure ratio at compressor extreme off-design conditions

2018 ◽  
Vol 20 (4) ◽  
pp. 393-404 ◽  
Author(s):  
José Galindo ◽  
Roberto Navarro ◽  
Luis Miguel García-Cuevas ◽  
Daniel Tarí ◽  
Hadi Tartoussi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Internal Combustion Engines ◽  
Pressure Ratio ◽  
Internal Combustion ◽  
Operating Conditions ◽  
Combustion Engines ◽  
One Dimensional ◽  
Performance Map

Zero-dimensional/one-dimensional computational fluid dynamics codes are used to simulate the performance of complete internal combustion engines. In such codes, the operation of a turbocharger compressor is usually addressed employing its performance map. However, simulation of engine transients may drive the compressor to work at operating conditions outside the region provided by the manufacturer map. Therefore, a method is required to extrapolate the performance map to extended off-design conditions. This work examines several extrapolating methods at the different off-design regions, namely, low-pressure ratio zone, low-speed zone and high-speed zone. The accuracy of the methods is assessed with the aid of compressor extreme off-design measurements. In this way, the best method is selected for each region and the manufacturer map is used in design conditions, resulting in a zonal extrapolating approach aiming to preserve accuracy. The transitions between extrapolated zones are corrected, avoiding discontinuities and instabilities.

One-Dimensional Zonal Model for the Unsteady Heat Transfer Analysis in an Open Volumetric Air Receiver

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Gurveer Singh ◽  
Vishwa Deepak Kumar ◽  
Laltu Chandra ◽  
R. Shekhar ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
High Heat Flux ◽  
Unsteady Heat Transfer ◽  
Volumetric Heating ◽  
One Dimensional ◽  
Zonal Model

Abstract The open volumetric air receiver (OVAR)-based central solar thermal systems provide air at a temperature > 1000 K. Such a receiver is comprised of porous absorbers, which are exposed to a high heat-flux > 800 Suns (1 Sun = 1 kW/m2). A reliable assessment of heat transfer in an OVAR is necessary to operate such a receiver under transient conditions. Based on a literature review, the need for developing a comprehensive, unsteady, heat transfer model is realized. In this paper, a seven-equations based, one-dimensional, zonal model is deduced. This includes heat transfer in porous absorber, primary-air, return-air, receiver casing, and their detailed interaction. The zonal model is validated with an inhouse experiment showing its predictive capability, for unsteady and steady conditions, within the reported uncertainty of ±7%. The validated model is used for investigating the effect of operating conditions and absorber geometry on the thermal performance of an absorber. Some of the salient observations are (a) the maximum absorber porosity of 70–90% may be preferred for non-volumetric and volumetric-heating conditions, (b) the minimum air-return ratio should be 0.7, and (c) the smallest gap to absorber-length ratio of 0.2 should suffice. Finally, suggestions are provided for extending the model.

scholarly journals Radial turbine sound and noise characterisation with acoustic transfer matrices by means of fast one-dimensional models

2019 ◽  
pp. 146808741988942
Author(s):  
Antonio Torregrosa ◽  
Luis Miguel García-Cuevas ◽  
Lukas Benjamin Inhestern ◽  
Pablo Soler
Keyword(s):  
Mean Value ◽  
Operating Conditions ◽  
Design Stage ◽  
Transfer Matrices ◽  
Efficient Manner ◽  
One Dimensional ◽  
Engine Design ◽  
Lookup Tables ◽  
Single Entry ◽  
Radial Turbines

Estimating correctly the turbine acoustics can be valuable during the engine design stage; in fact, it can lead to a more optimised design of the silencer and aftertreatment, as well as to better prediction of the scavenging effects. However, obtaining the sound and noise emissions of radial turbocharger turbines with low computational costs can be challenging. To consider these effects in a time-efficient manner, the acoustic response of single-entry radial turbines can be characterised by means of acoustic transfer matrices that change with the operating conditions. Exploiting the different time-scales of the acoustic phenomena and the change in the operating point of the turbine, lookup tables of acoustic transfer matrices can be computed. Then, the obtained characterisation can be used in mean-value engine models. This article presents a method for generating these lookup tables by means of fast one-dimensional simulations of thoroughly validated fidelity, in terms of both acoustics and extrapolation capabilities. Due to the inherent behaviour of radial turbines, the number of computations needed to fill the lookup tables is relatively small, so the method can be used as a simple preprocessing phase before mean-value simulation campaigns.

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