Turbulent Speed Research Articles

The Design, Simulation and Testing of V-shape Roof Guide Vane Integrated with an Eco-roof System

Abstract The aim of this study is to present the performance of an innovative wind–solar-rain water hybrid renewable energy generator and harvester roof system. A novel V-shape roof guide vane (VRGV) that located above the vertical axis wind turbine (VAWT) is introduced to guide and increase the wind speed by the venturi effect before it interacts with the rotor blades, hence improve the performance of the wind turbine. 2D CFD simulations was carried out to verify the optimized effect of VRGV out of nine different angles of roof designs and to estimate the increased speed by the VRGV. From the simulations, the optimum inclination arrangement of the V-shape roof guide vane is 25°. The wind speed augmented factor of the VRGV was 44%, from 2.00 m/s to 2.88 m/s. The working concept of the VRGV is to minimize the negative torque zone of a VAWT and to reduce turbulence and rotational speed fluctuation. Besides, the design of the VRGV that blends into the building architecture can be aesthetic as well. An experimental setup has been developed to verify the effect of VRGV using a prototype. Anemometric measurements were used to calculate the power of wind turbine. The system was also designed to provide optimum surface area and orientation for solar power generation. An automatic cooling and cleaning system with a stream of rain water was designed to clean and cool the roof which can improve the electrical efficiency of the solar photovoltaic modules. The ventilation vents of the system allow warm air inside the building to be ventilated out from the building by the pressure difference. The skylighting in the system improve the living comfort level and reduce power consumption of artificial lighting.

Tax policy in the contemporary world: peculiarities and prospects, implementation in Russia

The article describes the peculiarities of tax policy implementation in the system of international economic relations under conditions of contemporary development, characterized by turbulence, unpredictability and high speed of changes. The author estimates the influence of modern transformational changes on national tax systems and tax policies of the leading countries of the World, including their adaptation to the so-called “new normality”, the decline of liberalism and the deceleration of globalization, virtualization of economic activity and revival of the idea of national identity. Taking into account the impact of the above factors, the author forecasts a common vector of national tax systems’ development, as well as evaluates inter-state interactions in tax matters and determines perspectives of tax policy improvement in Russia on the eve of presidential elections of 2018. The main conclusions are following: 1) in the modern world the best is such a tax policy, which is focused on the regulating (stimulating), and not on the fiscal role of taxes; 2) the process of intensive international tax cooperation, which started just after beginning of the recent global economic crisis, is developing quite successful and it involves more and more interested countries; 3) modern tax systems at the present time are influenced by a large number of transformational factors, including global turbulent environment, which are reflected accordingly in the national tax policy and not always unequivocally positive; 4) tax policy of the Russian Federation ahead of the presidential elections in 2018 and after them should be continuity to the period of 2000-2017 years, considering appropriate progressive global trends. Highlights In the modern world the best is such a tax policy, which is focused on the regulating(stimulating), and not on the fiscal role of taxes The process of intensive international tax cooperation, which started just afterbeginning of the recent global economic crisis, is developing quite successful and itinvolves more and more interested countries Modern tax systems at the present time are influenced by a large number of transformational factors, including global turbulent environment, which are reflected accordingly in the national tax policy and not always unequivocally positive Tax policy of the Russian Federation ahead of the presidential elections in 2018and after them should be continuity to the period of 2000–2017 years, considering appropriate progressive global trends For citation Pogorletskiy A. I. Tax policy in the contemporary world: peculiarities and prospects, implementation in Russia. Journal of Tax Reform, 2017, vol. 3, no. 1, pp. 29–42. DOI : 10.15826/jtr.2017.3.1.029 Article info Received February 10, 2017; accepted March 20, 2017

Origin of the Universe: Wave and Turbulent Speed Velocity of the Nil

Origin of the Universe: Wave and Turbulent Speed Velocity of the Nil

Origin of the Universe: Wave and Turbulent Speed Velocity of the Nil

Origin of the Universe: Wave and Turbulent Speed Velocity of the Nil

The parameterisation of turbulence in the marine environment

ABSTRACTThere are many problems in the fields of flow modelling around structures and tidal stream energy yield analysis which require a thorough understanding of the turbulent and time-averaged flow speeds in marine environments. In this paper we examine the relationship between the turbulence intensity and mean tidal flow speed at a potential tidal stream power site. We report data from the Humber Estuary wherein an Acoustic Doppler Current Profiler were used to capture vertical profiles of the high frequency and mean tidal flow speeds throughout Spring and Neap, Flood and Ebb cycles. We show not only that our results extend earlier work but also suggest that the turbulence intensity, IT, can be described parametrically in terms of the mean flow, U, by an inverse power function where the coefficient appears to be dependent upon the anisotropic nature of the turbulence. For the data reported here, the coefficient has value of about 17–18 and the exponent lies between −0.6 and −1.0. Confirmation of this relationship should not only improve engineering design work and energy yield analyses in turbulent tidal flows but also be applicable to other problems such as the prediction of sediment mass transport and pollution dispersal in estuarine management studies.

Flame propagation of premixed liquefied petroleum gas explosion in a tube

Flame propagation in premixed liquefied petroleum gas (LPG) explosion was studied experimentally in a tube of diameter 2.6m and length 25m. Experiments on LPG explosion were conducted in a single zone first in this large explosion tube. The explosion tube was then divided into two zones with different mixing ratios of LPG and air. A thin polyvinyl chloride (PVC) film sheet was used to adjust the length of each zone. A total of three single-zone experiments and five two-zone experiments were carried out. Explosion phenomena and flame propagation in the tube were studied analytically using experimental results and theoretical analysis. A simple model for the flame propagation was proposed and tested using the experimental data in the present study and some literature results. Flame propagation characteristics were found with a general trend to vary with time as an exponential function for adequate fuel with uniform concentrations within a certain distance of the tube. The flame propagation speed at a point in explosion depends on the turbulent burning speed and expansion ratio. Experimental data deviated more from the empirical exponential function for larger variations of fuel concentrations.

Interplay of Darrieus-Landau instability and weak turbulence in premixed flame propagation.

In this study we investigate, both numerically and experimentally, the interplay between the intrinsic Darrieus-Landau (DL) or hydrodynamic instability of a premixed flame and the moderately turbulent flow field in which the flame propagates. The objective is threefold: to establish, unambiguously, through a suitably defined marker, the presence or absence of DL-induced effects on the turbulent flame, to quantify the DL effects on the flame propagation and morphology and, finally, to asses whether such effects are mitigated or suppressed as the turbulence intensity is increased. The numerical simulations are based on a deficient reactant model which lends itself to a wealth of results from asymptotic theory, such as the determination of stability limits. The skewness of the flame curvature probability density function is identified as an unambiguous morphological marker for the presence or absence of DL effects in a turbulent environment. In addition, the turbulent propagation speed is shown to exhibit a distinct dual behavior whereby it is noticeably enhanced in the presence of DL instability while it is unchanged otherwise. Furthermore, increasing the turbulence intensity is found to be mitigating with respect to DL-induced effects such as the mentioned dual behavior which disappears at higher intensities. Experimental propane and/or air Bunsen flames are also investigated, utilizing two distinct diameters, respectively, above and below the estimated DL cutoff wavelength. Curvature skewness is still clearly observed to act as a marker for DL instability while the turbulent propagation speed is concurrently enhanced in the presence of the instability.

Station-keeping control of an unmanned surface vehicle exposed to current and wind disturbances

Field trials of a 4m long, 180kg, unmanned surface vehicle (USV) have been conducted to evaluate the performance of station-keeping heading and position controllers in an outdoor marine environment disturbed by wind and current. The USV has a twin hull configuration and a custom-designed propulsion system, which consists of two azimuthing thrusters, one for each hull. Nonlinear proportional derivative, backstepping and sliding mode feedback controllers were tested in winds of about 4–5 knots, with and without wind feedforward control. The controllers were tested when the longitudinal axis of the USV was aligned with the mean wind direction and when the longitudinal axis was perpendicular to the mean wind direction. It was found that the sliding mode controller performed best overall and that the addition of wind feedforward control did not significantly improve its effectiveness. However, wind feedforward control did substantially improve the performance of the proportional derivative and backstepping controllers when the mean wind direction was perpendicular to the longitudinal axis of the USV. An analysis of the length scales present in the power spectrum of the turbulent speed fluctuations in the wind suggests that a single anemometer is sufficient to characterize the speed and direction of the wind acting on the USV.

Turbulence dependence on winds and stability in a weak‐wind canopy sublayer over complex terrain

AbstractThe daytime and nighttime turbulence profiles within a weak‐wind forest canopy were investigated by using data collected within a temperate mixed conifer canopy in northern Idaho, USA. Turbulence measurements made at three heights on a single tower within a Douglas fir canopy were compared. Data were split between the daytime and nighttime to determine the relationships among the local temperature gradient, wind direction, wind speed, and turbulence levels. The total flow field distributions and vertical statistical profiles were determined for the overnight and daytime periods to observe how the overall flow changed with time of day. During the day, the wind probability distribution function was consistent between heights but depended on the canopy depth overnight. The skewness changed with the dominant wind direction. The kurtosis increased with depth into the canopy and from during the day to overnight. The range of wind speeds observed was higher under unstable conditions than stable conditions. Daytime turbulence had no dependence on wind direction. Overnight, the relationship between turbulence and wind speed changed with wind direction and canopy depth. The highest turbulence values were associated with downslope winds near the canopy top, but the wind direction for the highest turbulence was variable within the trunk space.

Vibro-acoustic coupled analysis excited by correlated turbulent boundary layer

Vibro-acoustic coupling is one of the most concerned problems in the design stage of aircraft and aerospace vehicle. An algorithm that integrates the finite element method (FEM), the boundary element method (BEM) and an acquisition method of excitation correlation is proposed to conduct the vibro-acoustic coupled analysis under correlated excitations in time and spatial domains. The Corcos/Smol’yakov-Tkachenko (ST) power spectral density models are adopted for the correlated excitation with a divisional method, and the vibro-acoustic coupled analysis of complex structures can be greatly simplified. First, a simply supported panel under correlated TBL is investigated to validate the proposed algorithm. Then, the proposed algorithm is applied to a stiffened panel to carry out the vibro-acoustic coupled analysis under three types of excitation: (a) perfectly correlated TBL, (b) partially correlated TBL based on the Corcos or ST model, and (c) uncorrelated TBL. Parameters which may affect the vibro-acoustic coupled analysis, such as the coupled effect, the correlation of excitation and the speed and thickness of the turbulence, are also discussed. Results show that the proposed method is suitable for the vibro-acoustic coupled analysis of complex systems under correlated random excitations. The vibro-acoustic coupling effect will result in a decrease in both the natural frequency and structural response under perfectly correlated excitation, and an increase in the structural response for partial correlated and uncorrelated excitations. However, the coupling effect has little influence on the acoustical response. The structural and acoustic responses due to partially correlated excitation are larger than that due to perfectly correlated excitation. Moreover, the structural and acoustic responses increase with the increment in turbulence speed and thickness, and the difference among the responses under the three different types of excitations rapidly increase with the increasing of the turbulence speed.

Experimental study on turbulent expanding flames of lean hydrogen/air mixtures

The aim of this paper is to report new experimental results on the effect of turbulence on the combustion properties of lean to stoichiometric H2/air mixtures in a closed, fan-stirred, spherical vessel. To do so, a new experimental setup, spherical bomb, has been used to investigate the effect of a given and well-characterized turbulence intensity on the increase of hydrogen/air flame speed and on the combustion pressure. The initial hydrogen molar percent of H2 in air was comprised between 16% and 28%. The initial turbulence created in the vessel prior to ignition was varied between 0.56 and 2.81m/s for an integral length scale of around 50mm. It was shown that the turbulent speed increases drastically when the turbulence is increased but the maximum combustion pressure remains the same. A correlation was proposed in order to the turbulent speed. The proposed turbulent flame speed correlation was able to predict not only the present data but also the results of the literature (Kitagawa et al., 2008).

DUST COAGULATION IN THE VICINITY OF A GAP-OPENING JUPITER-MASS PLANET

ABSTRACT We analyze the coagulation of dust in and around a gap opened by a Jupiter-mass planet. To this end, we carry out a high-resolution magnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent due to the magnetorotational instability. From the MHD simulation, we obtain values of the gas velocities, densities, and turbulent stresses (a) close to the gap edge, (b) in one of the two gas streams that accrete onto the planet, (c) inside the low-density gap, and (d) outside the gap. The MHD values are then input into a Monte Carlo dust-coagulation algorithm which models grain sticking and compaction. We also introduce a simple implementation for bouncing, for comparison purposes. We consider two dust populations for each region: one whose initial size distribution is monodisperse, with monomer radius equal to 1 μm, and another one whose initial size distribution follows the Mathis–Rumpl–Nordsieck distribution for interstellar dust grains, with an initial range of monomer radii between 0.5 and 10 μm. Without bouncing, our Monte Carlo calculations show steady growth of dust aggregates in all regions, and the mass-weighted (m-w) average porosity of the initially monodisperse population reaches extremely high final values of 98%. The final m-w porosities in all other cases without bouncing range between 30% and 82%. The efficiency of compaction is due to high turbulent relative speeds between dust particles. When bouncing is introduced, growth is slowed down in the planetary wake and inside the gap. Future studies will need to explore the effect of different planet masses and electric charge on grains.

Experimental observations of turbulent flame propagation effected by flame acceleration in the end gas of closed combustion chamber

In present study, a new designed constant volume combustion bomb (CVCB) equipped with an orifice plate and visualized by high speed schlieren photography has been employed to study the turbulent flame propagation effected by flame acceleration in the end gas region. The orifice plate is employed to achieve flame acceleration and obtain different turbulent flames at different equivalence ratios. We investigate the flame propagation speed, the formation mechanism of compression front, the influence of flame acceleration on the end-gas as well as the flame structure changes. The results show that the laminar flame can be accelerated and transferred to a wrinkled turbulent flame through the orifice plate significantly and there forms a clear compression front ahead of the turbulent flame. The flame propagation speed without orifice plate shows the trend of initial increase and consequence decrease in the confined space. Moreover, the turbulent flame propagation speed shows the significantly different trend and demonstrates the “M” shape evolution including the self-acceleration, unstable and deceleration process. Finally, the evolution of turbulent flame in the end gas of the confined chamber was described in detail with three stages: compression front formation, flame front distortion and reverse propagation.

Numerical dissipation control in high order shock-capturing schemes for LES of low speed flows

The Yee & Sjögreen adaptive numerical dissipation control in high order scheme (High Order Filter Methods for Wide Range of Compressible Flow Speeds, ICOSAHOM 09, 2009) is further improved for DNS and LES of shock-free turbulence and low speed turbulence with shocklets. There are vastly different requirements in the minimization of numerical dissipation for accurate turbulence simulations of different compressible flow types and flow speeds. Traditionally, the method of choice for shock-free turbulence and low speed turbulence are by spectral, high order central or high order compact schemes with high order linear filters. With a proper control of a local flow sensor, appropriate amount of numerical dissipation in high order shock-capturing schemes can have spectral-like accuracy for compressible low speed turbulent flows. The development of the method includes an adaptive flow sensor with automatic selection on the amount of numerical dissipation needed at each flow location for more accurate DNS and LES simulations with less tuning of parameters for flows with a wide range of flow speed regime during the time-accurate evolution, e.g., time varying random forcing. An automatic selection of the different flow sensors catered to the different flow types is constructed. A Mach curve and high-frequency oscillation indicators are used to reduce the tuning of parameters in controlling the amount of shock-capturing numerical dissipation to be employed for shock-free turbulence, low speed turbulence and turbulence with strong shocks. In Kotov et al. (High Order Numerical Methods for LES of Turbulent Flows with Shocks, ICCFD8, Chengdu, Sichuan, China, July 14–18, 2014) the LES of a turbulent flow with a strong shock by the Yee & Sjögreen scheme indicated a good agreement with the filtered DNS data. A work in progress for the application of the adaptive flow sensor for compressible turbulence with time-varying random forcing is forthcoming. The present study examines the versatility of the Yee & Sjögreen scheme for DNS and LES of traditional low speed flows without forcing. Special attention is focused on the accuracy performance of this scheme using the Smagorinsky and the Germano–Lilly SGS models.

Direct numerical simulation of a turbulent lean premixed CH4/H2–Air slot flame

Nowadays, in the context of CO2 reduction and gas turbine fuel flexibility, the interest in acquiring know-how on lean Hydrogen Enriched Natural Gas (HENG) is growing. This article provides a detailed analysis of two turbulent (−) lean (−) CH4/H2–air premixed slot flames (unconfined and at atmospheric pressure) highlighting the effects of two different hydrogen contents in the inlet mixture (20% and 50% by volume respectively for flames named A and B).The data were generated and collected setting up a three-dimensional numerical experiment performed through the direct numerical simulation (DNS) approach. Finite difference schemes were adopted to solve the compressible Navier–Stokes equations in space (compact sixth-order in staggered formulation) and time (third-order Runge–Kutta). Accurate molecular transport properties and the Soret effect were also taken into account. A detailed skeletal chemical mechanism for methane–air combustion, consisting of 17 transported species and 73 elementary reactions, was used.A general description of the two flames is provided, evidencing their macroscopic differences by means of turbulent consumption speed, flame surface areas and mean flame brush thickness. Furthermore, topological features of the flames are explored by analyzing the probability density functions of several quantities: curvature, shape factor, alignment between vorticity and principal strain rate vectors with flame surface normal, displacement speed and its components. Correlations between the flame thickness and the progress variable and curvature are also investigated, as well as correlation between strain rates and curvature, and equivalence ratio and curvature. An expression of displacement speed with diffusion terms taking into account differential diffusion of progress variable species components is derived. The effects of differential diffusion of several species on the local equivalence ratio are quantified: the maximum variation from the nominal inlet value is ∼9% and it is due to H2 and O2.Increasing the hydrogen content the expected value and the skewness factor of the curvature PDF move towards negative values. The effect of thermal diffusion in thinning the flame front is greater for positive curvatures and at the trailing edge of the flame. The addition of hydrogen reduces the displacement speed at negative curvatures in a range that depends on the local progress variable value, with a maximum variation of − between the two flames. However, on average, increasing the hydrogen content increases the displacement speed in a wide range of progress variable values, i.e., the Sd in flame B is, on average, higher than in flame A by ∼25% in 0.25 < c < 0.75. The database will also be helpful to validate sub-grid models for Large Eddy Simulation.

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 1: Theory)

Generation, ascent and eruption of magma on the Moon: New insights into source depths, magma supply, intrusions and effusive/explosive eruptions (Part 1: Theory)

Effects of firm and environmental characteristics on supplier integration in new product development

In this paper, we explore how environmental and firm characteristics affect supplier integration in new product development, i.e. timing and depth of supplier integration. We examine such environmental and firm characteristics as market and technological turbulence, supplier innovativeness, and supplier knowledge intensity. Using the data from surveys of Korean Small- and Medium-Sized Enterprises (SMEs), we conduct a structural equation modelling. The results indicate that the market turbulence speeds up the supplier integration, but the technological turbulence delays it. Knowledge intensity makes the depth of supplier integration greater. Finally, integration timing and depth affect the performance of new product development differently. Rapid supplier integration affects the performance negatively, whereas deep supplier integration improves it. We explain the logic behind the analysis result and suggest managerial implications.

Fluidic flow control applied for improved performance of Darrieus wind turbines

AbstractThe focus of the present research is performance enhancement of a vertical axis Darrieus‐type wind turbine using flow control techniques. The academic and industrial interest in vertical‐axis wind turbines (VAWTs) is increasing because of its suitability to urban areas, characterized by high turbulence and low wind speeds. The paper describes experimental work performed on a GOE222 asymmetrical airfoil intended to be used in a straight‐bladed Darrieus VAWT. Airfoil characteristics were measured in a wide range of incidence angles and Reynolds numbers, relevant for the operation of a small to medium size wind turbine. A variety of passive flow control (passive porosity and surface roughness) and active flow control techniques (boundary layer suction, pulsed suction) were tested in order to evaluate their effects on the airfoil performance. The measured effects of flow control on the 2D airfoil are integrated into a modified version of a double‐multiple streamtube model in order to predict the effects on the performance and efficiency of the turbine. It was found that the improvement of 2D airfoil characteristics can be translated into improvement of total turbine performance. By the use of active flow control, it was possible to increase the VAWT maximum mechanical output. When active flow control is properly activated taking into account the azimuth and Reynolds number conditioning, the effects could be greatly increased while consuming less energy, increasing the net efficiency of the entire system. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Super-Twisting Sliding Mode Control Design for Cascaded Control System of PMSG Wind Turbine

This study focuses on an advanced second-order sliding mode control strategy for a variable speed wind turbine based on a permanent magnet synchronous generator to maximize wind power extraction while simultaneously reducing the mechanical stress effect. The control design based on a modified version of the super-twisting algorithm with variable gains can be applied to the cascaded system scheme comprising the current control loop and speed control loop. The proposed control inheriting the well-known robustness of the sliding technique successfully deals with the problems of essential nonlinearity of wind turbine systems, the effects of disturbance regarding variation on the parameters, and the random nature of wind speed. In addition, the advantages of the adaptive gains and the smoothness of the control action strongly reduce the chatter signals of wind turbine systems. Finally, with comparison with the traditional super-twisting algorithm, the performance of the system is verified through simulation results under wind speed turbulence and parameter variations.

Theoretical considerations for star formation at low and high redshift

AbstractStar formation processes in strongly self-gravitating cloud cores should be similar at all redshifts, forming single or multiple stars with a range of masses determined by local magneto-hydrodynamics and gravity. The formation processes for these cores, however, as well as their structures, temperatures, Mach numbers, etc., and the boundedness and mass distribution functions of the resulting stars, should depend on environment, as should the characteristic mass, density, and column density at which cloud self-gravity dominates other forces. Because the environments for high and low redshift star formation differ significantly, we expect the resulting gas to stellar conversion details to differ also. At high redshift, the universe is denser and more gas-rich, so the active parts of galaxies are denser and more gas rich too, leading to slightly shorter gas consumption timescales, higher cloud pressures, and denser, more massive, bound stellar clusters at the high mass end. With shorter consumption times corresponding to higher relative cosmic accretion rates, and with the resulting higher star formation rates and their higher feedback powers, the ISM has greater turbulent speeds relative to the rotation speeds, thicker gas disks, and larger cloud and star complex sizes at the characteristic Jeans length. The result is a more chaotic appearance at high redshift, bridging the morphology gap between today's quiescent spirals and today's major-mergers, with neither spiral nor major-merger processes actually in play at that time. The result is also a thick disk at early times, and after in-plane accretion from relatively large clump torques, a classical bulge. Today's disks are thinner, and torque-driven accretion is slower outside of inner barred regions. This paper reviews the basic processes involved with star formation in order to illustrate its evolution over time and environment.