scholarly journals Comparative turbulent three-dimensional Navier–Stokes hydrodynamic analysis and performance assessment of oscillating wings for renewable energy applications

2016 ◽  
Vol 16 ◽  
pp. 100-115 ◽  
Author(s):  
Jernej Drofelnik ◽  
M. Sergio Campobasso
Keyword(s):  
Renewable Energy ◽  
Performance Assessment ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Hydrodynamic Analysis ◽  
Energy Applications ◽  
And Performance

A Computational Analysis of Flow Field in Twin-Track Subway Tunnel to Improve Air Quality

2013 ◽  
Vol 319 ◽  
pp. 599-604
Author(s):  
Makhsuda Juraeva ◽  
Kyung Jin Ryu ◽  
Sang Hyun Jeong ◽  
Dong Joo Song
Keyword(s):  
Air Quality ◽  
Computational Model ◽  
Stokes Equations ◽  
Ventilation System ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Subway Tunnel ◽  
Air Supply ◽  
And Performance

A computational model of existing Seoul subway tunnelwas analyzed in this research. The computational model was comprised of one natural ventilationshaft, two mechanical ventilationshafts, one mechanical airsupply, a twin-track tunnel, and a train. Understanding the flow pattern of the train-induced airflow in the tunnel was necessary to improve ventilation performance. The research objective wasto improve the air quality in the tunnel by investigating train-induced airflow in the twin-track subway tunnel numerically. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The ventilation and aerodynamic characteristics in the tunnel were investigated by analyzing the mass flowrateat the exits of the ventilation mechanicalshafts. As the train passed the mechanical ventilation shafts, the amount of discharged-air in the ventilationshafts decreased rapidly. The air at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The developed mechanical air-supply for discharging dusty air and supplying clean airwas investigated.The computational results showed that the developed mechanical air-supplycould improve the air quality in the tunnel.

Aerodynamic Design and Performance of Aspirated Airfoils

2003 ◽  
Vol 125 (1) ◽  
pp. 141-148 ◽  
Author(s):  
Ali Merchant
Keyword(s):  
Guide Vane ◽  
Three Dimensional ◽  
High Loading ◽  
Navier Stokes ◽  
Aerodynamic Design ◽  
Design Studies ◽  
Controlled Diffusion ◽  
And Performance ◽  
The Impact ◽  
Profile Loss

The impact of boundary layer aspiration, or suction, on the aerodynamic design and performance of turbomachinery airfoils is discussed in this paper. Aspiration is studied first in the context of a controlled diffusion cascade, where the effect of discrete aspiration on loading levels and profile loss is computationally investigated. Blade design features which are essential in achieving high loading and minimizing the aspiration requirement are described. Design studies of two aspirated compressor stages and an aspirated turbine exit guide vane using three dimensional Navier-Stokes calculations are presented. The calculations show that high loading can be achieved over most of the blade span with a relatively small amount of aspiration. Three dimensional effects close to the endwalls are shown to degrade the performance to varying degrees depending on the loading level.

scholarly journals Impedance-Based Interactions in Grid-Tied Three-Phase Inverters in Renewable Energy Applications

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 464 ◽  
Author(s):  
Teuvo Suntio ◽  
Tuomas Messo ◽  
Matias Berg ◽  
Henrik Alenius ◽  
Tommi Reinikka ◽  
...  
Keyword(s):  
Renewable Energy ◽  
Experimental Measurements ◽  
Stability Assessment ◽  
Transient Performance ◽  
Energy Applications ◽  
Impedance Ratio ◽  
Three Phase ◽  
The Cross ◽  
And Performance ◽  
The Stability

Impedance-ratio-based interaction analyses in terms of stability and performance of DC-DC converters is well established. Similar methods are applied to grid-connected three-phase converters as well, but the multivariable nature of the converters and the grid makes these analyses very complex. This paper surveys the state of the interaction analyses in the grid-connected three-phase converters, which are used in renewable-energy applications. The surveys show clearly that the impedance-ratio-based stability assessment are usually performed neglecting the cross-couplings between the impedance elements for reducing the complexity of the analyses. In addition, the interactions, which affect the transient performance, are not treated usually at all due to the missing of the corresponding analytic formulations. This paper introduces the missing formulations as well as explicitly showing that the cross-couplings of the impedance elements have to be taken into account for the stability assessment to be valid. In addition, this paper shows that the most accurate stability information can be obtained by means of the determinant related to the associated multivariable impedance ratio. The theoretical findings are also validated by extensive experimental measurements.

scholarly journals Experimental and numerical research of the influence of thrust vector control on the missile aerodynamics by cold and hot jet simulations

2020 ◽  
Vol 48 (4) ◽  
pp. 770-778
Author(s):  
Goran Ocokoljić ◽  
Boško Rašuo ◽  
Dijana Damljanović ◽  
Saša Živković
Keyword(s):  
Vector Control ◽  
Three Dimensional ◽  
Combustion Products ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Cfd Model ◽  
Thrust Vector Control ◽  
Thrust Vector ◽  
And Performance ◽  
Definition Of

The flow field phenomena that occur as a result of thrust vector control (TVC) system activity on a missile with lateral jets are very complex and influence all other components of the missile. Influence is more significant when TVC is generating commands, when jets are asymmetrically directed. The main goal of these study was to determine the influence of of the hot rocket motor's combustion products on the basis of the CFD model proven with the cold-jet simulation. Based on obtained experimental aerodynamic coefficients for the cold-jet simulation the preliminary aerodynamic CFD model was designed. Three-dimensional Reynolds averaged Navier-Stokes numerical aerodynamic and hot-jet simulations were carried out to predict the aerodynamic loads of the missile based on the finite volume method. The study resulted in the definition of a methodology for the investigation of the jet reaction effects in a wind tunnel. A method for determining of the TVC system interference on the aerodynamic characteristics, as a basic prerequisite for structural, stability and performance analysis, was proposed. Mutual verification and validation process was carried out through experiment and proper application of the commercial CFD software code for calculation aerodynamic effects of the hot gases lateral jets on the performance of a guided missile. Experimental and computational results of the pitching moment coefficients are presented and agreed well with.

scholarly journals An enhanced 17-level hybridized multilevel inverter with stair case modulation

2020 ◽  
Vol 11 (4) ◽  
pp. 1872
Author(s):  
Hemalatha Javvaji ◽  
Basavaraja Banakara
Keyword(s):  
Renewable Energy ◽  
Solid State ◽  
Power Consumption ◽  
Output Voltage ◽  
Multilevel Inverter ◽  
Energy Applications ◽  
Multi Level ◽  
Simulation Results ◽  
And Performance ◽  
Cascaded Multilevel Inverter

This paper proposes a Hybridized Symmetric Cascaded Multilevel Inverter for voltage levels ranging from 5 levels to 17 levels. The proposed Multi Level Inverter (MLI) topology is built using a modified H-bridge inverter that results in an increased output voltage levels with a smaller number of solid-state switches. This technique enhances the h-bridge configuration from three level to five level by means of a bi-directional switch at source. Gating pulses of hybridized symmetric MLI are generated through staircase modulation. The operation and performance of the proposed topology is tested for different output voltage levels, simulation results prove that the proposed technique results in less THD at all levels with lesser power consumption and are easily applicable for renewable energy applications.

Wake and Performance Predictions of Two- and Three-Bladed Wind Turbines Based on the Actuator Line Model1

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Sebastian Henao Garcia ◽  
Aldo Benavides-Morán ◽  
Omar D. Lopez Mejia
Keyword(s):  
Wind Turbine ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Speed Ratio ◽  
Power Extraction ◽  
Low Incidence ◽  
And Performance ◽  
Turbine Design ◽  
Simulation Parameters

Abstract This paper challenges the standard wind turbine design numerically assessing the wake and aerodynamic performance of two- and three-bladed wind turbine models implementing downwind and upwind rotor configurations, respectively. The simulations are conducted using the actuator line model (ALM) coupled with a three-dimensional Navier Stokes solver implementing the k−ω shear stress transport turbulence model. The sensitivity of the ALM to multiple simulation parameters is analyzed in detail and numerical results are compared against experimental data. These analyses highlight the most suitable Gaussian radius at the rotor to be equal to twice the chord length at 95% of the blade for a tip-speed ratio (TSR) of ten, while the Gaussian radius at the tower and the number of actuator points have a low incidence on the flow field computations overall. The numerical axial velocity profiles show better agreement upstream than downstream the rotor, while the discrepancies are not consistent through all the assessed operating conditions, thus highlighting that the ALM parameters are also dependent on the wind turbine's operating conditions rather than being merely geometric parameters. Particularly, for the upwind three-bladed wind turbine model, the accuracy of the total thrust computations improves as the TSR increases, while the least accurate wake predictions are found for its design TSR. Finally, when comparing both turbine models, an accurate representation of the downwind configuration is observed as well as realistic power extraction estimates. Indeed, the results confirm that rotors with fewer blades are more suitable to operate at high TSRs.

Navier–Stokes Analysis of Turbine Blade Heat Transfer and Performance

1992 ◽  
Vol 114 (4) ◽  
pp. 795-806 ◽  
Author(s):  
D. J. Dorney ◽  
R. L. Davis
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Approximate Factorization ◽  
Absolute Level ◽  
Flow Angle ◽  
And Performance

A three-dimensional Navier–Stokes analysis of heat transfer and aerodynamic performance is presented for a low-speed linear turbine cascade. The numerical approach used in this analysis consists of an alternate-direction, implicit, approximate-factorization, time-marching technique. An objective of this investigation has been to establish the computational grid density requirements necessary to predict blade surface and endwall heat transfer accurately, as well as the exit plane aerodynamic total pressure loss and flow angle distributions. In addition, a study has been performed to determine the importance of modeling transition as well as a viable implementation strategy for the three-dimensional turbulence model in the turbine blade passage. Results are presented demonstrating that the present procedure can accurately predict three-dimensional turbine blade heat transfer as well as the absolute level and spanwise distribution of aerodynamic performance quantities.

scholarly journals Techniques for Turbulence Tripping of Boundary Layers in RANS Simulations

2021 ◽  
Author(s):  
Narges Tabatabaei ◽  
Ricardo Vinuesa ◽  
Ramis Örlü ◽  
Philipp Schlatter
Keyword(s):  
Boundary Layer ◽  
Passive Control ◽  
Target Location ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Transition Process ◽  
Navier Stokes ◽  
Test Cases ◽  
And Performance

AbstractThe exact placement of the laminar–turbulent transition has a significant effect on relevant characteristics of the boundary layer and aerodynamics, such as drag, heat transfer and flow separation on e.g. wings and turbine blades. Tripping, which fixes the transition position, has been a valuable aid to wind-tunnel testing during the past 70 years, because it makes the transition independent of the local condition of the free-stream. Tripping helps to obey flow similarity for scaled models and serves as a passive control mechanism. Fundamental fluid-mechanics studies and many engineering developments are based on tripped cases. Therefore, it is essential for computational fluid dynamics (CFD) simulations to replicate the same forced transition, in spite of the advanced improvements in transition modelling. In the last decade, both direct numerical simulation (DNS) and large-eddy simulations (LES) include tripping methods in an effort to avoid the need for modeling the complex mechanisms associated with the natural transition process, which we would like to bring over to Reynolds-averaged Navier–Stokes (RANS) turbulence models. This paper investigates the implementation and performance of such a technique in RANS and specifically in the $$k-\omega$$ k - ω SST model. This study assesses RANS tripping with three alternatives: First, a recent approach of turbulence generation, denoted as turbulence-injection method (kI), is evaluated and investigated through different test cases; second, a predefined transition point is used in a traditional transition model (denoted as IM method); and third a novel formulation combining the two previous methods is proposed, denoted $$\gamma -k$$ γ - k I. The model is compared with DNS, LES and experimental data in a variety of test cases ranging from a turbulent boundary layer on a flat plate to the three-dimensional (3D) flow over a wing section. The desired tripping is achieved at the target location and the simulation results compare very well with the reference results. With the application of the novel model, the challenging transition region can be excluded from a simulation, and consequently more reliable results can be provided.

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