Hydraulic power of slow-rotating waterwheels: a novel analytical approximation

2011 ◽  
Vol 225 (6) ◽  
pp. 1495-1506 ◽  
Author(s):  
T Pujol ◽  
L Montoro ◽  
X Silva
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Analytical Approximation ◽  
Hydraulic Power ◽  
Basic Principles ◽  
Classical Expression ◽  
Computational Fluid Dynamics Simulations ◽  
Hydraulic Turbines ◽  
Mechanical Devices ◽  
Dynamics Simulations

Slow-rotating waterwheels are mechanical devices of great historical relevance since they provided power to ancient communities for shifting from a subsistence to a market-oriented economy. Technical studies of these antecessors of hydraulic turbines mainly rely on basic principles that do not take into account the blade-to-blade distance and, therefore, the loss of energy from spillage (parts of the jet flow that do not interact with the moving blades). These effects are included in this article in a novel analytical approximation based on a sequential frame methodology. We apply this extended analytical expression to the analysis of three different sets of parameters referred to a laboratory-scale horizontal waterwheel. Results are compared with those obtained experimentally and, also, with computational fluid dynamics simulations. In contrast to the classical expression that clearly fails to explain the waterwheel behaviour when few blades are employed, our new analytical approximation remarkably agrees with both simulations and experimental data.

A New Alternative for Reduction in Secondary Flows in Low Pressure Turbines

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Diego Torre ◽  
Raúl Vázquez ◽  
Elena de la Rosa Blanco ◽  
Howard P. Hodson
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Physical Phenomenon ◽  
Low Pressure ◽  
Secondary Flows ◽  
Flow Mechanism ◽  
Linear Cascade ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

This paper describes a new flow mechanism for the reduction in secondary flows in low pressure turbines using the benefit of contoured endwalls. The extensive application of contoured endwalls in recent years has provided a deeper understanding of the physical phenomenon that governs the reduction in secondary flows. Based on this understanding, the endwall geometry of a linear cascade of solid-thin profiles typical of low pressure turbines has been redesigned. Experimental data are presented for the validation of this new solution. Based on these data, a reduction of 72% in the secondary kinetic energy helicity (SKEH) and 20% in the mixed-out endwall losses can be obtained. Computational fluid dynamics simulations are also presented to illustrate the effect of the new endwall on the secondary flows. Furthermore, an explanation of the flow mechanism that governs the reduction in the SKEH, and the losses is given.

Entrainment regimes and flame characteristics of wildland fires

2012 ◽  
Vol 21 (2) ◽  
pp. 127 ◽  
Author(s):  
Ralph M. Nelson ◽  
Bret W. Butler ◽  
David R. Weise
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Critical Value ◽  
Fire Behaviour ◽  
Regression Techniques ◽  
Computational Fluid Dynamics Simulations ◽  
Model Equations ◽  
Dynamics Simulations ◽  
Behaviour Data

This paper reports results from a study of the flame characteristics of 22 wind-aided pine litter fires in a laboratory wind tunnel and 32 field fires in southern rough and litter–grass fuels. Flame characteristic and fire behaviour data from these fires, simple theoretical flame models and regression techniques are used to determine whether the data support the derived models. When the data do not support the models, alternative models are developed. The experimental fires are used to evaluate entrainment constants and air/fuel mass ratios in the model equations. Both the models and the experimental data are consistent with recently reported computational fluid dynamics simulations that suggest the existence of buoyancy- and convection-controlled regimes of fire behaviour. The results also suggest these regimes are delimited by a critical value of Byram’s convection number. Flame heights and air/fuel ratios behave similarly in the laboratory and field, but flame tilt angle relationships differ.

scholarly journals A comparison of computational fluid dynamics predicted initial liquid penetration using rate of injection profiles generated using two different measurement techniques

2017 ◽  
Vol 20 (2) ◽  
pp. 226-235 ◽  
Author(s):  
Haiwen Ge ◽  
Jaclyn E Johnson ◽  
Hari Krishnamoorthy ◽  
Seong-Young Lee ◽  
Jeffrey D Naber ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Momentum Flux ◽  
Measurement Techniques ◽  
Liquid Penetration ◽  
Flux Method ◽  
Computational Fluid Dynamics Simulations ◽  
Bulk Charge ◽  
Dynamics Simulations

The rate of injection profile is a key parameter describing the fuel injection process for diesel injection. It is also an essential input parameter for computational fluid dynamics simulations of spray flows. In the present work, rate of injection profiles of a multi-hole diesel injector were measured using the Zeuch method and the momentum flux method. The rate of injection profiles measured by the momentum flux method had a faster rise in rate of injection during the initial ramp-up phase than with the Zeuch method. The measured rate of injection profiles were applied in three-dimensional computational fluid dynamics simulations of diesel sprays under non-vaporizing and vaporizing conditions with sweeps in injection pressure, bulk charge gas density, and bulk charge gas temperature. Analytical results were compared against experimental data for liquid penetration generated under those conditions. Computational fluid dynamics results with the rate of injection profile measured by the Zeuch method under-predict liquid penetration during the initial ramp-up phase, while computational fluid dynamics results with the rate of injection profiles measured by the momentum flux method showed much better agreement with the experimental data of liquid length and penetration. This suggests that current computational fluid dynamics spray models may be able to more accurately model transient liquid penetration when using the velocity profile developed from momentum flux measurements. Further study is needed to evaluate how computational fluid dynamics predictions of combustion and emissions of affected when using these two rate of injection profiles.

scholarly journals Aerodynamic analysis of uphill drafting in cycling

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
T. van Druenen ◽  
B. Blocken
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Scientific Literature ◽  
Sensitivity Analyses ◽  
Air Resistance ◽  
Wind Tunnel Measurements ◽  
Aerodynamic Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

AbstractSome teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

scholarly journals Evaluation of Active Heat Sinks Design under Forced Convection—Effect of Geometric and Boundary Parameters

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2041
Author(s):  
Eva C. Silva ◽  
Álvaro M. Sampaio ◽  
António J. Pontes
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Forced Convection ◽  
Thermal Performance ◽  
Heat Sinks ◽  
Trapezoidal Shape ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

This study shows the performance of heat sinks (HS) with different designs under forced convection, varying geometric and boundary parameters, via computational fluid dynamics simulations. Initially, a complete and detailed analysis of the thermal performance of various conventional HS designs was taken. Afterwards, HS designs were modified following some additive manufacturing approaches. The HS performance was compared by measuring their temperatures and pressure drop after 15 s. Smaller diameters/thicknesses and larger fins/pins spacing provided better results. For fins HS, the use of radial fins, with an inverted trapezoidal shape and with larger holes was advantageous. Regarding pins HS, the best option contemplated circular pins in combination with frontal holes in their structure. Additionally, lattice HS, only possible to be produced by additive manufacturing, was also studied. Lower temperatures were obtained with a hexagon unit cell. Lastly, a comparison between the best HS in each category showed a lower thermal resistance for lattice HS. Despite the increase of at least 38% in pressure drop, a consequence of its frontal area, the temperature was 26% and 56% lower when compared to conventional pins and fins HS, respectively, and 9% and 28% lower when compared to the best pins and best fins of this study.

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