Zonal Flows and Turbulence in Fluids and Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parker, Jeffrey

2014-09-01

In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking `zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetricmore » coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type Is instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system, and we calculate a stability diagram. The stability diagram is in agreement with direct numerical simulations of the

Zonal flows and turbulence in fluids and plasmas

NASA Astrophysics Data System (ADS)

Parker, Jeffrey Bok-Cheung

In geophysical and plasma contexts, zonal flows are well known to arise out of turbulence. We elucidate the transition from statistically homogeneous turbulence without zonal flows to statistically inhomogeneous turbulence with steady zonal flows. Starting from the Hasegawa--Mima equation, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking 'zonostrophic instability'. Zonostrophic instability can be understood in a very general way as the instability of some turbulent background spectrum to a zonally symmetric coherent mode. As a special case, the background spectrum can consist of only a single mode. We find that in this case the dispersion relation of zonostrophic instability from the CE2 formalism reduces exactly to that of the 4-mode truncation of generalized modulational instability. We then show that zonal flows constitute pattern formation amid a turbulent bath. Zonostrophic instability is an example of a Type I s instability of pattern-forming systems. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation, the real Ginzburg-Landau equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the zonal flow wavelength is not unique. In an idealized, infinite system, there is a continuous band of zonal flow wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system, and we calculate a stability diagram. The stability diagram is in agreement with direct numerical simulations of the quasilinear

On the wave forcing of the semi-annual zonal wind oscillation

NASA Technical Reports Server (NTRS)

Nagpal, O. P.; Raghavarao, R.

1991-01-01

Observational evidence of rather large period waves (23-60 d) in the troposphere/stratosphere, particularly during the winter months, is presented. Wind data collected on a regular basis employing high-altitude balloons and meteorological rockets over the past few years are used. Maximum entropy methods applied to the time series of zonal wind data indicate the presence of 23-60-waves more prominently than shorter-period waves. The waves have substantial amplitudes in the stratosphere and lower mesosphere, often larger than those noted in the troposphere. The mean zonal wind in the troposphere (5-15 km altitude) during December, January, and February exhibits the presence of strong westerlies at latitudes between 8 and 21 deg N.

Rethinking wave-kinetic theory applied to zonal flows

NASA Astrophysics Data System (ADS)

Parker, Jeffrey

2017-10-01

Over the past two decades, a number of studies have employed a wave-kinetic theory to describe fluctuations interacting with zonal flows. Recent work has uncovered a defect in this wave-kinetic formulation: the system is dominated by the growth of (arbitrarily) small-scale zonal structures. Theoretical calculations of linear growth rates suggest, and nonlinear simulations confirm, that this system leads to the concentration of zonal flow energy in the smallest resolved scales, irrespective of the numerical resolution. This behavior results from the assumption that zonal flows are extremely long wavelength, leading to the neglect of key terms responsible for conservation of enstrophy. A corrected theory, CE2-GO, is presented; it is free of these errors yet preserves the intuitive phase-space mathematical structure. CE2-GO properly conserves enstrophy as well as energy, and yields accurate growth rates of zonal flow. Numerical simulations are shown to be well-behaved and not dependent on box size. The steady-state limit simplifies into an exact wave-kinetic form which offers the promise of deeper insight into the behavior of wavepackets. The CE2-GO theory takes its place in a hierarchy of models as the geometrical-optics reduction of the more complete cumulant-expansion statistical theory CE2. The new theory represents the minimal statistical description, enabling an intuitive phase-space formulation and an accurate description of turbulence-zonal flow dynamics. This work was supported by an NSF Graduate Research Fellowship, a US DOE Fusion Energy Sciences Fellowship, and US DOE Contract Nos. DE-AC52-07NA27344 and DE-AC02-09CH11466.

On the tertiary instability formalism of zonal flows in magnetized plasmas

NASA Astrophysics Data System (ADS)

Rath, F.; Peeters, A. G.; Buchholz, R.; Grosshauser, S. R.; Seiferling, F.; Weikl, A.

2018-05-01

This paper investigates the so-called tertiary instabilities driven by the zonal flow in gyro-kinetic tokamak core turbulence. The Kelvin Helmholtz instability is first considered within a 2D fluid model and a threshold in the zonal flow wave vector kZF>kZF,c for instability is found. This critical scale is related to the breaking of the rotational symmetry by flux-surfaces, which is incorporated into the modified adiabatic electron response. The stability of undamped Rosenbluth-Hinton zonal flows is then investigated in gyro-kinetic simulations. Absolute instability, in the sense that the threshold zonal flow amplitude tends towards zero, is found above a zonal flow wave vector kZF,cρi≈1.3 ( ρi is the ion thermal Larmor radius), which is comparable to the 2D fluid results. Large scale zonal flows with kZFflow state at marginal stability by more than an order of magnitude, which therefore lies deeply in the stable parameter region. Furthermore, the impact of zonal temperature perturbations on the tertiary instability is examined. Although temperature perturbations favor instability, the realistic values of gradient-driven gyro-kinetic simulations still lie deeply in the stable parameter regime. Therefore, the relevance of the tertiary instability as a saturation mechanism to the zonal flow amplitude is questioned, as most of the zonal flow intensity is concentrated in modes satisfying kZF≪kZF,c as well as ωE×B≪ωE×B,c .

A zonal method for modeling powered-lift aircraft flow fields

NASA Technical Reports Server (NTRS)

Roberts, D. W.

1989-01-01

A zonal method for modeling powered-lift aircraft flow fields is based on the coupling of a three-dimensional Navier-Stokes code to a potential flow code. By minimizing the extent of the viscous Navier-Stokes zones the zonal method can be a cost effective flow analysis tool. The successful coupling of the zonal solutions provides the viscous/inviscid interations that are necessary to achieve convergent and unique overall solutions. The feasibility of coupling the two vastly different codes is demonstrated. The interzone boundaries were overlapped to facilitate the passing of boundary condition information between the codes. Routines were developed to extract the normal velocity boundary conditions for the potential flow zone from the viscous zone solution. Similarly, the velocity vector direction along with the total conditions were obtained from the potential flow solution to provide boundary conditions for the Navier-Stokes solution. Studies were conducted to determine the influence of the overlap of the interzone boundaries and the convergence of the zonal solutions on the convergence of the overall solution. The zonal method was applied to a jet impingement problem to model the suckdown effect that results from the entrainment of the inviscid zone flow by the viscous zone jet. The resultant potential flow solution created a lower pressure on the base of the vehicle which produces the suckdown load. The feasibility of the zonal method was demonstrated. By enhancing the Navier-Stokes code for powered-lift flow fields and optimizing the convergence of the coupled analysis a practical flow analysis tool will result.

Self-organization of large-scale ULF electromagnetic wave structures in their interaction with nonuniform zonal winds in the ionospheric E region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aburjania, G. D.; Chargazia, Kh. Z.

A study is made of the generation and subsequent linear and nonlinear evolution of ultralow-frequency planetary electromagnetic waves in the E region of a dissipative ionosphere in the presence of a nonuniform zonal wind (a sheared flow). Hall currents flowing in the E region and such permanent global factors as the spatial nonuniformity of the geomagnetic field and of the normal component of the Earth's angular velocity give rise to fast and slow planetary-scale electromagnetic waves. The efficiency of the linear amplification of planetary electromagnetic waves in their interaction with a nonuniform zonal wind is analyzed. When there are shearedmore » flows, the operators of linear problems are non-self-conjugate and the corresponding eigenfunctions are nonorthogonal, so the canonical modal approach is poorly suited for studying such motions and it is necessary to utilize the so-called nonmodal mathematical analysis. It is shown that, in the linear evolutionary stage, planetary electromagnetic waves efficiently extract energy from the sheared flow, thereby substantially increasing their amplitude and, accordingly, energy. The criterion for instability of a sheared flow in an ionospheric medium is derived. As the shear instability develops and the perturbation amplitude grows, a nonlinear self-localization mechanism comes into play and the process ends with the self-organization of nonlinear, highly localized, solitary vortex structures. The system thus acquires a new degree of freedom, thereby providing a new way for the perturbation to evolve in a medium with a sheared flow. Depending on the shape of the sheared flow velocity profile, nonlinear structures can be either purely monopole vortices or vortex streets against the background of the zonal wind. The accumulation of such vortices can lead to a strongly turbulent state in an ionospheric medium.« less

Thermal zonal winds in the Venus mesosphere from the Venus Express temperature soundings

NASA Astrophysics Data System (ADS)

Piccialli, Arianna; Titov, Dmitri; Tellmann, Silvia; Migliorini, Alessandra; Read, Peter; Grassi, Davide; Paetzold, Martin; Haeusler, Bernd; Piccioni, Giuseppe; Drossart, Pierre

The Venus mesosphere (60-100 km altitude) is a transition region characterized by extremely complex dynamics: strong retrograde zonal winds dominate in the troposphere and lower meso-sphere while a solar-antisolar circulation can be observed in the upper mesosphere. The super-rotation extends from the surface up to the cloud top (˜65 km altitude) with wind speeds of only a few meters per second near the surface and reaching a maximum value of ˜100 m s-1 at cloud top, corresponding to a rotation period of ˜4 Earth days (˜60 times faster than Venus itself). The solar-antisolar circulation is driven by the day-night contrast in solar heating, and occurs above 110 km altitude with speeds of 120 m s-1 . The processes responsible for maintain-ing the zonal super-rotation in the lower atmosphere and its transition to the solar-antisolar circulation in the upper atmosphere are still poorly understood (Schubert et al.,2007). Different techniques have been used to obtain direct observations of wind at various altitudes: tracking of clouds in ultraviolet (UV) and near infrared (NIR) images give information on wind speeds at the cloud top (Moissl et al., 2009; Sanchez-Lavega et al., 2008) and within the clouds (˜47 km, ˜61 km) (Sanchez-Lavega et al., 2008) while ground-based measurements of Doppler shifts in the CO2 band at 10 µm (Sornig et al., 2008) and in several CO millimiter lines (Rengel et al., 2008) provide wind speeds above the clouds up to ˜110 km altitude. The deep atmosphere from the surface up to the cloud top has been investigated through the Doppler tracking of descent probes and balloons (Counselman et al., 1980; Kerzhanovich and Limaye, 1985). In the mesosphere, between 45-85 km of altitude, where direct observations of wind are not possible, the zonal wind field can be derived from the vertical temperature structure using a special approximation of the thermal wind equation: based on cyclostrophic balance. Previous studies (Leovy, 1973; Newman et al

Deep Zonal Flow and Time Variation of Jupiter’s Magnetic Field

NASA Astrophysics Data System (ADS)

Cao, Hao; Stevenson, David J.

2017-10-01

All four giant planets in the Solar System feature zonal flows on the order of 100 m/s in the cloud deck, and large-scale intrinsic magnetic fields on the order of 1 Gauss near the surface. The vertical structure of the zonal flows remains obscure. The end-member scenarios are shallow flows confined in the radiative atmosphere and deep flows throughout the entire planet. The electrical conductivity increases rapidly yet smoothly as a function of depth inside Jupiter and Saturn. Deep zonal flows will advect the non-axisymmetric component of the magnetic field, at depth with even modest electrical conductivity, and create time variations in the magnetic field.The observed time variations of the geomagnetic field has been used to derive surface flows of the Earth’s outer core. The same principle applies to Jupiter, however, the connection between the time variation of the magnetic field (dB/dt) and deep zonal flow (Uphi) at Jupiter is not well understood due to strong radial variation of electrical conductivity. Here we perform a quantitative analysis of the connection between dB/dt and Uphi for Jupiter adopting realistic interior electrical conductivity profile, taking the likely presence of alkali metals into account. This provides a tool to translate expected measurement of the time variation of Jupiter’s magnetic field to deep zonal flows. We show that the current upper limit on the dipole drift rate of Jupiter (3 degrees per 20 years) is compatible with 10 m/s zonal flows with < 500 km vertical scale height below 0.972 Rj. We further demonstrate that fast drift of resolved magnetic features (e.g. magnetic spots) at Jupiter is a possibility.

Turbulence, transport, and zonal flows in the Madison symmetric torus reversed-field pinch

NASA Astrophysics Data System (ADS)

Williams, Z. R.; Pueschel, M. J.; Terry, P. W.; Hauff, T.

2017-12-01

The robustness and the effect of zonal flows in trapped electron mode (TEM) turbulence and Ion Temperature Gradient (ITG) turbulence in the reversed-field pinch (RFP) are investigated from numerical solutions of the gyrokinetic equations with and without magnetic external perturbations introduced to model tearing modes. For simulations without external magnetic field perturbations, zonal flows produce a much larger reduction of transport for the density-gradient-driven TEM turbulence than they do for the ITG turbulence. Zonal flows are studied in detail to understand the nature of their strong excitation in the RFP and to gain insight into the key differences between the TEM- and ITG-driven regimes. The zonal flow residuals are significantly larger in the RFP than in tokamak geometry due to the low safety factor. Collisionality is seen to play a significant role in the TEM zonal flow regulation through the different responses of the linear growth rate and the size of the Dimits shift to collisionality, while affecting the ITG only minimally. A secondary instability analysis reveals that the TEM turbulence drives zonal flows at a rate that is twice that of the ITG turbulence. In addition to interfering with zonal flows, the magnetic perturbations are found to obviate an energy scaling relation for fast particles.

Intra-seasonal Oscillations (ISO) of Zonal-Mean Meridional Winds and Temperatures as Measured by UARS

NASA Technical Reports Server (NTRS)

Huang, Frank T.; Mayr, Hans G.; Reber, Carl A.

2004-01-01

Based on an empirical analysis of measurements with the High Resolution Doppler Imager (HRDI) on the UARS spacecraft in the upper mesosphere (95 km), persistent and regular intra-seasonal oscillations (ISO) with periods of about 2 to 4 months have recently been reported in the zonal-mean meridional winds. Similar oscillations have also been discussed independently in a modeling study, and they were attributed to wave-mean-flow interactions. The observed and modeled meridional wind ISOs were largely confined to low latitudes. We report here an analysis of concurrent temperature measurements on UARS, which produces oscillations similar to those seen in the meridional winds. Although the temperature oscillations are observed at lower altitudes (55 km), their phase variations with latitude are qualitatively consistent with the inferred properties seen in the meridional winds and thus provide independent evidence for the existence of ISOs in the mesosphere.

Shape, zonal winds and gravitational field of Jupiter: a fully self-consistent, multi-layered model

NASA Astrophysics Data System (ADS)

Schubert, Gerald; Kong, Dali; Zhang, Keke

2016-10-01

We construct a three-dimensional, finite-element, fully self-consistent, multi-layered,non-spheroidal model of Jupiter consisting of an inner core, a metallic electrically conducting dynamo region and an outer molecular electrically insulating envelope. We assume that the Jovian zonal winds are on cylinders parallel to the rotation axis but, due to the effect of magnetic braking, are confined within the outer molecular envelope. Two related calculations are carried out. The first provides an accurate description of the shape and internal density profile of Jupiter; the effect of rotational distortion is not treated as a small perturbation on a spherically symmetric state. This calculation determines the density, size and shape of the inner core, the irregular shape of the 1-bar pressure level, and the internal structure of Jupiter; the full effect of rotational distortion, without the influence of the zonal winds, is accounted for. Our multi-layered model is able to produce the known mass, the known equatorial and polar radii, and the known zonal gravitational coefficient J2 of Jupiter within their error bars; it also yields the coefficients J4 and J6 within about 5% accuracy, and the core equatorial radius 0.09RJ containing 3.73 Earth masses.The second calculation determines the variation of the gravitational field caused solely by the effect of the zonal winds on the rotationally distorted non-spheroidal Jupiter. Four different cases, ranging from a deep wind profile to a very shallow profile, are considered and implications for accurate interpretation of the zonal gravitational coefficients expected from the Juno mission are discussed.

Effects of finite poloidal gyroradius, shaping, and collisions on the zonal flow residuala)

NASA Astrophysics Data System (ADS)

Xiao, Yong; Catto, Peter J.; Dorland, William

2007-05-01

Zonal flow helps reduce and regulate the turbulent transport level in tokamaks. Rosenbluth and Hinton have shown that zonal flow damps to a nonvanishing residual level in collisionless [M. Rosenbluth and F. Hinton, Phys. Rev. Lett. 80, 724 (1998)] and collisional [F. Hinton and M. Rosenbluth, Plasma Phys. Control. Fusion 41, A653 (1999)] banana regime plasmas. Recent zonal flow advances are summarized including the evaluation of the effects on the zonal flow residual by plasma cross-section shaping, shorter wavelengths including those less than an electron gyroradius, and arbitrary ion collisionality relative to the zonal low frequency. In addition to giving a brief summary of these new developments, the analytic results are compared with GS2 numerical simulations [M. Kotschenreuther, G. Rewoldt, and W. Tang, Comput. Phys. Commun. 88, 128 (1991)] to demonstrate their value as benchmarks for turbulence codes.

Generation of zonal flows by electrostatic drift waves in electron-positron-ion plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaladze, T. D.; I. Vekua Institute of Applied Mathematics, Tbilisi State University, 2 University Str., 0186 Tbilisi; Shad, M.

2010-02-15

Generation of large-scale zonal flows by comparatively small-scale electrostatic drift waves in electron-positron-ion plasmas is considered. The generation mechanism is based on the parametric excitation of convective cells by finite amplitude drift waves having arbitrary wavelengths (as compared with the ion Larmor radius of plasma ions at the plasma electron temperature). Temperature inhomogeneity of electrons and positrons is taken into account assuming ions to be cold. To describe the generation of zonal flow generalized Hasegawa-Mima equation containing both vector and two scalar (of different nature) nonlinearities is used. A set of coupled equations describing the nonlinear interaction of drift wavesmore » and zonal flows is deduced. Explicit expressions for the maximum growth rate as well as for the optimal spatial dimensions of the zonal flows are obtained. Enriched possibilities of zonal flow generation with different growth rates are revealed. The present theory can be used for interpretations of drift wave observations in laboratory and astrophysical plasmas.« less

GRAVOTURBULENT PLANETESIMAL FORMATION: THE POSITIVE EFFECT OF LONG-LIVED ZONAL FLOWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dittrich, K.; Klahr, H.; Johansen, A., E-mail: dittrich@mpia.de

2013-02-15

Recent numerical simulations have shown long-lived axisymmetric sub- and super-Keplerian flows in protoplanetary disks. These zonal flows are found in local as well as global simulations of disks unstable to the magnetorotational instability. This paper covers our study of the strength and lifetime of zonal flows and the resulting long-lived gas over- and underdensities as functions of the azimuthal and radial size of the local shearing box. We further investigate dust particle concentrations without feedback on the gas and without self-gravity. The strength and lifetime of zonal flows increase with the radial extent of the simulation box, but decrease withmore » the azimuthal box size. Our simulations support earlier results that zonal flows have a natural radial length scale of 5-7 gas pressure scale heights. This is the first study that combines three-dimensional MHD simulations of zonal flows and dust particles feeling the gas pressure. The pressure bumps trap particles with St = 1 very efficiently. We show that St = 0.1 particles (of some centimeters in size if at 5 AU in a minimum mass solar nebula) reach a hundred-fold higher density than initially. This opens the path for particles of St = 0.1 and dust-to-gas ratio of 0.01 or for particles of St {>=} 0.5 and dust-to-gas ratio 10{sup -4} to still reach densities that potentially trigger the streaming instability and thus gravoturbulent formation of planetesimals.« less

Theory of Fine-scale Zonal Flow Generation From Trapped Electron Mode Turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu Wang and T.S. Hahm

Most existing zonal flow generation theory has been developed with a usual assumption of qrρθ¡ << 1 (qr is the radial wave number of zonal flow, and ρθ¡ is the ion poloidal gyrora- dius). However, recent nonlinear gyrokinetic simulations of trapped electron mode (TEM) turbulence exhibit a relatively short radial scale of the zonal flows with qrρθ¡ ~ 1 [Z. Lin et al., IAEA-CN/TH/P2-8 (2006); D. Ernst et al., Phys. Plasmas 16, 055906 (2009)]. This work reports an extension of zonal flow growth calculation to this short wavelength regime via the wave kinetics approach. A generalized expression for the polarizationmore » shielding for arbitrary radial wavelength [Lu Wang and T.S. Hahm, to appear in Phys. Plasmas (2009)] which extends the Rosenbluth-Hinton formula in the long wavelength limit is applied.« less

The 4-5 day mode oscillation in zonal winds of Indian middle atmosphere during MONEX-79

NASA Astrophysics Data System (ADS)

Reddy, R. S.; Mukherjee, B. K.; Indira, K.; Murty, B. V. R.

1985-12-01

In the early studies based on time series of balloon observations, the existence of 4 to 5 day period waves and 10 to 20 day wind fluctuations were found in the tropical lower stratosphere, and they are identified theoretically as the mixed Rossby-gravity wave and the Kelvin wave, respectively. On the basis of these studies, it was established that the vertically propagating equatorial waves play an important role in producing the QBO (quasi-biennial oscillation) in the mean zonal wind through the mechanism of wave-zonal interaction. These studies are mainly concentrated over the equatorial Pacific and Atlantic Oceans. Similar prominent wave disturbances have been observed over the region east of the Indian Ocean during a quasi-biennial oscillation. Zonal winds in upper troposphere and lower stratosphere (10 to 20) km of the middle atmosphere over the Indian subcontinent may bear association with the activity of summer monsoon (June-September). Monsoon Experiment (MONEX-79) has provided upper air observations at Balasore (21 deg. 30 min.N; 85 deg. 56 min.E), during the peak of monsoon months July and August. A unique opportunity has, therefore, been provided to study the normal oscillations present in the zonal winds of lower middle atmosphere over India, which may have implication on large scale wave dynamics. This aspect is examined in the present study.

REVIEWS OF TOPICAL PROBLEMS: Generation of large-scale eddies and zonal winds in planetary atmospheres

NASA Astrophysics Data System (ADS)

Onishchenko, O. G.; Pokhotelov, O. A.; Astafieva, N. M.

2008-06-01

The review deals with a theoretical description of the generation of zonal winds and vortices in a turbulent barotropic atmosphere. These large-scale structures largely determine the dynamics and transport processes in planetary atmospheres. The role of nonlinear effects on the formation of mesoscale vortical structures (cyclones and anticyclones) is examined. A new mechanism for zonal wind generation in planetary atmospheres is discussed. It is based on the parametric generation of convective cells by finite-amplitude Rossby waves. Weakly turbulent spectra of Rossby waves are considered. The theoretical results are compared to the results of satellite microwave monitoring of the Earth's atmosphere.

Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma

PubMed Central

Arakawa, H.; Inagaki, S.; Sasaki, M.; Kosuga, Y.; Kobayashi, T.; Kasuya, N.; Nagashima, Y.; Yamada, T.; Lesur, M.; Fujisawa, A.; Itoh, K.; Itoh, S.-I.

2016-01-01

Turbulence and its structure formation are universal in neutral fluids and in plasmas. Turbulence annihilates global structures but can organize flows and eddies. The mutual-interactions between flow and the eddy give basic insights into the understanding of non-equilibrium and nonlinear interaction by turbulence. In fusion plasma, clarifying structure formation by Drift-wave turbulence, driven by density gradients in magnetized plasma, is an important issue. Here, a new mutual-interaction among eddy, drift wave and flow in magnetized plasma is discovered. A two-dimensional solitary eddy, which is a perturbation with circumnavigating motion localized radially and azimuthally, is transiently organized in a drift wave – zonal flow (azimuthally symmetric band-like shear flows) system. The excitation of the eddy is synchronized with zonal perturbation. The organization of the eddy has substantial impact on the acceleration of zonal flow. PMID:27628894

Simulations of Tokamak Edge Turbulence Including Self-Consistent Zonal Flows

NASA Astrophysics Data System (ADS)

Cohen, Bruce; Umansky, Maxim

2013-10-01

Progress on simulations of electromagnetic drift-resistive ballooning turbulence in the tokamak edge is summarized in this mini-conference talk. A more detailed report on this work is presented in a poster at this conference. This work extends our previous work to include self-consistent zonal flows and their effects. The previous work addressed the simulation of L-mode tokamak edge turbulence using the turbulence code BOUT. The calculations used realistic single-null geometry and plasma parameters of the DIII-D tokamak and produced fluctuation amplitudes, fluctuation spectra, and particle and thermal fluxes that compare favorably to experimental data. In the effect of sheared ExB poloidal rotation is included with an imposed static radial electric field fitted to experimental data. In the new work here we include the radial electric field self-consistently driven by the microturbulence, which contributes to the sheared ExB poloidal rotation (zonal flow generation). We present simulations with/without zonal flows for both cylindrical geometry, as in the UCLA Large Plasma Device, and for the DIII-D tokamak L-mode cases in to quantify the influence of self-consistent zonal flows on the microturbulence and the concomitant transport. This work was performed under the auspices of the US Department of Energy under contract DE-AC52-07NA27344 at the Lawrence Livermore National Laboratory.

Fluid simulation of tokamak ion temperature gradient turbulence with zonal flow closure model

NASA Astrophysics Data System (ADS)

Yamagishi, Osamu; Sugama, Hideo

2016-03-01

Nonlinear fluid simulation of turbulence driven by ion temperature gradient modes in the tokamak fluxtube configuration is performed by combining two different closure models. One model is a gyrofluid model by Beer and Hammett [Phys. Plasmas 3, 4046 (1996)], and the other is a closure model to reproduce the kinetic zonal flow response [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. By including the zonal flow closure, generation of zonal flows, significant reduction in energy transport, reproduction of the gyrokinetic transport level, and nonlinear upshift on the critical value of gradient scale length are observed.

Fluid simulation of tokamak ion temperature gradient turbulence with zonal flow closure model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamagishi, Osamu, E-mail: yamagisi@nifs.ac.jp; Sugama, Hideo

Nonlinear fluid simulation of turbulence driven by ion temperature gradient modes in the tokamak fluxtube configuration is performed by combining two different closure models. One model is a gyrofluid model by Beer and Hammett [Phys. Plasmas 3, 4046 (1996)], and the other is a closure model to reproduce the kinetic zonal flow response [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. By including the zonal flow closure, generation of zonal flows, significant reduction in energy transport, reproduction of the gyrokinetic transport level, and nonlinear upshift on the critical value of gradient scale length are observed.

On the long-term variability of Jupiter and Saturn zonal winds

NASA Astrophysics Data System (ADS)

Sanchez-Lavega, A.; Garcia-Melendo, E.; Hueso, R.; Barrado-Izagirre, N.; Legarreta, J.; Rojas, J. F.

2012-12-01

We present an analysis of the long-term variability of Jupiter and Saturn zonal wind profiles at their upper cloud level as retrieved from cloud motion tracking on images obtained at ground-based observatories and with different spacecraft missions since 1979, encompassing about three Jovian and one Saturn years. We study the sensitivity and variability of the zonal wind profile in both planets to major planetary-scale disturbances and to seasonal forcing. We finally discuss the implications that these results have for current model efforts to explain the global tropospheric circulation in these planets. Acknowledgements: This work has been funded by Spanish MICIIN AYA2009-10701 with FEDER support, Grupos Gobierno Vasco IT-464-07 and UPV/EHU UFI11/55. [1] Sánchez-Lavega A., et al., Icarus, 147, 405-420 (2000). [2] García-Melendo E., Sánchez LavegaA., Icarus, 152, 316-330 (2001) [3] Sánchez-Lavega A., et al., Nature, 423, 623-625 (2003). [4] García-Melendo E., et al., Geophysical Research Letters, 37, L22204 (2010).

The generation of a zonal-wind oscillation by nonlinear interactions of internal gravity waves

NASA Astrophysics Data System (ADS)

Campbell, Lucy

2003-11-01

Nonlinear interactions of internal gravity waves give rise to numerous large-scale phenomena that are observed in the atmosphere, for example the quasi-biennial oscillation (QBO). This is an oscillation in zonal wind direction which is observed in the equatorial stratosphere; it is characterized by alternating regimes of easterly and westerly shear that descend with time. In the past few decades, a number of theories have been developed to explain the mechanism by which the QBO is generated. These theories are all based on ``quasi-linear'' representations of wave-mean-flow interactions. In this presentation, a fully nonlinear numerical simulation of the QBO is described. A spectrum of gravity waves over a range of phase speeds is forced at the lower boundary of the computational domain and propagates upwards in a density-stratified shear flow. As a result of the absorption and reflection of the waves at their critical levels, regions of large shear develop in the background flow and propagate downwards with time.

A simple inertial model for Neptune's zonal circulation

NASA Technical Reports Server (NTRS)

Allison, Michael; Lumetta, James T.

1990-01-01

Voyager imaging observations of zonal cloud-tracked winds on Neptune revealed a strongly subrotational equatorial jet with a speed approaching 500 m/s and generally decreasing retrograde motion toward the poles. The wind data are interpreted with a speculative but revealingly simple model based on steady gradient flow balance and an assumed global homogenization of potential vorticity for shallow layer motion. The prescribed model flow profile relates the equatorial velocity to the mid-latitude shear, in reasonable agreement with the available data, and implies a global horizontal deformation scale L(D) of about 3000 km.

Statistical properties of Charney-Hasegawa-Mima zonal flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Johan, E-mail: anderson.johan@gmail.com; Botha, G. J. J.

2015-05-15

A theoretical interpretation of numerically generated probability density functions (PDFs) of intermittent plasma transport events in unforced zonal flows is provided within the Charney-Hasegawa-Mima (CHM) model. The governing equation is solved numerically with various prescribed density gradients that are designed to produce different configurations of parallel and anti-parallel streams. Long-lasting vortices form whose flow is governed by the zonal streams. It is found that the numerically generated PDFs can be matched with analytical predictions of PDFs based on the instanton method by removing the autocorrelations from the time series. In many instances, the statistics generated by the CHM dynamics relaxesmore » to Gaussian distributions for both the electrostatic and vorticity perturbations, whereas in areas with strong nonlinear interactions it is found that the PDFs are exponentially distributed.« less

Regulation of electron temperature gradient turbulence by zonal flows driven by trapped electron modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asahi, Y., E-mail: y.asahi@nr.titech.ac.jp; Tsutsui, H.; Tsuji-Iio, S.

2014-05-15

Turbulent transport caused by electron temperature gradient (ETG) modes was investigated by means of gyrokinetic simulations. It was found that the ETG turbulence can be regulated by meso-scale zonal flows driven by trapped electron modes (TEMs), which are excited with much smaller growth rates than those of ETG modes. The zonal flows of which radial wavelengths are in between the ion and the electron banana widths are not shielded by trapped ions nor electrons, and hence they are effectively driven by the TEMs. It was also shown that an E × B shearing rate of the TEM-driven zonal flows is larger thanmore » or comparable to the growth rates of long-wavelength ETG modes and TEMs, which make a main contribution to the turbulent transport before excitation of the zonal flows.« less

The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Staebler, G. M.; Candy, J.; Howard, N. T.

2016-06-15

The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the thresholdmore » for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. The zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ion-scale gyrokinetic simulations.« less

The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence

DOE PAGES

Staebler, Gary M.; Candy, John; Howard, Nathan T.; ...

2016-06-29

The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the thresholdmore » for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. Finally, the zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ionscale gyrokinetic simulations.« less

A PV view of the zonal mean distribution of temperature and wind in the extratropical troposphere

NASA Technical Reports Server (NTRS)

Sun, De-Zheng; Lindzen, Richard S.

1994-01-01

The dependence of the temperature and wind distribution of the zonal mean flow in the extratropical troposphere on the gradient of pontential vorticity along isentropes is examined. The extratropics here refer to the region outside the Hadley circulation. Of particular interest is whether the distribution of temperature and wind corresponding to a constant potential vorticity (PV) along isentropes resembles the observed, and the implications of PV homogenization along isentropes for the role of the tropics. With the assumption that PV is homogenized along isentropes, it is found that the temperature distribution in the extratropical troposphere may be determined by a linear, first-order partial differential equation. When the observed surface temperature distribution and tropical lapse rate are used as the boundary conditions, the solution of the equation is close to the observed temperature distribution except in the upper troposphere adjacent to the Hadley circulation, where the troposphere with no PV gradient is considerably colder. Consequently, the jet is also stronger. It is also found that the meridional distribution of the balanced zonal wind is very sensitive to the meridional distribution of the tropopause temperature. The result may suggest that the requirement of the global momentum balance has no practical role in determining the extratropical temperature distribution. The authors further investigated the sensitivity of the extratropical troposphere with constant PV along isentropes to changes in conditions at the tropical boundary (the edge of the Hadley circulation). It is found that the temperature and wind distributions in the extratropical troposphere are sensitive to the vertical distribution of PV at the tropical boundary. With a surface distribution of temperature that decreases linearly with latitude, the jet maximum occurs at the tropical boundary and moves with it. The overall pattern of wind distribution is not sensitive to the change of

The 10-30-day oscillation of winter zonal wind in the entrance region of the East Asian subtropical jet and its relationship with precipitation in southern China

NASA Astrophysics Data System (ADS)

Yao, Chenyu; Huang, Qian; Zhu, Bin; Liu, Fei

2018-06-01

Using ECMWF ERA-Interim 6-h reanalysis data, zonal wind intra-seasonal oscillations (ISOs) in the entrance region of the East Asian subtropical westerly jet (EASWJ) in winter from 1979/1980 to 2012/2013 are studied. The results first show that there is an area with large ISO strength in the northwest of the EASWJ; in the key region, zonal wind has a dominant period of 10-30 days. The composite analysis reveals that zonal wind at 200 hPa in this key region has 10-30-day oscillation characteristics. On the 10-30-day time scale, the center of zonal wind anomaly moves eastward. The propagation of zonal wind oscillation relates to temperature tendencies at different latitudes. The remarkable increase (or decrease) in zonal wind in the key region is mostly determined by temperature anomalies to the north. The 10-30-day filtered temperature advection to the north of the key region leads to either a decrease or an increase in temperature; on the other hand, temperature variations south of the key region have trends opposite of the northern trends, which changes the temperature gradient. On the 10-30-day time scale, zonal wind anomalies are associated with precipitation in southern China. When there are easterly wind anomalies over the key region, precipitation occurs over the Yangtze River basin and its south. Diabatic heating during precipitation corresponds with warming to the south of the key region, which combines with the temperature advection to weaken the easterly wind and strengths the westerly wind. Then, the intra-seasonal precipitation moves to southwest China with warm advection and the enhanced westerly wind, which brings the positive relative vorticity advection there.

Role of zonal flows in trapped electron mode turbulence through nonlinear gyrokinetic particle and continuum simulationa)

NASA Astrophysics Data System (ADS)

Ernst, D. R.; Lang, J.; Nevins, W. M.; Hoffman, M.; Chen, Y.; Dorland, W.; Parker, S.

2009-05-01

Trapped electron mode (TEM) turbulence exhibits a rich variety of collisional and zonal flow physics. This work explores the parametric variation of zonal flows and underlying mechanisms through a series of linear and nonlinear gyrokinetic simulations, using both particle-in-cell and continuum methods. A new stability diagram for electron modes is presented, identifying a critical boundary at ηe=1, separating long and short wavelength TEMs. A novel parity test is used to separate TEMs from electron temperature gradient driven modes. A nonlinear scan of ηe reveals fine scale structure for ηe≳1, consistent with linear expectation. For ηe<1, zonal flows are the dominant saturation mechanism, and TEM transport is insensitive to ηe. For ηe>1, zonal flows are weak, and TEM transport falls inversely with a power law in ηe. The role of zonal flows appears to be connected to linear stability properties. Particle and continuum methods are compared in detail over a range of ηe=d ln Te/d ln ne values from zero to five. Linear growth rate spectra, transport fluxes, fluctuation wavelength spectra, zonal flow shearing spectra, and correlation lengths and times are in close agreement. In addition to identifying the critical parameter ηe for TEM zonal flows, this paper takes a challenging step in code verification, directly comparing very different methods of simulating simultaneous kinetic electron and ion dynamics in TEM turbulence.

Jupiter cloud morphology and zonal winds from ground-based observations before and during Juno's first perijove

NASA Astrophysics Data System (ADS)

Hueso, R.; Sánchez-Lavega, A.; Iñurrigarro, P.; Rojas, J. F.; Pérez-Hoyos, S.; Mendikoa, I.; Gómez-Forrellad, J. M.; Go, C.; Peach, D.; Colas, F.; Vedovato, M.

2017-05-01

We analyze Jupiter observations between December 2015 and August 2016 in the 0.38-1.7 μm wavelength range from the PlanetCam instrument at the 2.2 m telescope at Calar Alto Observatory and in the optical range by amateur observers contributing to the Planetary Virtual Observatory Laboratory. Over this time Jupiter was in a quiescent state without notable disturbances. Analysis of ground-based images and Hubble Space Telescope observations in February 2016 allowed the retrieval of mean zonal winds from -74.5° to +73.2°. These winds did not change over 2016 or when compared with winds from previous years with the sole exception of intense zonal winds at the North Temperate Belt. We also present results concerning the major wave systems in the North Equatorial Belt and in the upper polar hazes visible in methane absorption bands, a description of the planet's overall cloud morphology and observations of Jupiter hours before Juno's orbit insertion.

Stationary zonal flows during the formation of the edge transport barrier in the JET tokamak

DOE PAGES

Hillesheim, J. C.; Meyer, H.; Maggi, C. F.; ...

2016-02-10

In this study, high spatial resolution Doppler backscattering measurements in JET have enabled new insights into the development of the edge E r. We observe fine-scale spatial structures in the edge E r well with a wave number k rρi ≈ 0.4-0.8, consistent with stationary zonal flows, the characteristics of which vary with density. The zonal flow amplitude and wavelength both decrease with local collisionality, such that the zonal flow E x B shear increases. Above the minimum of the L-H transition power threshold dependence on density, the zonal flows are present during L mode and disappear following the H-modemore » transition, while below the minimum they are reduced below measurable amplitude during L mode, before the L-H transition.« less

Shear-flow trapped-ion-mode interaction revisited. II. Intermittent transport associated with low-frequency zonal flow dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghizzo, A., E-mail: alain.ghizzo@univ-lorraine.fr; Palermo, F.

We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was foundmore » that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.« less

Rossby and drift wave turbulence and zonal flows: The Charney-Hasegawa-Mima model and its extensions

NASA Astrophysics Data System (ADS)

Connaughton, Colm; Nazarenko, Sergey; Quinn, Brenda

2015-12-01

A detailed study of the Charney-Hasegawa-Mima model and its extensions is presented. These simple nonlinear partial differential equations suggested for both Rossby waves in the atmosphere and drift waves in a magnetically-confined plasma, exhibit some remarkable and nontrivial properties, which in their qualitative form, survive in more realistic and complicated models. As such, they form a conceptual basis for understanding the turbulence and zonal flow dynamics in real plasma and geophysical systems. Two idealised scenarios of generation of zonal flows by small-scale turbulence are explored: a modulational instability and turbulent cascades. A detailed study of the generation of zonal flows by the modulational instability reveals that the dynamics of this zonal flow generation mechanism differ widely depending on the initial degree of nonlinearity. The jets in the strongly nonlinear case further roll up into vortex streets and saturate, while for the weaker nonlinearities, the growth of the unstable mode reverses and the system oscillates between a dominant jet, which is slightly inclined to the zonal direction, and a dominant primary wave. A numerical proof is provided for the extra invariant in Rossby and drift wave turbulence-zonostrophy. While the theoretical derivations of this invariant stem from the wave kinetic equation which assumes weak wave amplitudes, it is shown to be relatively well-conserved for higher nonlinearities also. Together with the energy and enstrophy, these three invariants cascade into anisotropic sectors in the k-space as predicted by the Fjørtoft argument. The cascades are characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model has demonstrated the well-known drift wave-zonal flow feedback loop. The drift wave turbulence is generated from this primary instability. The zonal flows are then excited by either one of the generation mechanisms, extracting energy from

Are Strong Zonal Winds in Giant Planets Caused by Density-Stratification?

NASA Astrophysics Data System (ADS)

Verhoeven, J.; Stellmach, S.

2012-12-01

One of the most striking features of giant planets like Jupiter and Saturn are the zonal wind patterns observed on their surfaces. The mechanism that drives this differential rotation is still not clearly identified and is currently strongly debated in the astro- and geophysics community. Different mechanisms have been proposed over the last decades. Here, a recently discovered mechanism based on background density stratification (Glatzmaier et al., 2009) is investigated. This mechanism has the potential to overcome known difficulties of previous explanations and its efficiency has been demonstrated in 2-d simulations covering equatorial planes. By performing highly resolved numerical simulations in a local Cartesian geometry, we are able to test the efficiency and functionality of this mechanism in turbulent, rotating convection in three spatial dimensions. The choice of a Cartesian model geometry naturally excludes other known mechanisms capable of producing differential rotation, thus allowing us to investigate the role of density stratification in isolation. Typically, the dynamics can be classified into two main regimes: A regime exhibiting strong zonal winds for weak to moderate thermal driving and a regime where zonal winds are largely absent in the case of a strong thermal forcing. Our results indicate that previous 2-d results must be handled with care and can only explain parts of the full 3-d behavior. We show that the density-stratification mechanism tends to operate in a more narrow parameter range in 3-d as compared to 2-d simulations. The dynamics of the regime transition is shown to differ in both cases, which renders scaling laws derived from two-dimensional studies questionable. Based on our results, we provide estimates for the importance of the density-stratification mechanism for giant planets like Jupiter (strong density stratification), for systems like the Earth's core (weak density stratification) and compare its efficiency with other

Climatology of mesopause region nocturnal temperature, zonal wind, and sodium density observed by sodium lidar over Hefei, China (32°N, 117°E)

NASA Astrophysics Data System (ADS)

Li, T.; Ban, C.; Fang, X.; Li, J.; Wu, Z.; Xiong, J.; Feng, W.; Plane, J. M. C.

2017-12-01

The University of Science and Technology of China narrowband sodium temperature/wind lidar, located in Hefei, China (32°N, 117°E), was installed in November 2011 and have made routine nighttime measurements since January 2012. We obtained 154 nights ( 1400 hours) of vertical profiles of temperature, sodium density, and zonal wind, and 83 nights ( 800 hours) of vertical flux of gravity wave (GW) zonal momentum in the mesopause region (80-105 km) during the period of 2012 to 2016. In temperature, it is likely that the diurnal tide dominates below 100 km in spring, while the semidiurnal tide dominates above 100 km throughout the year. A clear semiannual variation in temperature is revealed near 90 km, likely related to the tropical mesospheric semiannual oscillation (MSAO). The variability of sodium density is positively correlated with temperature, suggesting that in addition to dynamics, the chemistry may also play an important role in the formation of sodium atoms. The observed sodium peak density is 1000 cm-3 higher than that simulated by the model. In zonal wind, the diurnal tide dominates in both spring and fall, while semidiurnal tide dominates in winter. The observed semiannual variation in zonal wind near 90 km is out-of-phase with that in temperature, consistent with tropical MSAO. The GW zonal momentum flux is mostly westward in fall and winter, anti-correlated with eastward zonal wind. The annual mean flux averaged over 87-97 km is -0.3 m2/s2 (westward), anti-correlated with eastward zonal wind of 10 m/s. The comparisons of lidar results with those observed by satellite, nearby radar, and simulated by model show generally good agreements.

Zonal flow generation and its feedback on turbulence production in drift wave turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pushkarev, Andrey V.; Bos, Wouter J. T.; Nazarenko, Sergey V.

2013-04-15

Plasma turbulence described by the Hasegawa-Wakatani equations is simulated numerically for different models and values of the adiabaticity parameter C. It is found that for low values of C turbulence remains isotropic, zonal flows are not generated and there is no suppression of the meridional drift waves and particle transport. For high values of C, turbulence evolves towards highly anisotropic states with a dominant contribution of the zonal sector to the kinetic energy. This anisotropic flow leads to a decrease of turbulence production in the meridional sector and limits the particle transport across the mean isopycnal surfaces. This behavior allowsmore » to consider the Hasegawa-Wakatani equations a minimal PDE model, which contains the drift-wave/zonal-flow feedback loop mechanism.« less

Why do modelled and observed surface wind stress climatologies differ in the trade wind regions?

NASA Astrophysics Data System (ADS)

Simpson, I.; Bacmeister, J. T.; Sandu, I.; Rodwell, M. J.

2017-12-01

Global climate models (GCMs) exhibit stronger easterly zonal surface wind stress and near surface winds in the Northern Hemisphere (NH) trade winds than observationally constrained reanalyses or other observational products. A comparison, between models and reanalyses, of the processes that contribute to the zonal mean, vertically integrated balance of momentum, reveals that this wind stress discrepancy cannot be explained by either the resolved dynamics or parameterized tendencies that are common to each. Rather, a substantial residual exists in the momentum balance of the reanalyses, pointing toward a role for the analysis increments. Indeed, they are found to systematically weaken the NH near surface easterlies in winter, thereby reducing the surface wind stress. Similar effects are found in the Southern Hemisphere and further analysis of the spatial structure and seasonality of these increments, demonstrates that they act to weaken the near surface flow over much of the low latitude oceans in both summer and winter. This suggests an erroneous /missing process in GCMs that constitutes a missing drag on the low level zonal flow over oceans. Either this indicates a mis-representation of the drag between the surface and the atmosphere, or a missing internal atmospheric process that amounts to an additional drag on the low level zonal flow. If the former is true, then observation based surface stress products, which rely on similar drag formulations to GCMs, may be underestimating the strength of the easterly surface wind stress.

Some studies of zonal and meridional wind characteristics at low latitude Indian stations

NASA Astrophysics Data System (ADS)

Nagpal, O. P.; Kumar, S.

1985-12-01

At the beginning of the Indian Middle Atmosphere Programme (IMAP), it was decided that the preparation of consolidation reports of already available parameters for the middle atmosphere would be useful. Atmospheric wind data obtained by rockets and balloons constituted one such parameter which had to be consolidated. The present paper summaries the results of this consolidation study. Both zonal and meridional components of winds at four low latitude Indian stations namely Thumba, Shar, Hyderabad, and Balasore, have been analyzed to yield reference wind profiles for each month. The montly mean values have been used to bring out the amplitudes and phases of the annual, semiannual and quasi-biennial oscillations.

Some studies of zonal and meridional wind characteristics at low latitude Indian stations

NASA Technical Reports Server (NTRS)

Nagpal, O. P.; Kumar, S.

1985-01-01

At the beginning of the Indian Middle Atmosphere Programme (IMAP), it was decided that the preparation of consolidation reports of already available parameters for the middle atmosphere would be useful. Atmospheric wind data obtained by rockets and balloons constituted one such parameter which had to be consolidated. The present paper summaries the results of this consolidation study. Both zonal and meridional components of winds at four low latitude Indian stations namely Thumba, Shar, Hyderabad, and Balasore, have been analyzed to yield reference wind profiles for each month. The montly mean values have been used to bring out the amplitudes and phases of the annual, semiannual and quasi-biennial oscillations.

Zonal Flows and Long-lived Axisymmetric Pressure Bumps in Magnetorotational Turbulence

NASA Astrophysics Data System (ADS)

Johansen, A.; Youdin, A.; Klahr, H.

2009-06-01

We study the behavior of magnetorotational turbulence in shearing box simulations with a radial and azimuthal extent up to 10 scale heights. Maxwell and Reynolds stresses are found to increase by more than a factor of 2 when increasing the box size beyond two scale heights in the radial direction. Further increase of the box size has little or no effect on the statistical properties of the turbulence. An inverse cascade excites magnetic field structures at the largest scales of the box. The corresponding 10% variation in the Maxwell stress launches a zonal flow of alternating sub- and super-Keplerian velocity. This, in turn, generates a banded density structure in geostrophic balance between pressure and Coriolis forces. We present a simplified model for the appearance of zonal flows, in which stochastic forcing by the magnetic tension on short timescales creates zonal flow structures with lifetimes of several tens of orbits. We experiment with various improved shearing box algorithms to reduce the numerical diffusivity introduced by the supersonic shear flow. While a standard finite difference advection scheme shows signs of a suppression of turbulent activity near the edges of the box, this problem is eliminated by a new method where the Keplerian shear advection is advanced in time by interpolation in Fourier space.

Simulations of Turbulence in Tokamak Edge and Effects of Self-Consistent Zonal Flows

NASA Astrophysics Data System (ADS)

Cohen, Bruce; Umansky, Maxim

2013-10-01

Progress is reported on simulations of electromagnetic drift-resistive ballooning turbulence in the tokamak edge. This extends previous work to include self-consistent zonal flows and their effects. The previous work addressed simulation of L-mode tokamak edge turbulence using the turbulence code BOUT that solves Braginskii-based plasma fluid equations in tokamak edge domain. The calculations use realistic single-null geometry and plasma parameters of the DIII-D tokamak and produce fluctuation amplitudes, fluctuation spectra, and particle and thermal fluxes that compare favorably to experimental data. In the effect of sheared ExB poloidal rotation is included with an imposed static radial electric field fitted to experimental data. In the new work here we include the radial electric field self-consistently driven by the microturbulence, which contributes to the sheared ExB poloidal rotation (zonal flow generation). We present simulations with/without zonal flows for both cylindrical geometry, as in the UCLA Large Plasma Device, and for the DIII-D tokamak L-mode cases in to quantify the influence of self-consistent zonal flows on the microturbulence and the concomitant transport. This work was performed under the auspices of the U.S. Department of Energy under contract DE-AC52-07NA27344 at the Lawrence Livermore National Laboratory.

Geographic distribution of zonal wind and UV albedo at cloud top level from VMC camera on Venus Express: Influence of Venus topography through stationary gravity waves vertical propagation.

NASA Astrophysics Data System (ADS)

Bertaux, Jean-Loup; Khatunstsev, Igor; Hauchecorne, Alain; Markiewicz, Wojciech; Marcq, Emmanuel; Lebonnois, Sébastien; Patsaeva, Marina; Turin, Alexander

2015-04-01

UV images (at 365 nm) of Venus cloud top collected with VMC camera on board Venus Express allowed to derive a large number of wind measurements at altitude 67±2 km from tracking of cloud features in the period 2006-2012. Both manual (45,600) and digital (391,600) individual wind measurements over 127 orbits were analyzed showing various patterns with latitude and local time. A new longitude-latitude geographic map of the zonal wind shows a conspicuous region of strongly decreased zonal wind, a remarkable feature that was unknown up to now. While the average zonal wind near equator (from 5°S to 15°s) is -100.9 m/s in the longitude range 200-330°, it reaches -83.4 m/s in the range 60-100°, a difference of 17.5 m/s. When compared to the altimetry map of Venus, it is found that the zonal wind pattern is well correlated with the underlying relief in the region of Aphrodite Terra, with a downstream shift of about 30° (˜3,200 km). We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to cloud top level, break there and transfer their momentum to the zonal flow. A similar phenomenon is known to operate on Earth with an influence on mesospheric winds. The LMD-GCM for Venus was run with or without topography, with and without a parameterization of gravity waves and does not display such an observed change of velocity near equator. The cloud albedo map at 365 nm varies also in longitude and latitude. We speculate that it might be the result of increased vertical mixing associated to wave breaking, and decreased abundance of the UV absorber which makes the contrast in images. The impact of these new findings on current super rotation theories remains to be assessed. This work was triggered by the presence of a conspicuous peak at 117 days in a time series of wind measurements. This is the length of the solar day as seen at the

Periodical oscillation of zonal wind velocities at the cloud top of Venus

NASA Astrophysics Data System (ADS)

Kouyama, T.; Imamura, T.; Nakamura, M.; Satoh, T.; Futaana, Y.

2010-12-01

Zonal wind velocity of Venus increases with height and reaches about 100 m s-1 at the cloud top level (~70km). The speed is approximately 60 times faster than the rotation speed of the solid body of Venus (~1.6 m s-1, at the equator) and this phenomenon is called a "super-rotation". From previous observations, it is known that the super-rotation changes on a long timescale. At the cloud top level, it was suggested that the super-rotation has a few years period oscillation based on observations made by Pioneer Venus orbiter of USA from 1979 to 1985 (Del Genio et al.,1990). However, the period, the amplitude, the spatial structure and the mechanism of the long period oscillation have not been understood well. Venus Express (VEX) of European Space Agency has been observing Venus since its orbital insertion in April 2006. Venus Monitoring Camera (VMC) onboard VEX has an ultra violet (UV) filter (365 nm), and VMC has taken day-side cloud images at the cloud top level with this filter. Such images exhibit various cloud features made by unknown UV absorber in the atmosphere. For investigating the characteristics of long-timescale variations of the super-rotation, we analyzed zonal velocity fields derived from UV cloud images from May 2006 to January 2010 using a cloud tracking method. UV imaging of VMC is done when the spacecraft is in the ascending portion of its elongated polar orbit. Since the orbital plane is nearly fixed in the inertial space, the local time of VMC/UV observation changes with a periodicity of one Venus year. As a result, periods when VMC observation covered day-side areas of Venus, large enough for cloud trackings, are not continuous. For deriving wind velocities we were able to use cloud images taken in 280 orbits during this period. The derived zonal wind velocity from 10°S to 40°S latitude shows a prominent year-to-year variation, and the variation is well fitted by a periodical oscillation with a period of about 260 Earth days, although not all

Observed variability in the upper layers at the Equator, 90°E in the Indian Ocean during 2001-2008, 1: zonal currents

NASA Astrophysics Data System (ADS)

Rao, R. R.; Horii, T.; Masumoto, Y.; Mizuno, K.

2017-08-01

The observed variability of zonal currents (ZC) at the Equator, 90°E shows a strong seasonal cycle in the near-surface 40-350 m water column with periodic east-west reversals most pronounced at semiannual frequency. Superposed on this, a strong intraseasonal variability of 30-90 day periodicity is also prominently seen in the near-surface layer (40-80 m) almost throughout the year with the only exception of February-March. An eastward flowing equatorial undercurrent (EUC) is present in the depth range of 80-160 m during March-April and October-November. The observed intraseasonal variability in the near-surface layer is primarily determined by the equatorial zonal westerly wind bursts (WWBs) through local frictional coupling between the zonal flow in the surface layer and surface zonal winds and shows large interannual variability. The eastward flowing EUC maintained by the ZPG set up by the east-west slope of the thermocline remotely controlled by the zonal wind (ZW) and zonally propagating wave fields also shows significant interannual variability. This observed variability on interannual time scales appears to be controlled by the corresponding variability in the alongshore winds off the Somalia coast during the preceding boreal winter, the ZW field along the equator, and the associated zonally propagating Kelvin and Rossby waves. The salinity induced vertical stratification observed in the near-surface layer through barrier layer thickness (BLT) effects also shows a significant influence on the ZC field on intraseasonal time scale. Interestingly, among all the 8 years (2001-2008), relatively weaker annual cycle is seen in both ZC in the 40-350 m water column and boreal spring sea surface temperature (SST) only during 2001 and 2008 along the equator caused through propagating wave dynamics.

Jupiter: New estimates of mean zonal flow at the cloud level

NASA Technical Reports Server (NTRS)

Limaye, Sanjay S.

1986-01-01

In order to reexamine the magnitude differences of the Jovian atmosphere's jets, as determined by Voyager 1 and 2 images, a novel approach is used to ascertain the zonal mean east-west component of motion. This technique is based on digital pattern matching, and is applied on pairs of mapped images to yield a profile of the mean zonal component that reproduces the exact locations of the easterly and westerly jets between + and 60 deg latitude. Results were obtained for all of the Voyager 1 and 2 cylindrical mosaics; the correlation coefficient between Voyagers 1 and 2 in mean zonal flow between + and - 60 deg latitude, determined from violet filter mosaics, is 0.998.

Zonal wind indices to reconstruct United States winter precipitation during El Niño

NASA Astrophysics Data System (ADS)

Farnham, D. J.; Steinschneider, S.; Lall, U.

2017-12-01

The highly discussed 2015/16 El Niño event, which many likened to the similarly strong 1997/98 El Niño event, led to precipitation impacts over the continental United States (CONUS) inconsistent with general expectations given past events and model-based forecasts. This presents a challenge for regional water managers and others who use seasonal precipitation forecasts who previously viewed El Niño events as times of enhanced confidence in seasonal water availability and flood risk forecasts. It is therefore useful to understand the extent to which wintertime CONUS precipitation during El Niño events can be explained by seasonal sea surface temperature heating patterns and the extent to which the precipitation is a product of natural variability. In this work, we define two seasonal indices based on the zonal wind field spanning from the eastern Pacific to the western Atlantic over CONUS that can explain El Niño precipitation variation spatially throughout CONUS over 11 historic El Niño events from 1950 to 2016. The indices reconstruct El Niño event wintertime (Jan-Mar) gridded precipitation over CONUS through cross-validated regression much better than the traditional ENSO sea surface temperature indices or other known modes of variability. Lastly, we show strong relationships between sea surface temperature patterns and the phases of the zonal wind indices, which in turn suggests that some of the disparate CONUS precipitation during El Niño events can be explained by different heating patterns. The primary contribution of this work is the identification of intermediate variables (in the form of zonal wind indices) that can facilitate further studies into the distinct hydroclimatic response to specific El Niño events.

Why the stratospheric zonal and meridional wind changes trend in the mid -1990s?

NASA Astrophysics Data System (ADS)

Krizan, P.

2016-12-01

This poster tries to explain the reasons for trend change of the stratospheric zonal and meridional wind in the mid-1990s. In the areas of negative (positive) wind speed trend before 1995 the positive (negative) trend is observed after this point Similar change is observed also for total ozone where we observe negative trend before 1995 and positive one after. We use MERRA reanalysis data especially monthly mean of geopotential from January to March. We suppose the position and strength of polar vortex and Aleutian high plays here very important role..

Hubble Space Telescope observations of the 1990 equatorial disturbance on Saturn - Zonal winds and central meridian albedos

NASA Astrophysics Data System (ADS)

Barnet, C. D.; Westphal, J. A.; Beebe, R. F.; Huber, L. F.

1992-12-01

The present comparison of two sets of HST data from August and November 1990 with Voyager 1 and 2 data acquired in 1980 and 1981 gives attention to Saturn's equatorial-region disturbance of September 1990. Longitudinal variations in the equatorial zonal winds are interpreted as evidence for interaction between the storm nucleus that was generated during the disturbance and the local wind field.

Nonlinear saturation of the slab ITG instability and zonal flow generation with fully kinetic ions

NASA Astrophysics Data System (ADS)

Miecnikowski, Matthew T.; Sturdevant, Benjamin J.; Chen, Yang; Parker, Scott E.

2018-05-01

Fully kinetic turbulence models are of interest for their potential to validate or replace gyrokinetic models in plasma regimes where the gyrokinetic expansion parameters are marginal. Here, we demonstrate fully kinetic ion capability by simulating the growth and nonlinear saturation of the ion-temperature-gradient instability in shearless slab geometry assuming adiabatic electrons and including zonal flow dynamics. The ion trajectories are integrated using the Lorentz force, and the cyclotron motion is fully resolved. Linear growth and nonlinear saturation characteristics show excellent agreement with analogous gyrokinetic simulations across a wide range of parameters. The fully kinetic simulation accurately reproduces the nonlinearly generated zonal flow. This work demonstrates nonlinear capability, resolution of weak gradient drive, and zonal flow physics, which are critical aspects of modeling plasma turbulence with full ion dynamics.

A preliminary comparison of Na lidar and meteor radar zonal winds during quiet and sub-storm conditions

NASA Astrophysics Data System (ADS)

Grandhi, Kishore Kumar; Nesse Tyssøy, Hilde; Williams, Bifford P.; Stober, Gunter

2017-04-01

It is speculated that sufficiently large electric fields during geomagnetic disturbed conditions may decouple the meteor trail electron motions from the background neutral winds and leads to erroneous neutral wind estimation. As per our knowledge, the potential errors have never been reported. In the present case study, we have been using co-located meteor radar and sodium resonance lidar zonal wind measurements over Andenes (69.27oN,16.04oE) during intense sub storms in the declining phase of Jan 2005 solar proton event (21-22 Jan 2005). In total 14 hours of continuous measurements are available for the comparison, which covers both quiet and disturbed conditions. For comparison, the lidar zonal winds are averaged in meteor radar time and height bins. High cross correlations (˜0.8) are found in all height regions. The discrepancies can be explained in the light of differences in the observational volumes of the two instruments. Further, we extended the comparison to address the ionization impact on the meteor radar winds. For quiet hours, the observed meteor radar winds are quite consistent with lidar winds. While during the disturbed hours comparatively large differences are noticed at higher most altitudes. This might be due to ionization impact on meteor radar winds. At the present one event is not sufficient to make any consolidate conclusion. However, at least from this study we found some effect on the neutral wind measurements for the meteor radar. Further study with more co-located measurements are needed to test statistical significance of the result.

Zonal flow generation in inertial confinement fusion implosions

DOE PAGES

Peterson, J. L.; Humbird, K. D.; Field, J. E.; ...

2017-03-06

A supervised machine learning algorithm trained on a multi-petabyte dataset of inertial confinement fusion simulations has identified a class of implosions that robustly achieve high yield, even in the presence of drive variations and hydrodynamic perturbations. These implosions are purposefully driven with a time-varying asymmetry, such that coherent flow generation during hotspot stagnation forces the capsule to self-organize into an ovoid, a shape that appears to be more resilient to shell perturbations than spherical designs. Here this new class of implosions, whose configurations are reminiscent of zonal flows in magnetic fusion devices, may offer a path to robust inertial fusion.

Zonal flow generation in inertial confinement fusion implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peterson, J. L.; Humbird, K. D.; Field, J. E.

A supervised machine learning algorithm trained on a multi-petabyte dataset of inertial confinement fusion simulations has identified a class of implosions that robustly achieve high yield, even in the presence of drive variations and hydrodynamic perturbations. These implosions are purposefully driven with a time-varying asymmetry, such that coherent flow generation during hotspot stagnation forces the capsule to self-organize into an ovoid, a shape that appears to be more resilient to shell perturbations than spherical designs. Here this new class of implosions, whose configurations are reminiscent of zonal flows in magnetic fusion devices, may offer a path to robust inertial fusion.

Magnetic flux concentration and zonal flows in magnetorotational instability turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xue-Ning; Stone, James M., E-mail: xbai@cfa.harvard.edu

2014-11-20

Accretion disks are likely threaded by external vertical magnetic flux, which enhances the level of turbulence via the magnetorotational instability (MRI). Using shearing-box simulations, we find that such external magnetic flux also strongly enhances the amplitude of banded radial density variations known as zonal flows. Moreover, we report that vertical magnetic flux is strongly concentrated toward low-density regions of the zonal flow. Mean vertical magnetic field can be more than doubled in low-density regions, and reduced to nearly zero in high-density regions in some cases. In ideal MHD, the scale on which magnetic flux concentrates can reach a few diskmore » scale heights. In the non-ideal MHD regime with strong ambipolar diffusion, magnetic flux is concentrated into thin axisymmetric shells at some enhanced level, whose size is typically less than half a scale height. We show that magnetic flux concentration is closely related to the fact that the turbulent diffusivity of the MRI turbulence is anisotropic. In addition to a conventional Ohmic-like turbulent resistivity, we find that there is a correlation between the vertical velocity and horizontal magnetic field fluctuations that produces a mean electric field that acts to anti-diffuse the vertical magnetic flux. The anisotropic turbulent diffusivity has analogies to the Hall effect, and may have important implications for magnetic flux transport in accretion disks. The physical origin of magnetic flux concentration may be related to the development of channel flows followed by magnetic reconnection, which acts to decrease the mass-to-flux ratio in localized regions. The association of enhanced zonal flows with magnetic flux concentration may lead to global pressure bumps in protoplanetary disks that helps trap dust particles and facilitates planet formation.« less

A preliminary comparison of Na lidar and meteor radar zonal winds during geomagnetic quiet and disturbed conditions

NASA Astrophysics Data System (ADS)

Kishore Kumar, G.; Nesse Tyssøy, H.; Williams, Bifford P.

2018-03-01

We investigate the possibility that sufficiently large electric fields and/or ionization during geomagnetic disturbed conditions may invalidate the assumptions applied in the retrieval of neutral horizontal winds from meteor and/or lidar measurements. As per our knowledge, the possible errors in the wind estimation have never been reported. In the present case study, we have been using co-located meteor radar and sodium resonance lidar zonal wind measurements over Andenes (69.27°N, 16.04°E) during intense substorms in the declining phase of the January 2005 solar proton event (21-22 January 2005). In total, 14 h of measurements are available for the comparison, which covers both quiet and disturbed conditions. For comparison, the lidar zonal wind measurements are averaged over the same time and altitude as the meteor radar wind measurements. High cross correlations (∼0.8) are found in all height regions. The discrepancies can be explained in light of differences in the observational volumes of the two instruments. Further, we extended the comparison to address the electric field and/or ionization impact on the neutral wind estimation. For the periods of low ionization, the neutral winds estimated with both instruments are quite consistent with each other. During periods of elevated ionization, comparatively large differences are noticed at the highermost altitude, which might be due to the electric field and/or ionization impact on the wind estimation. At present, one event is not sufficient to make any firm conclusion. Further study with more co-located measurements are needed to test the statistical significance of the result.

Self-generated zonal flows in the plasma turbulence driven by trapped-ion and trapped-electron instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drouot, T.; Gravier, E.; Reveille, T.

This paper presents a study of zonal flows generated by trapped-electron mode and trapped-ion mode micro turbulence as a function of two plasma parameters—banana width and electron temperature. For this purpose, a gyrokinetic code considering only trapped particles is used. First, an analytical equation giving the predicted level of zonal flows is derived from the quasi-neutrality equation of our model, as a function of the density fluctuation levels and the banana widths. Then, the influence of the banana width on the number of zonal flows occurring in the system is studied using the gyrokinetic code. Finally, the impact of themore » temperature ratio T{sub e}/T{sub i} on the reduction of zonal flows is shown and a close link is highlighted between reduction and different gyro-and-bounce-average ion and electron density fluctuation levels. This reduction is found to be due to the amplitudes of gyro-and-bounce-average density perturbations n{sub e} and n{sub i} gradually becoming closer, which is in agreement with the analytical results given by the quasi-neutrality equation.« less

Observed correlation of Venus topography with the zonal wind and albedo at cloud top level: the role of stationary gravity waves.

NASA Astrophysics Data System (ADS)

Bertaux, Jean-Loup; Khatunstsev, Igor; Hauchecorne, Alain; Markiewicz, Wojtek; Emmanuel, Marcq; Sébastien, Lebonnois; Marina, Patsaeva; Alex, Turin; Anna, Fedorova

2016-04-01

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67±2 km) collected with VMC (Venus Monitoring Camera) on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°s) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to cloud top level, break there and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth by Lindzen [1981], but is not reproduced in a current GCM of Venus atmosphere. Consistent with present findings, the two VEGA mission balloons experienced a small, but significant, difference of westward velocity, at their 53 km floating altitude. The albedo at 365 nm varies also with longitude and latitude in a pattern strikingly similar in the low latitude regions to a recent map of cloud top H2O [Fedorova et al., 2015], in which a lower UV albedo is correlated with increased H2O. We argue that H2O enhancement is the sign of upwelling, suggesting that the UV absorber is also brought to cloud top by upwelling.

Ockham's Razorblade Shaving Wind-Induced Circulation

NASA Astrophysics Data System (ADS)

Bergmann, Juan Carlos

2010-05-01

Terrestrial physical oceanography is fortunate because of the existence of the continents that divide the low-latitude oceans into basins. At first glance, the previous statement appears to be not obvious because an ocean-planet should be much simpler to describe. Simple-case explanation is the central aspect of Ockham's Razorblade: If a theory fails to describe the most-simple case properly, the theory is, at least, ‘not good'. Also Descartes' methodical rules take the most-simple case as starting point. The analysis of wind-induced circulation on an ocean-planet will support the initial statement. Earth's south hemisphere is dominated by the oceans. The continents' influence on the zonal-average zonal-wind climate is relatively small. Therefore, South Hemisphere's zonal wind pattern is a relatively good proxy for that of an ocean planet. Application of this wind-stress pattern to an ocean planet yields reasonable meridional mass-flow results from the polar-regions down to the high-pressure belts: Down-welling and up-welling of water-mass are approximately balanced. However, the entire tropical circulation can in principle not be closed because there is only down-welling - even if the extreme down-welling in the equatorial belt (± 8°, with a singularity at the equator) is disregarded. The only input to the calculations is the observed terrestrial south-hemisphere zonal wind-stress pattern. Meridional stress is irrelevant because it produces a closed zonal Ekman-transport around the ocean planet (sic!). Vertical mass-transport is calculated from the divergence of the wind-induced meridional Ekman-mass-transport, which in its turn is a necessary consequence of angular-momentum conservation. No assumptions are made on how the return-flows at depth are forced because the wind-force equations cannot contribute hereto. This circumstance expresses a fundamental difference to atmospheric circulation, where mechanical forcing is caused by the pressure-fields that

Zonally averaged model of dynamics, chemistry and radiation for the atmosphere

NASA Technical Reports Server (NTRS)

Tung, K. K.

1985-01-01

A nongeostrophic theory of zonally averaged circulation is formulated using the nonlinear primitive equations on a sphere, taking advantage of the more direct relationship between the mean meridional circulation and diabatic heating rate which is available in isentropic coordinates. Possible differences between results of nongeostrophic theory and the commonly used geostrophic formulation are discussed concerning: (1) the role of eddy forcing of the diabatic circulation, and (2) the nonlinear nearly inviscid limit vs the geostrophic limit. Problems associated with the traditional Rossby number scaling in quasi-geostrophic formulations are pointed out and an alternate, more general scaling based on the smallness of mean meridional to zonal velocities for a rotating planet is suggested. Such a scaling recovers the geostrophic balanced wind relationship for the mean zonal flow but reveals that the mean meridional velocity is in general ageostrophic.

A theory of self-organized zonal flow with fine radial structure in tokamak

NASA Astrophysics Data System (ADS)

Zhang, Y. Z.; Liu, Z. Y.; Xie, T.; Mahajan, S. M.; Liu, J.

2017-12-01

The (low frequency) zonal flow-ion temperature gradient (ITG) wave system, constructed on Braginskii's fluid model in tokamak, is shown to be a reaction-diffusion-advection system; it is derived by making use of a multiple spatiotemporal scale technique and two-dimensional (2D) ballooning theory. For real regular group velocities of ITG waves, two distinct temporal processes, sharing a very similar meso-scale radial structure, are identified in the nonlinear self-organized stage. The stationary and quasi-stationary structures reflect a particular feature of the poloidal group velocity. The equation set posed to be an initial value problem is numerically solved for JET low mode parameters; the results are presented in several figures and two movies that show the spatiotemporal evolutions as well as the spectrum analysis—frequency-wave number spectrum, auto power spectrum, and Lissajous diagram. This approach reveals that the zonal flow in tokamak is a local traveling wave. For the quasi-stationary process, the cycle of ITG wave energy is composed of two consecutive phases in distinct spatiotemporal structures: a pair of Cavitons growing and breathing slowly without long range propagation, followed by a sudden decay into many Instantons that carry negative wave energy rapidly into infinity. A spotlight onto the motion of Instantons for a given radial position reproduces a Blob-Hole temporal structure; the occurrence as well as the rapid decay of Caviton into Instantons is triggered by zero-crossing of radial group velocity. A sample of the radial profile of zonal flow contributed from 31 nonlinearly coupled rational surfaces near plasma edge is found to be very similar to that observed in the JET Ohmic phase [J. C. Hillesheim et al., Phys. Rev. Lett. 116, 165002 (2016)]. The theory predicts an interior asymmetric dipole structure associated with the zonal flow that is driven by the gradients of ITG turbulence intensity.

First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer

NASA Astrophysics Data System (ADS)

Rüfenacht, R.; Kämpfer, N.; Murk, A.

2012-12-01

Today, the wind data for the upper stratosphere and lower mesosphere are commonly extrapolated using models or calculated from measurements of the temperature field, but are not measured directly. Still, such measurements would allow direct observations of dynamic processes and thus provide a better understanding of the circulation in this altitude region where the zonal wind speed reaches a maximum. Observations of middle-atmospheric winds are also expected to provide deeper insight in the coupling between the upper and the lower atmosphere, especially in the case of sudden stratospheric warming events. Furthermore, as the local chemical composition of the middle atmosphere can be measured with high accuracy, wind data could be beneficial for the interpretation of the associated transport processes. In future, middle-atmospheric wind measurements could help to improve atmospheric circulation models. Aiming to contribute to the closing of this data gap the Institute of Applied Physics of the University of Bern built a new ground-based 142 GHz Doppler-spectro-radiometer with the acronym WIRA (WInd RAdiometer) specifically designed for the measurement of middle-atmospheric wind. Currently wind speeds in five levels between 30 and 79 km can be retrieved what makes WIRA the first instrument continuously measuring profiles of horizontal wind in this altitude range. On the altitude levels where our measurement can be compared to ECMWF very good agreement has been found in the long-term statistics, with WIRA = (0.98±0.02) × ECMWF + (0.44±0.91) m/s on average, as well as in short time structures with a duration of a few days. WIRA uses a passive double sideband heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the

First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer

NASA Astrophysics Data System (ADS)

Rüfenacht, Rolf; Kämpfer, Niklaus; Murk, Axel

2013-04-01

Today, the wind data for the upper stratosphere and lower mesosphere are commonly extrapolated using models or calculated from measurements of the temperature field, but are not measured directly. Still, such measurements would allow direct observations of dynamic processes and thus provide a better understanding of the circulation in this altitude region where the zonal wind speed reaches a maximum. Observations of middle-atmospheric winds are also expected to provide deeper insight in the coupling between the upper and the lower atmosphere, especially in the case of sudden stratospheric warming events. Furthermore, as the local chemical composition of the middle atmosphere can be measured with high accuracy, wind data could be beneficial for the interpretation of the associated transport processes. In future, middle-atmospheric wind measurements could help to improve atmospheric circulation models. Aiming to contribute to the closing of this data gap the Institute of Applied Physics of the University of Bern built a new ground-based 142 GHz Doppler-spectro-radiometer with the acronym WIRA (WInd RAdiometer) specifically designed for the measurement of middle-atmospheric wind. Until now wind speeds in five levels between 30 and 79 km can be retrieved what made WIRA the first instrument continuously measuring profiles of horizontal wind in this altitude range. On the altitude levels where our measurement can be compared to ECMWF very good agreement has been found in the long-term statistics, with WIRA = (0.98±0.02) × ECMWF + (0.44±0.91) m/s on average, as well as in short time structures with a duration of a few days. WIRA uses a passive heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the instrument to scan a

Zonal Flow Velocimetry in Spherical Couette Flow using Acoustic Modes

NASA Astrophysics Data System (ADS)

Adams, Matthew M.; Mautino, Anthony R.; Stone, Douglas R.; Triana, Santiago A.; Lekic, Vedran; Lathrop, Daniel P.

2015-11-01

We present studies of spherical Couette flows using the technique of acoustic mode Doppler velocimetry. This technique uses rotational splittings of acoustic modes to infer the azimuthal velocity profile of a rotating flow, and is of special interest in experiments where direct flow visualization is impractical. The primary experimental system consists of a 60 cm diameter outer spherical shell concentric with a 20 cm diameter sphere, with air or nitrogen gas serving as the working fluid. The geometry of the system approximates that of the Earth's core, making these studies geophysically relevant. A turbulent shear flow is established in the system by rotating the inner sphere and outer shell at different rates. Acoustic modes of the fluid volume are excited using a speaker and measured via microphones, allowingdetermination of rotational splittings. Preliminary results comparing observed splittings with those predicted by theory are presented. While the majority of these studies were performed in the 60 cm diameter device using nitrogen gas, some work has also been done looking at acoustic modes in the 3 m diameter liquid sodium spherical Couette experiment. Prospects for measuring zonal velocity profiles in a wide variety of experiments are discussed.

First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer

NASA Astrophysics Data System (ADS)

Rüfenacht, R.; Kämpfer, N.; Murk, A.

2012-11-01

We report on the wind radiometer WIRA, a new ground-based microwave Doppler-spectro-radiometer specifically designed for the measurement of middle-atmospheric horizontal wind by observing ozone emission spectra at 142.17504 GHz. Currently, wind speeds in five levels between 30 and 79 km can be retrieved which makes WIRA the first instrument able to continuously measure horizontal wind in this altitude range. For an integration time of one day the measurement error on each level lies at around 25 m s-1. With a planned upgrade this value is expected to be reduced by a factor of 2 in the near future. On the altitude levels where our measurement can be compared to wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) very good agreement in the long-term statistics as well as in short time structures with a duration of a few days has been found. WIRA uses a passive double sideband heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the instrument to scan a wide range of azimuth angles including the directions east, west, north, and south for zonal and meridional wind measurements. The design of the radiometer is fairly compact and its calibration does not rely on liquid nitrogen which makes it transportable and suitable for campaign use. WIRA is conceived in a way that it can be operated remotely and does hardly require any maintenance. In the present paper, a description of the instrument is given, and the techniques used for the wind retrieval based on the determination of the Doppler shift of the measured atmospheric ozone emission spectra are outlined. Their reliability was tested using Monte Carlo simulations. Finally, a time series of 11 months of zonal wind measurements over Bern (46°57' N

First middle-atmospheric zonal wind profile measurements with a new ground-based microwave Doppler-spectro-radiometer

NASA Astrophysics Data System (ADS)

Rüfenacht, R.; Kämpfer, N.; Murk, A.

2012-07-01

We report on the wind radiometer WIRA, a new ground-based microwave Doppler-spectro-radiometer specifically designed for the measurement of middle-atmospheric horizontal wind by observing ozone emission spectra at 142.17504 GHz. Currently, wind speeds in five levels between 30 and 79 km can be retrieved what makes WIRA the first instrument able to continuously measure horizontal wind in this altitude range. For an integration time of one day the measurement error on each level lies at around 25 m s-1. With a planned upgrade this value is expected to be reduced by a factor of 2 in the near future. On the altitude levels where our measurement can be compared to wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) very good agreement in the long-term statistics as well as in short time structures with a duration of a few days has been found. WIRA uses a passive double sideband heterodyne receiver together with a digital Fourier transform spectrometer for the data acquisition. A big advantage of the radiometric approach is that such instruments can also operate under adverse weather conditions and thus provide a continuous time series for the given location. The optics enables the instrument to scan a wide range of azimuth angles including the directions east, west, north, and south for zonal and meridional wind measurements. The design of the radiometer is fairly compact and its calibration does not rely on liquid nitrogen what makes it transportable and suitable for campaign use. WIRA is conceived in a way that it can be operated remotely and does hardly require any maintenance. In the present paper, a description of the instrument is given, and the used techniques for the wind retrieval based on the determination of the Doppler shift of the measured atmospheric ozone emission spectra are outlined. Their reliability was tested using MonteCarlo simulations. Finally, a first time series of 11 months of zonal wind measurements over Bern (46°57

CALL FOR PAPERS: Special cluster issue on `Experimental studies of zonal flow and turbulence'

NASA Astrophysics Data System (ADS)

Itoh, S.-I.

2005-07-01

Plasma Physics and Controlled Fusion (PPCF) invites submissions on the topic of `Experimental studies of zonal flow and turbulence', for consideration for a special topical cluster of articles to be published early in 2006. The topical cluster will be published in an issue of PPCF, combined with regular articles. The Guest Editor for the special cluster will be S-I Itoh, Kyushu University, Japan. There has been remarkable progress in the area of structure formation by turbulence. One of the highlights has been the physics of zonal flow and drift wave turbulence in toroidal plasmas. Extensive theoretical as well as computational studies have revealed the various mechanisms in turbulence and zonal flows. At the same time, experimental research on the zonal flow, geodesic acoustic modes and generation of global electric field by turbulence has evolved rapidly. Fast growth in reports of experimental results has stimulated further efforts to develop increased knowledge and systematic understanding. Each paper considered for the special cluster should describe the present research status and new scientific knowledge/results from the authors on experimental studies of zonal flow, geodesic acoustic modes and generation of electric field by turbulence (including studies of Reynolds-Maxwell stresses, etc). Manuscripts submitted to this special cluster in Plasma Physics and Controlled Fusion will be refereed according to the normal criteria and procedures of the journal. The Guest Editor guides the progress of the cluster from the initial open call, through the standard refereeing process, to publication. To be considered for inclusion in the special cluster, articles must be submitted by 2 September 2005 and must clearly state `for inclusion in the Turbulent Plasma Cluster'. Articles submitted after this deadline may not be included in the cluster issue but may be published in a later issue of the journal. Please submit your manuscript electronically via our web site at www

Influence of Venus topography on the zonal wind and UV albedo at cloud top level: The role of stationary gravity waves

NASA Astrophysics Data System (ADS)

Bertaux, Jean-Loup; Khatuntsev, I. V.; Hauchecorne, A.; Markiewicz, W. J.; Marcq, E.; Lebonnois, S.; Patsaeva, M.; Turin, A.; Fedorova, A.

2016-06-01

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67 ± 2 km) collected with Venus Monitoring Camera on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°S) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the uplift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to the cloud top level, break there, and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth by Lindzen (1981) but is not reproduced in the current GCM of Venus atmosphere from LMD. (Laboratoire de Météorologie Dynamique) In the equatorial regions, the UV albedo at 365 nm varies also with longitude. We argue that this variation may be simply explained by the divergence of the horizontal wind field. In the longitude region (from 60° to -10°) where the horizontal wind speed is increasing in magnitude (stretch), it triggers air upwelling which brings the UV absorber at cloud top level and decreases the albedo and vice versa when the wind is decreasing in magnitude (compression). This picture is fully consistent with the classical view of Venus meridional circulation, with upwelling at equator revealed by horizontal air motions away from equator: the longitude effect is only an additional but important modulation of this effect. This interpretation is comforted by a recent map of cloud top H2O, showing that near the equator the lower UV albedo longitude region is correlated with increased H2O. We argue that H2O enhancement is the sign of upwelling, suggesting that the UV absorber is also brought to cloud top by upwelling.

Jupiter cloud morphology and zonal winds from ground-based observations during Juno's first year around Jupiter

NASA Astrophysics Data System (ADS)

Hueso, R.; Sánchez-Lavega, A.; Gómez-Forrellad, J. M.; Rojas, J. F.; Pérez-Hoyos, S.; Sanz-Requena, J. F.; Peralta, J.; Ordonez-Etxeberria, I.; Chen-Chen, H.; Mendikoa, I.; Peach, D.; Go, C.; Wesley, A.; Miles, P.; Olivetti, T.

2017-09-01

We present an analysis of Jupiter's atmospheric activity over Juno's first year around the planet based on ground-based observations. We present variability of the zonal winds associated to large outbreaks of convective activity at different belts in the planet, a study of short-scale atmospheric waves at low latitudes and examine polar views of the planet that can be compared with JunoCam observations.

Wave kinetics of drift-wave turbulence and zonal flows beyond the ray approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Hongxuan; Zhou, Yao; Ruiz, D. E.

Inhomogeneous drift-wave turbulence can be modeled as an effective plasma where drift waves act as quantumlike particles and the zonal-flow velocity serves as a collective field through which they interact. This effective plasma can be described by a Wigner-Moyal equation (WME), which generalizes the quasilinear wave-kinetic equation (WKE) to the full-wave regime, i.e., resolves the wavelength scale. Unlike waves governed by manifestly quantumlike equations, whose WMEs can be borrowed from quantum mechanics and are commonly known, drift waves have Hamiltonians very different from those of conventional quantum particles. This causes unusual phase-space dynamics that is typically not captured by themore » WKE. We demonstrate how to correctly model this dynamics with the WME instead. Specifically, we report full-wave phase-space simulations of the zonal-flow formation (zonostrophic instability), deterioration (tertiary instability), and the so-called predator-prey oscillations. We also show how the WME facilitates analysis of these phenomena, namely, (i) we show that full-wave effects critically affect the zonostrophic instability, particularly its nonlinear stage and saturation; (ii) we derive the tertiary-instability growth rate; and (iii) we demonstrate that, with full-wave effects retained, the predator-prey oscillations do not require zonal-flow collisional damping, contrary to previous studies. In conclusion, we also show how the famous Rayleigh-Kuo criterion, which has been missing in wave-kinetic theories of drift-wave turbulence, emerges from the WME.« less

Wave kinetics of drift-wave turbulence and zonal flows beyond the ray approximation

NASA Astrophysics Data System (ADS)

Zhu, Hongxuan; Zhou, Yao; Ruiz, D. E.; Dodin, I. Y.

2018-05-01

Inhomogeneous drift-wave turbulence can be modeled as an effective plasma where drift waves act as quantumlike particles and the zonal-flow velocity serves as a collective field through which they interact. This effective plasma can be described by a Wigner-Moyal equation (WME), which generalizes the quasilinear wave-kinetic equation (WKE) to the full-wave regime, i.e., resolves the wavelength scale. Unlike waves governed by manifestly quantumlike equations, whose WMEs can be borrowed from quantum mechanics and are commonly known, drift waves have Hamiltonians very different from those of conventional quantum particles. This causes unusual phase-space dynamics that is typically not captured by the WKE. We demonstrate how to correctly model this dynamics with the WME instead. Specifically, we report full-wave phase-space simulations of the zonal-flow formation (zonostrophic instability), deterioration (tertiary instability), and the so-called predator-prey oscillations. We also show how the WME facilitates analysis of these phenomena, namely, (i) we show that full-wave effects critically affect the zonostrophic instability, particularly its nonlinear stage and saturation; (ii) we derive the tertiary-instability growth rate; and (iii) we demonstrate that, with full-wave effects retained, the predator-prey oscillations do not require zonal-flow collisional damping, contrary to previous studies. We also show how the famous Rayleigh-Kuo criterion, which has been missing in wave-kinetic theories of drift-wave turbulence, emerges from the WME.

Wave kinetics of drift-wave turbulence and zonal flows beyond the ray approximation

DOE PAGES

Zhu, Hongxuan; Zhou, Yao; Ruiz, D. E.; ...

2018-05-29

Inhomogeneous drift-wave turbulence can be modeled as an effective plasma where drift waves act as quantumlike particles and the zonal-flow velocity serves as a collective field through which they interact. This effective plasma can be described by a Wigner-Moyal equation (WME), which generalizes the quasilinear wave-kinetic equation (WKE) to the full-wave regime, i.e., resolves the wavelength scale. Unlike waves governed by manifestly quantumlike equations, whose WMEs can be borrowed from quantum mechanics and are commonly known, drift waves have Hamiltonians very different from those of conventional quantum particles. This causes unusual phase-space dynamics that is typically not captured by themore » WKE. We demonstrate how to correctly model this dynamics with the WME instead. Specifically, we report full-wave phase-space simulations of the zonal-flow formation (zonostrophic instability), deterioration (tertiary instability), and the so-called predator-prey oscillations. We also show how the WME facilitates analysis of these phenomena, namely, (i) we show that full-wave effects critically affect the zonostrophic instability, particularly its nonlinear stage and saturation; (ii) we derive the tertiary-instability growth rate; and (iii) we demonstrate that, with full-wave effects retained, the predator-prey oscillations do not require zonal-flow collisional damping, contrary to previous studies. In conclusion, we also show how the famous Rayleigh-Kuo criterion, which has been missing in wave-kinetic theories of drift-wave turbulence, emerges from the WME.« less

Remote sensing of mesospheric winds with the High-Resolution Doppler Imager

NASA Technical Reports Server (NTRS)

Hays, Paul B.; Abreu, V. J.; Burrage, M. D.; Gell, D. A.; Grassi, H. J.; Marshall, A. R.; Morton, Y. T.; Ortland, D. A.; Skinner, W. R.; Wu, D. L.

1992-01-01

Observations of the winds in the upper atmosphere obtained with the High-Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) are discussed. This instrument is a very stable high-resolution triple-etalon Fabry-Perot interferometer, which is used to observe the slight Doppler shifts of absorption and emission lines in the O2 Atmospheric bands induced by atmospheric motions. Preliminary observations indicate that the winds in the mesosphere and lower thermosphere are a mixture of migrating and non-migrating tides, and planetary-scale waves. The mean meridional winds are dominated by the 1,1 diurnal tide which is easily extracted from the daily zonal means of the satellite observations. The daily mean zonal winds are a mixture of the diurnal tide and a zonal flow which is consistent with theoretical expectations.

Direct evidence of stationary zonal flows and critical gradient behavior for Er during formation of the edge pedestal in JET

NASA Astrophysics Data System (ADS)

Hillesheim, Jon

2015-11-01

High spatial resolution measurements with Doppler backscattering in JET have provided new insights into the development of the edge radial electric field during pedestal formation. The characteristics of Er have been studied as a function of density at 2.5 MA plasma current and 3 T toroidal magnetic field. We observe fine-scale spatial structure in the edge Er well prior to the LH transition, consistent with stationary zonal flows. Zonal flows are a fundamental mechanism for the saturation of turbulence and this is the first direct evidence of stationary zonal flows in a tokamak. The radial wavelength of the zonal flows systematically decreases with density. The zonal flows are clearest in Ohmic conditions, weaker in L-mode, and absent in H-mode. Measurements also show that after neutral beam heating is applied, the edge Er builds up at a constant gradient into the core during L-mode, at radii where Er is mainly due to toroidal velocity. The local stability of velocity shear driven turbulence, such as the parallel velocity gradient mode, will be assessed with gyrokinetic simulations. This critical Er shear persists across the LH transition into H-mode. Surprisingly, a reduction in the apparent magnitude of the Er well depth is observed directly following the LH transition at high densities. Establishing the physics basis for the LH transition is important for projecting scalings to ITER and these observations challenge existing models based on increased Er shear or strong zonal flows as the trigger for the transition. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Computation of transonic separated wing flows using an Euler/Navier-Stokes zonal approach

NASA Technical Reports Server (NTRS)

Kaynak, Uenver; Holst, Terry L.; Cantwell, Brian J.

1986-01-01

A computer program called Transonic Navier Stokes (TNS) has been developed which solves the Euler/Navier-Stokes equations around wings using a zonal grid approach. In the present zonal scheme, the physical domain of interest is divided into several subdomains called zones and the governing equations are solved interactively. The advantages of the Zonal Grid approach are as follows: (1) the grid for any subdomain can be generated easily; (2) grids can be, in a sense, adapted to the solution; (3) different equation sets can be used in different zones; and, (4) this approach allows for a convenient data base organization scheme. Using this code, separated flows on a NACA 0012 section wing and on the NASA Ames WING C have been computed. First, the effects of turbulence and artificial dissipation models incorporated into the code are assessed by comparing the TNS results with other CFD codes and experiments. Then a series of flow cases is described where data are available. The computed results, including cases with shock-induced separation, are in good agreement with experimental data. Finally, some futuristic cases are presented to demonstrate the abilities of the code for massively separated cases which do not have experimental data.

Frequency-dependent behavior of the barotropic and baroclinic modes of zonal jet variability

NASA Astrophysics Data System (ADS)

Sheshadri, A.; Plumb, R. A.

2016-12-01

Stratosphere-troposphere interactions are frequently described in terms of the leading modes of variability, i.e. the annular modes. An idealized dynamical core model is used to explore the differences between the low- and high- frequency (periods greater and less than 30 days) behavior of the first two principal components of zonal mean zonal wind and eddy kinetic energy, i.e., the barotropic/baroclinic annular modes of variability of the extratropical circulation. The modes show similar spatial characteristics in the different frequency ranges considered, however the ranking of the modes switches in some cases from one range to the other. There is some cancelation in the signatures of eddy heat flux and eddy kinetic energy in the leading low-pass and high-pass filtered zonal wind mode, partly explaining their small signature in the total. At low frequencies, the first zonal wind mode describes latitudinal shifts of both the midlatitude jet and its associated storm tracks, and the persistence of zonal wind anomalies appears to be sustained primarily by a baroclinic, rather than a barotropic, feedback. On shorter time scales, the behavior is more complicated and transient.

A Simulation Model for Drift Resistive Ballooning Turbulence Examining the Influence of Self-consistent Zonal Flows

NASA Astrophysics Data System (ADS)

Cohen, Bruce; Umansky, Maxim; Joseph, Ilon

2015-11-01

Progress is reported on including self-consistent zonal flows in simulations of drift-resistive ballooning turbulence using the BOUT + + framework. Previous published work addressed the simulation of L-mode edge turbulence in realistic single-null tokamak geometry using the BOUT three-dimensional fluid code that solves Braginskii-based fluid equations. The effects of imposed sheared ExB poloidal rotation were included, with a static radial electric field fitted to experimental data. In new work our goal is to include the self-consistent effects on the radial electric field driven by the microturbulence, which contributes to the sheared ExB poloidal rotation (zonal flow generation). We describe a model for including self-consistent zonal flows and an algorithm for maintaining underlying plasma profiles to enable the simulation of steady-state turbulence. We examine the role of Braginskii viscous forces in providing necessary dissipation when including axisymmetric perturbations. We also report on some of the numerical difficulties associated with including the axisymmetric component of the fluctuating fields. This work was performed under the auspices of the U.S. Department of Energy under contract DE-AC52-07NA27344 at the Lawrence Livermore National Laboratory (LLNL-ABS-674950).

Zonal flow dynamics and control of turbulent transport in stellarators.

PubMed

Xanthopoulos, P; Mischchenko, A; Helander, P; Sugama, H; Watanabe, T-H

2011-12-09

The relation between magnetic geometry and the level of ion-temperature-gradient (ITG) driven turbulence in stellarators is explored through gyrokinetic theory and direct linear and nonlinear simulations. It is found that the ITG radial heat flux is sensitive to details of the magnetic configuration that can be understood in terms of the linear behavior of zonal flows. The results throw light on the question of how the optimization of neoclassical confinement is related to the reduction of turbulence.

Jupiter cloud morphology and zonal winds from ground-based observations before and during Juno exploration

NASA Astrophysics Data System (ADS)

Sanchez-Lavega, A.; Hueso, R.; Perez-Hoyos, S.; Iñurrigarro, P.; Mendikoa, I.; Rojas, J. F.

2016-12-01

We present the results of a long term campaign between September 2015 and August 2016 of imaging of Jupiter's cloud morphology and zonal winds in the 0.38 - 1.7 μm wavelength spectral range. We use PlanetCam lucky imaging camera at the 2.2m telescope at Calar Alto Observatory in Spain, and for the optical range, the contribution of a network of observers to the Planetary Virtual Observatory Laboratory database (PVOL-IOPW at http://pvol.ehu.eus). We have complemented the study with Hubble Space Telescope WFC3 camera images taken in the 0.275 - 0.89 μm wavelength spectral range during the OPAL program on 9 February 2016. The PlanetCam images have been calibrated in radiance using spectrophotometric standard stars providing absolute reflectivity across the disk in a large series of broadband and narrowband filters sensitive to the altitude distribution and size of aerosols above the ammonia cloud level, and to the spectral dependence of the chromophore coloring agents. The cloud morphology evolution has been studied with an horizontal resolution ranging from 150 to 1000 km. Zonal wind profiles have been retrieved along the whole observing period from tracking cloud motions that span the latitude range from -80° to +77º. Combining all these results we characterized the 3D-dynamical state and cloud and haze distribution in Jupiter's atmosphere in the altitude range between 10 mbar and 1.5 bar before and during Juno initial exploration.

Indian Ocean zonal mode activity in 20th century observations and simulations

NASA Astrophysics Data System (ADS)

Sendelbeck, Anja; Mölg, Thomas

2016-04-01

The Indian Ocean zonal mode (IOZM) is a coupled ocean-atmosphere system with anomalous cooling in the east, warming in the west and easterly wind anomalies, resulting in a complete reversal of the climatological zonal sea surface temperature (SST) gradient. The IOZM has a strong influence on East African climate by causing anomalously strong October - December (OND) precipitation. Using observational data and historical CMIP5 (Coupled Model Intercomparison Project phase 5) model output, the September - November (SON) dipole mode index (DMI), OND East African precipitation and SON zonal wind index (ZWI) are calculated. We pay particular attention to detrending SSTs for calculating the DMI, which seems to have been neglected in some published research. The ZWI is defined as the area-averaged zonal wind component at 850 hPa over the central Indian Ocean. Regression analysis is used to evaluate the models' capability to represent the IOZM and its impact on east African climate between 1948 and 2005. Simple correlations are calculated between SST, zonal wind and precipitation to show their interdependence. High correlation in models implies a good representation of the influence of IOZM on East African climate variability and our goal is to detect the models with the highest correlation coefficients. In future research, these model data might be used to investigate the impact of IOZM on the East African climate variability in the late 20's century with regard to anthropogenic causes and internal variability.

Jet and storm track variability and change: adiabatic QG zonal averages and beyond... (Invited)

NASA Astrophysics Data System (ADS)

Robinson, W. A.

2013-12-01

The zonally averaged structures of extratropical jets and stormtracks, their slow variations, and their responses to climate change are all tightly constrained on the one hand by thermal wind balance and the necessary application of eddy torques to produce zonally averaged meridional motion, and, on the other hand, by the necessity that eddies propagate upshear to extract energy from the mean flow. Combining these constraints with the well developed theory of linear Rossby-wave propagation on zonally symmetric basic states has led to a large and growing number of plausible mechanisms to explain observed and modeled jet/storm track variability and responses to climate change and idealized forcing. Hidden within zonal averages is the reality that most baroclinic eddy activity is destroyed at the same latitude at which is generated: from one end to another of the fixed stormtracks in the Northern Hemisphere and baroclinic wave packets in the Southern Hemisphere. Ignored within adiabatic QG theory is the reality that baroclinic eddies gain significant energy from latent heating that involves sub-syntopic scale structures and dynamics. Here we use results from high-resolution regional and global simulations of the Northern Hemisphere storm tracks to explore the importance of non-zonal and diabatic dynamics in influencing jet change and variability and their influences on the much-studied zonal means.

Rossby waves and two-dimensional turbulence in a large-scale zonal jet

NASA Technical Reports Server (NTRS)

Shepherd, Theodor G.

1987-01-01

Homogeneous barotropic beta-plane turbulence is investigated, taking into account the effects of spatial inhomogeneity in the form of a zonal shear flows. Attention is given to the case of zonal flows that are barotropically stable and of larger scale than the resulting transient eddy field. Numerical simulations reveal that large-scale zonal flows alter the picture of classical beta-plane turbulence. It is found that the disturbance field penetrates to the largest scales of motion, that the larger disturbance scales show a tendency to meridional rather than zonal anisotropy, and that the initial spectral transfer rate away from an isotropic intermediate-scale source is enhanced by the shear-induced transfer associated with straining by the zonal flow.

Nonlinear growth of zonal flows by secondary instability in general magnetic geometry

DOE PAGES

Plunk, G. G.; Navarro, A. Banon

2017-02-23

Here we present a theory of the nonlinear growth of zonal flows in magnetized plasma turbulence, by the mechanism of secondary instability. The theory is derived for general magnetic geometry, and is thus applicable to both tokamaks and stellarators. The predicted growth rate is shown to compare favorably with nonlinear gyrokinetic simulations, with the error scaling as expected with the small parameter of the theory.

The vertical structure of Jupiter and Saturn zonal winds from nonlinear simulations of major vortices and planetary-scale disturbances

NASA Astrophysics Data System (ADS)

Garcia-Melendo, E.; Legarreta, J.; Sanchez-Lavega, A.

2012-12-01

Direct measurements of the structure of the zonal winds of Jupiter and Saturn below the upper cloud layer are very difficult to retrieve. Except from the vertical profile at a Jupiter hot spot obtained from the Galileo probe in 1995 and measurements from cloud tracking by Cassini instruments just below the upper cloud, no other data are available. We present here our inferences of the vertical structure of Jupiter and Saturn zonal wind across the upper troposphere (deep down to about 10 bar level) obtained from nonlinear simulations using the EPIC code of the stability and interactions of large-scale vortices and planetary-scale disturbances in both planets. Acknowledgements: This work has been funded by Spanish MICIIN AYA2009-10701 with FEDER support, Grupos Gobierno Vasco IT-464-07 and UPV/EHU UFI11/55. [1] García-Melendo E., Sánchez-Lavega A., Dowling T.., Icarus, 176, 272-282 (2005). [2] García-Melendo E., Sánchez-Lavega A., Hueso R., Icarus, 191, 665-677 (2007). [3] Sánchez-Lavega A., et al., Nature, 451, 437- 440 (2008). [4] Sánchez-Lavega A., et al., Nature, 475, 71-74 (2011).

Saturn's North Polar Vortex Revealed by Cassini/VIMS: Zonal Wind Structure and Constraints on Cloud Distributions

NASA Astrophysics Data System (ADS)

Baines, Kevin H.; Momary, T. W.; Fletcher, L. N.; Buratti, B. J.; Roos-Serote, M.; Showman, A. P.; Brown, R. H.; Clark, R. N.; Nicholson, P. D.

2008-09-01

We present the first high-spatial resolution, near-nadir imagery and movies of Saturn's north polar region that reveal the wind structure of a north polar vortex. Obtained by Cassini/VIMS on June 15, 2008 from high over Saturn's polar region (sub-spacecraft latitude of 65 degrees N. lat) at an altitude of 0.42 million km during the long polar night, these 210-per-pixel images of the polar region north of 73 degrees N. latitude show several concentric cloud rings and hundreds of individual cloud features in silhouette against the 5-micron background thermal glow of Saturn's deep atmosphere. In contrast to the clear eye of the south polar vortex, the north polar vortex sports a central cloud feature about 650-km in diameter. Zonal winds reach a maximum of 150 m/s near 88 degrees N. latitude (planetocentric) - comparable to the south polar vortex maximum of 190 m/s near 88 degrees S. latitude - and fall off nearly monotonically to 10 m/s near 80 degrees N. latitude. At slightly greater distance from the pole, inside the north polar hexagon in the 75-77 degree N. latitude region, zonal winds increase dramatically to 130 m/s, as silhouetted clouds are seen speeding aroud the "race track” of the hexagonal feature. VIMS 5-micron thermal observations over a 1.6-year period from October 29, 2006 to June 15, 2008 are consistent with the polar hexagon structure itself remaining fixed in the Voyager-era radio rotation rate (Desch and Kaiser, Geophys. Res. Lett, 8, 253-256, 1981) to within an accuracy of 3 seconds per rotational period. This agrees with the stationary nature of the wave in this rotation system found by Godfrey (Icarus 76, 335-356, 1988), but is inconsistent with rotation rates found during the current Cassini era.

Non-isomorphic radial wavenumber dependencies of residual zonal flows in ion and electron Larmor radius scales, and effects of initial parallel flow and electromagnetic potentials in a circular tokamak

NASA Astrophysics Data System (ADS)

Yamagishi, Osamu

2018-04-01

Radial wavenumber dependencies of the residual zonal potential for E × B flow in a circular, large aspect ratio tokamak is investigated by means of the collisionless gyrokinetic simulations of Rosenbluth-Hinton (RH) test and the semi-analytic approach using an analytic solution of the gyrokinetic equation Rosenbluth and Hinton (1998 Phys. Rev. Lett. 80 724). By increasing the radial wavenumber from an ion Larmor radius scale {k}r{ρ }i≲ 1 to an electron Larmor radius scale {k}r{ρ }e≲ 1, the well-known level ˜ O[1/(1+1.6{q}2/\\sqrt{r/{R}0})] is retained, while the level remains O(1) when the wavenumber is decreased from the electron to the ion Larmor radius scale, if physically same adiabatic assumption is presumed for species other than the main species that is treated kinetically. The conclusion is not modified by treating both species kinetically, so that in the intermediate scale between the ion and electron Larmor radius scale it seems difficult to determine the level uniquely. The toroidal momentum conservation property in the RH test is also investigated by including an initial parallel flow in addition to the perpendicular flow. It is shown that by taking a balance between the initial parallel flow and perpendicular flows which include both E × B flow and diamagnetic flow in the initial condition, the mechanical toroidal angular momentum is approximately conserved despite the toroidal symmetry breaking due to the finite radial wavenumber zonal modes. Effect of electromagnetic potentials is also investigated. When the electromagnetic potentials are applied initially, fast oscillations which are faster than the geodesic acoustic modes are introduced in the decay phase of the zonal modes. Although the residual level in the long time limit is not modified, this can make the time required to reach the stationary zonal flows longer and may weaken the effectiveness of the turbulent transport suppression by the zonal flows.

Sensitivity of Gravity Wave Fluxes to Interannual Variations in Tropical Convection and Zonal Wind.

PubMed

Alexander, M Joan; Ortland, David A; Grimsdell, Alison W; Kim, Ji-Eun

2017-09-01

Using an idealized model framework with high-frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds, the authors examine the properties and effects of gravity waves in the lower stratosphere, contrasting conditions in an El Niño year and a La Niña year. The model generates a broad spectrum of tropical waves including planetary-scale waves through mesoscale gravity waves. The authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite- and balloon-based estimates of gravity wave momentum flux. Some interesting changes in the gravity spectrum of momentum flux are found in the model, which are discussed in terms of the interannual variations in clouds, precipitation, and large-scale winds. While regional variations in clouds, precipitation, and winds are dramatic, the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11%. The modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations, and the largest-amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere. This strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency. These results suggest a way forward to improve model representations of the lowermost stratospheric quasi-biennial oscillation winds and teleconnections.

Zero potential vorticity envelopes for the zonal-mean velocity of the Venus/Titan atmospheres

NASA Technical Reports Server (NTRS)

Allison, Michael; Del Genio, Anthony D.; Zhou, Wei

1994-01-01

The diagnostic analysis of numerical simulations of the Venus/Titan wind regime reveals an overlooked constraint upon the latitudinal structure of their zonal-mean angular momentum. The numerical experiments, as well as the limited planetary observations, are approximately consistent with the hypothesis that within the latitudes bounded by the wind maxima the total Ertel potential vorticity associated with the zonal-mean motion is approximately well mixed with respect to the neutral equatorial value for a stable circulation. The implied latitudinal profile of angular momentum is of the form M equal to or less than M(sub e)(cos lambda)(exp 2/Ri), where lambda is the latitude and Ri the local Richardson number, generally intermediate between the two extremes of uniform angular momentum (Ri approaches infinity) and uniform angular velocity (Ri = 1). The full range of angular momentum profile variation appears to be realized within the observed meridional - vertical structure of the Venus atmosphere, at least crudely approaching the implied relationship between stratification and zonal velocity there. While not itself indicative of a particular eddy mechanism or specific to atmospheric superrotation, the zero potential vorticity (ZPV) constraint represents a limiting bound for the eddy - mean flow adjustment of a neutrally stable baroclinic circulation and may be usefully applied to the diagnostic analysis of future remote sounding and in situ measurements from planetary spacecraft.

WIND Flow Solver Released

NASA Technical Reports Server (NTRS)

Towne, Charles E.

1999-01-01

The WIND code is a general-purpose, structured, multizone, compressible flow solver that can be used to analyze steady or unsteady flow for a wide range of geometric configurations and over a wide range of flow conditions. WIND is the latest product of the NPARC Alliance, a formal partnership between the NASA Lewis Research Center and the Air Force Arnold Engineering Development Center (AEDC). WIND Version 1.0 was released in February 1998, and Version 2.0 will be released in February 1999. The WIND code represents a merger of the capabilities of three existing computational fluid dynamics codes--NPARC (the original NPARC Alliance flow solver), NXAIR (an Air Force code used primarily for unsteady store separation problems), and NASTD (the primary flow solver at McDonnell Douglas, now part of Boeing).

Drift-wave turbulence and zonal flow generation.

PubMed

Balescu, R

2003-10-01

Drift-wave turbulence in a plasma is analyzed on the basis of the wave Liouville equation, describing the evolution of the distribution function of wave packets (quasiparticles) characterized by position x and wave vector k. A closed kinetic equation is derived for the ensemble-averaged part of this function by the methods of nonequilibrium statistical mechanics. It has the form of a non-Markovian advection-diffusion equation describing coupled diffusion processes in x and k spaces. General forms of the diffusion coefficients are obtained in terms of Lagrangian velocity correlations. The latter are calculated in the decorrelation trajectory approximation, a method recently developed for an accurate measure of the important trapping phenomena of particles in the rugged electrostatic potential. The analysis of individual decorrelation trajectories provides an illustration of the fragmentation of drift-wave structures in the radial direction and the generation of long-wavelength structures in the poloidal direction that are identified as zonal flows.

Longitudinal differences and inter-annual variations of zonal wind in the tropical stratosphere and troposphere

NASA Astrophysics Data System (ADS)

Reddy, C. A.; Raghava Reddi, C.

1986-12-01

A quantitative assessment has been made of the longitude-dependent differences and the interannual variations of the zonal wind components in the equatorial stratosphere and troposphere, from the analysis of rocket and balloon data for 1979 and 1980 for three stations near ±8.5° latitude (Ascension Island at 14.4°W, Thumba at 76.9°E and Kwajalein at 67.7°E) and two stations near 21.5° latitude (Barking Sands at 159.6°W and Balasore at 86.9°E). The longitude-dependent differences are found to be about 10-20 m s -1 (amounting to 50-200% in some cases) for the semi-annual oscillation (SAO) and the annual oscillation (AO) amplitudes, depending upon the altitude and latitude. Inter-annual variations of about 10 m s -1 also exist in both oscillations. The phase of the SAO exhibits an almost 180° shift at Kwajalein compared to that at the other two stations near 8.5°, while the phase of the AO is independent of longitude, in the stratosphere. The amplitude and phase of the quasi-biennial oscillation (QBO) are found to be almost independent of longitude in the 18-38 km range, but above 40 km height the QBO amplitude and phase have different values in different longitude sectors for the three stations near ±8.5° latitude. The mean zonal wind shows no change from 1979 to 1980, but in the troposphere at 8.5° latitude strong easterlies prevail in the Indian zone, in contrast to the westerlies at the Atlantic and Pacific stations.

The Relationship of High-Latitude Thermospheric Wind With Ionospheric Horizontal Current, as Observed by CHAMP Satellite

NASA Astrophysics Data System (ADS)

Huang, Tao; Lühr, Hermann; Wang, Hui; Xiong, Chao

2017-12-01

The relationship between high-latitude ionospheric currents (Hall current and field-aligned current) and thermospheric wind is investigated. The 2-D patterns of horizontal wind and equivalent current in the Northern Hemisphere derived from the CHAMP satellite are considered for the first time simultaneously. The equivalent currents show strong dependences on both interplanetary magnetic field (IMF) By and Bz components. However, IMF By orientation is more important in controlling the wind velocity patterns. The duskside wind vortex as well as the antisunward wind in the morning polar cap is more evident for positive By. To better understand their spatial relation in different sectors, a systematic superposed epoch analysis is applied. Our results show that in the dusk sector, the vectors of the zonal wind and equivalent current are anticorrelated, and both of them form a vortical flow pattern for different activity levels. The currents and zonal wind are intensified with the increase of merging electric field. However, on the dawnside, where the relation is less clear, antisunward zonal winds dominate. Plasma drift seems to play a less important role for the wind than neutral forces in this sector. In the noon sector, the best anticorrelation between equivalent current and wind is observed for a positive IMF By component and it is less obvious for negative By. A clear seasonal effect with current intensities increasing from winter to summer is observed in the noon sector. Different from the currents, the zonal wind intensity shows little dependence on seasons. Our results indicate that the plasma drift and the neutral forces are of comparable influence on the zonal wind at CHAMP altitude in the noon sector.

Observed longitude variations of zonal wind, UV albedo and H2O at Venus cloud top level: the role of stationary gravity waves generated by Venus topography

NASA Astrophysics Data System (ADS)

Bertaux, Jean-Loup; Hauchecorne, Alain; khatuntsev, Igor; Markiewicz, Wojciech; Marcq, emmanuel; Lebonnois, Sebastien; Patsaeva, Marina; Turin, Alexander; Fedorova, Anna

2016-10-01

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67±2 km) collected with VMC (Venus Monitoring Camera) on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°S) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to the cloud top level, break there and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth but is not reproduced in the current GCM of Venus atmosphere from LMD.In the equatorial regions, the UV albedo of clouds at 365 nm and the H2O mixing ratio at cloud top varies also with longitude, with an anti-correlation: the more H2O, the darker are the clouds. We argue that these variations may be simply explained by the divergence of the horizontal wind field. In the longitude region (from 60° to -10°) where the horizontal wind speed is increasing in magnitude (stretch), it triggers air upwelling which brings both the UV absorber and H2O at cloud top level and decreases the albedo, and vice-versa when the wind is decreasing in magnitude (compression). This picture is fully consistent with the classical view of Venus meridional circulation, with upwelling at equator revealed by horizontal air motions away from equator: the longitude effect is only an additional but important modulation of this effect. We argue that H2O enhancement is the sign of upwelling because the H2O mixing ratio decreases with altitude, comforting the view that the UV absorber is also brought to cloud top by upwelling.

Relationship between eastern tropical Pacific cooling and recent trends in the Southern Hemisphere zonal-mean circulation

NASA Astrophysics Data System (ADS)

Clem, Kyle R.; Renwick, James A.; McGregor, James

2017-07-01

During 1979-2014, eastern tropical Pacific sea surface temperatures significantly cooled, which has generally been attributed to the transition of the Pacific Decadal Oscillation to its negative phase after 1999. We find the eastern tropical Pacific cooling to be associated with: (1) an intensified Walker Circulation during austral summer (December-February, DJF) and autumn (March-May, MAM); (2) a weakened South Pacific Hadley cell and subtropical jet during MAM; and (3) a strengthening of the circumpolar westerlies between 50 and 60°S during DJF and MAM. Observed cooling in the eastern tropical Pacific is linearly congruent with 60-80 % of the observed Southern Hemisphere positive zonal-mean zonal wind trend between 50 and 60°S during DJF ( 35 % of the interannual variability), and around half of the observed positive zonal-mean zonal wind trend during MAM ( 15 % of the interannual variability). Although previous studies have linked the strengthened DJF and MAM circumpolar westerlies to stratospheric ozone depletion and increasing greenhouse gases, we note that the continuation of the positive SAM trends into the twenty-first century is partially associated with eastern tropical Pacific cooling, especially during MAM when zonal wind anomalies associated with eastern tropical Pacific cooling project strongly onto the observed trends. Outside of DJF and MAM, eastern tropical Pacific cooling is associated with opposing zonal wind anomalies over the Pacific and Indian sectors, which we infer is the reason for the absence of significant positive SAM trends outside of DJF and MAM despite significant eastern tropical Pacific cooling seen during all seasons.

A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves

NASA Technical Reports Server (NTRS)

Alexander, M. J.; Holton, James R.

1997-01-01

A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO.

The role of zonal flows in reactive fluid closures

NASA Astrophysics Data System (ADS)

Jan, WEILAND

2018-07-01

We will give an overview of results obtained by our reactive fluid model. It is characterised as a fluid model where all moments with sources in the experiment are kept. Furthermore, full account is taken for the highest moments appearing in unexpanded denominators also including full toroidicity. It has been demonstrated that the strength of zonal flows is dramatically larger in reactive fluid closures than in those which involve dissipation. This gives a direct connection between the fluid closure and the level of excitation of turbulence. This is because zonal flows are needed to absorb the inverse cascade in quasi 2D turbulence. This also explains the similarity in structure of the transport coefficients in our model with a reactive closure in the energy equation and models which have a reactive closure because of zero ion temperature such as the Hasegawa–Wakatani model. Our exact reactive closure unifies several well-known features of tokamak experiments such as the L–H transition, internal transport barriers and the nonlinear Dimits upshift of the critical gradient for onset of transport. It also gives transport of the same level as that in nonlinear gyrokinetic codes. Since these include the kinetic resonance this confirms the validity of the thermodynamic properties of our model. Furthermore, we can show that while a strongly nonlinear model is needed in kinetic theory a quasilinear model is sufficient in the fluid description. Thus our quasilinear fluid model will be adequate for treating all relevant problems in bulk transport. This is finally confirmed by the reproduction by the model of the experimental power scaling of the confinement time τ E ∼ P ‑2/3. This confirms the validity of our reactive fluid model. This also gives credibility to our ITER simulations including the H-mode barrier. A new result is here, that alpha heating strongly reduces the slope of the H-mode barrier. This should significantly reduce the effects of ELM’s.

Cloud level winds from UV and IR images obtained by VMC onboard Venus Express

NASA Astrophysics Data System (ADS)

Khatuntsev, Igor; Patsaeva, Marina; Titov, Dmitri; Ignatiev, Nikolay; Turin, Alexander; Bertaux, Jean-Loup

2017-04-01

During eight years Venus Monitoring Camera (VMC) [1] onboard the Venus Express orbiter has observed the upper cloud layer of Venus. The largest set of images was obtained in the UV (365 nm), visible (513 nm) and two infrared channels - 965 nm and 1010 nm. The UV dayside images were used to study the atmospheric circulation at the Venus cloud tops [2], [3]. Mean zonal and meridional profiles of winds and their variability were derived from cloud tracking of UV images. In low latitudes the mean retrograde zonal wind at the cloud top (67±2 km) is about 95 m/s with a maximum of about 102 m/s at 40-50°S. Poleward from 50°S the zonal wind quickly fades out with latitude. The mean poleward meridional wind slowly increases from zero value at the equator to about 10 m/s at 50°S. Poleward from this latitude, the absolute value of the meridional component monotonically decreases to zero at the pole. The VMC observations suggest clear diurnal signature in the wind field. They also indicate a long term trend for the zonal wind speed at low latitudes to increase from 85 m/s in the beginning of the mission to 110 m/s by the middle of 2012. The trend was explained by influence of the surface topography on the zonal flow [4]. Cloud features tracking in the IR images provided information about winds in the middle cloud deck (55±4 km). In the low and middle latitudes (5-65°S) the IR mean retrograde zonal velocity is about 68-70 m/s. In contrast to poleward flow at the cloud tops, equatorward motions dominate in the middle cloud with maximum speed of 5.8±1.2 m/s at latitude 15°S. The meridional speed slowly decreases to 0 at 65-70°S. At low latitudes the zonal and meridional speed demonstrate long term variations. Following [4] we explain the observed long term trend of zonal and meridional components by the influence of surface topography of highland region Aphrodite Terra on dynamic processes in the middle cloud deck through gravity waves. Acknowledgements: I.V. Khatuntsev

Influence of large-scale zonal flows on the evolution of stellar and planetary magnetic fields

NASA Astrophysics Data System (ADS)

Petitdemange, Ludovic; Schrinner, Martin; Dormy, Emmanuel; ENS Collaboration

2011-10-01

Zonal flows and magnetic field are present in various objects as accretion discs, stars and planets. Observations show a huge variety of stellar and planetary magnetic fields. Of particular interest is the understanding of cyclic field variations, as known from the sun. They are often explained by an important Ω-effect, i.e., by the stretching of field lines because of strong differential rotation. We computed the dynamo coefficients for an oscillatory dynamo model with the help of the test-field method. We argue that this model is of α2 Ω -type and here the Ω-effect alone is not responsible for its cyclic time variation. More general conditions which lead to dynamo waves in global direct numerical simulations are presented. Zonal flows driven by convection in planetary interiors may lead to secondary instabilities. We showed that a simple, modified version of the MagnetoRotational Instability, i.e., the MS-MRI can develop in planteray interiors. The weak shear yields an instability by its constructive interaction with the much larger rotation rate of planets. We present results from 3D simulations and show that 3D MS-MRI modes can generate wave pattern at the surface of the spherical numerical domain. Zonal flows and magnetic field are present in various objects as accretion discs, stars and planets. Observations show a huge variety of stellar and planetary magnetic fields. Of particular interest is the understanding of cyclic field variations, as known from the sun. They are often explained by an important Ω-effect, i.e., by the stretching of field lines because of strong differential rotation. We computed the dynamo coefficients for an oscillatory dynamo model with the help of the test-field method. We argue that this model is of α2 Ω -type and here the Ω-effect alone is not responsible for its cyclic time variation. More general conditions which lead to dynamo waves in global direct numerical simulations are presented. Zonal flows driven by convection

Zonal Winds Between 25 and 120 Km Retrieved from Solar Occultation Spectra. Ph.D. Thesis Final Report

NASA Technical Reports Server (NTRS)

Vancleef, Garrett Warren; Shaw, John H.

1989-01-01

Atmospheric winds at heights between 25 and 120 km have been retrieved with precisions of 5/ms from the Doppler shifts of atmospheric absorption lines measured from a satellite-borne instrument. Lines of the upsilon 3 CO2 and upsilon 2 H2O rotation-vibration bands caused by gases in the instrument allowed the instrumental frequency scale to be absolutely calibrated so that accurate relative speeds could be obtained. By comparing the positions of both sets of instrumental lines the calibration of the frequency scale was determined to be stable to a precision of less than 2 x 10(-5) cm during the course of each occultation. It was found that the instrumental resolution of 0.015 cm after apodization, the signal to noise ratio of about 100 and stable calibration allowed relative speeds to be determined to a precision of 5 ms or better by using small numbers of absorption lines between 1600 and 3200 cm. Absolute absorption line positions were simultaneously recovered to precisions of 5 x 10(-5) cm or better. The wind speed profiles determined from four sunset occultations and one sunrise occultation show remarkable similarities in the magnitudes and directions of the zonal wind velocities as functions of height. These wind profiles appear to be manifestations of atmospheric tides.

Role of zonal flow predator-prey oscillations in triggering the transition to H-mode confinement.

PubMed

Schmitz, L; Zeng, L; Rhodes, T L; Hillesheim, J C; Doyle, E J; Groebner, R J; Peebles, W A; Burrell, K H; Wang, G

2012-04-13

Direct evidence of zonal flow (ZF) predator-prey oscillations and the synergistic roles of ZF- and equilibrium E×B flow shear in triggering the low- to high-confinement (L- to H-mode) transition in the DIII-D tokamak is presented. Periodic turbulence suppression is first observed in a narrow layer at and just inside the separatrix when the shearing rate transiently exceeds the turbulence decorrelation rate. The final transition to H mode with sustained turbulence and transport reduction is controlled by equilibrium E×B shear due to the increasing ion pressure gradient.

Observing Equatorial Thermospheric Winds and Temperatures with a New Mapping Technique

NASA Astrophysics Data System (ADS)

Faivre, M. W.; Meriwether, J. W.; Sherwood, P.; Veliz, O.

2005-12-01

Application of the Fabry-Perot interferometer (FPI) at Arequipa, Peru (16.4S, 71.4 W) to measure the Doppler shifts and Doppler broadenings in the equatorial O(1D) 630-nm nightglow has resulted in numerous detections of a large-scale thermospheric phenomenon called the Midnight Temperature Maximum (MTM). A recent detector upgrade with a CCD camera has improved the accuracy of these measurements by a factor of 5. Temperature increases of 50 to 150K have been measured during nights in April and July, 2005, with error bars less than 10K after averaging in all directions. Moreover, the meridional wind measurements show evidence for a flow reversal from equatorward to poleward near local midnight for such events. A new observing strategy based upon the pioneering work of Burnside et al.[1981] maps the equatorial wind and temperature fields by observing in eight equally-spaced azimuth directions, each with a zenith angle of 60 degrees. Analysis of the data obtained with this technique gives the mean wind velocities in the meridional and zonal directions as well as the horizontal gradients of the wind field for these directions. Significant horizontal wind gradients are found for the meridional direction but not for the zonal direction. The zonal wind blows eastward throughout the night with a maximum speed of ~150 m/s near the middle of the night and then decreases towards zero just before dawn. In general, the fastest poleward meridional wind is observed near mid-evening. By the end of the night, the meridional flow tends to be more equatorward at speeds of about 50 m/s. Using the assumption that local time and longitude are equivalent over a period of 30 minutes, a map of the horizontal wind field vector field is constructed over a range of 12 degrees latitude centered at 16.5 S. Comparison between MTM nights and quiet nights (no MTM) revealed significant differences in the horizontal wind fields. Using the method of Fourier decomposition of the line-of-sight winds

Numerical aspects and implementation of a two-layer zonal wall model for LES of compressible turbulent flows on unstructured meshes

NASA Astrophysics Data System (ADS)

Park, George Ilhwan; Moin, Parviz

2016-01-01

This paper focuses on numerical and practical aspects associated with a parallel implementation of a two-layer zonal wall model for large-eddy simulation (LES) of compressible wall-bounded turbulent flows on unstructured meshes. A zonal wall model based on the solution of unsteady three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations on a separate near-wall grid is implemented in an unstructured, cell-centered finite-volume LES solver. The main challenge in its implementation is to couple two parallel, unstructured flow solvers for efficient boundary data communication and simultaneous time integrations. A coupling strategy with good load balancing and low processors underutilization is identified. Face mapping and interpolation procedures at the coupling interface are explained in detail. The method of manufactured solution is used for verifying the correct implementation of solver coupling, and parallel performance of the combined wall-modeled LES (WMLES) solver is investigated. The method has successfully been applied to several attached and separated flows, including a transitional flow over a flat plate and a separated flow over an airfoil at an angle of attack.

Equinoctial asymmetry in the zonal distribution of scintillation as observed by GPS receivers in Indonesia

NASA Astrophysics Data System (ADS)

Abadi, P.; Otsuka, Y.; Shiokawa, K.; Husin, A.; Liu, Huixin; Saito, S.

2017-08-01

We investigate the azimuthal distribution of amplitude scintillation observed by Global Positioning System (GPS) ground receivers at Pontianak (0.0°S, 109.3°E; magnetic latitude: 9.8°S) and Bandung (6.9°S, 107.6°E; magnetic latitude: 16.7°S) in Indonesia in March and September from 2011 to 2015. The scintillation is found to occur more to the west than to the east in March at both stations, whereas no such zonal difference is found in September. We also analyze the zonal scintillation drift as estimated using three closely spaced single-frequency GPS receivers at Kototabang (0.2°S, 100.3°E; magnetic latitude: 9.9°S) in Indonesia during 2003-2015 and the zonal thermospheric neutral wind as measured by the CHAMP satellite at longitudes of 90°-120°E during 2001-2008. We find that the velocities of both the zonal scintillation drift and the neutral wind decrease with increasing latitudes. Interestingly, the latitudinal gradients of both the zonal scintillation drift and the neutral wind are steeper in March than in September. These steeper March gradients may be responsible for the increased westward altitudinal and latitudinal tilting of plasma bubbles in March. This equinoctial asymmetry could be responsible for the observed westward bias in scintillation in March, because the scintillation is more likely to occur when radio waves pass through longer lengths of plasma irregularities in the plasma bubbles.

Zonal-flow dynamics from a phase-space perspective

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruiz, D. E.; Parker, J. B.; Shi, E. L.

The wave kinetic equation (WKE) describing drift-wave (DW) turbulence is widely used in the studies of zonal flows (ZFs) emerging from DW turbulence. But, this formulation neglects the exchange of enstrophy between DWs and ZFs and also ignores effects beyond the geometrical-optics limit. Furthermore, we derive a modified theory that takes both of these effects into account, while still treating DW quanta (“driftons”) as particles in phase space. The drifton dynamics is described by an equation of the Wigner–Moyal type, which is commonly known in the phase-space formulation of quantum mechanics. In the geometrical-optics limit, this formulation features additional termsmore » missing in the traditional WKE that ensure exact conservation of the total enstrophy of the system, in addition to the total energy, which is the only conserved invariant in previous theories based on the WKE. We present numerical simulations to illustrate the importance of these additional terms. The proposed formulation can be considered as a phase-space representation of the second-order cumulant expansion, or CE2.« less

Zonal-flow dynamics from a phase-space perspective

DOE PAGES

Ruiz, D. E.; Parker, J. B.; Shi, E. L.; ...

2016-12-16

The wave kinetic equation (WKE) describing drift-wave (DW) turbulence is widely used in the studies of zonal flows (ZFs) emerging from DW turbulence. But, this formulation neglects the exchange of enstrophy between DWs and ZFs and also ignores effects beyond the geometrical-optics limit. Furthermore, we derive a modified theory that takes both of these effects into account, while still treating DW quanta (“driftons”) as particles in phase space. The drifton dynamics is described by an equation of the Wigner–Moyal type, which is commonly known in the phase-space formulation of quantum mechanics. In the geometrical-optics limit, this formulation features additional termsmore » missing in the traditional WKE that ensure exact conservation of the total enstrophy of the system, in addition to the total energy, which is the only conserved invariant in previous theories based on the WKE. We present numerical simulations to illustrate the importance of these additional terms. The proposed formulation can be considered as a phase-space representation of the second-order cumulant expansion, or CE2.« less

On the role of the Kelvin wave in the westerly phase of the semiannual zonal wind oscillation

NASA Technical Reports Server (NTRS)

Dunkerton, T.

1979-01-01

The role of the Kelvin wave, discovered by Hirota (1978), in producing the westerly accelerations of the semiannual zonal wind oscillation in the tropical upper stratosphere is examined quantitatively. It is shown that, for reasonable values of the wave parameters, this Kelvin wave could indeed give rise to the observed accelerations. For the thermal damping rates of Dickinson (1973), the most likely range of phase speeds for a wavenumber 1 disturbance is from 45 to 60 m/sec. For 'photochemically accelerated' damping rates (Blake and Lindzen, 1973), a phase speed in excess of 70 m/sec would be required. The possibility of a significant modulation of the semiannual westerlies by the quasi-biennial oscillation is also suggested.

Winds in the Middle Cloud Deck From the Near-IR Imaging by the Venus Monitoring Camera Onboard Venus Express

NASA Astrophysics Data System (ADS)

Khatuntsev, I. V.; Patsaeva, M. V.; Titov, D. V.; Ignatiev, N. I.; Turin, A. V.; Fedorova, A. A.; Markiewicz, W. J.

2017-11-01

For more than 8 years the Venus Monitoring Camera (VMC) onboard the Venus Express orbiter performed continuous imaging of the Venus cloud layer in UV, visible and near-IR filters. We applied the correlation approach to sequences of the near-IR images at 965 nm to track cloud features and determine the wind field in the middle and lower cloud (49-57 km). From the VMC images that spanned from December of 2006 through August of 2013 we derived zonal and meridional components of the wind field. In low-to-middle latitudes (5-65°S) the velocity of the retrograde zonal wind was found to be 68-70 m/s. The meridional wind velocity slowly decreases from peak value of +5.8 ± 1.2 m/s at 15°S to 0 at 65-70°S. The mean meridional speed has a positive sign at 5-65°S suggesting equatorward flow. This result, together with the earlier measurements of the poleward flow at the cloud tops, indicates the presence of a closed Hadley cell in the altitude range 55-65 km. Long-term variations of zonal and meridional velocity components were found during 1,200 Earth days of observation. At 20° ± 5°S the zonal wind speed increases from -67.18 ± 1.81 m/s to -77.30 ± 2.49 m/s. The meridional wind gradually increases from +1.30 ± 1.82 m/s to +8.53 ± 2.14 m/s. Following Bertaux et al. (2016) we attribute this long-term trend to the influence from the surface topography on the dynamical process in the atmosphere via the upward propagation of gravity waves that became apparent in the VMC observations due to slow drift of the Venus Express orbit over Aphrodite Terra.

Comparison between reference atmosphere winds and radar winds from selected locations

NASA Technical Reports Server (NTRS)

Manson, A. H.; Meek, C. E.; Vincent, R. A.; Craig, R. L.; Phillips, A.; Fraser, G. J.; Smith, M. J.; Fellous, J. L.; Massebeuf, M.; Chandra, S.

1990-01-01

Zonal and meridional 60-110-km wind profiles obtained by radar measurements at Saskatoon, Adelaide, Christchurch, Puerto Rico, and Mawson are presented graphically and compared with those from the COSPAR International Reference Atmosphere (CIRA) for 1986. Good general agreement is found below about 80 km, but above 80 km the CIRA 1986 models show discrepancies, including: (1) no spring tongue of weak westward flow at latitudes 20-70 deg; (2) too strong an eastward flow at 20-52 deg in summer; (3) too great reversal heights at 35-43 deg N in summer; and (4) too strong (by a factor of 2) summer and winter jets at 65-70 deg N.

High-Latitude Observations of a Localized Wind Wall and Its Coupling to the Lower Thermosphere

NASA Astrophysics Data System (ADS)

Shepherd, Gordon G.; Shepherd, Marianna G.

2018-05-01

Reversals in the thermospheric zonal winds at altitudes of 140 to 250 km from eastward to westward have been found at southern geographic latitudes between 60° and 70°. These are confined to a narrow region between 100° and 200° in longitude with zonal velocities regularly of -400 m/s, sometimes reaching -600 m/s, so sharply defined that the authors describe it as a "wind wall." The observations were made by the Wind Imaging Interferometer on National Aeronautics and Space Administration's Upper Atmosphere Research Satellite, and they occur as the field of view crosses the high polar cap wind field. The wind reversals at the wall boundaries create a convergence on the west side of the wall and a divergence on the east side that potentially generate vertical flows, consistent with observed perturbations in the O(1S) emission rate. They are present about one half of the time in local summer and autumn.

Transient response of sap flow to wind speed.

PubMed

Chu, Chia R; Hsieh, Cheng-I; Wu, Shen-Yuang; Phillips, Nathan G

2009-01-01

Transient responses of sap flow to step changes in wind speed were experimentally investigated in a wind tunnel. A Granier-type sap flow sensor was calibrated and tested in a cylindrical tube for analysis of its transient time response. Then the sensor was used to measure the transient response of a well-watered Pachira macrocarpa plant to wind speed variations. The transient response of sap flow was described using the resistance-capacitance model. The steady sap flow rate increased as the wind speed increased at low wind speeds. Once the wind speed exceeded 8.0 m s(-1), the steady sap flow rate did not increase further. The transpiration rate, measured gravimetrically, showed a similar trend. The response of nocturnal sap flow to wind speed variation was also measured and compared with the results in the daytime. Under the same wind speed, the steady sap flow rate was smaller than that in the daytime, indicating differences between diurnal and nocturnal hydraulic function, and incomplete stomatal closure at night. In addition, it was found that the temporal response of the Granier sensor is fast enough to resolve the transient behaviour of water flux in plant tissue.

Impact of Stratospheric Ozone Zonal Asymmetries on the Tropospheric Circulation

NASA Technical Reports Server (NTRS)

Tweedy, Olga; Waugh, Darryn; Li, Feng; Oman, Luke

2015-01-01

The depletion and recovery of Antarctic ozone plays a major role in changes of Southern Hemisphere (SH) tropospheric climate. Recent studies indicate that the lack of polar ozone asymmetries in chemistry climate models (CCM) leads to a weaker and warmer Antarctic vortex, and smaller trends in the tropospheric mid-latitude jet and the surface pressure. However, the tropospheric response to ozone asymmetries is not well understood. In this study we report on a series of integrations of the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to further examine the effect of zonal asymmetries on the state of the stratosphere and troposphere. Integrations with the full, interactive stratospheric chemistry are compared against identical simulations using the same CCM except that (1) the monthly mean zonal mean stratospheric ozone from first simulation is prescribed and (2) ozone is relaxed to the monthly mean zonal mean ozone on a three day time scale. To analyze the tropospheric response to ozone asymmetries, we examine trends and quantify the differences in temperatures, zonal wind and surface pressure among the integrations.

Flow adjustment inside large finite-size wind farms approaching the infinite wind farm regime

NASA Astrophysics Data System (ADS)

Wu, Ka Ling; Porté-Agel, Fernando

2017-04-01

Due to the increasing number and the growing size of wind farms, the distance among them continues to decrease. Thus, it is necessary to understand how these large finite-size wind farms and their wakes could interfere the atmospheric boundary layer (ABL) dynamics and adjacent wind farms. Fully-developed flow inside wind farms has been extensively studied through numerical simulations of infinite wind farms. The transportation of momentum and energy is only vertical and the advection of them is neglected in these infinite wind farms. However, less attention has been paid to examine the length of wind farms required to reach such asymptotic regime and the ABL dynamics in the leading and trailing edges of the large finite-size wind farms. Large eddy simulations are performed in this study to investigate the flow adjustment inside large finite-size wind farms in conventionally-neutral boundary layer with the effect of Coriolis force and free-atmosphere stratification from 1 to 5 K/km. For the large finite-size wind farms considered in the present work, when the potential temperature lapse rate is 5 K/km, the wind farms exceed the height of the ABL by two orders of magnitude for the incoming flow inside the farms to approach the fully-developed regime. An entrance fetch of approximately 40 times of the ABL height is also required for such flow adjustment. At the fully-developed flow regime of the large finite-size wind farms, the flow characteristics match those of infinite wind farms even though they have different adjustment length scales. The role of advection at the entrance and exit regions of the large finite-size wind farms is also examined. The interaction between the internal boundary layer developed above the large finite-size wind farms and the ABL under different potential temperature lapse rates are compared. It is shown that the potential temperature lapse rate plays a role in whether the flow inside the large finite-size wind farms adjusts to the fully

Climatology of the relationship of cusp-related density anomaly with zonal wind and large-scale FAC based on CHAMP observations: IMF By and solar cycle dependence

NASA Astrophysics Data System (ADS)

Kervalishvili, Guram; Lühr, Hermann

2014-05-01

We present climatology of the relationship of cusp-related density enhancement with the neutral zonal wind velocity, large-scale field-aligned current (FAC), small-scale FAC, and electron temperature using the superposed epoch analysis (SEA) method. The dependence of these variables on the interplanetary magnetic field (IMF) By component orientation and solar cycle are of particular interest. In addition, the obtained results of relative density enhancement (ρrel), zonal wind, electron temperature and FAC are subdivided into three local seasons of 130 days each: local winter (1 January ±65 days), combined equinoxes (1 April ±32 days and 1 October ±32 days), and local summer (1 July ±65 days). Our investigation is based on CHAMP satellite observations and NASA/GSFC's OMNI online data set for solar maximum (Mar/2002-2007) and minimum (Mar/2004-2009) conditions in the Northern Hemisphere. The SEA technique uses the time and location of the thermospheric mass density anomaly peaks as reference parameters. The relative amplitude of cusp-related density enhancement does on average not depend on the IMF By orientation, solar cycle phase, and local season. Also, it is apparent that the IMF By amplitude does not have a big influence on the relative amplitude of the density anomaly. Conversely, there exists a good correlation between ρrel and the negative amplitude of IMF Bz prevailing about half an hour earlier. In the cusp region, both large-scale FAC distribution and thermospheric zonal wind velocity exhibit a clear dependence on the IMF By orientation. In the case of positive (negative) IMF By there is a systematic imbalance between downward (upward) and upward (downward) FACs peaks equatorward and poleward of the reference point, respectively. The zonal wind velocity is directed towards west i.e. towards dawn in a geomagnetic latitude-magnetic local time (MLat-MLT) frame. This is true for all local seasons and solar conditions. The thermospheric density

Wind Tunnel Modeling Of Wind Flow Over Complex Terrain

NASA Astrophysics Data System (ADS)

Banks, D.; Cochran, B.

2010-12-01

This presentation will describe the finding of an atmospheric boundary layer (ABL) wind tunnel study conducted as part of the Bolund Experiment. This experiment was sponsored by Risø DTU (National Laboratory for Sustainable Energy, Technical University of Denmark) during the fall of 2009 to enable a blind comparison of various air flow models in an attempt to validate their performance in predicting airflow over complex terrain. Bohlund hill sits 12 m above the water level at the end of a narrow isthmus. The island features a steep escarpment on one side, over which the airflow can be expected to separate. The island was equipped with several anemometer towers, and the approach flow over the water was well characterized. This study was one of only two only physical model studies included in the blind model comparison, the other being a water plume study. The remainder were computational fluid dynamics (CFD) simulations, including both RANS and LES. Physical modeling of air flow over topographical features has been used since the middle of the 20th century, and the methods required are well understood and well documented. Several books have been written describing how to properly perform ABL wind tunnel studies, including ASCE manual of engineering practice 67. Boundary layer wind tunnel tests are the only modelling method deemed acceptable in ASCE 7-10, the most recent edition of the American Society of Civil Engineers standard that provides wind loads for buildings and other structures for buildings codes across the US. Since the 1970’s, most tall structures undergo testing in a boundary layer wind tunnel to accurately determine the wind induced loading. When compared to CFD, the US EPA considers a properly executed wind tunnel study to be equivalent to a CFD model with infinitesimal grid resolution and near infinite memory. One key reason for this widespread acceptance is that properly executed ABL wind tunnel studies will accurately simulate flow separation

Another look at zonal flows: Resonance, shearing, and frictionless saturation

NASA Astrophysics Data System (ADS)

Li, J. C.; Diamond, P. H.

2018-04-01

We show that shear is not the exclusive parameter that represents all aspects of flow structure effects on turbulence. Rather, wave-flow resonance enters turbulence regulation, both linearly and nonlinearly. Resonance suppresses the linear instability by wave absorption. Flow shear can weaken the resonance, and thus destabilize drift waves, in contrast to the near-universal conventional shear suppression paradigm. Furthermore, consideration of wave-flow resonance resolves the long-standing problem of how zonal flows (ZFs) saturate in the limit of weak or zero frictional drag, and also determines the ZF scale. We show that resonant vorticity mixing, which conserves potential enstrophy, enables ZF saturation in the absence of drag, and so is effective at regulating the Dimits up-shift regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect in an extended 0D predator-prey model of drift-ZF turbulence. This analysis determines the saturated ZF shear and shows that the mesoscopic ZF width scales as LZ F˜f3 /16(1-f ) 1 /8ρs5/8l03 /8 in the (relevant) adiabatic limit (i.e., τckk‖2D‖≫1 ). f is the fraction of turbulence energy coupled to ZF and l0 is the base state mixing length, absent ZF shears. We calculate and compare the stationary flow and turbulence level in frictionless, weakly frictional, and strongly frictional regimes. In the frictionless limit, the results differ significantly from conventionally quoted scalings derived for frictional regimes. To leading order, the flow is independent of turbulence intensity. The turbulence level scales as E ˜(γL/εc) 2 , which indicates the extent of the "near-marginal" regime to be γL<εc , for the case of avalanche-induced profile variability. Here, εc is the rate of dissipation of potential enstrophy and γL is the characteristic linear growth rate of fluctuations. The implications for dynamics near marginality of the strong scaling of saturated E with γL are discussed.

Convection driven zonal flows and vortices in the major planets.

PubMed

Busse, F. H.

1994-06-01

The dynamical properties of convection in rotating cylindrical annuli and spherical shells are reviewed. Simple theoretical models and experimental simulations of planetary convection through the use of the centrifugal force in the laboratory are emphasized. The model of columnar convection in a cylindrical annulus not only serves as a guide to the dynamical properties of convection in rotating sphere; it also is of interest as a basic physical system that exhibits several dynamical properties in their most simple form. The generation of zonal mean flows is discussed in some detail and examples of recent numerical computations are presented. The exploration of the parameter space for the annulus model is not yet complete and the theoretical exploration of convection in rotating spheres is still in the beginning phase. Quantitative comparisons with the observations of the dynamics of planetary atmospheres will have to await the consideration in the models of the effects of magnetic fields and the deviations from the Boussinesq approximation.

WIND- THREE DIMENSIONAL POTENTIAL COMPRESSIBLE FLOW ABOUT WIND TURBINE ROTOR BLADES

NASA Technical Reports Server (NTRS)

Dulikravich, D. S.

1994-01-01

This computer program, WIND, was developed to numerically solve the exact, full-potential equation for three-dimensional, steady, inviscid flow through an isolated wind turbine rotor. The program automatically generates a three-dimensional, boundary-conforming grid and iteratively solves the full-potential equation while fully accounting for both the rotating and Coriolis effects. WIND is capable of numerically analyzing the flow field about a given blade shape of the horizontal-axis type wind turbine. The rotor hub is assumed representable by a doubly infinite circular cylinder. An arbitrary number of blades may be attached to the hub and these blades may have arbitrary spanwise distributions of taper and of the twist, sweep, and dihedral angles. An arbitrary number of different airfoil section shapes may be used along the span as long as the spanwise variation of all the geometeric parameters is reasonably smooth. The numerical techniques employed in WIND involve rotated, type-dependent finite differencing, a finite volume method, artificial viscosity in conservative form, and a successive overrelaxation combined with the sequential grid refinement procedure to accelerate the iterative convergence rate. Consequently, WIND is cabable of accurately analyzing incompressible and compressible flows, including those that are locally transonic and terminated by weak shocks. Along with the three-dimensional results, WIND provides the results of the two-dimensional calculations to aid the user in locating areas of possible improvement in the aerodynamic design of the blade. Output from WIND includes the chordwise distribution of the coefficient of pressure, the Mach number, the density, and the relative velocity components at spanwise stations along the blade. In addition, the results specify local values of the lift coefficient and the tangent and axial aerodynamic force components. These are also given in integrated form expressing the total torque and the total axial

Temporal Variability and Latitudinal Jets in Venus's Zonal Wind Profiles

NASA Astrophysics Data System (ADS)

Young, Eliot F.; Bullock, M. A.; Tavenner, T.; Coyote, S.; Murphy, J. R.

2008-09-01

We have observed Venus's night hemisphere from NASA's IRTF (Infrared Telescope Facility) during each inferior conjunction since 2001 to quantify the motion of features in Venus's lower and middle cloud decks. We now present latitudinal profiles from 11 nights, obtained in May and July 2004, February 2006 and September 2007. In about 7 of the 11 nights there are zonal jets near 45N and/or -50S, with speed differentials of 5 to 15 m/s relative to the adjacent equatorward latitude bands. These jets may be evidence of episodic Hadley cell-type circulation. About half of the nights show relatively constant velocity profiles between the latitudes of 50N to 50S, suggesting that considerable mixing is taking place between latitudes. Our most remarkable result is the temporal variability in the median zonal speeds from day to day. For example, the median velocity near the equator increases from 53 to 65 m/s over the period from July 11 - 13, 2004, and increases from 65 to 82 m/s over the period from Sept. 9 - 11, 2007. These velocity changes are too great to be due to the tracking of clouds that are in the middle vs. lower cloud deck, nor can they be caused by clouds that occupy different altitudes; a velocity variation of 25% corresponds to an altitude difference of 15 km, based on vertical profiles of zonal windspeeds from tracking of Pioneer Venus and Venera descent probes. Fifteen km is greater than the expected variation in either cloud base. VIRTIS observations of Venus's southern hemisphere were also obtained in September 2007 and should be able to corroborate or contradict the observed variations. This work was supported by NASA's Planetary Astronomy and Atmospheres programs.

Conservative zonal schemes for patched grids in 2 and 3 dimensions

NASA Technical Reports Server (NTRS)

Hessenius, Kristin A.

1987-01-01

The computation of flow over complex geometries, such as realistic aircraft configurations, poses difficult grid generation problems for computational aerodynamicists. The creation of a traditional, single-module grid of acceptable quality about an entire configuration may be impossible even with the most sophisticated of grid generation techniques. A zonal approach, wherein the flow field is partitioned into several regions within which grids are independently generated, is a practical alternative for treating complicated geometries. This technique not only alleviates the problems of discretizing a complex region, but also facilitates a block processing approach to computation thereby circumventing computer memory limitations. The use of such a zonal scheme, however, requires the development of an interfacing procedure that ensures a stable, accurate, and conservative calculation for the transfer of information across the zonal borders.

The Role of Reversed Equatorial Zonal Transport in Terminating an ENSO Event

NASA Astrophysics Data System (ADS)

Chen, H. C.; Hu, Z. Z.; Huang, B.; Sui, C. H.

2016-02-01

In this study, we demonstrate that a sudden reversal of anomalous equatorial zonal current at the peaking ENSO phase triggers the rapid termination of an ENSO event. Throughout an ENSO cycle, the anomalous equatorial zonal current is strongly controlled by the concavity of the anomalous thermocline meridional structure near the equator. During the ENSO developing phase, the anomalous zonal current in the central and eastern Pacific generally enhances the ENSO growth through its zonal SST advection. In the mature phase of ENSO, however, the equatorial thermocline depth anomalies are reflected in the eastern Pacific and slowly propagate westward off the equator in both hemispheres. As a result, the concavity of the thermocline anomalies near the equator is reversed, i.e., the off-equatorial thermocline depth anomalies become higher than that on the equator for El Niño events and lower for La Niño events. This meridional change of thermocline structure reverses zonal transport rapidly in the central-to-eastern equatorial Pacific, which weakens the ENSO SST anomalies by reversed advection. More importantly, the reversed zonal mass transport weakens the existing zonal tilting of equatorial thermocline and suppresses the thermocline feedback. Both processes are concentrated in the eastern equatorial Pacific and can be effective on subseasonal time scales. These current reversal effects are built-in to the ENSO peak phase and independent of the zonal wind effect on thermocline slope. It functions as an oceanic control on ENSO evolution during both El Niño and La Niña events.

Wind structure and small-scale wind variability in the stratosphere and mesosphere during the November 1980 Energy Budget Campaign

NASA Technical Reports Server (NTRS)

Schmidlin, F. J.; Carlson, M.; Rees, D.; Offermann, D.; Philbrick, C. R.; Widdel, H. U.

1982-01-01

Rocket observations made from two sites in northern Scandinavia between November 6 and December 1, 1980, as part of the Energy Budget Campaign are discussed. It was found that significant vertical and temporal changes in the wind structure were present and that they coincided with different geomagnetic conditions, that is, quiet and enhanced. Before November 16, the meridional wind component above 60 km was found to be positive (southerly), whereas the magnitude of the zonal wind component increased with altitude. After November 16 the meridional component became negative (northerly), and the magnitude of the zonal wind component was observed to decrease with altitude. Time sections of the perturbations of the zonal wind reveal the presence of vertically propagating waves, suggesting gravity wave activity. The waves are found to increase in wavelength from 3-4 km near 40 km to more than 12 km near 80 km. The observational techniques made use of chaff foil, chemical trails, inflatable spheres, and parachutes.

Transonic Navier-Stokes wing solutions using a zonal approach. Part 2: High angle-of-attack simulation

NASA Technical Reports Server (NTRS)

Chaderjian, N. M.

1986-01-01

A computer code is under development whereby the thin-layer Reynolds-averaged Navier-Stokes equations are to be applied to realistic fighter-aircraft configurations. This transonic Navier-Stokes code (TNS) utilizes a zonal approach in order to treat complex geometries and satisfy in-core computer memory constraints. The zonal approach has been applied to isolated wing geometries in order to facilitate code development. Part 1 of this paper addresses the TNS finite-difference algorithm, zonal methodology, and code validation with experimental data. Part 2 of this paper addresses some numerical issues such as code robustness, efficiency, and accuracy at high angles of attack. Special free-stream-preserving metrics proved an effective way to treat H-mesh singularities over a large range of severe flow conditions, including strong leading-edge flow gradients, massive shock-induced separation, and stall. Furthermore, lift and drag coefficients have been computed for a wing up through CLmax. Numerical oil flow patterns and particle trajectories are presented both for subcritical and transonic flow. These flow simulations are rich with complex separated flow physics and demonstrate the efficiency and robustness of the zonal approach.

Solar-QBO Interaction and Its Impact on Stratospheric Ozone in a Zonally Averaged Photochemical Transport Model of the Middle Atmosphere

DTIC Science & Technology

2007-08-28

Solar- QBO interaction and its impact on stratospheric ozone in a zonally averaged photochemical transport model of the middle atmosphere J. P...investigate the solar cycle modulation of the quasi-biennial oscillation ( QBO ) in stratospheric zonal winds and its impact on stratospheric ozone with an...updated version of the zonally averaged CHEM2D middle atmosphere model. We find that the duration of the westerly QBO phase at solar maximum is 3 months

New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa

NASA Astrophysics Data System (ADS)

Tesema, Fasil; Mesquita, Rafael; Meriwether, John; Damtie, Baylie; Nigussie, Melessew; Makela, Jonathan; Fisher, Daniel; Harding, Brian; Yizengaw, Endawoke; Sanders, Samuel

2017-03-01

Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry-Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between November 2015 and April 2016. The monthly-averaged values, which include local winter and equinox seasons, show the magnitude of the maximum monthly-averaged zonal wind is typically within the range of 70 to 90 ms-1 and is eastward between 19:00 and 21:00 LT. Compared to prior studies of the equatorial thermospheric wind for this local time period, the magnitude is considerably weaker as compared to the maximum zonal wind speed observed in the Peruvian sector but comparable to Brazilian FPI results. During the early evening, the meridional wind speeds are 30 to 50 ms-1 poleward during the winter months and 10 to 25 ms-1 equatorward in the equinox months. The direction of the poleward wind during the winter months is believed to be mainly caused by the existence of the interhemispheric wind flow from the summer to winter hemispheres. An equatorial wind surge is observed later in the evening and is shifted to later local times during the winter months and to earlier local times during the equinox months. Significant night-to-night variations are also observed in the maximum speed of both zonal and meridional winds. The temperature observations show the midnight temperature maximum (MTM) to be generally present between 00:30 and 02:00 LT. The amplitude of the MTM was ˜ 110 K in January 2016 with values smaller than this in the other months. The local time difference between the appearance of the MTM and a pre-midnight equatorial wind was generally 60 to 180 min. A meridional wind reversal was also observed after the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and MSIS-00, were compared to the

Wind-Driven Ecological Flow Regimes Downstream from Hydropower Dams

NASA Astrophysics Data System (ADS)

Kern, J.; Characklis, G. W.

2012-12-01

Conventional hydropower can be turned on and off quicker and less expensively than thermal generation (coal, nuclear, or natural gas). These advantages enable hydropower utilities to respond to rapid fluctuations in energy supply and demand. More recently, a growing renewable energy sector has underlined the need for flexible generation capacity that can complement intermittent renewable resources such as wind power. While wind power entails lower variable costs than other types of generation, incorporating it into electric power systems can be problematic. Due to variable and unpredictable wind speeds, wind power is difficult to schedule and must be used when available. As a result, integrating large amounts of wind power into the grid may result in atypical, swiftly changing demand patterns for other forms of generation, placing a premium on sources that can be rapidly ramped up and down. Moreover, uncertainty in wind power forecasts will stipulate increased levels of 'reserve' generation capacity that can respond quickly if real-time wind supply is less than expected. These changes could create new hourly price dynamics for energy and reserves, altering the short-term financial signals that hydroelectric dam operators use to schedule water releases. Traditionally, hourly stream flow patterns below hydropower dams have corresponded in a very predictable manner to electricity demand, whose primary factors are weather (hourly temperature) and economic activity (workday hours). Wind power integration has the potential to yield more variable, less predictable flows at hydro dams, flows that at times could resemble reciprocal wind patterns. An existing body of research explores the impacts of standard, demand-following hydroelectric dams on downstream ecological flows; but weighing the benefits of increased reliance on wind power against further impacts to ecological flows may be a novel challenge for the environmental community. As a preliminary step in meeting this

Mean winds and momemtum fluxes over Jicamarca, Peru, during June and August 1987

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hitchman, M.H.; Bywaters, K.W.; Fritts, D.C.

1992-12-15

Data from the mesophere-stratosphere-troposphere (MST) radar at Jicamarca, Peru, together with other available data, are used to diagnose the mean structure of winds and gravity-wave momentum fluxes from the surface to 90 km during two ten-day campaigns in June and August of 1987. In the stratosphere a layer of maximum eastward flow associated with the quasi-biennial oscillation (QBO) was seen to strengthen and descend rapidly from June to August, overlying persitent westward flow. A layer of enhanced signal return, suggestive of a turbulent layer, was observed just above the descending QBO eastward maximum. Notable zonal asymmetries were present during thismore » transition and the local meridional circulation departed form zonal-mean QBO theory. A substantial northeastward momentum flux was found below 25 km, which may be related to topographic gravity waves excited by southeastward flow across the Andes. In the lower mesosphere a relatively weak second mesopause semiannual oxcillation is confirmed. Gravity-wave zonal and meridional momentum fluxes usually opposed the flow, yielding body forces of [approximately]10-100 ms[sup [minus]1] day [sup [minus]1]. In both the lower stratosphere and mesosphere, body forces were comparable in magnitude to inferred Coriolis torques. 52 refs., 9 figs.« less

Generation of zonal flows through symmetry breaking of statistical homogeneity

NASA Astrophysics Data System (ADS)

Parker, Jeffrey B.; Krommes, John A.

2014-03-01

In geophysical and plasma contexts, zonal flows (ZFs) are well known to arise out of turbulence. We elucidate the transition from homogeneous turbulence without ZFs to inhomogeneous turbulence with steady ZFs. Starting from the equation for barotropic flow on a β plane, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking zonostrophic instability and show that it is an example of a Type {{\\text{I}}_{s}} instability within the pattern formation literature. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the ZF wavelength is not unique. In an idealized, infinite system, there is a continuous band of ZF wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system. We also conclude that the stability of the equilibria near the bifurcation point, which is governed by the Eckhaus instability, is independent of the Rayleigh-Kuo criterion.

Experiments on tropical stratospheric mean-wind variations in a spectral general circulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamilton, K.; Yuan, L.

1992-12-15

A 30-level version of the rhomboidal-15 GFDL spectral climate model was constructed with roughly 2-km vertical resolution. This model fails to produce a realistic quasi-biennial oscillation (QBO) in the tropical stratosphere. Several simulations were conducted in which the zonal-mean winds and temperatures in the equatorial lower and middle stratosphere were instantaneously perturbed and the model was integrated while the mean state relaxed toward its equilibrium. The time scale for the mean wind relaxation varied from over one month at 40 km to a few months in the lower stratosphere. The wind relaxations in the model also displayed the downward phasemore » propagation characteristic of QBO wind reversals, and mean wind anomalies of opposite sign to the imposed perturbation appear at higher levels. In the GCM the downward propagation is clear only above about 20 mb. Detailed investigations were made of the zonal-mean zonal momentum budget in the equatorial stratosphere. The mean flow relaxations above 20 mb were mostly driven by the vertical Eliassen-Palm flux convergence. The anomalies in the horizontal Eliassen-Palm fluxes from extratropical planetary waves were found to be the dominant effect forcing the mean flow to its equilibrium at altitudes below 20 mb. The vertical eddy momentum fluxes near the equator in the model were decomposed using space-time Fourier analysis. While total fluxes associated with easterly and westerly waves are comparable to those used in simple mechanistic models of the QBO, the GCM has its flux spread over a broad range of wavenumbers and phase speeds. The effects of vertical resolution were studied by repeating part of the control integration with a 69-level version of the model with greatly enhance vertical resolution in the lower and middle stratosphere. The results showed that there is almost no sensitivity of the simulation in the tropical stratosphere to the increased vertical resolution. 34 refs., 16 figs., 3 tabs.« less

Unusual behavior of quiet-time zonal and vertical plasma drift velocities over Jicamarca during the recent extended solar minimum of 2008

NASA Astrophysics Data System (ADS)

Santos, Ângela M.; Abdu, Mangalathayil A.; Souza, Jonas R.; Batista, Inez S.; Sobral, José H. A.

2017-11-01

The influence of the recent deep and prolonged solar minimum on the daytime zonal and vertical plasma drift velocities during quiet time is investigated in this work. Analyzing the data obtained from incoherent scatter radar from Jicamarca (11.95° S, 76.87° W) we observe an anomalous behavior of the zonal plasma drift during June 2008 characterized by lower than usual daytime westward drift and its early afternoon reversal to eastward. As a case study the zonal drift observed on 24 June 2008 is modeled using a realistic low-latitude ionosphere simulated by the Sheffield University Plasmasphere-Ionosphere Model-INPE (SUPIM-INPE). The results show that an anomalously low zonal wind was mainly responsible for the observed anomalous behavior in the zonal drift. A comparative study of the vertical plasma drifts obtained from magnetometer data for some periods of maximum (2000-2002) and minimum solar activity (1998, 2008, 2010) phases reveal a considerable decrease on the E-region conductivity and the dynamo electric field during 2008. However, we believe that the contribution of these characteristics to the unusual behavior of the zonal plasma drift is significantly smaller than that arising from the anomalously low zonal wind. The SUPIM-INPE result of the critical frequency of the F layer (foF2) over Jicamarca suggested a lower radiation flux than that predicted by solar irradiance model (SOLAR2000) for June 2008.

Influence of the parallel nonlinearity on zonal flows and heat transport in global gyrokinetic particle-in-cell simulations

NASA Astrophysics Data System (ADS)

Jolliet, S.; McMillan, B. F.; Vernay, T.; Villard, L.; Hatzky, R.; Bottino, A.; Angelino, P.

2009-07-01

In this paper, the influence of the parallel nonlinearity on zonal flows and heat transport in global particle-in-cell ion-temperature-gradient simulations is studied. Although this term is in theory orders of magnitude smaller than the others, several authors [L. Villard, P. Angelino, A. Bottino et al., Plasma Phys. Contr. Fusion 46, B51 (2004); L. Villard, S. J. Allfrey, A. Bottino et al., Nucl. Fusion 44, 172 (2004); J. C. Kniep, J. N. G. Leboeuf, and V. C. Decyck, Comput. Phys. Commun. 164, 98 (2004); J. Candy, R. E. Waltz, S. E. Parker et al., Phys. Plasmas 13, 074501 (2006)] found different results on its role. The study is performed using the global gyrokinetic particle-in-cell codes TORB (theta-pinch) [R. Hatzky, T. M. Tran, A. Könies et al., Phys. Plasmas 9, 898 (2002)] and ORB5 (tokamak geometry) [S. Jolliet, A. Bottino, P. Angelino et al., Comput. Phys. Commun. 177, 409 (2007)]. In particular, it is demonstrated that the parallel nonlinearity, while important for energy conservation, affects the zonal electric field only if the simulation is noise dominated. When a proper convergence is reached, the influence of parallel nonlinearity on the zonal electric field, if any, is shown to be small for both the cases of decaying and driven turbulence.

Comparison of analytical models for zonal flow generation in ion-temperature-gradient mode turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, J.; Miki, K.; Uzawa, K.

2006-11-30

During the past years the understanding of the multi scale interaction problems have increased significantly. However, at present there exists a flora of different analytical models for investigating multi scale interactions and hardly any specific comparisons have been performed among these models. In this work two different models for the generation of zonal flows from ion-temperature-gradient (ITG) background turbulence are discussed and compared. The methods used are the coherent mode coupling model and the wave kinetic equation model (WKE). It is shown that the two models give qualitatively the same results even though the assumption on the spectral difference ismore » used in the (WKE) approach.« less

Zonal-flow dynamics from a phase-space perspective

NASA Astrophysics Data System (ADS)

Ruiz, D. E.; Parker, J. B.; Shi, E. L.; Dodin, I. Y.

2017-10-01

The wave kinetic equation (WKE) describing drift-wave (DW) turbulence is widely used in the studies of zonal flows (ZFs) emerging from DW turbulence. However, this formulation neglects the exchange of enstrophy between DWs and ZFs and also ignores effects beyond the geometrical-optics (GO) limit. Here we present a new theory that captures both of these effects, while still treating DW quanta (``driftons'') as particles in phase space. In this theory, the drifton dynamics is described by an equation of the Wigner-Moyal type, which is analogous to the phase-space formulation of quantum mechanics. The ``Hamiltonian'' and the ``dissipative'' parts of the DW-ZF interactions are clearly identified. Moreover, this theory can be interpreted as a phase-space representation of the second-order cumulant expansion (CE2). In the GO limit, this formulation features additional terms missing in the traditional WKE that ensure conservation of the total enstrophy of the system, in addition to the total energy, which is the only conserved invariant in previous theories based on the traditional WKE. Numerical simulations are presented to illustrate the importance of these additional terms. Supported by the U.S. DOE through Contract Nos. DE-AC02-09CH11466 and DE-AC52-07NA27344, by the NNSA SSAA Program through DOE Research Grant No. DE-NA0002948, and by the U.S. DOD NDSEG Fellowship through Contract No. 32-CFR-168a.

Measurement of winds in Venus' upper mesosphere based on Doppler shifts of the 2.6-mm (C-12)O line

NASA Technical Reports Server (NTRS)

Shah, Kathryn P.; Muhleman, Duane O.; Berge, Glenn L.

1991-01-01

Venus observations conducted in 1988 at the first rotational transition of (C-12)O finely sampled this absorption line by means of a 32-channel filter bank; with this spatial and spectral resolution, it proved possible to measure Doppler shifts of the absorption line across the planet due to strong winds in Venus' upper mesosphere. The Doppler shifts change in a way that is indicative of westward horizontal winds. The radial wind speeds from the Doppler shifts were smoothed to reduce noise and then fitted in least-squares fashion to canonical forms of the lower atmosphere's westward zonal flow. The two flows exhibit a high correlation in orientation.

Role of isotope mass and evidence of fluctuating zonal flows during the L–H transition in the TJ-II stellarator

NASA Astrophysics Data System (ADS)

Losada, U.; Estrada, T.; Liu, B.; van Milligen, B.; Cheng, J.; Silva, C.; Pastor, I.; Fontdecaba, J. M.; Hidalgo, C.; TJ-II team1, the

2018-07-01

Mean radial electric fields as well as low frequency Zonal Flow-like global oscillations in radial electric field have been identified during the low to high (L–H) transition in Hydrogen and Deuterium dominated plasmas in the stellarator TJ-II. No evidence of isotope effect on the L–H transition dynamics was observed in the investigated TJ-II plasma scenarios. These observations emphasize the critical role of both zero frequency (equilibrium) and low frequency varying large-scale flows for stabilizing turbulence during the triggering of the L–H transition in magnetically confined toroidal plasmas.

Synthetic thermosphere winds based on CHAMP neutral and plasma density measurements

NASA Astrophysics Data System (ADS)

Gasperini, F.; Forbes, J. M.; Doornbos, E. N.; Bruinsma, S. L.

2016-04-01

Meridional winds in the thermosphere are key to understanding latitudinal coupling and thermosphere-ionosphere coupling, and yet global measurements of this wind component are scarce. In this work, neutral and electron densities measured by the Challenging Minisatellite Payload (CHAMP) satellite at solar low and geomagnetically quiet conditions are converted to pressure gradient and ion drag forces, which are then used to solve the horizontal momentum equation to estimate low latitude to midlatitude zonal and meridional "synthetic" winds. We validate the method by showing that neutral and electron densities output from National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Mesosphere Electrodynamics-General Circulation Model (TIME-GCM) can be used to derive solutions to the momentum equations that replicate reasonably well (over 85% of the variance) the winds self-consistently calculated within the TIME-GCM. CHAMP cross-track winds are found to share over 65% of the variance with the synthetic zonal winds, providing further reassurance that this wind product should provide credible results. Comparisons with the Horizontal Wind Model 14 (HWM14) show that the empirical model largely underestimates wind speeds and does not reproduce much of the observed variability. Additionally, in this work we reveal the longitude, latitude, local time, and seasonal variability in the winds; show evidence of ionosphere-thermosphere (IT) coupling, with enhanced postsunset eastward winds due to depleted ion drag; demonstrate superrotation speeds of ˜27 m/s at the equator; discuss vertical wave coupling due the diurnal eastward propagating tide with zonal wave number 3 and the semidiurnal eastward propagating tide with zonal wave number 2.

Flow separation on wind turbines blades

NASA Astrophysics Data System (ADS)

Corten, G. P.

2001-01-01

In the year 2000, 15GW of wind power was installed throughout the world, producing 100PJ of energy annually. This contributes to the total electricity demand by only 0.2%. Both the installed power and the generated energy are increasing by 30% per year world-wide. If the airflow over wind turbine blades could be controlled fully, the generation efficiency and thus the energy production would increase by 9%. Power Control To avoid damage to wind turbines, they are cut out above 10 Beaufort (25 m/s) on the wind speed scale. A turbine could be designed in such a way that it converts as much power as possible in all wind speeds, but then it would have to be to heavy. The high costs of such a design would not be compensated by the extra production in high winds, since such winds are rare. Therefore turbines usually reach maximum power at a much lower wind speed: the rated wind speed, which occurs at about 6 Beaufort (12.5 m/s). Above this rated speed, the power intake is kept constant by a control mechanism. Two different mechanisms are commonly used. Active pitch control, where the blades pitch to vane if the turbine maximum is exceeded or, passive stall control, where the power control is an implicit property of the rotor. Stall Control The flow over airfoils is called "attached" when it flows over the surface from the leading edge to the trailing edge. However, when the angle of attack of the flow exceeds a certain critical angle, the flow does not reach the trailing edge, but leaves the surface at the separation line. Beyond this line the flow direction is reversed, i.e. it flows from the trailing edge backward to the separation line. A blade section extracts much less energy from the flow when it separates. This property is used for stall control. Stall controlled rotors always operate at a constant rotation speed. The angle of attack of the flow incident to the blades is determined by the blade speed and the wind speed. Since the latter is variable, it determines

Apparatus and method for using radar to evaluate wind flow fields for wind energy applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroeder, John; Hirth, Brian; Guynes, Jerry

The present invention provides an apparatus and method for obtaining data to determine one or more characteristics of a wind flow field using one or more radars. Data is collected from the one or more radars, and analyzed to determine the one or more characteristics of the wind flow field. The one or more radars are positioned to have a portion of the wind flow field within a scanning sector of the one or more radars.

Laboratory modeling of multiple zonal jets on the polar beta-plane

NASA Astrophysics Data System (ADS)

Afanasyev, Y.

2011-12-01

Zonal jets observed in the oceans and atmospheres of planets are studied in a laboratory rotating tank. The fluid layer in the rotating tank has parabolic free surface and dynamically simulates the polar beta-plane where the Coriolis parameter varies quadratically with distance from the pole. Velocity and surface elevation fields are measured with an optical altimetry method (Afanasyev et al., Exps Fluids 2009). The flows are induced by a localized buoyancy source along radial direction. The baroclinic flow consisting of a field of eddies propagates away from the source due West and forms zonal jets (Fig. 1). Barotropic jets ahead of the baroclinic flow are formed by radiation of beta plumes. Inside the baroclinic flow the jets flow between the chains of eddies. Experimental evidence of so-called noodles (baroclinic instability mode with motions in the radial, North-South direction) theoretically predicted by Berloff et al. (JFM, JPO 2009) was found in our experiments. Beta plume radiation mechanism and the mechanism associated with the instability of noodles are likely to contribute to formation of jets in the baroclinic flow.

Free Flow Zonal Electrophoresis for Fractionation of Plant Membrane Compartments Prior to Proteomic Analysis.

PubMed

Barkla, Bronwyn J

2018-01-01

Free flow zonal electrophoresis (FFZE) is a versatile, reproducible, and potentially high-throughput technique for the separation of plant organelles and membranes by differences in membrane surface charge. It offers considerable benefits over traditional fractionation techniques, such as density gradient centrifugation and two-phase partitioning, as it is relatively fast, sample recovery is high, and the method provides unparalleled sample purity. It has been used to successfully purify chloroplasts and mitochondria from plants but also, to obtain highly pure fractions of plasma membrane, tonoplast, ER, Golgi, and thylakoid membranes. Application of the technique can significantly improve protein coverage in large-scale proteomics studies by decreasing sample complexity. Here, we describe the method for the fractionation of plant cellular membranes from leaves by FFZE.

Quantification of wind flow in the European Mars Simulation Wind Tunnel Facility

NASA Astrophysics Data System (ADS)

Holstein-Rathlou, C.; Merrison, J. P.; Iversen, J. J.; Nornberg, P.

2012-04-01

We present the European Mars Simulation Wind Tunnel facility, a unique prototype facility capable of simulating a wide range of environmental conditions, such as those which can be found at the surface of Earth or Mars. The chamber complements several other large-scale simulation facilities at Aarhus University, Denmark. The facility consists of a 50 m3 environmental chamber capable of operating at low pressure (0.02 - 1000 mbar) and cryogenic temperatures (-130 °C up to +60 °C). This chamber houses a re-circulating wind tunnel capable of generating wind speeds up to 25 m/s and has a dust injection system that can produce suspended particulates (aerosols). It employs a unique LED based optical illumination system (solar simulator) and an advanced network based control system. Laser based optoelectronic instrumentation is used to quantify and monitor wind flow, dust suspension and deposition. This involves a commercial Laser Doppler Anemometer (LDA) and a Particle Dynamics Analysis receiver (PDA), which are small laser based instruments specifically designed for measuring wind speed and sizes of particles situated in a wind flow. Wind flow calibrations will be performed with the LDA system and presented. Pressure and temperature calibrations will follow in order to enable the facility to be used for the testing, development, calibration and comparison of e.g. meteorological sensors under a wide range of environmental conditions as well as multi-disciplinary scientific studies. The wind tunnel is accessible to international collaborators and space agencies for instrument testing, calibration and qualification. It has been financed by the European Space Agency (ESA) as well as the Aarhus University Science Faculty and the Villum Kann Rasmussen Foundation.

Magnetic energy flow in the solar wind.

NASA Technical Reports Server (NTRS)

Modisette, J. L.

1972-01-01

Discussion of the effect of rotation (tangential flow) of the solar wind on the conclusions of Whang (1971) suggesting an increase in the solar wind velocity due to the conversion of magnetic energy to kinetic energy. It is shown that the effect of the rotation of the sun on the magnetic energy flow results in most of the magnetic energy being transported by magnetic shear stress near the sun.

Impact of impurities on zonal flow driven by trapped electron mode turbulence

NASA Astrophysics Data System (ADS)

Guo, Weixin; Wang, Lu; Zhuang, Ge

2017-12-01

The impact of impurities on the generation of zonal flow (ZF) driven by collisonless trapped electron mode turbulence in deuterium (D)-tritium (T) plasmas is investigated. An expression for ZF growth rate with impurities is derived by balancing the ZF potential shielded by polarization effects and the ZF modulated radial turbulent current. Then, it is shown that the maximum normalized ZF growth rate is reduced by the presence of fully ionized non-trace light impurities with relatively flat density profile, and slightly reduced by highly ionized trace tungsten, while the maximum normalized ZF growth rate can be enhanced by fully ionized non-trace light impurities with relatively steep density profile. In particular, the effects of high temperature helium from D-T reaction on ZF depend on the temperature ratio between electrons and high temperature helium. The possible relevance of our findings to recent experimental results and future burning plasmas is also discussed.

FPI observations of nighttime mesospheric and thermospheric winds in China and their comparisons with HWM07

NASA Astrophysics Data System (ADS)

Yuan, Wei

2015-04-01

We analyzed the nighttime horizontal neutral winds in the middle atmosphere (˜87 and ˜98 km) and thermosphere (˜250 km) derived from a Fabry-Perot interferometer (FPI), which was installed at Xinglong station (40.2◦ N, 117.4◦ E) in central China. The wind data covered the period from April 2010 to July 2012. We studied the annual, semiannual and terannual variations of the midnight winds at ˜87 km, ˜98 km and ˜250 km for the first time and compared them with Horizontal Wind Model 2007 (HWM07). Our results show the following: (1) at ˜ 87 km, both the observed and model zonal winds have similar phases in the annual and semiannual variations. However, the HWM07 amplitudes are much larger. (2) At ˜98 km, the model shows strong eastward wind in the summer solstice, resulting in a large annual variation, while the observed strongest component is semiannual. The observation and model midnight meridional winds agree well. Both are equatorward throughout the year and have small amplitudes in the annual and semiannual variations. (3) There are large discrepancies between the observed and HWM07 winds at ˜250 km. This discrepancy is largely due to the strong semiannual zonal wind in the model and the phase difference in the annual variation of the meridional wind. The FPI annual variation coincides with the results from Arecibo, which has similar geomagnetic latitude as Xinglong station. In General, the consistency of FPI winds with model winds is better at ˜87 and ˜98 km than that at ˜250 km. We also studied the seasonally and monthly averaged nighttime winds. The most salient features include the following: (1) the seasonally averaged zonal winds at ˜87 and ˜98 km typically have small variations throughout the night. (2) The model zonal and meridional nighttime wind variations are typically much larger than those of observations at ˜87 km and ˜98 km. (3) At ˜250 km, model zonal wind compares well with the observation in the winter. For spring and autumn

Saturn meteorology - A diagnostic assessment of thin-layer configurations for the zonal flow

NASA Technical Reports Server (NTRS)

Allison, M.; Stone, P. H.

1983-01-01

Voyager imaging, infrared, and radio observations for Saturn have been recently interpreted by Smith et al. (1982) as an indication that the jet streams observed at the cloud tops extend to depths greater than the 10,000-bar level. This analysis assumes a maximum latitudinal temperature contrast of a few percent, a mean atmospheric rotation rate at depth given by Saturn's ratio period, and no variation with latitude of the bottom pressure level for the zonal flow system. These assumptions are not, however, firmly constrained by observation. The diagnostic analysis of plausible alternative configurations for Saturn's atmospheric structure demonstrates that a thin weather layer system (confined at mid to high latitudes to levels above 200 bar) cannot be excluded by any of the available observations. A quantitative estimate of the effects of moisture condensation (including the differentiation of mean molecular weight) suggests that these might provide the buoyancy contrasts necessary to support a thin-layer flow provided that Saturn's outer envelope is enriched approximately 10 times in water abundance relative to a solar composition atmosphere and strongly differentiated with latitude at the condensation level.

The vertical profile of winds on Titan.

PubMed

Bird, M K; Allison, M; Asmar, S W; Atkinson, D H; Avruch, I M; Dutta-Roy, R; Dzierma, Y; Edenhofer, P; Folkner, W M; Gurvits, L I; Johnston, D V; Plettemeier, D; Pogrebenko, S V; Preston, R A; Tyler, G L

2005-12-08

One of Titan's most intriguing attributes is its copious but featureless atmosphere. The Voyager 1 fly-by and occultation in 1980 provided the first radial survey of Titan's atmospheric pressure and temperature and evidence for the presence of strong zonal winds. It was realized that the motion of an atmospheric probe could be used to study the winds, which led to the inclusion of the Doppler Wind Experiment on the Huygens probe. Here we report a high resolution vertical profile of Titan's winds, with an estimated accuracy of better than 1 m s(-1). The zonal winds were prograde during most of the atmospheric descent, providing in situ confirmation of superrotation on Titan. A layer with surprisingly slow wind, where the velocity decreased to near zero, was detected at altitudes between 60 and 100 km. Generally weak winds (approximately 1 m s(-1)) were seen in the lowest 5 km of descent.

Results of a zonally truncated three-dimensional model of the Venus middle atmosphere

NASA Technical Reports Server (NTRS)

Newman, M.

1992-01-01

Although the equatorial rotational speed of the solid surface of Venus is only 4 m s(exp-1), the atmospheric rotational speed reaches a maximum of approximately 100 m s(exp-1) near the equatorial cloud top level (65 to 70 km). This phenomenon, known as superrotation, is the central dynamical problem of the Venus atmosphere. We report here the results of numerical simulations aimed at clarifying the mechanism for maintaining the equatorial cloud top rotation. Maintenance of an equatorial rotational speed maximum above the surface requires waves or eddies that systematically transport angular momentum against its zonal mean gradient. The zonally symmetric Hadley circulation is driven thermally and acts to reduce the rotational speed at the equatorial cloud top level; thus wave or eddy transport must counter this tendency as well as friction. Planetary waves arising from horizontal shear instability of the zonal flow (barotropic instability) could maintain the equatorial rotation by transporting angular momentum horizontally from midlatitudes toward the equator. Alternatively, vertically propagating waves could provide the required momentum source. The relative motion between the rotating atmosphere and the pattern of solar heating, which as a maximum where solar radiation is absorbed near the cloud tops, drives diurnal and semidiurnal thermal tides that propagate vertically away from the cloud top level. The effect of this wave propagation is to transport momentum toward the cloud top level at low latitudes and accelerate the mean zonal flow there. We employ a semispectral primitive equation model with a zonal mean flow and zonal wavenumbers 1 and 2. These waves correspond to the diurnal and semidiurnal tides, but they can also be excited by barotropic or baroclinic instability. Waves of higher wavenumbers and interactions between the waves are neglected. Symmetry about the equator is assumed, so the model applies to one hemisphere and covers the altitude range 30 to

Convectively driven decadal zonal accelerations in Earth's fluid core

NASA Astrophysics Data System (ADS)

More, Colin; Dumberry, Mathieu

2018-04-01

Azimuthal accelerations of cylindrical surfaces co-axial with the rotation axis have been inferred to exist in Earth's fluid core on the basis of magnetic field observations and changes in the length-of-day. These accelerations have a typical timescale of decades. However, the physical mechanism causing the accelerations is not well understood. Scaling arguments suggest that the leading order torque averaged over cylindrical surfaces should arise from the Lorentz force. Decadal fluctuations in the magnetic field inside the core, driven by convective flows, could then force decadal changes in the Lorentz torque and generate zonal accelerations. We test this hypothesis by constructing a quasi-geostrophic model of magnetoconvection, with thermally driven flows perturbing a steady, imposed background magnetic field. We show that when the Alfvén number in our model is similar to that in Earth's fluid core, temporal fluctuations in the torque balance are dominated by the Lorentz torque, with the latter generating mean zonal accelerations. Our model reproduces both fast, free Alfvén waves and slow, forced accelerations, with ratios of relative strength and relative timescale similar to those inferred for the Earth's core. The temporal changes in the magnetic field which drive the time-varying Lorentz torque are produced by the underlying convective flows, shearing and advecting the magnetic field on a timescale associated with convective eddies. Our results support the hypothesis that temporal changes in the magnetic field deep inside Earth's fluid core drive the observed decadal zonal accelerations of cylindrical surfaces through the Lorentz torque.

Analyzing wind turbine flow interaction through vibration data

NASA Astrophysics Data System (ADS)

Castellani, Francesco; D'Elia, Gianluca; Astolfi, Davide; Mucchi, Emiliano; Giorgio, Dalpiaz; Terzi, Ludovico

2016-09-01

Wind turbines commonly undergo non-stationary flow and, not rarely, even rather extreme phenomena. In particular, rough terrains represent a challenging testing ground, because of the combination of terrain-driven flow and wakes. It is therefore crucial to assess the impact of dynamic loads on the turbines. In this work, tower and drive-train vibrations are analyzed, from a subcluster of four turbines of a wind farm sited in a very complex terrain. The main outcome of the study is that it is possible to start from the analysis of wind conditions and interpret how wakes manifest in the vibrations of the turbines, both at structural level (tower vibrations) and at the drive-train level. This wind to gear approach therefore allows to build a connection between a flow phenomenon and a mechanical phenomenon (vibrations) and can be precious to assess loads in different working conditions.

Wind regime peculiarities in the lower thermosphere in the winter of 1983/84

NASA Technical Reports Server (NTRS)

Lysenko, I. A.; Makarov, N. A.; Portnyagin, Yu. I.; Petrov, B. I.; Greisiger, K. M.; Schminder, R.; Kurschner, D.

1987-01-01

Temporal variations of prevailing winds at 90 to 100 km obtained from measurements carried out in winter 1983 to 1984 at three sites in the USSR and two sites in East Germany are reported. These variations are compared with those of the thermal stratospheric regime. Measurements were carried out using the drifts D2 method (meteor wind radar) and the D1 method (ionospheric drifts). Temporal variations of zonal and meridional prevailing wind components for all the sites are given. Also presented are zonal wind data obtained using the partial reflection wind radar. Wind velocity values were obtained by averaging data recorded at between 105 and 91 km altitude. Wind velocity data averaged in such a way can be related to about the same height interval to which the data obtained by the meteor radar and ionospheric methods at other sites, i.e., the mean height of the meteor zone (about 95 km). The results presented show that there are significant fluctuations about the seasonal course of both zonal and meridional prevailing winds.

The GalileoJupiter Probe Doppler Wind Experiment

NASA Astrophysics Data System (ADS)

Atkinson, D. H.

2001-09-01

The GalileoJupiter atmospheric entry probe was launched along with the Galileoorbiter spacecraft from Cape Canaveral in Florida, USA, on October 18, 1989. Following a cruise of greater than six years, the probe arrived at Jupiter on December 7, 1995. During its 57-minute descent, instruments on the probe studied the atmospheric composition and structure, the clouds, lightning, and energy structure of the upper Jovian atmosphere. One of the two radio channels over which the experiment data was transmitted to the orbiter was driven by an ultrastable oscillator. All motions of the probe and orbiter, including the speed of probe descent, Jupiter's rotation, and the atmospheric winds, contributed to a Doppler shift of the probe radio frequency. By accurately measuring the frequency of the probe radio signal, an accurate time history of the probe-orbiter relative motions could be reconstructed. Knowledge of the nominal probe and orbiter trajectories allowed the nominal Doppler shift to be removed from the probe radio frequency leaving a measurable frequency residual arising primarily from the zonal winds in Jupiter's atmosphere, and micromotions of the probe arising from probe spin, swing under the parachute, atmospheric turbulence, and aerodynamic effects. Assuming that the zonal horizontal winds dominate the residual probe motion, a profile of frequency residuals was generated. Inversion of the frequency residuals resulted in the first in situ measurements of the vertical profile of Jupiter's deep zonal winds. It is found that beneath 700 mb, the winds are strong and prograde, rising rapidly to 170 m/s between 1 and 4 bars. Beneath 4 bars to 21 bars, the depth at which the link with the probe was lost, the winds remain constant and strong. When corrections for the high temperatures encountered by the probe are considered, there is no evidence of diminishing or strengthening of the zonal winds in the deepest regions explored by the Galileoprobe. Following the wind

Zonal-Mean Temperature Variations Inferred from SABER Measurements on TIMED Compared with UARS Observations

NASA Technical Reports Server (NTRS)

Huang, Frank T.; Mayr, Hans; Russell, James; Mlynczak, Marty; Reber, Carl A.

2005-01-01

In the Numerical Spectral Model (NSM, Mayr et al., 2003), small-scale gravity waves propagating in the north/south direction can generate zonal mean (m = 0) meridional wind oscillations with periods between 2 and 4 months. These oscillations tend to be confined to low latitudes and have been interpreted to be the meridional counterpart of the wave-driven Quasi Biennial Oscillation in the zonal circulation. Wave driven meridional winds across the equator should generate, due to dynamical heating and cooling, temperature oscillations with opposite phase in the two hemispheres. We have analyzed SABER temperature measurements in the altitude range between 55 and 95 km to investigate the existence such variations. Because there are also strong tidal signatures (up to approximately 20 K) in the data, our algorithm estimates both mean values and tides together from the data. Based on SABER temperature data, the intra-annual variations with periods between 2 and 4 months can have amplitudes up to 5 K or more, depending on the altitude. Their amplitudes are in qualitative agreement with those inferred Erom UARS data (from different years). The SABER temperature variations also reveal pronounced hemispherical asymmetries, which are qualitatively consistent with wave driven meridional wind oscillations across the equator. Oscillations with similar periods have been seen in the meridional winds based on UARS data (Huang and Reber, 2003).

WIND measurements of proton and alpha particle flow and number density

NASA Technical Reports Server (NTRS)

Steinberg, J. T.; Lazarus, A. J.; Ogilvie, J. T.; Lepping, R.; Byrnes, J.; Chornay, D.; Keller, J.; Torbert, R. B.; Bodet, D.; Needell, G. J.

1995-01-01

We propose to review measurements of the solar wind proton and alpha particle flow velocities and densities made since launch with the WIND SWE instrument. The SWE Faraday cup ion sensors are designed to be able to determine accurately flow vector directions, and thus can be used to detect proton-alpha particle differential flow. Instances of differential flow, and the solar wind features with which they are associated will be discussed. Additionally, the variability of the percentage of alpha particles as a fraction of the total solar wind ion density will be presented.

Wind Effects on Flow Patterns and Net Fluxes in Density-Driven High-Latitude Channel Flow

NASA Astrophysics Data System (ADS)

Huntley, Helga S.; Ryan, Patricia

2018-01-01

A semianalytic two-dimensional model is used to analyze the interplay between the different forces acting on density-driven flow in high-latitude channels. In particular, the balance between wind stress, viscous forces, baroclinicity, and sea surface slope adjustments under specified flux conditions is examined. Weak winds are found not to change flow patterns appreciably, with minimal (<7%) adjustments to horizontal velocity maxima. In low-viscosity regimes, strong winds change the flow significantly, especially at the surface, by either strengthening the dual-jet pattern, established without wind, by a factor of 2-3 or initiating return flow at the surface. A nonzero flux does not result in the addition of a uniform velocity throughout the channel cross section, but modifies both along-channel and cross-channel velocities to become more symmetric, dominated by a down-channel jet centered in the domain and counter-clockwise lateral flow. We also consider formulations of the model that allow adjustments of the net flux in response to the wind. Flow patterns change, beyond uniform intensification or weakening, only for strong winds and high Ekman number. Comparisons of the model results to observational data collected in Nares Strait in the Canadian Archipelago in the summer of 2007 show rough agreement, but the model misses the upstream surface jet on the east side of the strait and propagates bathymetric effects too strongly in the vertical for this moderately high eddy viscosity. Nonetheless, the broad strokes of the observed high-latitude flow are reproduced.

Tertiary instability of zonal flows within the Wigner-Moyal formulation of drift turbulence

NASA Astrophysics Data System (ADS)

Zhu, Hongxuan; Ruiz, D. E.; Dodin, I. Y.

2017-10-01

The stability of zonal flows (ZFs) is analyzed within the generalized-Hasegawa-Mima model. The necessary and sufficient condition for a ZF instability, which is also known as the tertiary instability, is identified. The qualitative physics behind the tertiary instability is explained using the recently developed Wigner-Moyal formulation and the corresponding wave kinetic equation (WKE) in the geometrical-optics (GO) limit. By analyzing the drifton phase space trajectories, we find that the corrections proposed in Ref. to the WKE are critical for capturing the spatial scales characteristic for the tertiary instability. That said, we also find that this instability itself cannot be adequately described within a GO formulation in principle. Using the Wigner-Moyal equations, which capture diffraction, we analytically derive the tertiary-instability growth rate and compare it with numerical simulations. The research was sponsored by the U.S. Department of Energy.

Leptokurtic pollen-flow, non-leptokurtic gene-flow in a wind-pollinated herb, Plantago lanceolata L.

PubMed

Tonsor, Stephen J

1985-10-01

The purpose of this study was to simultaneously measure pollen dispersal distance and actual pollen-mediated gene-flow distance in a wind-pollinated herb, Plantago lanceolata. The pollen dispersal distribution, measured as pollen deposition in a wind tunnel, is leptokurtic, as expected from previous studies of wind-pollinated plants. Gene-flow, measured as seeds produced on rows of male-sterile inflorescences in the wind tunnel, is non-leptokurtic, peaking at an intermediate distance. The difference between the two distributions results from the tendency of the pollen grains to cluster. These pollen clusters are the units of gene dispersal, with clusters of intermediate and large size contributing disproportionately to gene-flow. Since many wind-pollinated species show pollen clustering (see text), the common assumption for wind-pollinated plants that gene-flow is leptokurtic requires re-examination. Gene-flow was also measured in an artifical outdoor population of male-steriles, containing a single pollen source plant in the center of the array. The gene flow distribution is significantly platykurtic, and has the same general properties outdoors, where wind speed and turbulence are uncontrolled, as it does in the wind tunnel. I estimated genetic neighborhood size based on my measure of gene-flow in the outdoor population. The estimate shows that populations of Plantago lanceolata will vary in effective number from a few tens of plants to more than five hundred plants, depending on the density of the population in question. Thus, the measured pollen-mediated gene-flow distribution and population density will interact to produce effective population sizes ranging from those in which there is no random genetic drift to those in which random genetic drift plays an important role in determining gene frequencies within and among populations. Despite the platykurtosis in the distribution, pollen-mediated gene dispersal distances are still quite limited, and considerable

Dynamics of zonal shear collapse with hydrodynamic electrons

NASA Astrophysics Data System (ADS)

Hajjar, R. J.; Diamond, P. H.; Malkov, M. A.

2018-06-01

This paper presents a theory for the collapse of the edge zonal shear layer, as observed at the density limit at low β. This paper investigates the scaling of the transport and mean profiles with the adiabaticity parameter α, with special emphasizes on fluxes relevant to zonal flow (ZF) generation. We show that the adiabaticity parameter characterizes the strength of production of zonal flows and so determines the state of turbulence. A 1D reduced model that self-consistently describes the spatiotemporal evolution of the mean density n ¯ , the azimuthal flow v¯ y , and the turbulent potential enstrophy ɛ=⟨(n˜ -∇2ϕ˜ ) 2/2 ⟩ —related to fluctuation intensity—is presented. Quasi-linear analysis determines how the particle flux Γn and vorticity flux Π=-χy∇2vy+Πre s scale with α, in both hydrodynamic and adiabatic regimes. As the plasma response passes from adiabatic (α > 1) to hydrodynamic (α < 1), the particle flux Γn is enhanced and the turbulent viscosity χy increases. However, the residual flux Πres—which drives the flow—drops with α. As a result, the mean vorticity gradient ∇2v¯ y=Πre s/χy —representative of the strength of the shear—also drops. The shear layer then collapses and turbulence is enhanced. The collapse is due to a decrease in ZF production, not an increase in damping. A physical picture for the onset of collapse is presented. The findings of this paper are used to motivate an explanation of the phenomenology of low β density limit evolution. A change from adiabatic ( α=kz2vth 2/(|ω|νei)>1 ) to hydrodynamic (α < 1) electron dynamics is associated with the density limit.

Solar wind flow past Venus - Theory and comparisons

NASA Technical Reports Server (NTRS)

Spreiter, J. R.; Stahara, S. S.

1980-01-01

Advanced computational procedures are applied to an improved model of solar wind flow past Venus to calculate the locations of the ionopause and bow wave and the properties of the flowing ionosheath plasma in the intervening region. The theoretical method is based on a single-fluid, steady, dissipationless, magneto-hydrodynamic continuum model and is appropriate for the calculation of axisymmetric supersonic, super-Alfvenic solar wind flow past a nonmagnetic planet possessing a sufficiently dense ionosphere to stand off the flowing plasma above the subsolar point and elsewhere. Determination of time histories of plasma and magnetic field properties along an arbitrary spacecraft trajectory and provision for an arbitrary oncoming direction of the interplanetary solar wind have been incorporated in the model. An outline is provided of the underlying theory and computational procedures, and sample comparisons of the results are presented with observations from the Pioneer Venus orbiter.

Flow interaction of diffuser augmented wind turbines

NASA Astrophysics Data System (ADS)

Göltenbott, U.; Ohya, Y.; Yoshida, S.; Jamieson, P.

2016-09-01

Up-scaling of wind turbines has been a major trend in order to reduce the cost of energy generation from the wind. Recent studies however show that for a given technology, the cost always rises with upscaling, notably due to the increased mass of the system. To reach capacities beyond 10 MW, multi-rotor systems (MRS) have promising advantages. On the other hand, diffuser augmented wind turbines (DAWTs) can significantly increase the performance of the rotor. Up to now, diffuser augmentation has only been applied to single small wind turbines. In the present research, DAWTs are used in a multi-rotor system. In wind tunnel experiments, the aerodynamics of two and three DAWTs, spaced in close vicinity in the same plane normal to a uniform flow, have been analysed. Power increases of up to 5% and 9% for the two and three rotor configurations are respectively achieved in comparison to a stand-alone turbine. The physical dynamics of the flows are analysed on the basis of the results obtained with a stand-alone turbine.

Disturbance zonal and vertical plasma drifts in the Peruvian sector during solar minimum phases

NASA Astrophysics Data System (ADS)

Santos, A. M.; Abdu, M. A.; Souza, J. R.; Sobral, J. H. A.; Batista, I. S.

2016-03-01

In the present work, we investigate the behavior of the equatorial F region zonal plasma drifts over the Peruvian region under magnetically disturbed conditions during two solar minimum epochs, one of them being the recent prolonged solar activity minimum. The study utilizes the vertical and zonal components of the plasma drifts measured by the Jicamarca (11.95°S; 76.87°W) incoherent scatter radar during two events that occurred on 10 April 1997 and 24 June 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the Sheffield University Plasmasphere-Ionosphere Model-INPE. Two main points are focused: (1) the connection between electric fields and plasma drifts under prompt penetration electric field during a disturbed periods and (2) anomalous behavior of daytime zonal drift in the absence of any magnetic storm. A perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm. For the first time, based on a realistic low-latitude ionosphere, we will show, on a detailed quantitative basis, that this anticorrelation is driven mainly by a vertical Hall electric field induced by the primary zonal electric field in the presence of an enhanced nighttime E region ionization. It is shown that an increase in the field line-integrated Hall-to-Pedersen conductivity ratio (∑H/∑P), which can arise from precipitation of energetic particles in the region of the South American Magnetic Anomaly, is capable of explaining the observed anticorrelation between the vertical and zonal plasma drifts. Evidence for the particle ionization is provided from the occurrence of anomalous sporadic E layers over the low-latitude station, Cachoeira Paulista (22.67°S; 44.9°W)—Brazil. It will also be shown that the zonal plasma drift reversal to eastward in the afternoon two hours earlier than its reference quiet time pattern is possibly caused by weakening of the zonal wind

Fundamental Scalings of Zonal Flows in a Basic Plasma Physics Experiment

NASA Astrophysics Data System (ADS)

Sokolov, Vladimir; Wei, Xiao; Sen, Amiya K.

2007-11-01

A basic physics experimental study of zonal flows (ZF) associated with ITG (ion temperature gradient) drift modes has been performed in the Columbia Linear Machine (CLM) and ZF has been definitively identified [1]. However, in contrast to most tokamak experiments, the stabilizing effect of ZF shear to ITG appears to be small in CLM. We now report on the study of important scaling behavior of ZF. First and most importantly, we report on the collisional damping scaling of ZF, which is considered to be its saturation mechanism [2]. By varying the sum of ion-ion and ion-neutral collision frequency over nearly half an order of magnitude, we find no change in the amplitude of ZF. Secondly, we study the scaling of ZF amplitude with ITG amplitude via increasing ITG drive though ηi, as well as feedback (stabilizing / destabilizing). We have observed markedly different scaling near and far above marginal stability. [1] V. Sokolov, X. Wei, A.K. Sen and K. Avinash, Plasma Phys.Controlled Fusion 48, S111 (2006). [2] P.H. Diamond, S.-I. Itoh, K.Itoh and T.S. Hahm, Plasma Phys.Controlled Fusion 47, R35 (2005).

Turbulent flow and scalar transport in a large wind farm

NASA Astrophysics Data System (ADS)

Porte-Agel, F.; Markfort, C. D.; Zhang, W.

2012-12-01

Wind energy is one of the fastest growing sources of renewable energy world-wide, and it is expected that many more large-scale wind farms will be built and cover a significant portion of land and ocean surfaces. By extracting kinetic energy from the atmospheric boundary layer and converting it to electricity, wind farms may affect the transport of momentum, heat, moisture and trace gases (e.g. CO_2) between the atmosphere and the land surface locally and globally. Understanding wind farm-atmosphere interaction is complicated by the effects of turbine array configuration, wind farm size, land-surface characteristics, and atmospheric thermal stability. A wind farm of finite length may be modeled as an added roughness or as a canopy in large-scale weather and climate models. However, it is not clear which analogy is physically more appropriate. Also, surface scalar flux is affected by wind farms and needs to be properly parameterized in meso-scale and/or high-resolution numerical models. Experiments involving model wind farms, with perfectly aligned and staggered configurations, having the same turbine distribution density, were conducted in a thermally-controlled boundary-layer wind tunnel. A neutrally stratified turbulent boundary layer was developed with a surface heat source. Measurements of the turbulent flow and fluxes over and through the wind farm were made using a custom x-wire/cold-wire anemometer; and surface scalar flux was measured with an array of surface-mounted heat flux sensors far within the quasi-developed region of the wind-farm. The turbulence statistics exhibit similar properties to those of canopy-type flows, but retain some characteristics of surface-layer flows in a limited region above the wind farms as well. The flow equilibrates faster and the overall momentum absorption is higher for the staggered compared to the aligned farm, which is consistent with canopy scaling and leads to a larger effective roughness. Although the overall surface

Vertical axis wind turbine wake in boundary layer flow in a wind tunnel

NASA Astrophysics Data System (ADS)

Rolin, Vincent; Porté-Agel, Fernando

2016-04-01

A vertical axis wind turbine is placed in a boundary layer flow in a wind tunnel, and its wake is investigated. Measurements are performed using an x-wire to measure two components of velocity and turbulence statistics in the wake of the wind turbine. The study is performed at various heights and crosswind positions in order to investigate the full volume of the wake for a range of tip speed ratios. The velocity deficit and levels of turbulence in the wake are related to the performance of the turbine. The asymmetric incoming boundary layer flow causes the rate of recovery in the wake to change as a function of height. Higher shear between the wake and unperturbed flow occurs at the top edge of the wake, inducing stronger turbulence and mixing in this region. The difference in flow relative to the blades causes the velocity deficit and turbulence level to change as a function of crosswind position behind the rotor. The relative difference diminishes with increasing tip speed ratio. Therefore, the wake becomes more homogeneous as tip speed ratio increases.

Improving urban wind flow predictions through data assimilation

NASA Astrophysics Data System (ADS)

Sousa, Jorge; Gorle, Catherine

2017-11-01

Computational fluid dynamic is fundamentally important to several aspects in the design of sustainable and resilient urban environments. The prediction of the flow pattern for example can help to determine pedestrian wind comfort, air quality, optimal building ventilation strategies, and wind loading on buildings. However, the significant variability and uncertainty in the boundary conditions poses a challenge when interpreting results as a basis for design decisions. To improve our understanding of the uncertainties in the models and develop better predictive tools, we started a pilot field measurement campaign on Stanford University's campus combined with a detailed numerical prediction of the wind flow. The experimental data is being used to investigate the potential use of data assimilation and inverse techniques to better characterize the uncertainty in the results and improve the confidence in current wind flow predictions. We consider the incoming wind direction and magnitude as unknown parameters and perform a set of Reynolds-averaged Navier-Stokes simulations to build a polynomial chaos expansion response surface at each sensor location. We subsequently use an inverse ensemble Kalman filter to retrieve an estimate for the probabilistic density function of the inflow parameters. Once these distributions are obtained, the forward analysis is repeated to obtain predictions for the flow field in the entire urban canopy and the results are compared with the experimental data. We would like to acknowledge high-performance computing support from Yellowstone (ark:/85065/d7wd3xhc) provided by NCAR.

The Huygens Doppler Wind Experiment: Ten Years Ago

NASA Astrophysics Data System (ADS)

Bird, Michael; Dutta-Roy, Robin; Dzierma, Yvonne; Atkinson, David; Allison, Michael; Asmar, Sami; Folkner, William; Preston, Robert; Plettemeier, Dirk; Tyler, Len; Edenhofer, Peter

2015-04-01

The Huygens Doppler Wind Experiment (DWE) achieved its primary scientific goal: the derivation of Titan's vertical wind profile from the start of Probe descent to the surface. The carrier frequency of the ultra-stable Huygens radio signal at 2040 MHz was recorded using special narrow-band receivers at two large radio telescopes on Earth: the Green Bank Telescope in West Virginia and the Parkes Radio Telescope in Australia. Huygens drifted predominantly eastward during the parachute descent, providing the first in situ confirmation of Titan's prograde super-rotational zonal winds. A region of surprisingly weak wind with associated strong vertical shear reversal was discovered within the range of altitudes from 65 to 100 km. Below this level, the zonal wind subsided monotonically from 35 m/s to about 7 km, at which point it reversed direction. The vertical profile of the near-surface winds implies the existence of a planetary boundary layer. Recent results on Titan atmospheric circulation within the context of the DWE will be reviewed.

Evaluation of the Wind Flow Variability Using Scanning Doppler Lidar Measurements

NASA Astrophysics Data System (ADS)

Sand, S. C.; Pichugina, Y. L.; Brewer, A.

2016-12-01

Better understanding of the wind flow variability at the heights of the modern turbines is essential to accurately assess of generated wind power and efficient turbine operations. Nowadays the wind energy industry often utilizes scanning Doppler lidar to measure wind-speed profiles at high spatial and temporal resolution.The study presents wind flow features captured by scanning Doppler lidars during the second Wind Forecast and Improvement Project (WFIP 2) sponsored by the Department of Energy (DOE) and National Oceanic and Atmospheric Administration (NOAA). This 18-month long experiment in the Columbia River Basin aims to improve model wind forecasts complicated by mountain terrain, coastal effects, and numerous wind farms.To provide a comprehensive dataset to use for characterizing and predicting meteorological phenomena important to Wind Energy, NOAA deployed scanning, pulsed Doppler lidars to two sites in Oregon, one at Wasco, located upstream of all wind farms relative to the predominant westerly flow in the region, and one at Arlington, located in the middle of several wind farms.In this presentation we will describe lidar scanning patterns capable of providing data in conical, or vertical-slice modes. These individual scans were processed to obtain 15-min averaged profiles of wind speed and direction in real time. Visualization of these profiles as time-height cross sections allows us to analyze variability of these parameters with height, time and location, and reveal periods of rapid changes (ramp events). Examples of wind flow variability between two sites of lidar measurements along with examples of reduced wind velocity downwind of operating turbines (wakes) will be presented.

Coherency Between Volume Transport in the Antarctic Circumpolar Current and Southern Hemisphere Winds

NASA Astrophysics Data System (ADS)

Makowski, Jessica; Chambers, Don; Bonin, Jennifer

2013-04-01

Previous studies have suggested that ocean bottom pressure (OBP) can be used to measure the transport variability of the Antarctic Circumpolar Current (ACC). The OBP observations from the Gravity Recovery and Climate Experiment (GRACE) will be used to calculate transport along the 150°E longitude choke point, between Antarctica and Australia. We will examine whether zonally averaged wind stress, wind stress curl, or local zonal winds are more coherent with zonal mass transport variability. Preliminary studies suggest that seasonal variation in transport across 150°E is more correlated with winds along and north of the northern front of the ACC: the Sub Tropical front (STF). It also appears that interannual variations in transport along 150°E are related to wind variations south of the STF and centered south of the Sub Antarctic Front (SAF). We have observed a strong anti-correlation across the SAF, in the Indian Ocean, which suggests wind stress curl may also be responsible for transport variations. Preliminary results will be presented.

Large Scale Winter Time Disturbances in Meteor Winds over Central and Eastern Europe

NASA Technical Reports Server (NTRS)

Greisiger, K. M.; Portnyagin, Y. I.; Lysenko, I. A.

1984-01-01

Daily zonal wind data of the four pre-MAP-winters 1978/79 to 1981/82 obtained over Central Europe and Eastern Europe by the radar meteor method were studied. Available temperature and satellite radiance data of the middle and upper stratosphere were used for comparison, as well as wind data from Canada. The existence or nonexistence of coupling between the observed large scale zonal wind disturbances in the upper mesopause region (90 to 100 km) and corresponding events in the stratosphere are discussed.

An Assessment of Wind Plant Complex Flows Using Advanced Doppler Radar Measurements

NASA Astrophysics Data System (ADS)

Gunter, W. S.; Schroeder, J.; Hirth, B.; Duncan, J.; Guynes, J.

2015-12-01

As installed wind energy capacity continues to steadily increase, the need for comprehensive measurements of wind plant complex flows to further reduce the cost of wind energy has been well advertised by the industry as a whole. Such measurements serve diverse perspectives including resource assessment, turbine inflow and power curve validation, wake and wind plant layout model verification, operations and maintenance, and the development of future advanced wind plant control schemes. While various measurement devices have been matured for wind energy applications (e.g. meteorological towers, LIDAR, SODAR), this presentation will focus on the use of advanced Doppler radar systems to observe the complex wind flows within and surrounding wind plants. Advanced Doppler radars can provide the combined advantage of a large analysis footprint (tens of square kilometers) with rapid data analysis updates (a few seconds to one minute) using both single- and dual-Doppler data collection methods. This presentation demonstrates the utility of measurements collected by the Texas Tech University Ka-band (TTUKa) radars to identify complex wind flows occurring within and nearby operational wind plants, and provide reliable forecasts of wind speeds and directions at given locations (i.e. turbine or instrumented tower sites) 45+ seconds in advance. Radar-derived wind maps reveal commonly observed features such as turbine wakes and turbine-to-turbine interaction, high momentum wind speed channels between turbine wakes, turbine array edge effects, transient boundary layer flow structures (such as wind streaks, frontal boundaries, etc.), and the impact of local terrain. Operational turbine or instrumented tower data are merged with the radar analysis to link the observed complex flow features to turbine and wind plant performance.

Absolute wind measurements in the lower thermosphere of Venus using infrared heterodyne spectroscopy

NASA Technical Reports Server (NTRS)

Goldstein, Jeffrey J.

1990-01-01

The first absolute wind velocities above the Venusian cloud-tops were obtained using NASA/Goddard infrared heterodyne spectrometers at the NASA Infrared Telescope Facility (IRTF) and the McMath Solar Telescope. Beam-integrated Doppler displacements in the non-thermal emission core of (12)C(16)O2 10.33 micron R(8) sampled the line of sight projection of the lower thermospheric wind field (100 to 120 km). A field-usable Lamb-dip laser stabilization system, developed for spectrometer absolute frequency calibration to less than + or - 0.1 MHz, allowed S/N-limited line of sight velocity resolution at the 1 m/s level. The spectrometer's diffraction-limited beam (1.7 arc-second HPBW at McMath, 0.9 arc-second HPBW at IRTF), and 1 to 2 arc-second seeing, provided the spatial resolution necessary for circulation model discrimination. Qualitative analysis of beam-integrated winds provided definitive evidence of a dominant subsolar-antisolar circulation in the lower thermosphere. Beam-integrated winds were modelled with a 100x100 grid over the beam, incorporating beam spatial rolloff and across-the-beam gradients in non-thermal emission intensity, line of sight projection geometry, and horizontal wind velocity. Horizontal wind velocity was derived from a 2-parameter model wind field comprised of subsolar-antisolar and zonal components. Best-fit models indicated a dominant subsolar-antisolar flow with 120 m/s cross-terminator winds and a retrograde zonal component with a 25 m/s equatorial velocity. A review of all dynamical indicators above the cloud-tops allowed development of an integrated and self-consistent picture of circulation in the 70 to 200 km range.

Absolute wind velocities in the lower thermosphere of Venus using infrared heterodyne spectroscopy

NASA Technical Reports Server (NTRS)

Goldstein, Jeffrey J.; Mumma, Michael J.; Kostiuk, Theodor; Deming, Drake; Espenak, Fred; Zipoy, David

1991-01-01

NASA's IR Telescope Facility and the McMath Solar Telescope have yielded absolute wind velocities in the Venus thermosphere for December 1985 to March 1987 with sufficient spatial resolution for circulation model discrimination. A qualitative analysis of beam-integrated winds indicates subsolar-to-antisolar circulation in the lower thermosphere; horizontal wind velocity was derived from a two-parameter model wind field of subsolar-antisolar and zonal components. A unique model fit common to all observing periods possessed 120 m/sec subsolar-antisolar and 25 m/sec zonal retrograde components, consistent with the Bougher et al. (1986, 1988) hydrodynamical models for 110 km.

Measurement Techniques for Flow Diagnostic in ITAM Impulse Wind Tunnels

DTIC Science & Technology

2010-04-01

time of wind - tunnel operation, so that oscillations caused by initial shock loads could decay and a comparatively long time period with constant flow...Flow Diagnostic in ITAM Impulse Wind Tunnels 7 - 4 RTO-EN-AVT-186 A strain-gauge pressure probe is an elastic element (membrane) in a sealed...Diagnostic in ITAM Impulse Wind Tunnels RTO-EN-AVT-186 7 - 5 probes are individually calibrated. Piezoelectric pressure gauges are based

Development of a mobile Doppler lidar system for wind and temperature measurements at 30-70 km

NASA Astrophysics Data System (ADS)

Yan, Zhaoai; Hu, Xiong; Guo, Wenjie; Guo, Shangyong; Cheng, Yongqiang; Gong, Jiancun; Yue, Jia

2017-02-01

A mobile Doppler lidar system has been developed to simultaneously measure zonal and meridional winds and temperature from 30 to 70 km. Each of the two zonal and meridional wind subsystems employs a 15 W power, 532 nm laser and a 1 m diameter telescope. Iodine vapor filters are used to stabilize laser frequency and to detect the Doppler shift of backscattered signal. The integration method is used for temperature measurement. Experiments were carried out using the mobile Doppler lidar in August 2014 at Qinghai, China (91°E, 38°N). The zonal wind was measured from 20 to 70 km at a 3 km spatial resolution and 2 h temporal resolution. The measurement error is about 0.5 m/s at 30 km, and 10 m/s at 70 km. In addition, the temperature was measured from 30 to 70 km at 1 km spatial resolution and 1 h temporal resolution. The temperature measurement error is about 0.4 K at 30 km, and 8.0 K at 70 km. Comparison of the lidar results with the temperature of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), the zonal wind of the Modern-Era Retrospective Analysis for Re-search and Applications (MERRA), and radiosonde zonal wind shows good agreement, indicating that the Doppler lidar results are reliable.

Numerical investigation of air flow in a supersonic wind tunnel

NASA Astrophysics Data System (ADS)

Drozdov, S. M.; Rtishcheva, A. S.

2017-11-01

In the framework of TsAGI’s supersonic wind tunnel modernization program aimed at improving flow quality and extending the range of test regimes it was required to design and numerically validate a new test section and a set of shaped nozzles: two flat nozzles with flow Mach number at nozzle exit M=4 and M=5 and two axisymmetric nozzles with M=5 and M=6. Geometric configuration of the nozzles, the test section (an Eiffel chamber) and the diffuser was chosen according to the results of preliminary calculations of two-dimensional air flow in the wind tunnel circuit. The most important part of the work are three-dimensional flow simulation results obtained using ANSYS Fluent software. The following flow properties were investigated: Mach number, total and static pressure, total and static temperature and turbulent viscosity ratio distribution, heat flux density at wind tunnel walls (for high-temperature flow regimes). It is demonstrated that flow perturbations emerging from the junction of the nozzle with the test section and spreading down the test section behind the boundaries of characteristic rhomb’s reverse wedge are nearly impossible to eliminate. Therefore, in order to perform tests under most uniform flow conditions, the model’s center of rotation and optical window axis should be placed as close to the center of the characteristic rhomb as possible. The obtained results became part of scientific and technical basis of supersonic wind tunnel design process and were applied to a generalized class of similar wind tunnels.

Jovian vortices by simulated annealing

NASA Astrophysics Data System (ADS)

Morrison, P. J.; Flierl, G. R.; Swaminathan, R. V.

2017-11-01

We explore the conditions required for isolated vortices to exist in sheared zonal flows and the stability of the underlying zonal winds. This is done using the standard 2-layer quasigeostrophic model with the lower layer depth becoming infinite; however, this model differs from the usual layer model because the lower layer is not assumed to be motionless but has a steady configuration of alternating zonal flows. Steady state vortices are obtained by a simulated annealing computational method introduced in, generalized and applied in in fluid flow, and used in the context of magnetohydrodynamics in. Various cases of vortices with a constant potential vorticity anomaly atop zonal winds and the stability of the underlying winds are considered using a mix of computational and analytical techniques. U.S. Department of Energy Contract DE-FG05-80ET-53088.

Flow Simulation of Modified Duct System Wind Turbines Installed on Vehicle

NASA Astrophysics Data System (ADS)

Rosly, N.; Mohd, S.; Zulkafli, M. F.; Ghafir, M. F. Abdul; Shamsudin, S. S.; Muhammad, W. N. A. Wan

2017-10-01

This study investigates the characteristics of airflow with a flow guide installed and output power generated by wind turbine system being installed on a pickup truck. The wind turbine models were modelled by using SolidWorks 2015 software. In order to investigate the characteristic of air flow inside the wind turbine system, a computer simulation (by using ANSYS Fluent software) is used. There were few models being designed and simulated, one without the rotor installed and another two with rotor installed in the wind turbine system. Three velocities being used for the simulation which are 16.7 m/s (60 km/h), 25 m/s (90 km/h) and 33.33 m/s (120 km/h). The study proved that the flow guide did give an impact to the output power produced by the wind turbine system. The predicted result from this study is the velocity of the air inside the ducting system of the present model is better that reference model. Besides, the flow guide implemented in the ducting system gives a big impact on the characteristics of the air flow.

Enhanced separation of membranes during free flow zonal electrophoresis in plants.

PubMed

Barkla, Bronwyn J; Vera-Estrella, Rosario; Pantoja, Omar

2007-07-15

Free flow zonal electrophoresis (FFZE) is a versatile technique that allows for the separation of cells, organelles, membranes, and proteins based on net surface charge during laminar flow through a thin aqueous layer. We have been optimizing the FFZE technique to enhance separation of plant vacuolar membranes (tonoplast) from other endomembranes to pursue a directed proteomics approach to identify novel tonoplast transporters. Addition of ATP to a mixture of endomembranes selectively enhanced electrophoretic mobility of acidic vesicular compartments during FFZE toward the positive electrode. This has been attributed to activation of the V-ATPase generating a more negative membrane potential outside the vesicles, resulting in enhanced migration of acidic vesicles, including tonoplast, to the anode (Morré, D. J.; Lawrence, J.; Safranski, K.; Hammond, T.; Morré, D. M. J. Chromatogr., A 1994, 668, 201-213). We confirm that ATP does induce a redistribution of membranes during FFZE of microsomal membranes isolated from several plant species, including Arabidopsis thaliana, Thellungiella halophila, Mesembryanthemum crystallinum, and Ananas comosus. However, we demonstrate, using V-ATPase-specific inhibitors, nonhydrolyzable ATP analogs, and ionophores to dissipate membrane potential, that the ATP-dependent migrational shift of membranes under FFZE is not due to activation of the V-ATPase. Addition of EDTA to chelate Mg2+, leading to the production of the tetravalent anionic form of ATP, resulted in a further enhancement of membrane migration toward the anode, and manipulation of cell surface charge by addition of polycations also influenced the ATP-dependent migration of membranes. We propose that ATP enhances the mobility of endomembranes by screening positive surface charges on the membrane surface.

Binary stellar winds. [flow and magnetic field geometry

NASA Technical Reports Server (NTRS)

Siscoe, G. L.; Heinemann, M. A.

1974-01-01

Stellar winds from a binary star pair will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters is discussed.

Binary stellar winds. [flow and magnetic field interactions

NASA Technical Reports Server (NTRS)

Siscoe, G. L.; Heinemann, M. A.

1974-01-01

Stellar winds from a binary star will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters are discussed.

Venus upper atmosphere winds from ground-based heterodyne spectroscopy of CO2 at 10μm wavelength

NASA Astrophysics Data System (ADS)

Sornig, M.; Sonnabend, G.; Krötz, P.; Stupar, D.; Livengood, T.; Schieder, R.; Kostiuk, T.

2008-09-01

We present wind measurements in the Venusian upper mesosphere / lower thermosphere (at an altitude of 100-120km) by means of infrared heterodyne spectroscopy of CO2 P(2) features at 959.3917 cm-1. Provided high spectral resolution winds can be retrieved from Doppler-shifts of CO2 non-thermal emission lines.The mesosphere is the not very well understood transitions zone form the superrotating zonal circulation (RSZ) dominated troposphere and the subsolar to anti-solar flow (SS-AS flow) dominated thermosphere [1,2] hence the addressed altitude region is of special interest. Observations are carried out systematically on the day-side of the planet using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS). Measurements were gathered during two observing runs: a) May 25 to June 6 2007 at the McMath-Pierce solar telescope on KittPeak/Arizona; b) November 21-28 2007 at the McMath-Pierce solar telescope on KittPeak/Arizona; Both times Venus illumination was about 50%. Run a) took place shortly before Venus superior conjunction and b) shortly after Venus superior conjunction. Several positions on the planet with a diameter of approx. 20" were measured during each observing run. The telescope with a 1.5m main mirror provided a beamsize of 1.7". Zonal wind velocities as well as values for the SS-AS flow were retrieved and will be presented. The data analyzed so far show weak zonal wind velocities (from 3±7m/s to 32 ±4m/s ) with minimum values at the equator and maximum values at mid latitudes. Also the retrieved speed of the SS-AS flow was significantly lower than found by previous observations [3,4,5]. Together with results from space missions [6,7] and complementary ground based observing methods [8,3,4,5] probing wind velocities at different altitudes in the atmosphere of Venus, these measurements can provide global information about dynamical properties and increase the understanding about our neighbor planet. [1] Gierasch, P.J. et al. (1997) University of

A preliminary study of thermosphere and mesosphere wind observed by Fabry-Perot over Kelan, China

NASA Astrophysics Data System (ADS)

Yu, Tao; Huang, Cong; Zhao, Guangxin; Mao, Tian; Wang, Yungang; Zeng, Zhongcao; Wang, Jingsong; Xia, Chunliang

2014-06-01

A Fabry-Perot interferometer (FPI) system was deployed in Kelan (38.7°N, 111.6°E), center China in November 2011, which observes the airglows at wavelengths of 892.0 nm, 557.7 nm, and 630.0 nm from OH and OI emissions in the upper atmosphere, to derive the wind and temperature at heights around 87 km, 97 km, and 250 km, respectively. From late 2011 through 2013 a series of more than 4500 measurements at each height are validated according to manufacture data quality criteria. By using these data, the morphology of wind in the mesosphere and thermosphere is investigated in this study. Preliminary results are as follows: (1) As for the diurnal variation, meridional and zonal winds at heights of 87 km and 97 km, which are derived through 892.0 nm and 557.7 nm airglows, usually range from -50 m/s to 30 m/s and -50 m/s to 50 m/s, respectively, with typical random errors of about 6-10 m/s at 87 km and 2-3 m/s at 97 km. Meridional winds usually are northward at dusk, southward at middle night, and back to northward at dawn; and zonal winds usually are eastward at dusk, westward at middle night, and back to eastward at dawn. The monthly mean winds are in good agreement with those of HWM93 results. Meridional and zonal winds at a height of 250 km, which are derived through 630.0 nm nightglow, range from -110 m/s to 80 m/s with typical random errors of about 8-10 m/s. Meridional winds usually are northward at dusk, southward at middle night, and back to northward at dawn; and zonal winds usually are eastward at dusk, zero at middle night, and westward at dawn; and they are also well consistent with HWM93 results. (2) As for the seasonal variation, meridional winds at the heights of 87 km and 97 km have a visible annual variation at 12-17 LT and with a little semiannual variation at all other hours, but the zonal winds at the heights of 87 km and 97 km have a semiannual variation all night. The seasonal dependence of the winds, both meridional and zonal winds, at the height

Analysis of counter flow of corona wind for heat transfer enhancement

NASA Astrophysics Data System (ADS)

Shin, Dong Ho; Baek, Soo Hong; Ko, Han Seo

2018-03-01

A heat sink for cooling devices using the counter flow of a corona wind was developed in this study. Detailed information about the numerical investigations of forced convection using the corona wind was presented. The fins of the heat sink using the counter flow of a corona wind were also investigated. The corona wind generator with a wire-to-plate electrode arrangement was used for generating the counter flow to the fin. The compact and simple geometric characteristics of the corona wind generator facilitate the application of the heat sink using the counter flow, demonstrating the heat sink is effective for cooling electronic devices. Parametric studies were performed to analyze the effect of the counter flow on the fins. Also, the velocity and temperature were measured experimentally for the test mock-up of the heat sink with the corona wind generator to verify the numerical results. From a numerical study, the type of fin and its optimal height, length, and pitch were suggested for various heat fluxes. In addition, the correlations to calculate the mass of the developed heat sink and its cooling performance in terms of the heat transfer coefficient were derived. Finally, the cooling efficiencies corresponding to the mass, applied power, total size, and noise of the devices were compared with the existing commercial central processing unit (CPU) cooling devices with rotor fans. As a result, it was confirmed that the heat sink using the counter flow of the corona wind showed appropriate efficiencies for cooling electronic devices, and is a suitable replacement for the existing cooling device for high power electronics.

A review of wind turbine-oriented active flow control strategies

NASA Astrophysics Data System (ADS)

Aubrun, Sandrine; Leroy, Annie; Devinant, Philippe

2017-10-01

To reduce the levelized cost of energy, the energy production, robustness and lifespan of horizontal axis wind turbines (HAWTs) have to be improved to ensure optimal energy production and operational availability during periods longer than 15-20 years. HAWTs are subject to unsteady wind loads that generate combinations of unsteady mechanical loads with characteristic time scales from seconds to minutes. This can be reduced by controlling the aerodynamic performance of the wind turbine rotors in real time to compensate the overloads. Mitigating load fluctuations and optimizing the aerodynamic performance at higher time scales need the development of fast-response active flow control (AFC) strategies located as close as possible to the torque generation, i.e., directly on the blades. The most conventional actuators currently used in HAWTs are mechanical flaps/tabs (similar to aeronautical accessories), but some more innovative concepts based on fluidic and plasma actuators are very promising since they are devoid of mechanical parts, have a fast response and can be driven in unsteady modes to influence natural instabilities of the flow. In this context, the present paper aims at giving a state-of-the-art review of current research in wind turbine-oriented flow control strategies applied at the blade scale. It provides an overview of research conducted in the last decade dealing with the actuators and devices devoted to developing AFC on rotor blades, focusing on the flow phenomena that they cause and that can lead to aerodynamic load increase or decrease. After providing some general background on wind turbine blade aerodynamics and on the atmospheric flows in which HAWTs operate, the review focuses on flow separation control and circulation control mainly through experimental investigations. It is followed by a discussion about the overall limitations of current studies in the wind energy context, with a focus on a few studies that attempt to provide a global

Wind tunnel study of a vertical axis wind turbine in a turbulent boundary layer flow

NASA Astrophysics Data System (ADS)

Rolin, Vincent; Porté-Agel, Fernando

2015-04-01

Vertical axis wind turbines (VAWTs) are in a relatively infant state of development when compared to their cousins the horizontal axis wind turbines. Very few studies have been carried out to characterize the wake flow behind VAWTs, and virtually none to observe the influence of the atmospheric boundary layer. Here we present results from an experiment carried out at the EPFL-WIRE boundary-layer wind tunnel and designed to study the interaction between a turbulent boundary layer flow and a VAWT. Specifically we use stereoscopic particle image velocimetry to observe and quantify the influence of the boundary layer flow on the wake generated by a VAWT, as well as the effect the VAWT has on the boundary layer flow profile downstream. We find that the wake behind the VAWT is strongly asymmetric, due to the varying aerodynamic forces on the blades as they change their position around the rotor. We also find that the wake adds strong turbulence levels to the flow, particularly on the periphery of the wake where vortices and strong velocity gradients are present. The boundary layer is also shown to cause greater momentum to be entrained downwards rather than upwards into the wake.

Three-dimensional vapor intrusion modeling approach that combines wind and stack effects on indoor, atmospheric, and subsurface domains.

PubMed

Shirazi, Elham; Pennell, Kelly G

2017-12-13

Vapor intrusion (IV) exposure risks are difficult to characterize due to the role of atmospheric, building and subsurface processes. This study presents a three-dimensional VI model that extends the common subsurface fate and transport equations to incorporate wind and stack effects on indoor air pressure, building air exchange rate (AER) and indoor contaminant concentration to improve VI exposure risk estimates. The model incorporates three modeling programs: (1) COMSOL Multiphysics to model subsurface fate and transport processes, (2) CFD0 to model atmospheric air flow around the building, and (3) CONTAM to model indoor air quality. The combined VI model predicts AER values, zonal indoor air pressures and zonal indoor air contaminant concentrations as a function of wind speed, wind direction and outdoor and indoor temperature. Steady state modeling results for a single-story building with a basement demonstrate that wind speed, wind direction and opening locations in a building play important roles in changing the AER, indoor air pressure, and indoor air contaminant concentration. Calculated indoor air pressures ranged from approximately -10 Pa to +4 Pa depending on weather conditions and building characteristics. AER values, mass entry rates and indoor air concentrations vary depending on weather conditions and building characteristics. The presented modeling approach can be used to investigate the relationship between building features, AER, building pressures, soil gas concentrations, indoor air concentrations and VI exposure risks.

Surface flow visualization of separated flows on the forebody of an F-18 aircraft and wind-tunnel model

NASA Technical Reports Server (NTRS)

Fisher, David F.; Richwine, David M.; Banks, Daniel W.

1988-01-01

A method of in-flight surface flow visualization similar to wind-tunnel-model oil flows is described for cases where photo-chase planes or onboard photography are not practical. This method, used on an F-18 aircraft in flight at high angles of attack, clearly showed surface flow streamlines in the fuselage forebody. Vortex separation and reattachment lines were identified with this method and documented using postflight photography. Surface flow angles measured at the 90 and 270 degrees meridians show excellent agreement with the wind tunnel data for a pointed tangent ogive with an aspect ratio of 3.5. The separation and reattachment line locations were qualitatively similar to the F-18 wind-tunnel-model oil flows but neither the laminar separation bubble nor the boundary-layer transition on the wind tunnel model were evident in the flight surface flows. The separation and reattachment line locations were in fair agreement with the wind tunnel data for the 3.5 ogive. The elliptical forebody shape of the F-18 caused the primary separation lines to move toward the leeward meridian. Little effect of angle of attack on the separation locations was noted for the range reported.

Wind tunnel simulations of wind turbine wake interactions in neutral and stratified wind flow.

NASA Astrophysics Data System (ADS)

Hancock, P. E.; Pascheke, F.

2010-09-01

A second programme of work is about to commence as part of a further four years of funding for the UK-EPSRC SUPERGEN-Wind large-wind-farm consortium. The first part of the initial programme at Surrey was to establish and set up appropriate techniques for both on- and off-shore boundary layers (though with an emphasis on the latter) at a suitable scale, and to build suitable rotating model wind turbines. The EnFlo wind tunnel, a UK-NCAS special facility, is capable of creating scaled neutral, stable and unstable boundary layers in its 20m long working section. The model turbines are 1/300-scale of 5MW-size, speed controlled with phase-lock measurement capability, and the blade design takes into account low Reynolds-number effects. Velocity measurements are primarily made using two-component LDA, combined with a ‘cold-wire' probe in order to measure the local turbulent heat flux. Simulation of off-shore wakes is particularly constrained because i) at wind tunnel scale the inherently low surface roughness can be below that for fully rough conditions, ii) the power required to stratify the flow varies as the square of the flow speed, and could easily be impractically large, iii) low blade Reynolds number. The boundary layer simulations, set up to give near-equilibrium conditions in terms of streamwise development, and the model turbines have been designed against these constraints, but not all constraints can be always met simultaneously in practice. Most measurements so far have been made behind just one or two turbines in neutral off- and on-shore boundary layers, at stations up to 12 disk diameters downstream. These show how, for example, the wake of a turbine affects the development of the wake of a downwind turbine that is laterally off-set by say half or one diameter, and how the unaffected part from the first turbine merges with the affected wake of the second. As expected a lower level of atmospheric turbulence causes the wakes to develop and fill-in more

Mitigation of wind tunnel wall interactions in subsonic cavity flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, Justin L.; Casper, Katya Marie; Beresh, Steven J.

In this study, the flow over an open aircraft bay is often represented in a wind tunnel with a cavity. In flight, this flow is unconfined, though in experiments, the cavity is surrounded by wind tunnel walls. If untreated, wind tunnel wall effects can lead to significant distortions of cavity acoustics in subsonic flows. To understand and mitigate these cavity–tunnel interactions, a parametric approach was taken for flow over an L/D = 7 cavity at Mach numbers 0.6–0.8. With solid tunnel walls, a dominant cavity tone was observed, likely due to an interaction with a tunnel duct mode. Furthermore, anmore » acoustic liner opposite the cavity decreased the amplitude of the dominant mode and its harmonics, a result observed by previous researchers. Acoustic dampeners were also placed in the tunnel sidewalls, which further decreased the dominant mode amplitudes and peak amplitudes associated with nonlinear interactions between cavity modes. This then indicates that cavity resonance can be altered by tunnel sidewalls and that spanwise coupling should be addressed when conducting subsonic cavity experiments. Though mechanisms for dominant modes and nonlinear interactions likely exist in unconfined cavity flows, these effects can be amplified by the wind tunnel walls.« less

Mitigation of wind tunnel wall interactions in subsonic cavity flows

DOE PAGES

Wagner, Justin L.; Casper, Katya Marie; Beresh, Steven J.; ...

2015-03-06

In this study, the flow over an open aircraft bay is often represented in a wind tunnel with a cavity. In flight, this flow is unconfined, though in experiments, the cavity is surrounded by wind tunnel walls. If untreated, wind tunnel wall effects can lead to significant distortions of cavity acoustics in subsonic flows. To understand and mitigate these cavity–tunnel interactions, a parametric approach was taken for flow over an L/D = 7 cavity at Mach numbers 0.6–0.8. With solid tunnel walls, a dominant cavity tone was observed, likely due to an interaction with a tunnel duct mode. Furthermore, anmore » acoustic liner opposite the cavity decreased the amplitude of the dominant mode and its harmonics, a result observed by previous researchers. Acoustic dampeners were also placed in the tunnel sidewalls, which further decreased the dominant mode amplitudes and peak amplitudes associated with nonlinear interactions between cavity modes. This then indicates that cavity resonance can be altered by tunnel sidewalls and that spanwise coupling should be addressed when conducting subsonic cavity experiments. Though mechanisms for dominant modes and nonlinear interactions likely exist in unconfined cavity flows, these effects can be amplified by the wind tunnel walls.« less

Validation of WIND for a Series of Inlet Flows

NASA Technical Reports Server (NTRS)

Slater, John W.; Abbott, John M.; Cavicchi, Richard H.

2002-01-01

Validation assessments compare WIND CFD simulations to experimental data for a series of inlet flows ranging in Mach number from low subsonic to hypersonic. The validation procedures follow the guidelines of the AIAA. The WIND code performs well in matching the available experimental data. The assessments demonstrate the use of WIND and provide confidence in its use for the analysis of aircraft inlets.

High-fidelity simulations of unsteady civil aircraft aerodynamics: stakes and perspectives. Application of zonal detached eddy simulation

PubMed Central

Deck, Sébastien; Gand, Fabien; Brunet, Vincent; Ben Khelil, Saloua

2014-01-01

This paper provides an up-to-date survey of the use of zonal detached eddy simulations (ZDES) for unsteady civil aircraft applications as a reflection on the stakes and perspectives of the use of hybrid methods in the framework of industrial aerodynamics. The issue of zonal or non-zonal treatment of turbulent flows for engineering applications is discussed. The ZDES method used in this article and based on a fluid problem-dependent zonalization is briefly presented. Some recent landmark achievements for conditions all over the flight envelope are presented, including low-speed (aeroacoustics of high-lift devices and landing gear), cruising (engine–airframe interactions), propulsive jets and off-design (transonic buffet and dive manoeuvres) applications. The implications of such results and remaining challenges in a more global framework are further discussed. PMID:25024411

Wind flow modulation due to variations of the water surface roughness

NASA Astrophysics Data System (ADS)

Shomina, Olga; Ermakov, Stanislav; Kapustin, Ivan; Lazareva, Tatiana

2016-04-01

Air-ocean interaction is a classical problem in atmosphere and ocean physics, which has important geophysical applications related to calculation of vertical and horizontal humidity, aerosol and gas fluxes, development of global climate models and weather forecasts. The structure of wind flow over fixed underlying surfaces, such as forestry, buildings, mountains, is well described, while the interaction between a rough water surface and turbulent wind is far more complicated because of the presence of wind waves with different wavelength and amplitudes and propagating with different velocities and directions. The aim of this study was to investigate experimentally the variability of the wind profile structure due to variations of wave characteristics. The surface roughness variations were produced using a) surfactant films (oleic acid) spread on the water surface and b) mechanically generated waves superimposed on wind waves. The first case is related to oil slicks on sea surface, the second one - to the sea swell, which propagates into zones with lower wind velocities and interacts with wind flow. Laboratory experiments were conducted in the Oval Wind Wave Tank (OWWT) at the Institute of Applied Physics, cross-section of the wind channel is 30 cm x30 cm. Wave amplitude and the spectrum of surface waves were measured by a wire wave gauge, the wind speed was measured using a hot-wire anemometer DISA and a Pitot tube. In the experiments with surfactants, two frequencies of dripping of the oleic acid were studied, so that low concentration films with the elasticity parameters of about 19 mN/m and the high concentration ("thick") films with the elasticity of 34 mN/m were formed. In the experiments with mechanically generated waves (MGW) different regimes were studied with MGW amplitude of 3.4 mm and of 4.4 mm, and with MGW frequencies of 3.3 Hz and 3.7 Hz. It was shown, that: a) the mean velocity of the wind flow in the presence of surfactant and MGW can be described

Fuselage ventilation due to wind flow about a postcrash aircraft

NASA Technical Reports Server (NTRS)

Stuart, J. W.

1980-01-01

Postcrash aircraft fuselage fire development, dependent on the internal and external fluid dynamics is discussed. The natural ventilation rate, a major factor in the internal flow patterns and fire development is reviewed. The flow about the fuselage as affected by the wind and external fire is studied. An analysis was performend which estimated the rates of ventilation produced by the wind for a limited idealized environmental configuration. The simulation utilizes the empirical pressure coefficient distribution of an infinite circular cylinder near a wall with its boundary later flow to represent the atmospheric boundary layer. The resulting maximum ventilation rate for two door size openings, with varying circumferential location in a common 10 mph wind was an order of magnitude greater than the forced ventilation specified in full scale fire testing. The parameter discussed are: (1) fuselage size and shape, (2) fuselage orientation and proximity to the ground, (3) fuselage-openings size and location, (4) wind speed and direction, and (5) induced flow of the external fire plume is recommended. The fire testing should be conducted to a maximum ventilation rate at least an order of magnitude greater than the inflight air conditioning rates.

The steady-state flow quality in a model of a non-return wind tunnel

NASA Technical Reports Server (NTRS)

Mort, K. W.; Eckert, W. T.; Kelly, M. W.

1972-01-01

The structural cost of non-return wind tunnels is significantly less than that of the more conventional closed-circuit wind tunnels. However, because of the effects of external winds, the flow quality of non-return wind tunnels is an area of concern at the low test speeds required for V/STOL testing. The flow quality required at these low speeds is discussed and alternatives to the traditional manner of specifying the flow quality requirements in terms of dynamic pressure and angularity are suggested. The development of a non-return wind tunnel configuration which has good flow quality at low as well as at high test speeds is described.

Theoretical and experimental zonal drift velocities of the ionospheric plasma bubbles over the Brazilian region

NASA Astrophysics Data System (ADS)

Arruda, Daniela C. S.; Sobral, J. H. A.; Abdu, M. A.; Castilho, Vivian M.; Takahashi, H.; Medeiros, A. F.; Buriti, R. A.

2006-01-01

This work presents equatorial ionospheric plasma bubble zonal drift velocity observations and their comparison with model calculations. The bubble zonal velocities were measured using airglow OI630 nm all-sky digital images and the model calculations were performed taking into account flux-tube integrated Pedersen conductivity and conductivity weighted neutral zonal winds. The digital images were obtained from an all-sky imaging system operated over the low-latitude station Cachoeira Paulista (Geogr. 22.5S, 45W, dip angle 31.5S) during the period from October 1998 to August 2000. Out of the 138 nights of imager observation, 29 nights with the presence of plasma bubbles are used in this study. These 29 nights correspond to geomagnetically rather quiet days (∑K P < 24+) and were grouped according to season. During the early night hours, the calculated zonal drift velocities were found to be larger than the experimental values. The best matching between the calculated and observed zonal velocities were seen to be for a few hours around midnight. The model calculation showed two humps around 20 LT and 24 LT that were not present in the data. Average decelerations obtained from linear regression between 20 LT and 24 LT were found to be: (a) Spring 1998, -8.61 ms -1 h -1; (b) Summer 1999, -0.59 ms -1 h -1; (c) Spring 1999, -11.72 ms -1 h -1; and (d) Summer 2000, -8.59 ms -1 h -1. Notice that Summer and Winter here correspond to southern hemisphere Summer and Winter, not northern hemisphere.

Wind noise spectra in small Reynolds number turbulent flows.

PubMed

Zhao, Sipei; Cheng, Eva; Qiu, Xiaojun; Burnett, Ian; Liu, Jacob Chia-Chun

2017-11-01

Wind noise spectra caused by wind from fans in indoor environments have been found to be different from those measured in outdoor atmospheric conditions. Although many models have been developed to predict outdoor wind noise spectra under the assumption of large Reynolds number [Zhao, Cheng, Qiu, Burnett, and Liu (2016). J. Acoust. Soc. Am. 140, 4178-4182, and the references therein], they cannot be applied directly to the indoor situations because the Reynolds number of wind from fans in indoor environments is usually much smaller than that experienced in atmospheric turbulence. This paper proposes a pressure structure function model that combines the energy-containing and dissipation ranges so that the pressure spectrum for small Reynolds number turbulent flows can be calculated. The proposed pressure structure function model is validated with the experimental results in the literature, and then the obtained pressure spectrum is verified with the numerical simulation and experiment results. It is demonstrated that the pressure spectrum obtained from the proposed pressure structure function model can be utilized to estimate wind noise spectra caused by turbulent flows with small Reynolds numbers.

Wind-induced flow velocity effects on nutrient concentrations at Eastern Bay of Lake Taihu, China.

PubMed

Jalil, Abdul; Li, Yiping; Du, Wei; Wang, Jianwei; Gao, Xiaomeng; Wang, Wencai; Acharya, Kumud

2017-07-01

Shallow lakes are highly sensitive to respond internal nutrient loading due to wind-induced flow velocity effects. Wind-induced flow velocity effects on nutrient suspension were investigated at a long narrow bay of large shallow Lake Taihu, the third largest freshwater lake in China. Wind-induced reverse/compensation flow and consistent flow field probabilities at vertical column of the water were measured. The probabilities between the wind field and the flow velocities provided a strong correlation at the surface (80.6%) and the bottom (65.1%) layers of water profile. Vertical flow velocity profile analysis provided the evidence of delay response time to wind field at the bottom layer of lake water. Strong wind field generated by the west (W) and west-north-west (WNW) winds produced displaced water movements in opposite directions to the prevailing flow field. An exponential correlation was observed between the current velocities of the surface and the bottom layers while considering wind speed as a control factor. A linear model was developed to correlate the wind field-induced flow velocity impacts on nutrient concentration at the surface and bottom layers. Results showed that dominant wind directions (ENE, E, and ESE) had a maximum nutrient resuspension contribution (nutrient resuspension potential) of 34.7 and 43.6% at the surface and the bottom profile layers, respectively. Total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) average concentrations were 6.38, 1.5, and 0.03 mg/L during our field experiment at Eastern Bay of Lake Taihu. Overall, wind-induced low-to-moderate hydrodynamic disturbances contributed more in nutrient resuspension at Eastern Bay of Lake Taihu. The present study can be used to understand the linkage between wind-induced flow velocities and nutrient concentrations for shallow lakes (with uniform morphology and deep margins) water quality management and to develop further models.

The dispersion analysis of drift velocity in the study of solar wind flows

NASA Astrophysics Data System (ADS)

Olyak, Maryna

2013-09-01

In this work I consider a method for the study of the solar wind flows at distances from the Sun more than 1 AU. The method is based on the analysis of drift velocity dispersion that was obtained from the simultaneous scintillation observations in two antennas. I considered dispersion dependences for different models of the solar wind, and I defined its specificity for each model. I have determined that the presence of several solar wind flows significantly affects the shape and the slope of the dispersion curve. The maximum slope angle is during the passage of the fast solar wind flow near the Earth. If a slow flow passes near the Earth, the slope of the dispersion curve decreases. This allows a more precise definition of the velocity and flow width compared to the traditional scintillation method. Using the comparison of experimental and theoretical dispersion curves, I calculated the velocity and width of solar wind flows and revealed the presence of significant velocity fluctuations which accounted for about 60% of the average velocity.

Effects of Southern Hemisphere Wind Changes on the Meridional Overturning Circulation in Ocean Models.

PubMed

Gent, Peter R

2016-01-01

Observations show that the Southern Hemisphere zonal wind stress maximum has increased significantly over the past 30 years. Eddy-resolving ocean models show that the resulting increase in the Southern Ocean mean flow meridional overturning circulation (MOC) is partially compensated by an increase in the eddy MOC. This effect can be reproduced in the non-eddy-resolving ocean component of a climate model, providing the eddy parameterization coefficient is variable and not a constant. If the coefficient is a constant, then the Southern Ocean mean MOC change is balanced by an unrealistically large change in the Atlantic Ocean MOC. Southern Ocean eddy compensation means that Southern Hemisphere winds cannot be the dominant mechanism driving midlatitude North Atlantic MOC variability.

Laminar-flow wind tunnel experiments

NASA Technical Reports Server (NTRS)

Harvey, William D.; Harris, Charles D.; Sewall, William G.; Stack, John P.

1989-01-01

Although most of the laminar flow airfoils recently developed at the NASA Langley Research Center were intended for general aviation applications, low-drag airfoils were designed for transonic speeds and wind tunnel performance tested. The objective was to extend the technology of laminar flow to higher Mach and Reynolds numbers and to swept leading edge wings representative of transport aircraft to achieve lower drag and significantly improved operation costs. This research involves stabilizing the laminar boundary layer through geometric shaping (Natural Laminar Flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (Laminar-Flow Control, LFC), either through discrete slots or perforated surface. Results show that extensive regions of laminar flow with large reductions in skin friction drag can be maintained through the application of passive NLF boundary-layer control technologies to unswept transonic wings. At even greater extent of laminar flow and reduction in the total drag level can be obtained on a swept supercritical airfoil with active boundary layer-control.

Wind-Induced Air-Flow Patterns in an Urban Setting: Observations and Numerical Modeling

NASA Astrophysics Data System (ADS)

Sattar, Ahmed M. A.; Elhakeem, Mohamed; Gerges, Bishoy N.; Gharabaghi, Bahram; Gultepe, Ismail

2018-04-01

City planning can have a significant effect on wind flow velocity patterns and thus natural ventilation. Buildings with different heights are roughness elements that can affect the near- and far-field wind flow velocity. This paper aims at investigating the impact of an increase in building height on the nearby velocity fields. A prototype urban setting of buildings with two different heights (25 and 62.5 cm) is built up and placed in a wind tunnel. Wind flow velocity around the buildings is mapped at different heights. Wind tunnel measurements are used to validate a 3D-numerical Reynolds averaged Naviers-Stokes model. The validated model is further used to calculate the wind flow velocity patterns for cases with different building heights. It was found that increasing the height of some buildings in an urban setting can lead to the formation of large horseshoe vortices and eddies around building corners. A separation area is formed at the leeward side of the building, and the recirculation of air behind the building leads to the formation of slow rotation vortices. The opposite effect is observed in the wake (cavity) region of the buildings, where both the cavity length and width are significantly reduced, and this resulted in a pronounced increase in the wind flow velocity. A significant increase in the wind flow velocity in the wake region of tall buildings with a value of up to 30% is observed. The spatially averaged velocities around short buildings also increased by 25% compared to those around buildings with different heights. The increase in the height of some buildings is found to have a positive effect on the wind ventilation at the pedestrian level.

Flow Sources of The Solar Wind Stream Structieres

NASA Astrophysics Data System (ADS)

Lotova, N. A.; Obridko, V. N.; Vladimirskii, K. V.

The large-scale stream structure of the solar wind flow was studied at the main acceler- ation area of 10 to 40 solar radii from the Sun. Three independent sets of experimental data were used: radio astronomy observations of radio wave scattering on near-solar plasmas (large radio telescopes of the P.N.Lebedev Physical Institute were used); mor- phology of the WLC as revealed by the SOHO optical solar corona observations; solar magnetic field strength and configuration computed using the Wilcox Solar Observa- tory data. Experimental data of 1997-1998 years on the position of the transition, tran- sonic region of the solar wind flow were used as a parameter reflecting the intensity of the solar plasmas acceleration process. Correlation studies of these data combined with the magnetic field strength at the solar corona level revealed several types of the solar wind streams differing in the final result, the velocity at large distances from the Sun. Besides of the well-known flows stemming from the polar coronal holes, high-speed streams were observed arising in lateral areas of the streamer structures in contrast to the main body of the streamers, being a known source of the slow solar wind. The slowest streams arise at areas of mixed magnetic field structure compris- ing both open and closed (loop-like) filed lines. In the white-light corona images this shows extensive areas of bright amorphous luminosity.

Wake flow control using a dynamically controlled wind turbine

NASA Astrophysics Data System (ADS)

Castillo, Ricardo; Wang, Yeqin; Pol, Suhas; Swift, Andy; Hussain, Fazle; Westergaard, Carsten; Texas Tech University Team

2016-11-01

A wind tunnel based "Hyper Accelerated Wind Farm Kinematic-Control Simulator" (HAWKS) is being built at Texas Tech University to emulate controlled wind turbine flow physics. The HAWKS model turbine has pitch, yaw and speed control which is operated in real model time, similar to that of an equivalent full scale turbine. Also, similar to that of a full scale wind turbine, the controls are developed in a Matlab Simulink environment. The current diagnostic system consists of power, rotor position, rotor speed measurements and PIV wake characterization with four cameras. The setup allows up to 7D downstream of the rotor to be mapped. The purpose of HAWKS is to simulate control strategies at turnaround times much faster than CFD and full scale testing. The fundamental building blocks of the simulator have been tested, and demonstrate wake steering for both static and dynamic turbine actuation. Parameters which have been studied are yaw, rotor speed and combinations hereof. The measured wake deflections for static yaw cases are in agreement with previously reported research implying general applicability of the HAWKS platform for the purpose of manipulating the wake. In this presentation the general results will be introduced followed by an analysis of the wake turbulence and coherent structures when comparing static and dynamic flow cases. The outcome of such studies could ultimately support effective wind farm wake flow control strategies. Texas Emerging Technology Fund (ETF).

Wind-US Unstructured Flow Solutions for a Transonic Diffuser

NASA Technical Reports Server (NTRS)

Mohler, Stanley R., Jr.

2005-01-01

The Wind-US Computational Fluid Dynamics flow solver computed flow solutions for a transonic diffusing duct. The calculations used an unstructured (hexahedral) grid. The Spalart-Allmaras turbulence model was used. Static pressures along the upper and lower wall agreed well with experiment, as did velocity profiles. The effect of the smoothing input parameters on convergence and solution accuracy was investigated. The meaning and proper use of these parameters are discussed for the benefit of Wind-US users. Finally, the unstructured solver is compared to the structured solver in terms of run times and solution accuracy.

Algorithms for Zonal Methods and Development of Three Dimensional Mesh Generation Procedures.

DTIC Science & Technology

1984-02-01

a r-re complete set of equations is used, but their effect is imposed by means of a right hand side forcing function, not by means of a zonal boundary...modifications of flow-simulation algorithms The explicit finite-difference code of Magnus and are discussed. Computational tests in two dimensions...used to simplify the task of grid generation without an adverse achieve computational efficiency. More recently, effect on flow-field algorithms and

Wind effect on diurnal thermally driven flow in vegetated nearshore of a lake

NASA Astrophysics Data System (ADS)

Lin, Y. T.

2014-12-01

In this study, a highly idealized model is developed to discuss the interplay of diurnal heating/cooling induced buoyancy and wind stress on thermally driven flow over a vegetated slope. Since the model is linear, the horizontal velocity components can be broken into buoyancy-driven and surface wind-driven parts. Due to the presence of rooted emergent vegetation, the circulation strength even under the surface wind condition is still significantly reduced, and the transient (adjustment) stage for the initial conditions is shorter than that without vegetation. The flow in shallows is dominated by a viscosity/buoyancy balance as the case without wind, while the effect of wind stress is limited to the upper layer in deep water. In the lower layer of deep regions, vegetative drag is prevailing except the near bottom regions, where viscosity dominates. Under the unidirectional wind condition, a critical dimensionless shear stress to stop the induced flow can be found and is a function of horizontal location . For the periodic wind condition, if the two forcing mechanisms work in concert, the circulation magnitude can be increased. For the case where buoyancy and wind shear stress act against each other, the circulation strength is reduced and its structure becomes more complex. However, the flow magnitudes near the bottom for and are comparable because surface wind almost has no influence.

Separated Flow over Wind Turbines

NASA Astrophysics Data System (ADS)

Brown, David; Lewalle, Jacques

2015-11-01

The motion of the separation point on an airfoil under unsteady flow can affect its performance and longevity. Of interest is to understand and control the performance decrease in wind turbines subject to turbulent flow. We examine flow separation on an airfoil at a 19 degree angle of attack under unsteady flow conditions. We are using a DU-96-W180 airfoil of chord length 242 mm. The unsteadiness is generated by a cylinder with diameter 203 mm located 7 diameters upstream of the airfoil's leading edge. The data comes from twenty surface pressure sensors located on the top and bottom of the airfoil as well as on the upstream cylinder. Methods of analysis include Mexican hat transforms, Morlet wavelet transforms, power spectra, and various cross correlations. With this study I will explore how the differences of signals on the pressure and suction sides of an airfoil are related to the motion of the separation point.

Numerical simulations of flow fields through conventionally controlled wind turbines & wind farms

NASA Astrophysics Data System (ADS)

Emre Yilmaz, Ali; Meyers, Johan

2014-06-01

In the current study, an Actuator-Line Model (ALM) is implemented in our in-house pseudo-spectral LES solver SP-WIND, including a turbine controller. Below rated wind speed, turbines are controlled by a standard-torque-controller aiming at maximum power extraction from the wind. Above rated wind speed, the extracted power is limited by a blade pitch controller which is based on a proportional-integral type control algorithm. This model is used to perform a series of single turbine and wind farm simulations using the NREL 5MW turbine. First of all, we focus on below-rated wind speed, and investigate the effect of the farm layout on the controller calibration curves. These calibration curves are expressed in terms of nondimensional torque and rotational speed, using the mean turbine-disk velocity as reference. We show that this normalization leads to calibration curves that are independent of wind speed, but the calibration curves do depend on the farm layout, in particular for tightly spaced farms. Compared to turbines in a lone-standing set-up, turbines in a farm experience a different wind distribution over the rotor due to the farm boundary-layer interaction. We demonstrate this for fully developed wind-farm boundary layers with aligned turbine arrangements at different spacings (5D, 7D, 9D). Further we also compare calibration curves obtained from full farm simulations with calibration curves that can be obtained at a much lower cost using a minimal flow unit.

Simulation of air-droplet mixed phase flow in icing wind-tunnel

NASA Astrophysics Data System (ADS)

Mengyao, Leng; Shinan, Chang; Menglong, Wu; Yunhang, Li

2013-07-01

Icing wind-tunnel is the main ground facility for the research of aircraft icing, which is different from normal wind-tunnel for its refrigeration system and spraying system. In stable section of icing wind-tunnel, the original parameters of droplets and air are different, for example, to keep the nozzles from freezing, the droplets are heated while the temperature of air is low. It means that complex mass and heat transfer as well as dynamic interactive force would happen between droplets and air, and the parameters of droplet will acutely change along the passageway. Therefore, the prediction of droplet-air mixed phase flow is necessary in the evaluation of icing researching wind-tunnel. In this paper, a simplified droplet-air mixed phase flow model based on Lagrangian method was built. The variation of temperature, diameter and velocity of droplet, as well as the air flow field, during the flow process were obtained under different condition. With calculating three-dimensional air flow field by FLUENT, the droplet could be traced and the droplet distribution could also be achieved. Furthermore, the patterns about how initial parameters affect the parameters in test section were achieved. The numerical simulation solving the flow and heat and mass transfer characteristics in the mixing process is valuable for the optimization of experimental parameters design and equipment adjustment.

Wind structure and variability in the middle atmosphere during the November 1980 energy budget campaign

NASA Technical Reports Server (NTRS)

Schmidlin, F. J.; Carlson, M.; Rees, D.; Offermann, D.; Philbrick, C. R.; Widdel, H. U.

1985-01-01

Between November 6 and December 1, 1980 series of rocket observations were obtained from two sites in northern Scandinavia (68 deg N) as part of the Energy Budget Campaign, revealing the presence of significant vertical and temporal changes in the wind structure. These changes coincided with different geomagnetic conditions, i.e. quiet and enhanced. Large amounts of rocket data were gathered from high latitudes over such a short interval of time. Prior to November 16 the meridional wind component above 60 km was found to be positive (southerly), while the magnitude of the zonal wind component incresed with altitude. After November 16 the meridional component became negative (northerly) and the magnitude of the zonal wind component was noted to decrease with altitude. Time-sections of the perturbations of the zonal wind show the presence of vertically propagating waves, which suggest gravity wave activity. These waves increase in length from 1 km near 30 km to over 12 km near 80 km. The observational techniques employed Andoya (69 deg N), Norway, and Esrange (67.9 deg N), Sweden, consisted of chaff foil, instrumented rigid spheres, chemical trails, inflatable spheres and parachutes.

Brief Communication: Synoptic-scale differences between Sundowner and Santa Ana wind regimes in the Santa Ynez Mountains, California

NASA Astrophysics Data System (ADS)

Hatchett, Benjamin J.; Smith, Craig M.; Nauslar, Nicholas J.; Kaplan, Michael L.

2018-02-01

Downslope Sundowner winds in southern California's Santa Ynez Mountains favor wildfire growth. To explore differences between Sundowners and Santa Ana winds (SAWs), we use surface observations from 1979 to 2014 to develop a climatology of extreme Sundowner days. The climatology was compared to an existing SAW index from 1979 to 2012. Sundowner (SAW) occurrence peaks in late spring (winter). SAWs demonstrate amplified 500 hPa geopotential heights over western North America and anomalous positive inland mean sea-level pressures. Sundowner-only conditions display zonal 500 hPa flow and negative inland sea-level pressure anomalies. A low-level northerly coastal jet is present during Sundowners but not SAWs.

Numerical analysis of ion wind flow using space charge for optimal design

NASA Astrophysics Data System (ADS)

Ko, Han Seo; Shin, Dong Ho; Baek, Soo Hong

2014-11-01

Ion wind flow has been widly studied for its advantages of a micro fluidic device. However, it is very difficult to predict the performance of the ion wind flow for various conditions because of its complicated electrohydrodynamic phenomena. Thus, a reliable numerical modeling is required to design an otimal ion wind generator and calculate velocity of the ion wind for the proper performance. In this study, the numerical modeling of the ion wind has been modified and newly defined to calculate the veloctiy of the ion wind flow by combining three basic models such as electrostatics, electrodynamics and fluid dynamics. The model has included presence of initial space charges to calculate transfer energy between space charges and air gas molecules using a developed space charge correlation. The simulation has been performed for a geometry of a pin to parallel plate electrode. Finally, the results of the simulation have been compared with the experimental data for the ion wind velocity to confirm the accuracy of the modified numerical modeling and to obtain the optimal design of the ion wind generator. This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Korean government (MEST) (No. 2013R1A2A2A01068653).

High-fidelity simulations of unsteady civil aircraft aerodynamics: stakes and perspectives. Application of zonal detached eddy simulation.

PubMed

Deck, Sébastien; Gand, Fabien; Brunet, Vincent; Ben Khelil, Saloua

2014-08-13

This paper provides an up-to-date survey of the use of zonal detached eddy simulations (ZDES) for unsteady civil aircraft applications as a reflection on the stakes and perspectives of the use of hybrid methods in the framework of industrial aerodynamics. The issue of zonal or non-zonal treatment of turbulent flows for engineering applications is discussed. The ZDES method used in this article and based on a fluid problem-dependent zonalization is briefly presented. Some recent landmark achievements for conditions all over the flight envelope are presented, including low-speed (aeroacoustics of high-lift devices and landing gear), cruising (engine-airframe interactions), propulsive jets and off-design (transonic buffet and dive manoeuvres) applications. The implications of such results and remaining challenges in a more global framework are further discussed. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Effect of external plasma flows on the interaction between turbulence and convective cells

NASA Astrophysics Data System (ADS)

Uzawa, Ken; Li, Jiquan

2005-10-01

It is widely recognized that large scale structures, such as zonal flows, streamers and also long wavelength Kelvin-Helmholtz modes are nonlinearly generated from maternal turbulence through modulational instability process and play a crucial role in regulating the transport in tokamaks. In order to control the transport, it is desirable to control such structures and/or modulational process. One of control parameters may be mean flow which intrinsically exists in tokamak plasmas. Besides the direct influence on the transport through vortex decorrelation, the mean flow may indirectly change the zonal flow generation by acting on the modulational process itself. In this work, we theoretically investigate the characteristics of zonal flow generation due to the electron temperature gradient (ETG) turbulence in the presence of long wavelength ITG driven zonal flow. This was done by extending our previous modulational analyses[1]. We have numerically analyzed the influence of mean flow on zonal flow generation. The main result is that the zonal flow generation is suppressed by the presence of the mean flow. [1]J. Li, Y. Kishimoto, Physics of Plasmas, 9, 1241 (2002)

Influence of omni-directional guide vane on the performance of cross-flow rotor for urban wind energy

NASA Astrophysics Data System (ADS)

Wicaksono, Yoga Arob; Tjahjana, Dominicus Danardono Dwi Prija; Hadi, Syamsul

2018-02-01

Vertical axis wind turbine like cross-flow rotor have some advantage there are, high self-starting torque, low noise, and high stability; so, it can be installed in the urban area to produce electricity. But, the urban area has poor wind condition, so the cross-flow rotor needs a guide vane to increase its performance. The aim of this study is to determine experimentally the effect of Omni-Directional Guide Vane (ODGV) on the performance of a cross-flow wind turbine. Wind tunnel experiment has been carried out for various configurations. The ODGV was placed around the cross-flow rotor in order to increase ambient wind environment of the wind turbine. The maximum power coefficient is obtained as Cpmax = 0.125 at 60° wind direction. It was 21.46% higher compared to cross-flow wind turbine without ODGV. This result showed that the ODGV able to increase the performance of the cross-flow wind turbine.

Calculation of solar wind flows about terrestrial planets

NASA Technical Reports Server (NTRS)

Stahara, S. S.; Spreiter, J. R.

1982-01-01

A computational model was developed for the determination of the plasma and magnetic field properties of the global interaction of the solar wind with terrestrial planetary magneto/ionospheres. The theoretical method is based on an established single fluid, steady, dissipationless, magnetohydrodynamic continuum model, and is appropriate for the calculation of supersonic, super Alfvenic solar wind flow past terrestrial planets. A summary is provided of the important research results.

Linearized simulation of flow over wind farms and complex terrains

NASA Astrophysics Data System (ADS)

Segalini, Antonio

2017-03-01

The flow over complex terrains and wind farms is estimated here by numerically solving the linearized Navier-Stokes equations. The equations are linearized around the unperturbed incoming wind profile, here assumed logarithmic. The Boussinesq approximation is used to model the Reynolds stress with a prescribed turbulent eddy viscosity profile. Without requiring the boundary-layer approximation, two new linear equations are obtained for the vertical velocity and the wall-normal vorticity, with a reduction in the computational cost by a factor of 8 when compared with a primitive-variables formulation. The presence of terrain elevation is introduced as a vertical coordinate shift, while forestry or wind turbines are included as body forces, without any assumption about the wake structure for the turbines. The model is first validated against some available experiments and simulations, and then a simulation of a wind farm over a Gaussian hill is performed. The speed-up effect of the hill is clearly beneficial in terms of the available momentum upstream of the crest, while downstream of it the opposite can be said as the turbines face a decreased wind speed. Also, the presence of the hill introduces an additional spanwise velocity component that may also affect the turbines' operations. The linear superposition of the flow over the hill and the flow over the farm alone provided a first estimation of the wind speed along the farm, with discrepancies of the same order of magnitude for the spanwise velocity. Finally, the possibility of using a parabolic set of equations to obtain the turbulent kinetic energy after the linearized model is investigated with promising results. This article is part of the themed issue 'Wind energy in complex terrains'.

Study on blade surface flow around wind turbine by using LDV measurements

NASA Astrophysics Data System (ADS)

Phengpom, Tinnapob; Kamada, Yasunari; Maeda, Takao; Murata, Junsuke; Nishimura, Shogo; Matsuno, Tasuku

2015-04-01

This paper has attempted to study a mechanism of three-dimensional flow around a horizontal axis wind turbine (HAWT) rotor blade. An experimental study of the flow phenomenon in the vicinity of the wind turbine blade is a challenging endeavor. In this research, the HAWT model with 2.4 m diameter was tested in the large wind tunnel. The flow around the rotating blade surface was measured simultaneously for three velocity components, and two probes were used for the synchronized measurement of three-dimensional flow components. The local velocity was detected for the single seeding particle measured in the point where three pairs of laser beams intersected. Blade sections of interest in this study are composed of radial positions r/R = 0.3, 0.5 and 0.7. Optimum and low tip speed ratio flow characteristics were also compared. The velocity flow vector, skin friction coefficient and bound circulation were calculated from LDV measurements, and the experimental research showed reasonably and clearly the experimental results.

Real-Gas Flow Properties for NASA Langley Research Center Aerothermodynamic Facilities Complex Wind Tunnels

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

1996-01-01

A computational algorithm has been developed which can be employed to determine the flow properties of an arbitrary real (virial) gas in a wind tunnel. A multiple-coefficient virial gas equation of state and the assumption of isentropic flow are used to model the gas and to compute flow properties throughout the wind tunnel. This algorithm has been used to calculate flow properties for the wind tunnels of the Aerothermodynamics Facilities Complex at the NASA Langley Research Center, in which air, CF4. He, and N2 are employed as test gases. The algorithm is detailed in this paper and sample results are presented for each of the Aerothermodynamic Facilities Complex wind tunnels.

Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode

NASA Astrophysics Data System (ADS)

Sallée, J. B.; Speer, K. G.; Rintoul, S. R.

2010-04-01

Interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface. The depth of this layer is determined by wind forcing and heating from the atmosphere. Variations in mixed-layer depth affect the rate of exchange between the atmosphere and deeper ocean, the capacity of the ocean to store heat and carbon and the availability of light and nutrients to support the growth of phytoplankton. However, the response of the Southern Ocean mixed layer to changes in the atmosphere is not well known. Here we analyse temperature and salinity data from Argo profiling floats to show that the Southern Annular Mode (SAM), the dominant mode of atmospheric variability in the Southern Hemisphere, leads to large-scale anomalies in mixed-layer depth that are zonally asymmetric. From a simple heat budget of the mixed layer we conclude that meridional winds associated with departures of the SAM from zonal symmetry cause anomalies in heat flux that can, in turn, explain the observed changes of mixed-layer depth and sea surface temperature. Our results suggest that changes in the SAM, including recent and projected trends attributed to human activity, drive variations in Southern Ocean mixed-layer depth, with consequences for air-sea exchange, ocean sequestration of heat and carbon, and biological productivity.

Low-latitude Temperatures, Pressures, and Winds on Saturn from Cassini Radio Occultations

NASA Astrophysics Data System (ADS)

Flasar, F. M.; Schinder, P. J.; Kliore, A. J.; French, R. G.; Marouf, E. A.; Nagy, A.; Rappaport, N. J.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischman, D. U.; Goltz, G. L.; Johnston, D. V.; Rochblatt, D.; McGhee, C. A.

2005-12-01

We present results from 12 ingress and egress soundings done within 10 degrees of Saturn's equator. Above the 100-mbar level, near the tropopause, the vertical profiles of temperature are marked by undulatory structure that may be associated with vertically propagating waves. Below the 200-mbar level, in the upper troposphere, the vertical profiles are smoother, and the overall trend of temperatures is to increase away from the equator. This implies a decay of the zonal winds with altitude. The zonal winds can actually be inferred directly from the meridional gradient in pressure, without the need of a boundary condition on the winds. We summarize results of these calculations. This is of interest because recent cloud tracking studies have indicated lower equatorial winds than found earlier, but whether this indicates a real change in the winds at a given altitude or a change in the altitudes of the features tracked is controversial.

Flow Visualization and Laser Velocimetry for Wind Tunnels

NASA Technical Reports Server (NTRS)

Hunter, W. W., Jr. (Editor); Foughner, J. T., Jr. (Editor)

1982-01-01

The need for flow visualization and laser velocimetry were discussed. The purpose was threefold: (1) provide a state-of-the-art overview; (2) provide a forum for industry, universities, and government agencies to address problems in developing useful and productive flow visualization and laser velocimetry measurement techniques; and (3) provide discussion of recent developments and applications of flow visualization and laser velocimetry measurement techniques and instrumentation systems for wind tunnels including the 0.3-Meter Transonic Cryogenic Tunnel.

Wind Patterns in Jupiter's Equatorial Region (Time set 1)

NASA Technical Reports Server (NTRS)

1997-01-01

Wind patterns of Jupiter's equatorial region. This mosaic covers an area of 34,000 kilometers by 22,000 kilometers and was taken using the 756 nanometer (nm) near-infrared continuum filter. The dark region near the center of the mosaic is an equatorial 'hotspot' similar to the Galileo Probe entry site. The near-infrared continuum filter shows the features of Jupiter's main visible cloud deck.

Jupiter's atmospheric circulation is dominated by alternating jets of east/west (zonal) winds. The bands have different widths and wind speeds but have remained constant as long as telescopes and spacecraft have measured them. The top half of these mosaics lies within Jupiter's North Equatorial Belt, a westward (left) current. The bottom half shows part of the Equatorial Zone, a fast moving eastward current. The clouds near the hotspot are the fastest moving features in these mosaics, moving at about 100 meters per second, or 224 miles per hour.

Superimposed on the zonal wind currents is the Jovian 'weather'. The arrows show the winds measured by an observer moving eastward (right) at the speed of the hotspot. (The observer's perspective is that the hotspot is 'still' while the rest of the planet moves around it.) Clouds south of the hotspot appear to be moving towards it, as seen in the flow aligned with cloud streaks to the southwest and in the clockwise flow to the southeast. Interestingly, there is little cloud motion away from the hotspot in any direction. This is consistent with the idea that dry air is converging over this region and sinking, maintaining the cloud-free nature of the hotspot.

North is at the top. The mosaic covers latitudes 1 to 19 degrees and is centered at longitude 336 degrees West. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers by the Solid State Imaging system aboard NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA

Initial results from SKiYMET meteor radar at Thumba (8.5°N, 77°E): 1. Comparison of wind measurements with MF spaced antenna radar system

NASA Astrophysics Data System (ADS)

Kumar, Karanam Kishore; Ramkumar, Geetha; Shelbi, S. T.

2007-12-01

In the present communication, initial results from the allSKy interferometric METeor (SKiYMET) radar installed at Thumba (8.5°N, 77°E) are presented. The meteor radar system provides hourly zonal and meridional winds in the mesosphere lower thermosphere (MLT) region. The meteor radar measured zonal and meridional winds are compared with nearby MF radar at Tirunalveli (8.7°N, 77.8°E). The present study provided an opportunity to compare the winds measured by the two different techniques, namely, interferometry and spaced antenna drift methods. Simultaneous wind measurements for a total number of 273 days during September 2004 to May 2005 are compared. The comparison showed a very good agreement between these two techniques in the height region 82-90 km and poor agreement above this height region. In general, the zonal winds compare very well as compared to the meridional winds. The observed discrepancies in the wind comparison above 90 km are discussed in the light of existing limitations of both the radars. The detailed analysis revealed the consistency of the measured winds by both the techniques. However, the discrepancies are observed at higher altitudes and are attributed to the contamination of MF radar neutral wind measurements with Equatorial Electro Jet (EEJ) induced inospheric drifts rather than the limitations of the spaced antenna technique. The comparison of diurnal variation of zonal winds above 90 km measured by both the radars is in reasonably good agreement in the absence of EEJ (during local nighttime). It is also been noted that the difference in the zonal wind measurements by both the radars is directly related to the strength of EEJ, which is a noteworthy result from the present study.

Global characteristics of zonal flows due to the effect of finite bandwidth in drift wave turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uzawa, K.; Li Jiquan; Kishimoto, Y.

2009-04-15

The spectral effect of the zonal flow (ZF) on its generation is investigated based on the Charney-Hasegawa-Mima turbulence model. It is found that the effect of finite ZF bandwidth qualitatively changes the characteristics of ZF instability. A spatially localized (namely, global) nonlinear ZF state with an enhanced, unique growth rate for all spectral components is created under a given turbulent fluctuation. It is identified that such state originates from the successive cross couplings among Fourier components of the ZF and turbulence spectra through the sideband modulation. Furthermore, it is observed that the growth rate of the global ZF is determinedmore » not only by the spectral distribution and amplitudes of turbulent pumps as usual, but also statistically by the turbulence structure, namely, their probabilistic initial phase factors. A ten-wave coupling model of the ZF modulation instability involving the essential effect of the ZF spectrum is developed to clarify the basic features of the global nonlinear ZF state.« less

Development of flow separation control system to reduce the vibration of wind turbine blades

NASA Astrophysics Data System (ADS)

Kim, Ho-Young; Kim, Ho-Hyun; Han, Jong-Seob; Han, Jae-Hung

2017-04-01

The size of wind turbine blade has been continuously increased. Large-scale wind turbine blades induce loud noise, vibration; and maintenance difficulty is also increased. It causes the eventual increases of the cost of energy. The vibration of wind turbine blade is caused by several reasons such as a blade rotation, tower shadow, wind shear, and flow separation of a wind turbine blade. This wind speed variation changes in local angle of attack of the blades and create the vibration. The variation of local angle of attack influences the lift coefficient and causes the large change of the lift. In this study, we focus on the lift coefficient control using a flow control device to reduce the vibration. DU35-A15 airfoil was employed as baseline model. A plasma actuator was installed to generate the upwind jet in order to control the lift coefficient. Wind tunnel experiment was performed to demonstrate of the performance of the plasma actuator. The results show the plasma actuator can induce the flow separation compared with the baseline model. In addition, the actuator can delay the flow separation depending on the input AC frequency with the same actuator configuration.

Linearized simulation of flow over wind farms and complex terrains.

PubMed

Segalini, Antonio

2017-04-13

The flow over complex terrains and wind farms is estimated here by numerically solving the linearized Navier-Stokes equations. The equations are linearized around the unperturbed incoming wind profile, here assumed logarithmic. The Boussinesq approximation is used to model the Reynolds stress with a prescribed turbulent eddy viscosity profile. Without requiring the boundary-layer approximation, two new linear equations are obtained for the vertical velocity and the wall-normal vorticity, with a reduction in the computational cost by a factor of 8 when compared with a primitive-variables formulation. The presence of terrain elevation is introduced as a vertical coordinate shift, while forestry or wind turbines are included as body forces, without any assumption about the wake structure for the turbines. The model is first validated against some available experiments and simulations, and then a simulation of a wind farm over a Gaussian hill is performed. The speed-up effect of the hill is clearly beneficial in terms of the available momentum upstream of the crest, while downstream of it the opposite can be said as the turbines face a decreased wind speed. Also, the presence of the hill introduces an additional spanwise velocity component that may also affect the turbines' operations. The linear superposition of the flow over the hill and the flow over the farm alone provided a first estimation of the wind speed along the farm, with discrepancies of the same order of magnitude for the spanwise velocity. Finally, the possibility of using a parabolic set of equations to obtain the turbulent kinetic energy after the linearized model is investigated with promising results.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).

Multiple zonal jets and convective heat transport barriers in a quasi-geostrophic model of planetary cores

NASA Astrophysics Data System (ADS)

Guervilly, C.; Cardin, P.

2017-10-01

We study rapidly rotating Boussinesq convection driven by internal heating in a full sphere. We use a numerical model based on the quasi-geostrophic approximation for the velocity field, whereas the temperature field is 3-D. This approximation allows us to perform simulations for Ekman numbers down to 10-8, Prandtl numbers relevant for liquid metals (˜10-1) and Reynolds numbers up to 3 × 104. Persistent zonal flows composed of multiple jets form as a result of the mixing of potential vorticity. For the largest Rayleigh numbers computed, the zonal velocity is larger than the convective velocity despite the presence of boundary friction. The convective structures and the zonal jets widen when the thermal forcing increases. Prograde and retrograde zonal jets are dynamically different: in the prograde jets (which correspond to weak potential vorticity gradients) the convection transports heat efficiently and the mean temperature tends to be homogenized; by contrast, in the cores of the retrograde jets (which correspond to steep gradients of potential vorticity) the dynamics is dominated by the propagation of Rossby waves, resulting in the formation of steep mean temperature gradients and the dominance of conduction in the heat transfer process. Consequently, in quasi-geostrophic systems, the width of the retrograde zonal jets controls the efficiency of the heat transfer.

Sensitivity of ocean oxygenation to variations in tropical zonal wind stress magnitude

NASA Astrophysics Data System (ADS)

Ridder, Nina N.; England, Matthew H.

2014-09-01

Ocean oxygenation has been observed to have changed over the past few decades and is projected to change further under global climate change due to an interplay of several mechanisms. In this study we isolate the effect of modified tropical surface wind stress conditions on the evolution of ocean oxygenation in a numerical climate model. We find that ocean oxygenation varies inversely with low-latitude surface wind stress. Approximately one third of this response is driven by sea surface temperature anomalies; the remaining two thirds result from changes in ocean circulation and marine biology. Global mean O2 concentration changes reach maximum values of +4 μM and -3.6 μM in the two most extreme perturbation cases of -30% and +30% wind change, respectively. Localized changes lie between +92 μM under 30% reduced winds and -56 μM for 30% increased winds. Overall, we find that the extent of the global low-oxygen volume varies with the same sign as the wind perturbation; namely, weaker winds reduce the low-oxygen volume on the global scale and vice versa for increased trade winds. We identify two regions, one in the Pacific Ocean off Chile and the other in the Indian Ocean off Somalia, that are of particular importance for the evolution of oxygen minimum zones in the global ocean.

Comparison of horizontal winds from the LIMS satellite instrument with rocket measurements

NASA Technical Reports Server (NTRS)

Smith, A. K.; Bailey, P. L.

1985-01-01

Statistical results are given for a comparison between horizontal geostrophic winds computed from satellite height data and all available in situ rocket wind soundings during a 7-month period. The satellite data are the daily mapped fields from the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument, which extend from 100 to 0.1 mbar. Results indicate that in both the tropics and the extratropical Northern Hemisphere, the average zonal and meridional wind speeds agree to within 2-4 m/s throughout the stratosphere. The rms differences are much larger, with values of 5-10 m/s in the lower stratosphere, increasing to 20-40 m/s in the lower mesosphere. Time series show that LIMS and rocketsonde zonal wind speeds show coherent variations with temporal periods of 1-2 weeks and more, and both exhibit irregular variations on time scales of less than one week.

Low-latitude thermospheric neutral winds determined from AE-E measurements of the 6300-A nightglow at solar maximum

NASA Technical Reports Server (NTRS)

Burrage, M. D.; Abreu, V. J.; Fesen, C. G.

1990-01-01

Atmosphere Explorer E (AE-E) measurements of the O(1D) 6300-A emission in the nighttime equatorial thermosphere are used to infer the height of the F2 layer peak as a function of latitude and local time. The investigation is conducted both for northern hemisphere winter solstice and for spring equinox, under solar maximum conditions. The layer heights are used to derive magnetic meridional components of the transequatorial neutral wind, in conjunction with the MSIS-86 model and previous Jicamarca incoherent scatter measurements of the zonal electric field. The AE-E wind estimates indicate a predominant summer to winter flow for the winter solstice case. Comparisons are made with the empirical horizontal wind model HWM87 and with winds generated by the thermospheric general circulation model. The model predictions and experimental results are generally in good agreement, confirming the applicability of visible airglow data to studies of the global neutral wind pattern.

Substorm-related thermospheric density and wind disturbances

NASA Astrophysics Data System (ADS)

Ritter, P.; Luhr, H.; Doornbos, E. N.

2009-12-01

The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere-thermosphere. The phenomenon we are focusing on here is the magnetospheric substorm. This paper presents substorm related observations of the thermosphere derived from the CHAMP satellite. With its sensitive accelerometer the satellite can measure the air density and zonal winds. Based on a large number of substorm events the average high and low latitude thermosphere response to substorm onsets was deduced. During magnetic substorms the thermospheric density is enhanced first at high latitudes. Then the disturbance travels at sonic speed to lower latitudes, and 3-4 hours later the bulge reaches the equator on the night side. Under the influence of the Coriolis force the traveling atmospheric disturbance (TAD) is deflected westward. In accordance with present-day atmospheric models the disturbance zonal wind velocities during substorms are close to zero near the equator before midnight and attain moderate westward velocities after midnight. In general, the wind system is only weakly perturbed by substorms.

Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear

NASA Astrophysics Data System (ADS)

Mendoza, Victor; Goude, Anders

2017-05-01

The current trend of the wind energy industry aims for large scale turbines installed in wind farms. This brings a renewed interest in vertical axis wind turbines (VAWTs) since they have several advantages over the traditional Horizontal Axis Wind Tubines (HAWTs) for mitigating the new challenges. However, operating VAWTs are characterized by complex aerodynamics phenomena, presenting considerable challenges for modeling tools. An accurate and reliable simulation tool for predicting the interaction between the obtained wake of an operating VAWT and the flow in atmospheric open sites is fundamental for optimizing the design and location of wind energy facility projects. The present work studies the wake produced by a VAWT and how it is affected by the surface roughness of the terrain, without considering the effects of the ambient turbulence intensity. This study was carried out using an actuator line model (ALM), and it was implemented using the open-source CFD library OpenFOAM to solve the governing equations and to compute the resulting flow fields. An operational H-shaped VAWT model was tested, for which experimental activity has been performed at an open site north of Uppsala-Sweden. Different terrains with similar inflow velocities have been evaluated. Simulated velocity and vorticity of representative sections have been analyzed. Numerical results were validated using normal forces measurements, showing reasonable agreement.

WIND: Computer program for calculation of three dimensional potential compressible flow about wind turbine rotor blades

NASA Technical Reports Server (NTRS)

Dulikravich, D. S.

1980-01-01

A computer program is presented which numerically solves an exact, full potential equation (FPE) for three dimensional, steady, inviscid flow through an isolated wind turbine rotor. The program automatically generates a three dimensional, boundary conforming grid and iteratively solves the FPE while fully accounting for both the rotating cascade and Coriolis effects. The numerical techniques incorporated involve rotated, type dependent finite differencing, a finite volume method, artificial viscosity in conservative form, and a successive line overrelaxation combined with the sequential grid refinement procedure to accelerate the iterative convergence rate. Consequently, the WIND program is capable of accurately analyzing incompressible and compressible flows, including those that are locally transonic and terminated by weak shocks. The program can also be used to analyze the flow around isolated aircraft propellers and helicopter rotors in hover as long as the total relative Mach number of the oncoming flow is subsonic.

Laminar Flow Supersonic Wind Tunnel primary air injector

NASA Technical Reports Server (NTRS)

Smith, Brooke Edward

1993-01-01

This paper describes the requirements, design, and prototype testing of the flex-section and hinge seals for the Laminar Flow Supersonic Wind Tunnel Primary Injector. The supersonic atmospheric primary injector operates between Mach 1.8 and Mach 2.2 with mass-flow rates of 62 to 128 lbm/s providing the necessary pressure reduction to operate the tunnel in the desired Reynolds number (Re) range.

Analysis of environmental dispersion in a wetland flow under the effect of wind: Extended solution

NASA Astrophysics Data System (ADS)

Wang, Huilin; Huai, Wenxin

2018-02-01

The accurate analysis of the contaminant transport process in wetland flows is essential for environmental assessment. However, dispersivity assessment becomes complicated when the wind strength and direction are taken into consideration. Prior studies illustrating the wind effect on environmental dispersion in wetland flows simply focused on the mean longitudinal concentration distribution. Moreover, the results obtained by these analyses are not accurate when done on a smaller scale, namely, the initial stage of the contaminant transport process. By combining the concentration moments method (the Aris' method) and Gill's expansion theory, the previous researches on environmental dispersion in wetland flows with effect of wind have been extended. By adopting up to 4th-order moments, the wind effect-as illustrated by dimensionless parameters Er (wind force) and ω (wind direction)-on kurtosis and skewness is discussed, the up to 4th-order vertical concentration distribution is obtained, and the two-dimensional concentration distribution is illustrated. This work demonstrates that wind intensity and direction can significantly affect the contaminant dispersion. Moreover, the study presents a more accurate analytical solution of environmental dispersion in wetland flows under various wind conditions.

Fan array wind tunnel: a multifunctional, complex environmental flow manipulator

NASA Astrophysics Data System (ADS)

Dougherty, Christopher; Veismann, Marcel; Gharib, Morteza

2017-11-01

The recent emergence of small unmanned aerial vehicles (UAVs) has reshaped the aerospace testing environment. Traditional closed-loop wind tunnels are not particularly suited nor easily retrofit to take advantage of these coordinated, controls-based rotorcraft. As such, a highly configurable, novel wind tunnel aimed at addressing the unmet technical challenges associated with single or formation flight performance of autonomous drone systems is presented. The open-loop fan array wind tunnel features 1296 individually controllable DC fans arranged in a 2.88m x 2.88m array. The fan array can operate with and without a tunnel enclosure and is able to rotate between horizontal and vertical testing configurations. In addition to standard variable speed uniform flow, the fan array can generate both unsteady and shear flows. Through the aid of smaller side fan array units, vortex flows are also possible. Conceptual design, fabrication, and validation of the tunnel performance will be presented, including theoretical and computational predictions of flow speed and turbulence intensity. Validation of these parameters is accomplished through standard pitot-static and hot-wire techniques. Particle image velocimetry (PIV) of various complex flows will also be shown. This material is based upon work supported by the Center for Autonomous Systems and Technologies (CAST) at the Graduate Aerospace Laboratories of the California Institute of Technology (GALCIT).

Observations of the effect of wind on the cooling of active lava flows

USGS Publications Warehouse

Keszthelyi, L.; Harris, A.J.L.; Dehn, J.

2003-01-01

We present the first direct observations of the cooling of active lava flows by the wind. We confirm that atmospheric convective cooling processes (i.e., the wind) dominate heat loss over the lifetime of a typical pahochoe lava flow. In fact, the heat extracted by convection is greater than predicted, especially at wind speeds less than 5 m/s and surface temperatures less than 400??C. We currently estimate that the atmospheric heat transfer coefficient is about 45-50 W m-2 K-1 for a 10 m/s wind and a surface temperature ???500??C. Further field experiments and theoretical studies should expand these results to a broader range of surface temperatures and wind speeds.

First absolute wind measurements in the middle atmosphere of Mars

NASA Astrophysics Data System (ADS)

Lellouch, Emmanuel; Goldstein, Jeffrey J.; Bougher, Stephen W.; Paubert, Gabriel; Rosenqvist, Jan

1991-12-01

The first absolute wind measurements in the middle atmosphere of Mars (40-70 km) were obtained from Doppler shifts in the J = 2-1 CO transition at 230.538 GHz. During the 1988 opposition, this line was observed at 100 kHz resolution with the IRAM 30 m telescope. The 12-arcsec FWHM beam of the facility allowed spatial resolution of the Martian disk (23.8 arcsec). The high S/N of the data allowed measurement of winds with a 1-sigma absolute line-of-sight accuracy of 20 m/s. The measurements, performed during southern summer solstice, stress the Southern Hemisphere and clearly indicate a global easterlies flow. If modeled by a broad easterly jet with a maximum centered at 20 S, and extending 80 deg in latitude, the jet core velocity is found to have a chi-sq minimum at 160 m/s, generally consistent with predictions for broad summer easterly jets near 50 km as proposed by theoretical models. If the flow is modeled instead by a planet-wide solid rotator zonal flow which is restricted to the Southern Hemisphere or equatorial regions, the velocity of the easterlies is nearly the same. These wind measurements, together with the temperature measurements of Deming et al. (1986), provide the first experimental rough picture of the middle atmosphere circulation of Mars, in general agreement with the Jaquin axisymmetric middle atmosphere model and the current Mars GCM model of Pollack et al. (1990).

Flow widening through a Darrieus wind turbine - Theory and experiment

NASA Astrophysics Data System (ADS)

Comolet, R.; Harajli, I.; Mercier Des Rochettes, P.; Yeznasni, A.

1982-11-01

A two-dimensional multiple stream tube model is developed for the air flow through a Darrieus wind turbine. The model is configured to account for the widening of the flux tubes as they cross the interior of the actuator disk. Note is made of the lateral broadening of the flow as it moves through the area, leaving a turbulent wake. A relation is defined between the variation in the kinetic energy of the flow and the aerodynamic forces acting on the blades. The global efficiency and the power output of the machine are calculated. Experimental results are reported for a machine equipped with two NACA 0015 blades, each 110 cm long and with a 10 cm chord. The Darrieus had a 1 m diam and was tested in a wind tunnel at wind speeds of 0-18 m/sec. Soap bubbles inflated with He were used for visualization. Power output was found to match prediction. The model is recommended for use in calculating the forces acting on the machine and studying vibration and fatigue causative mechanisms.

Effects of anisotropic thermal conduction on wind properties in hot accretion flow

NASA Astrophysics Data System (ADS)

Bu, De-Fu; Wu, Mao-Chun; Yuan, Ye-Fei

2016-06-01

Previous works have clearly shown the existence of winds from black hole hot accretion flow and investigated their detailed properties. In extremely low accretion rate systems, the collisional mean-free path of electrons is large compared with the length-scale of the system, thus thermal conduction is dynamically important. When the magnetic field is present, the thermal conduction is anisotropic and energy transport is along magnetic field lines. In this paper, we study the effects of anisotropic thermal conduction on the wind production in hot accretion flows by performing two-dimensional magnetohydrodynamic simulations. We find that thermal conduction has only moderate effects on the mass flux of wind. But the energy flux of wind can be increased by a factor of ˜10 due to the increase of wind velocity when thermal conduction is included. The increase of wind velocity is because of the increase of driving forces (e.g. gas pressure gradient force and centrifugal force) when thermal conduction is included. This result demonstrates that thermal conduction plays an important role in determining the properties of wind.

Computer investigations of the turbulent flow around a NACA2415 airfoil wind turbine

NASA Astrophysics Data System (ADS)

Driss, Zied; Chelbi, Tarek; Abid, Mohamed Salah

2015-12-01

In this work, computer investigations are carried out to study the flow field developing around a NACA2415 airfoil wind turbine. The Navier-Stokes equations in conjunction with the standard k-ɛ turbulence model are considered. These equations are solved numerically to determine the local characteristics of the flow. The models tested are implemented in the software "SolidWorks Flow Simulation" which uses a finite volume scheme. The numerical results are compared with experiments conducted on an open wind tunnel to validate the numerical results. This will help improving the aerodynamic efficiency in the design of packaged installations of the NACA2415 airfoil type wind turbine.

The Ultimate Flow Controlled Wind Turbine Blade Airfoil

NASA Astrophysics Data System (ADS)

Seifert, Avraham; Dolgopyat, Danny; Friedland, Ori; Shig, Lior

2015-11-01

Active flow control is being studied as an enabling technology to enhance and maintain high efficiency of wind turbine blades also with contaminated surface and unsteady winds as well as at off-design operating conditions. The study is focused on a 25% thick airfoil (DU91-W2-250) suitable for the mid blade radius location. Initially a clean airfoil was fabricated and tested, as well as compared to XFoil predictions. From these experiments, the evolution of the separation location was identified. Five locations for installing active flow control actuators are available on this airfoil. It uses both Piezo fluidic (``Synthetic jets'') and the Suction and Oscillatory Blowing (SaOB) actuators. Then we evaluate both actuation concepts overall energy efficiency and efficacy in controlling boundary layer separation. Since efficient actuation is to be found at low amplitudes when placed close to separation location, distributed actuation is used. Following the completion of the baseline studies the study has focused on the airfoil instrumentation and extensive wind tunnel testing over a Reynolds number range of 0.2 to 1.5 Million. Sample results will be presented and outline for continued study will be discussed.

The role of zonal flows and predator–prey oscillations in triggering the formation of edge and core transport barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmitz, Lothar; Zeng, Lei; Rhodes, Terry L.

2014-04-24

Here, we present direct evidence of low frequency, radially sheared, turbulence-driven flows (zonal flows (ZFs)) triggering edge transport barrier formation preceding the L- to H-mode transition via periodic turbulence suppression in limit-cycle oscillations (LCOs), consistent with predator–prey dynamics. The final transition to edge-localized mode-free H-mode occurs after the equilibrium E × B flow shear increases due to ion pressure profile evolution. ZFs are also observed to initiate formation of an electron internal transport barrier (ITB) at the q = 2 rational surface via local suppression of electron-scale turbulence. Multi-channel Doppler backscattering (DBS) has revealed the radial structure of the ZF-induced shear layer and the E × B shearing rate, ω E×B, in both barrier types. During edge barrier formation, the shearing rate lags the turbulence envelope during the LCO by 90°, transitioning to anti-correlation (180°) when the equilibrium shear dominates the turbulence-driven flow shear due to the increasing edge pressure gradient. The time-dependent flow shear and the turbulence envelope are anti-correlated (180° out of phase) in the electron ITB. LCOs with time-reversed evolution dynamics (transitioning from an equilibrium-flow dominated to a ZF-dominated state) have also been observed during the H–L back-transition and are potentially of interest for controlled ramp-down of the plasma stored energy and pressure (normalized to the poloidal magnetic field)more » $$\\beta_{\\theta} =2\\mu_{0} n{( {T_{{\\rm e}} +T_{{\\rm i}}})}/{B_{\\theta}^{2}}$$ in ITER.« less

The role of zonal flows and predator-prey oscillations in triggering the formation of edge and core transport barriers

NASA Astrophysics Data System (ADS)

Schmitz, L.; Zeng, L.; Rhodes, T. L.; Hillesheim, J. C.; Peebles, W. A.; Groebner, R. J.; Burrell, K. H.; McKee, G. R.; Yan, Z.; Tynan, G. R.; Diamond, P. H.; Boedo, J. A.; Doyle, E. J.; Grierson, B. A.; Chrystal, C.; Austin, M. E.; Solomon, W. M.; Wang, G.

2014-07-01

We present direct evidence of low frequency, radially sheared, turbulence-driven flows (zonal flows (ZFs)) triggering edge transport barrier formation preceding the L- to H-mode transition via periodic turbulence suppression in limit-cycle oscillations (LCOs), consistent with predator-prey dynamics. The final transition to edge-localized mode-free H-mode occurs after the equilibrium E × B flow shear increases due to ion pressure profile evolution. ZFs are also observed to initiate formation of an electron internal transport barrier (ITB) at the q = 2 rational surface via local suppression of electron-scale turbulence. Multi-channel Doppler backscattering (DBS) has revealed the radial structure of the ZF-induced shear layer and the E × B shearing rate, ωE×B, in both barrier types. During edge barrier formation, the shearing rate lags the turbulence envelope during the LCO by 90°, transitioning to anti-correlation (180°) when the equilibrium shear dominates the turbulence-driven flow shear due to the increasing edge pressure gradient. The time-dependent flow shear and the turbulence envelope are anti-correlated (180° out of phase) in the electron ITB. LCOs with time-reversed evolution dynamics (transitioning from an equilibrium-flow dominated to a ZF-dominated state) have also been observed during the H-L back-transition and are potentially of interest for controlled ramp-down of the plasma stored energy and pressure (normalized to the poloidal magnetic field) \\beta_{\\theta} =2\\mu_{0} n{( {T_{e} +T_{i}})}/{B_{\\theta}^{2}} in ITER.

Large-Eddy Simulation of Atmospheric Boundary-Layer Flow Through a Wind Farm Sited on Topography

NASA Astrophysics Data System (ADS)

Shamsoddin, Sina; Porté-Agel, Fernando

2017-04-01

Large-eddy simulation (LES) has recently been well validated and applied in the context of wind turbines over flat terrain; however, to date its accuracy has not been tested systematically in the case of turbine-wake flows over topography. Here, we investigate the wake flow in a wind farm situated on hilly terrain using LES for a case where wind-tunnel experimental data are available. To this end, first boundary-layer flow is simulated over a two-dimensional hill in order to characterize the spatial distribution of the mean velocity and the turbulence statistics. A flow simulation is then performed through a wind farm consisting of five horizontal-axis wind turbines sited over the same hill in an aligned layout. The resulting flow characteristics are compared with the former case, i.e., without wind turbines. To assess the validity of the simulations, the results are compared with the wind-tunnel measurements. It is found that LES can reproduce the flow field effectively, and, specifically, the speed-up over the hilltop and the velocity deficit and turbulence intensity enhancement induced by the turbines are well captured by the simulations. Besides, the vertical profiles of the mean velocity and turbulence intensity at different streamwise positions match well those for the experiment. In addition, another numerical experiment is carried out to show how higher (and more realistic) thrust coefficients of the turbines lead to stronger wakes and, at the same time, higher turbulence intensities.

Thermal wind from hot accretion flows at large radii

NASA Astrophysics Data System (ADS)

Bu, De-Fu; Yang, Xiao-Hong

2018-06-01

We study slowly rotating accretion flow at parsec and subparsec scales irradiated by low-luminosity active galactic nuclei. We take into account the Compton heating, photoionization heating by the central X-rays. The bremsstrahlung cooling, recombination, and line cooling are also included. We find that due to the Compton heating, wind can be thermally driven. The power of wind is in the range (10-6-10-3) LEdd, with LEdd being the Eddington luminosity. The mass flux of wind is in the range (0.01-1) \\dot{M}_Edd (\\dot{M}_Edd= L_Edd/0.1c^2 is the Eddington accretion rate, c is speed of light). We define the wind generation efficiency as ɛ = P_W/\\dot{M}_BHc^2, with PW being wind power, \\dot{M}_BH being the mass accretion rate on to the black hole. ɛ lies in the range 10-4-1.18. Wind production efficiency decreases with increasing mass accretion rate. The possible role of the thermally driven wind in the active galactic feedback is briefly discussed.

Numerical modeling of the wind flow over a transverse dune

PubMed Central

Araújo, Ascânio D.; Parteli, Eric J. R.; Pöschel, Thorsten; Andrade, José S.; Herrmann, Hans J.

2013-01-01

Transverse dunes, which form under unidirectional winds and have fixed profile in the direction perpendicular to the wind, occur on all celestial objects of our solar system where dunes have been detected. Here we perform a numerical study of the average turbulent wind flow over a transverse dune by means of computational fluid dynamics simulations. We find that the length of the zone of recirculating flow at the dune lee — the separation bubble — displays a surprisingly strong dependence on the wind shear velocity, u*: it is nearly independent of u* for shear velocities within the range between 0.2 m/s and 0.8 m/s but increases linearly with u* for larger shear velocities. Our calculations show that transport in the direction opposite to dune migration within the separation bubble can be sustained if u* is larger than approximately 0.39 m/s, whereas a larger value of u* (about 0.49 m/s) is required to initiate this reverse transport. PMID:24091456

A control-oriented dynamic wind farm flow model: “WFSim”

NASA Astrophysics Data System (ADS)

Boersma, S.; Gebraad, P. M. O.; Vali, M.; Doekemeijer, B. M.; van Wingerden, J. W.

2016-09-01

In this paper, we present and extend the dynamic medium fidelity control-oriented Wind Farm Simulator (WFSim) model. WFSim resolves flow fields in wind farms in a horizontal, two dimensional plane. It is based on the spatially and temporally discretised two dimensional Navier-Stokes equations and the continuity equation and solves for a predefined grid and wind farm topology. The force on the flow field generated by turbines is modelled using actuator disk theory. Sparsity in system matrices is exploited in WFSim, which enables a relatively fast flow field computation. The extensions to WFSim we present in this paper are the inclusion of a wake redirection model, a turbulence model and a linearisation of the nonlinear WFSim model equations. The first is important because it allows us to carry out wake redirection control and simulate situations with an inflow that is misaligned with the rotor plane. The wake redirection model is validated against a theoretical wake centreline known from literature. The second extension makes WFSim more realistic because it accounts for wake recovery. The amount of recovery is validated using a high fidelity simulation model Simulator fOr Wind Farm Applications (SOWFA) for a two turbine test case. Finally, a linearisation is important since it allows the application of more standard analysis, observer and control techniques.

Dependence of wind speed and UV albedo at Venus top cloud layer on topography and local time revealed from VMC images

NASA Astrophysics Data System (ADS)

Patsaeva, Marina; Khatuntsev, Igor; Turin, Alexander; Zasova, Ludmila; Bertaux, Jean-loup

2017-04-01

A set of UV (365 nm) and IR (965 nm) images obtained by the Venus Monitoring Camera (VMC) was used to study the circulation of the mesosphere at two altitude levels. Displacement vectors were obtained by wind tracking in automated mode for observation period from 2006 to 2014 for UV images [1,2] and from 2006 to 2012 for IR images. The long observation period and good longitude-latitude coverage by single measurements allowed us to focus on the study of the slow-periodic component. The influence of the underlying surface topography on the change of speed of the average zonal wind at UV level at low latitudes, discovered by visual methods has been described in [3]. Analysis of the longitude-latitude distribution of the zonal and meridional components for 172000 (257 orbits) digital individual wind measurements at UV level and for 32,000 (150 orbits) digital individual wind measurements at IR level allows us to compare the influence of Venus topography on the change of the zonal and meridional components at both cloud levels. At the UV level (67±2 km) longitudinal profiles of the zonal speed for different latitude bins in low latitudes correlate with surface profiles. These correlations are most noticeable in the region of Aphrodite Terra. The correlation shift depends on the surface height. Albedo profiles correlate with surface profiles also at high latitudes. Zonal speed profiles at low latitude (5-15°S) depend not only on altitude, but also on local time. Minimum of the zonal speed is observed over Aphrodite Terra (90-100°E) at about 12 LT. A diurnal harmonic with an extremum over Aphrodite Terra was found. It can be considered as a superposition of a solar-synchronous tide and a stationary wave caused by interaction of the windstream with the surface. At the IR level (55±4 km) a correlation between surface topography and meridional speed was found in the region 10-30°S. The average meridional flow is equatorward at the IR level, but in the region Aphrodite

Empirical wind model for the middle and lower atmosphere. Part 1: Local time average

NASA Technical Reports Server (NTRS)

Hedin, A. E.; Fleming, E. L.; Manson, A. H.; Schmidlin, F. J.; Avery, S. K.; Franke, S. J.

1993-01-01

The HWM90 thermospheric wind model was revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating zonal and meridional wind profiles representative of the climatological average for various geophysical conditions. Gradient winds from CIRA-86 plus rocket soundings, incoherent scatter radar, MF radar, and meteor radar provide the data base and are supplemented by previous data driven model summaries. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and longitude (stationary wave 1). The model represents a smoothed compromise between the data sources. Although agreement between various data sources is generally good, some systematic differences are noted, particularly near the mesopause. Root mean square differences between data and model are on the order of 15 m/s in the mesosphere and 10 m/s in the stratosphere for zonal wind, and 10 m/s and 4 m/s, respectively, for meridional wind.

Operational flow visualization techniques in the Langley Unitary Plan Wind Tunnel

NASA Technical Reports Server (NTRS)

Corlett, W. A.

1982-01-01

The unitary plan wind tunnel (UPWT) uses in daily operation are shown. New ideas for improving the quality of established flow visualization methods are developed and programs on promising new flow visualization techniques are pursued. The unitary plan wind tunnel is a supersonic facility, referred to as a production facility, although the majority of tests are inhouse basic research investigations. The facility has two 4 ft. by 4 ft. test sections which span a Mach range from 1.5 to 4.6. The cost of operation is about $10 per minute. Problems are the time required for a flow visualization test setup and investigation costs and the ability to obtain consistently repeatable results. Examples of sublimation, vapor screen, oil flow, minitufts, schlieren, and shadowgraphs taken in UPWT are presented. All tests in UPWT employ one or more of the flow visualization techniques.

Processed Movie of Zonal Jets

NASA Technical Reports Server (NTRS)

2000-01-01

This movie is a manipulated sequence showing motions in Jupiter's atmosphere over the course of five days beginning Oct. 1, 2000, as seen by a camera on NASA's Cassini spacecraft, using a blue filter.

Beginning with seven images taken at uneven time intervals, this sequence was made by using information on wind speeds derived from actual Jupiter images to create evenly spaced time steps throughout. The final result is a smooth movie sequence consisting of both real and false frames.

The view is of the opposite side of the planet from Jupiter's Great Red Spot. The region shown reaches from 50 degrees north to 50 degrees south of Jupiter's equator, and extends 100 degrees east-to-west, about one-quarter of Jupiter's circumference. The smallest features are about 500 kilometers (about 300 miles) across.

Towards the end of the sequence, a shadow appears from one of Jupiter's moons, Europa.

The movie shows the remains of a historic merger that began several years ago, when three white oval storms that had existed for 60 years merged into two, then one. The resulting oval is visible in the lower left portion of the movie.

The movie also shows zonal jets that circle the planet on constant latitudes. Winds seen moving toward the left (westward) correspond to features that are rotating a little slower than Jupiter's magnetic field, and winds moving the opposite direction correspond to features that are rotating a little faster than the magnetic field. Since Jupiter has no solid surface, the rotation of the magnetic field is the point of reference for the rotation of the planet.

Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.

Optical Flow for Flight and Wind Tunnel Background Oriented Schlieren Imaging

NASA Technical Reports Server (NTRS)

Smith, Nathanial T.; Heineck, James T.; Schairer, Edward T.

2017-01-01

Background oriented Schlieren images have historically been generated by calculating the observed pixel displacement between a wind-on and wind-o image pair using normalized cross-correlation. This work uses optical flow to solve the displacement fields which generate the Schlieren images. A well established method used in the computer vision community, optical flow is the apparent motion in an image sequence due to brightness changes. The regularization method of Horn and Schunck is used to create Schlieren images using two data sets: a supersonic jet plume shock interaction from the NASA Ames Unitary Plan Wind Tunnel, and a transonic flight test of a T-38 aircraft using a naturally occurring background, performed in conjunction with NASA Ames and Armstrong Research Centers. Results are presented and contrasted with those using normalized cross-correlation. The optical flow Schlieren images are found to provided significantly more detail. We apply the method to historical data sets to demonstrate the broad applicability and limitations of the technique.

Aerodynamic study of a small wind turbine with emphasis on laminar and transition flows

NASA Astrophysics Data System (ADS)

Niculescu, M. L.; Cojocaru, M. G.; Crunteanu, D. E.

2016-06-01

The wind energy is huge but unfortunately, wind turbines capture only a little part of this enormous green energy. Furthermore, it is impossible to put multi megawatt wind turbines in the cities because they generate a lot of noise and discomfort. Instead, it is possible to install small Darrieus and horizontal-axis wind turbines with low tip speed ratios in order to mitigate the noise as much as possible. Unfortunately, the flow around this wind turbine is quite complex because the run at low Reynolds numbers. Therefore, this flow is usually a mixture of laminar, transition and laminar regimes with bubble laminar separation that is very difficult to simulate from the numerical point of view. Usually, transition and laminar regimes with bubble laminar separation are ignored. For this reason, this paper deals with laminar and transition flows in order to provide some brightness in this field.

Analytical Model for Mean Flow and Fluxes of Momentum and Energy in Very Large Wind Farms

NASA Astrophysics Data System (ADS)

Markfort, Corey D.; Zhang, Wei; Porté-Agel, Fernando

2018-01-01

As wind-turbine arrays continue to be installed and the array size continues to grow, there is an increasing need to represent very large wind-turbine arrays in numerical weather prediction models, for wind-farm optimization, and for environmental assessment. We propose a simple analytical model for boundary-layer flow in fully-developed wind-turbine arrays, based on the concept of sparsely-obstructed shear flows. In describing the vertical distribution of the mean wind speed and shear stress within wind farms, our model estimates the mean kinetic energy harvested from the atmospheric boundary layer, and determines the partitioning between the wind power captured by the wind turbines and that absorbed by the underlying land or water. A length scale based on the turbine geometry, spacing, and performance characteristics, is able to estimate the asymptotic limit for the fully-developed flow through wind-turbine arrays, and thereby determine if the wind-farm flow is fully developed for very large turbine arrays. Our model is validated using data collected in controlled wind-tunnel experiments, and its usefulness for the prediction of wind-farm performance and optimization of turbine-array spacing are described. Our model may also be useful for assessing the extent to which the extraction of wind power affects the land-atmosphere coupling or air-water exchange of momentum, with implications for the transport of heat, moisture, trace gases such as carbon dioxide, methane, and nitrous oxide, and ecologically important oxygen.

How pattern is selected in drift wave turbulence: Role of parallel flow shear

NASA Astrophysics Data System (ADS)

Kosuga, Y.

2017-12-01

The role of parallel shear flow in the pattern selection problem in drift wave turbulence is discussed. Patterns of interest here are E × B convective cells, which include poloidally symmetric zonal flows and radially elongated streamers. The competition between zonal flow formation and streamer formation is analyzed in the context of modulational instability analysis, with the parallel flow shear as a parameter. For drift wave turbulence with k⊥ρs ≲ O (1 ) and without parallel flow coupling, zonal flows are preferred structures. While increasing the magnitude of parallel flow shear, streamer growth overcomes zonal flow growth. This is because the self-focusing effect of the modulational instability becomes more effective for streamers through density and parallel velocity modulation. As a consequence, the bursty release of free energy may result as the parallel flow shear increases.

Advances in the computation of transonic separated flows over finite wings

NASA Technical Reports Server (NTRS)

Kaynak, Unver; Flores, Jolen

1989-01-01

Problems encountered in numerical simulations of transonic wind-tunnel experiments with low-aspect-ratio wings are surveyed and illustrated. The focus is on the zonal Euler/Navier-Stokes program developed by Holst et al. (1985) and its application to shock-induced separation. The physical basis and numerical implementation of the method are reviewed, and results are presented from studies of the effects of artificial dissipation, boundary conditions, grid refinement, the turbulence model, and geometry representation on the simulation accuracy. Extensive graphs and diagrams and typical flow visualizations are provided.

Large-scale solar wind flow around Saturn's nonaxisymmetric magnetosphere

NASA Astrophysics Data System (ADS)

Sulaiman, A. H.; Jia, X.; Achilleos, N.; Sergis, N.; Gurnett, D. A.; Kurth, W. S.

2017-09-01

The interaction between the solar wind and a magnetosphere is central to the dynamics of a planetary system. Here we address fundamental questions on the large-scale magnetosheath flow around Saturn using a 3-D magnetohydrodynamic (MHD) simulation. We find Saturn's polar-flattened magnetosphere to channel 20% more flow over the poles than around the flanks at the terminator. Further, we decompose the MHD forces responsible for accelerating the magnetosheath plasma to find the plasma pressure gradient as the dominant driver. This is by virtue of a high-β magnetosheath and, in turn, the high-MA bow shock. Together with long-term magnetosheath data by the Cassini spacecraft, we present evidence of how nonaxisymmetry substantially alters the conditions further downstream at the magnetopause, crucial for understanding solar wind-magnetosphere interactions such as reconnection and shear flow-driven instabilities. We anticipate our results to provide a more accurate insight into the global conditions upstream of Saturn and the outer planets.

Longitudinal Variations in Jupiter's Winds

NASA Astrophysics Data System (ADS)

Simon-Miller, Amy A.; Gierasch, P. J.; Tierney, G.

2010-10-01

Long-term studies of Jupiter's zonal wind field revealed temporal variations on the order of 20 to 40 m/s at many latitudes, greater than the typical data uncertainties of 1 to 10 m/s. No definitive periodicities were evident, however, though some latitudinally-confined signals did appear at periods relevant to the Quasi-Quadrennial Oscillation (Simon-Miller & Gierasch, Icarus, in press). As the QQO appears, from vertical temperature profiles, to propagate downward, it is unclear why a signal is not more obvious, unless other processes dominate over possibly weaker forcing from the QQO. An additional complication is that zonal wind profiles represent an average over some particular set of longitudes for an image pair and most data sets do not offer global wind coverage. Even avoiding known features, such as the large anticyclonic vortices especially prevalent in the south, there can be distinct variations in longitude. We present results on the full wind field from Voyager and Cassini data, showing apparent longitudinal variations of up to 60 m/s or more. These are particularly obvious near disruptions such as the South Equatorial Disturbance, even when the feature itself is not clearly visible. These two dates represent very different states of the planet for comparison: Voyagers 1 & 2 flew by Jupiter shortly after a global upheaval, while many regions were in a disturbed state, while the Cassini view is typical of a more quiescent period present during much of the 1990s and early 2000s.

Longitudinal Variations in Jupiter's Winds

NASA Technical Reports Server (NTRS)

Simon-Miller, Amy A.; Gierasch, P. J.; Tierney, G.

2010-01-01

Long-term studies of Jupiter's zonal wind field revealed temporal variations on the order of 20 to 40 m/s at many latitudes, greater than the typical data uncertainties of 1 to 10 m/s. No definitive periodicities were evident, however, though some latitudinally-confined signals did appear at periods relevant to the Quasi- Quadrennial Oscillation (Simon-Miller & Gierasch, Icarus, in press). As the QQO appears, from vertical temperature profiles, to propagate downward, it is unclear why a signal is not more obvious, unless other processes dominate over possibly weaker forcing from the QQO. An additional complication is that zonal wind profiles represent an average over some particular set of longitudes for an image pair and most data sets do not offer global wind coverage. Lien avoiding known features, such as the large anticyclonic vortices especially prevalent in the south, there can be distinct variations in longitude. We present results on the full wind field from Voyager and Cassini data, showing apparent longitudinal variations of up to 60 m/s or more. These are particularly obvious near disruptions such as the South Equatorial Disturbance, even when the feature itself is not clearly visible. These two dates represent very different states of the planet for comparison: Voyagers 1 & 2 flew by Jupiter shortly after a global upheaval, while many regions were in a disturbed state, while the Cassini view is typical of a more quiescent period present during much of the 1990s and early 2000s.

On the wind production from hot accretion flows with different accretion rates

NASA Astrophysics Data System (ADS)

Bu, De-Fu; Gan, Zhao-Ming

2018-02-01

We perform two-dimensional simulations to study how the wind strength changes with accretion rate. We take into account bremsstrahlung, synchrotron radiation and the Comptonization. We find that when the accretion rate is low, radiative cooling is not important, and the accretion flow is hot. For the hot accretion flow, wind is very strong. The mass flux of wind can be ˜ 50 per cent of the mass inflow rate. When the accretion rate increases to a value at which radiative cooling rate is roughly equal to or slightly larger than viscous heating rate, cold clumps can form around the equatorial plane. In this case, the gas pressure gradient force is small and wind is very weak. Our results may be useful for the sub-grid model of active galactic nuclear feedback study.

Winds in the meteor zone over Trivandrum

NASA Astrophysics Data System (ADS)

Reddi, C. R.; Rajeev, K.; Ramakumar, Geetha

1991-04-01

The height profiles of the zonal and meridional wind obtained from the meteor wind radar data recorded at Trivandrum (8 deg 36 min N, 77 deg E) are presented. Large wind shears were found to exist in the meteor zone over Trivandrum. The profiles showed quasi-sinusoidal variations with altitude and vertical wavelength of the oscillation in the range 15-25 km. Further, there was a large day-to-day variability in the profiles obtained for the same local time on consecutive days. The results are discussed in the light of the winds due to tides and equatorial waves in the low latitudes. The implications of the large wind shears with reference to the local wind effects on the equatorial electrojet are outlined.

Mapping potential vorticity dynamics on saturn: Zonal mean circulation from Cassini and Voyager data

NASA Astrophysics Data System (ADS)

Read, P. L.; Conrath, B. J.; Fletcher, L. N.; Gierasch, P. J.; Simon-Miller, A. A.; Zuchowski, L. C.

2009-12-01

Maps of Ertel potential vorticity on isentropic surfaces (IPV) and quasi-geostrophic potential vorticity (QGPV) are well established in dynamical meteorology as powerful sources of insight into dynamical processes involving 'balanced' flow (i.e. geostrophic or similar). Here we derive maps of zonal mean IPV and QGPV in Saturn's upper troposphere and lower stratosphere by making use of a combination of velocity measurements, derived from the combined tracking of cloud features in images from the Voyager and Cassini missions, and thermal measurements from the Cassini Composite Infrared Spectrometer (CIRS) instrument. IPV and QGPV are mapped and compared for the entire globe between latitudes 89∘S-82∘N. As on Jupiter, profiles of zonally averaged PV show evidence for a step-like "stair-case" pattern suggestive of local PV homogenisation, separated by strong PV gradients in association with eastward jets. The northward gradient of PV (IPV or QGPV) is found to change sign in several places in each hemisphere, however, even when baroclinic contributions are taken into account. The stability criterion with respect to Arnol'd's second stability theorem may be violated near the peaks of westward jets. Visible, near-IR and thermal-IR Cassini observations have shown that these regions exhibit many prominent, large-scale eddies and waves, e.g. including 'storm alley'. This suggests the possibility that at least some of these features originate from instabilities of the background zonal flow.

Wind Tunnel Investigation of the Near-wake Flow Dynamics of a Horizontal Axis Wind Turbine

NASA Astrophysics Data System (ADS)

Hashemi-Tari, P.; Siddiqui, K.; Refan, M.; Hangan, H.

2014-06-01

Experiments conducted in a large wind tunnel set-up investigate the 3D flow dynamics within the near-wake region of a horizontal axis wind turbine. Particle Image Velocimetry (PIV) measurements quantify the mean and turbulent components of the flow field. Measurements are performed in multiple adjacent horizontal planes in order to cover the area behind the rotor in a large radial interval, at several locations downstream of the rotor. The measurements were phase-locked in order to facilitate the re-construction of the threedimensional flow field. The mean velocity and turbulence characteristics clearly correlate with the near-wake vortex dynamics and in particular with the helical structure of the flow, formed immediately behind the turbine rotor. Due to the tip and root vortices, the mean and turbulent characteristics of the flow are highly dependent on the azimuth angle in regions close to the rotor and close to the blade tip and root. Further from the rotor, the characteristics of the flow become phase independent. This can be attributed to the breakdown of the vortical structure of the flow, resulting from the turbulent diffusion. In general, the highest levels of turbulence are observed in shear layer around the tip of the blades, which decrease rapidly downstream. The shear zone grows in the radial direction as the wake moves axially, resulting in velocity recovery toward the centre of the rotor due to momentum transport.

Magnetosheath for almost-aligned solar wind magnetic field and flow vectors: Wind observations across the dawnside magnetosheath at X = -12 Re

NASA Astrophysics Data System (ADS)

Farrugia, C. J.; Erkaev, N. V.; Torbert, R. B.; Biernat, H. K.; Gratton, F. T.; Szabo, A.; Kucharek, H.; Matsui, H.; Lin, R. P.; Ogilvie, K. W.; Lepping, R. P.; Smith, C. W.

2010-08-01

While there are many approximations describing the flow of the solar wind past the magnetosphere in the magnetosheath, the case of perfectly aligned (parallel or anti-parallel) interplanetary magnetic field (IMF) and solar wind flow vectors can be treated exactly in a magnetohydrodynamic (MHD) approach. In this work we examine a case of nearly-opposed (to within 15°) interplanetary field and flow vectors, which occurred on October 24-25, 2001 during passage of the last interplanetary coronal mass ejection in an ejecta merger. Interplanetary data are from the ACE spacecraft. Simultaneously Wind was crossing the near-Earth (X ˜ -13 Re) geomagnetic tail and subsequently made an approximately 5-hour-long magnetosheath crossing close to the ecliptic plane (Z = -0.7 Re). Geomagnetic activity was returning steadily to quiet, “ground” conditions. We first compare the predictions of the Spreiter and Rizzi theory with the Wind magnetosheath observations and find fair agreement, in particular as regards the proportionality of the magnetic field strength and the product of the plasma density and bulk speed. We then carry out a small-perturbation analysis of the Spreiter and Rizzi solution to account for the small IMF components perpendicular to the flow vector. The resulting expression is compared to the time series of the observations and satisfactory agreement is obtained. We also present and discuss observations in the dawnside boundary layer of pulsed, high-speed (v ˜ 600 km/s) flows exceeding the solar wind flow speeds. We examine various generating mechanisms and suggest that the most likely cause is a wave of frequency 3.2 mHz excited at the inner edge of the boundary layer by the Kelvin-Helmholtz instability.

Estimation of Venus wind velocities from high-resolution infrared spectra. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Smith, M. A. H.

1978-01-01

Zonal velocity profiles in the Venus atmosphere above the clouds were estimated from measured asymmetries of HCl and HF infrared absorption lines in high-resolution Fourier interferometer spectra of the planet. These asymmetries are caused by both pressure-induced shifts in the positions of the hydrogen-halide lines perturbed by CO2 and Doppler shifts due to atmospheric motions. Particularly in the case of the HCl 2-0 band, the effects of the two types of line shifts can be easily isolated, making it possible to estimate a profile of average Venus equatorial zonal velocity as a function of pressure in the region roughly 60 to 70 km above the surface of the planet. The mean profiles obtained show strong vertical shear in the Venus zonal winds near the cloud-top level, and both the magnitude and direction of winds at all levels in this region appear to vary greatly with longitude relative to the sub-solar point.

Zonal Rate Model for Axial and Radial Flow Membrane Chromatography. Part I: Knowledge Transfer Across Operating Conditions and Scales

PubMed Central

Ghosh, Pranay; Vahedipour, Kaveh; Lin, Min; Vogel, Jens H; Haynes, Charles A; von Lieres, Eric

2013-01-01

The zonal rate model (ZRM) has previously been applied for analyzing the performance of axial flow membrane chromatography capsules by independently determining the impacts of flow and binding related non-idealities on measured breakthrough curves. In the present study, the ZRM is extended to radial flow configurations, which are commonly used at larger scales. The axial flow XT5 capsule and the radial flow XT140 capsule from Pall are rigorously analyzed under binding and non-binding conditions with bovine serum albumin (BSA) as test molecule. The binding data of this molecule is much better reproduced by the spreading model, which hypothesizes different binding orientations, than by the well-known Langmuir model. Moreover, a revised cleaning protocol with NaCl instead of NaOH and minimizing the storage time has been identified as most critical for quantitatively reproducing the measured breakthrough curves. The internal geometry of both capsules is visualized by magnetic resonance imaging (MRI). The flow in the external hold-up volumes of the XT140 capsule was found to be more homogeneous as in the previously studied XT5 capsule. An attempt for model-based scale-up was apparently impeded by irregular pleat structures in the used XT140 capsule, which might lead to local variations in the linear velocity through the membrane stack. However, the presented approach is universal and can be applied to different capsules. The ZRM is shown to potentially help save valuable material and time, as the experiments required for model calibration are much cheaper than the predicted large-scale experiment at binding conditions. Biotechnol. Bioeng. 2013; 110: 1129–1141. © 2012 Wiley Periodicals, Inc. PMID:23097218

Compliant flow designs for optimum lift control of wind turbine rotors

NASA Astrophysics Data System (ADS)

Williams, Theodore J. H.

An optimization approach was formulated to determine geometric designs that are most compliant to flow control devices. Single dielectric barrier discharge (SDBD) plasma actuators are used in the flow control design optimization as they are able to be incorporated into CFD simulations. An adjoint formulation was derived in order to have a numerically efficient way of calculating the shape derivatives on the surface of the geometric design. The design of a wind turbine blade retrofit for the JIMP 25kW wind turbine at Notre Dame is used to motivate analyses that utilize the optimization approach. The CFD simulations of the existing wind turbine blade were validated against wind tunnel testing. A one-parameter optimization was performed in order to design a trailing edge addition for the current wind turbine blade. The trailing edge addition was designed to meet a desired lift target while maximizing the lift-to-drag ratio. This analysis was performed at seven radial locations on the wind turbine blade. The new trailing edge retrofits were able to achieve the lift target for the outboard radial locations. The designed geometry has been fabricated and is currently being validated on a full-scale turbine and it is predicted to have an increase in annual energy production of 4.30%. The design of a trailing edge retrofit that includes the use of a SDBD plasma actuator was performed using a two-parameter optimization. The objective of this analysis was to meet the lift target and maximize the controllability of the design. The controllability is defined as the difference in lift between plasma on and plasma off cases. A trailing edge retrofit with the plasma actuator located on the pressure side was able to achieve the target passive lift increase while using plasma flow control to reduce the lift to below the original design. This design resulted in a highly compliant flow.

Computational techniques for solar wind flows past terrestrial planets: Theory and computer programs

NASA Technical Reports Server (NTRS)

Stahara, S. S.; Chaussee, D. S.; Trudinger, B. C.; Spreiter, J. R.

1977-01-01

The interaction of the solar wind with terrestrial planets can be predicted using a computer program based on a single fluid, steady, dissipationless, magnetohydrodynamic model to calculate the axisymmetric, supersonic, super-Alfvenic solar wind flow past both magnetic and nonmagnetic planets. The actual calculations are implemented by an assemblage of computer codes organized into one program. These include finite difference codes which determine the gas-dynamic solution, together with a variety of special purpose output codes for determining and automatically plotting both flow field and magnetic field results. Comparisons are made with previous results, and results are presented for a number of solar wind flows. The computational programs developed are documented and are presented in a general user's manual which is included.

Residual zonal flows in tokamaks and stellarators at arbitrary wavelengths

NASA Astrophysics Data System (ADS)

Monreal, Pedro; Calvo, Iván; Sánchez, Edilberto; Parra, Félix I.; Bustos, Andrés; Könies, Axel; Kleiber, Ralf; Görler, Tobias

2016-04-01

In the linear collisionless limit, a zonal potential perturbation in a toroidal plasma relaxes, in general, to a non-zero residual value. Expressions for the residual value in tokamak and stellarator geometries, and for arbitrary wavelengths, are derived. These expressions involve averages over the lowest order particle trajectories, that typically cannot be evaluated analytically. In this work, an efficient numerical method for the evaluation of such expressions is reported. It is shown that this method is faster than direct gyrokinetic simulations performed with the Gene and EUTERPE codes. Calculations of the residual value in stellarators are provided for much shorter wavelengths than previously available in the literature. Electrons must be treated kinetically in stellarators because, unlike in tokamaks, kinetic electrons modify the residual value even at long wavelengths. This effect, that had already been predicted theoretically, is confirmed by gyrokinetic simulations.

The variety of MHD shock waves interactions in the solar wind flow

NASA Technical Reports Server (NTRS)

Grib, S. A.

1995-01-01

Different types of nonlinear shock wave interactions in some regions of the solar wind flow are considered. It is shown, that the solar flare or nonflare CME fast shock wave may disappear as the result of the collision with the rotational discontinuity. By the way the appearance of the slow shock waves as the consequence of the collision with other directional discontinuity namely tangential is indicated. Thus the nonlinear oblique and normal MHD shock waves interactions with different solar wind discontinuities (tangential, rotational, contact, shock and plasmoidal) both in the free flow and close to the gradient regions like the terrestrial magnetopause and the heliopause are described. The change of the plasma pressure across the solar wind fast shock waves is also evaluated. The sketch of the classification of the MHD discontinuities interactions, connected with the solar wind evolution is given.

A surface flow visualisation technique for use in cryogenic wind tunnels

NASA Technical Reports Server (NTRS)

Kell, D. M.

1978-01-01

A method of surface flow visualization for use in cryogenic wind tunnels is described which requires injection of a cryogenic liquid onto the model while the tunnel is running. This necessitates the use of a substance that remains liquid over a large range of cryogenic wind tunnel operating temperatures. It is found that propane (C3H8) is a suitable substance. Experiments are conducted in a subsonic cryogenic wind tunnel to assess the practical application of liquid propane flow visualization. The propane is stored in a chamber cooled by liquid nitrogen and when required is pumped through pipes to a gallery inside the model and then out onto the surface through small holes. To color the liquid a suspension of pigment particles is used. Propane is supplied to the cooled chamber in gaseous form from a standard liquefied gas cylinder. The sequence of events is illustrated on a propane temperature-entropy diagram. The use of liquefied propane for flow visualization in a cryogenic tunnel operating at pressures up to 40 atm appears to be feasible. Illustrative examples are provided.

Soil dust aerosols and wind as predictors of seasonal meningitis incidence in Niger.

PubMed

Pérez García-Pando, Carlos; Stanton, Michelle C; Diggle, Peter J; Trzaska, Sylwia; Miller, Ron L; Perlwitz, Jan P; Baldasano, José M; Cuevas, Emilio; Ceccato, Pietro; Yaka, Pascal; Thomson, Madeleine C

2014-07-01

Epidemics of meningococcal meningitis are concentrated in sub-Saharan Africa during the dry season, a period when the region is affected by the Harmattan, a dry and dusty northeasterly trade wind blowing from the Sahara into the Gulf of Guinea. We examined the potential of climate-based statistical forecasting models to predict seasonal incidence of meningitis in Niger at both the national and district levels. We used time series of meningitis incidence from 1986 through 2006 for 38 districts in Niger. We tested models based on data that would be readily available in an operational framework, such as climate and dust, population, and the incidence of early cases before the onset of the meningitis season in January-May. Incidence was used as a proxy for immunological state, susceptibility, and carriage in the population. We compared a range of negative binomial generalized linear models fitted to the meningitis data. At the national level, a model using early incidence in December and averaged November-December zonal wind provided the best fit (pseudo-R2 = 0.57), with zonal wind having the greatest impact. A model with surface dust concentration as a predictive variable performed indistinguishably well. At the district level, the best spatiotemporal model included zonal wind, dust concentration, early incidence in December, and population density (pseudo-R2 = 0.41). We showed that wind and dust information and incidence in the early dry season predict part of the year-to-year variability of the seasonal incidence of meningitis at both national and district levels in Niger. Models of this form could provide an early-season alert that wind, dust, and other conditions are potentially conducive to an epidemic.

Simulation of Turbulent Flow Inside and Above Wind Farms: Model Validation and Layout Effects

NASA Astrophysics Data System (ADS)

Wu, Yu-Ting; Porté-Agel, Fernando

2013-02-01

A recently-developed large-eddy simulation framework is validated and used to investigate turbulent flow within and above wind farms under neutral conditions. Two different layouts are considered, consisting of thirty wind turbines occupying the same total area and arranged in aligned and staggered configurations, respectively. The subgrid-scale (SGS) turbulent stress is parametrized using a tuning-free Lagrangian scale-dependent dynamic SGS model. The turbine-induced forces are modelled using two types of actuator-disk models: (a) the `standard' actuator-disk model (ADM-NR), which calculates only the thrust force based on one-dimensional momentum theory and distributes it uniformly over the rotor area; and (b) the actuator-disk model with rotation (ADM-R), which uses blade-element momentum theory to calculate the lift and drag forces (that produce both thrust and rotation), and distributes them over the rotor disk based on the local blade and flow characteristics. Validation is performed by comparing simulation results with turbulence measurements collected with hot-wire anemometry inside and above an aligned model wind farm placed in a boundary-layer wind tunnel. In general, the ADM-R model yields improved predictions compared with the ADM-NR in the wakes of all the wind turbines, where including turbine-induced flow rotation and accounting for the non-uniformity of the turbine-induced forces in the ADM-R appear to be important. Another advantage of the ADM-R model is that, unlike the ADM-NR, it does not require a priori specification of the thrust coefficient (which varies within a wind farm). Finally, comparison of simulations of flow through both aligned and staggered wind farms shows important effects of farm layout on the flow structure and wind-turbine performance. For the limited-size wind farms considered in this study, the lateral interaction between cumulated wakes is stronger in the staggered case, which results in a farm wake that is more homogeneous

Alternative experiments using the geophysical fluid flow cell

NASA Technical Reports Server (NTRS)

Hart, J. E.

1984-01-01

This study addresses the possibility of doing large scale dynamics experiments using the Geophysical Fluid Flow Cell. In particular, cases where the forcing generates a statically stable stratification almost everywhere in the spherical shell are evaluated. This situation is typical of the Earth's atmosphere and oceans. By calculating the strongest meridional circulation expected in the spacelab experiments, and testing its stability using quasi-geostrophic stability theory, it is shown that strongly nonlinear baroclinic waves on a zonally symmetric modified thermal wind will not occur. The Geophysical Fluid Flow Cell does not have a deep enough fluid layer to permit useful studies of large scale planetary wave processes arising from instability. It is argued, however, that by introducing suitable meridional barriers, a significant contribution to the understanding of the oceanic thermocline problem could be made.

The impacts of wind power integration on sub-daily variation in river flows downstream of hydroelectric dams.

PubMed

Kern, Jordan D; Patino-Echeverri, Dalia; Characklis, Gregory W

2014-08-19

Due to their operational flexibility, hydroelectric dams are ideal candidates to compensate for the intermittency and unpredictability of wind energy production. However, more coordinated use of wind and hydropower resources may exacerbate the impacts dams have on downstream environmental flows, that is, the timing and magnitude of water flows needed to sustain river ecosystems. In this paper, we examine the effects of increased (i.e., 5%, 15%, and 25%) wind market penetration on prices for electricity and reserves, and assess the potential for altered price dynamics to disrupt reservoir release schedules at a hydroelectric dam and cause more variable and unpredictable hourly flow patterns (measured in terms of the Richards-Baker Flashiness (RBF) index). Results show that the greatest potential for wind energy to impact downstream flows occurs at high (∼25%) wind market penetration, when the dam sells more reserves in order to exploit spikes in real-time electricity prices caused by negative wind forecast errors. Nonetheless, compared to the initial impacts of dam construction (and the dam's subsequent operation as a peaking resource under baseline conditions) the marginal effects of any increased wind market penetration on downstream flows are found to be relatively minor.

Diurnal, monthly and seasonal variation of mean winds in the MLT region observed over Kolhapur using MF radar

NASA Astrophysics Data System (ADS)

Sharma, A. K.; Gaikwad, H. P.; Ratnam, M. Venkat; Gurav, O. B.; Ramanjaneyulu, L.; Chavan, G. A.; Sathishkumar, S.

2018-04-01

Medium Frequency (MF) radar located at Kolhapur (16.8°N, 74.2°E) has been upgraded in August 2013. Since then continuous measurements of zonal and meridional winds are obtained covering larger altitudes from the Mesosphere and Lower Thermosphere (MLT) region. Diurnal, monthly and seasonal variation of these mean winds is presented in this study using four years (2013-2017) of observations. The percentage occurrence of radar echoes show maximum between 80 and 105 km. The mean meridional wind shows Annual Oscillation (AO) between 80 and 90 km altitudes with pole-ward motion during December solstice and equatorial motion during June solstice. Quasi-biennial oscillation (QBO) with weaker amplitudes are also observed between 90 and 104 km. Zonal winds show semi-annual oscillation (SAO) with westward winds during equinoxes and eastward winds during solstices between 80 and 90 km. AO with eastward winds during December solstice and westward wind in the June solstice is also observed in the mean zonal wind between 100 and 110 km. These results match well with that reported from other latitudes within Indian region between 80 and 90 km. However, above 90 km the results presented here provide true mean background winds for the first time over Indian low latitude region as the present station is away from equatorial electro-jet and are not contaminated by ionospheric processes. Further, the results presented earlier with an old version of this radar are found contaminated due to unknown reasons and are corrected in the present work. This upgraded MF radar together with other MLT radars in the Indian region forms unique network to investigate the vertical and lateral coupling.

Zonal wavefront reconstruction in quadrilateral geometry for phase measuring deflectometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Lei; Xue, Junpeng; Gao, Bo

2017-06-14

There are wide applications for zonal reconstruction methods in slope-based metrology due to its good capability of reconstructing the local details on surface profile. It was noticed in the literature that large reconstruction errors occur when using zonal reconstruction methods designed for rectangular geometry to process slopes in a quadrilateral geometry, which is a more general geometry with phase measuring deflectometry. In this paper, we present a new idea for the zonal methods for quadrilateral geometry. Instead of employing the intermediate slopes to set up height-slope equations, we consider the height increment as a more general connector to establish themore » height-slope relations for least-squares regression. The classical zonal methods and interpolation-assisted zonal methods are compared with our proposal. Results of both simulation and experiment demonstrate the effectiveness of the proposed idea. In implementation, the modification on the classical zonal methods is addressed. Finally, the new methods preserve many good aspects of the classical ones, such as the ability to handle a large incomplete slope dataset in an arbitrary aperture, and the low computational complexity comparable with the classical zonal method. Of course, the accuracy of the new methods is much higher when integrating the slopes in quadrilateral geometry.« less

Wind-US Flow Calculations for the M2129 S-Duct Using Structured and Unstructured Grids

NASA Technical Reports Server (NTRS)

Mohler, Stanley R., Jr.

2003-01-01

Computational Fluid Dynamics (CFD) flow solutions for the M2129 diffusing S-duct with and without vane effectors were computed by the Wind-US flow solver. Both structured and unstructured 3-D grids were used. Without vane effectors, the duct exhibited massive flow separation in both experiment and CFD. With vane effectors installed, the flow remained attached and aerodynamic losses were reduced. Total pressure recovery and distortion near the duct outlet were computed from the solutions and compared favorably to experimental values. These calculations are part of a validation effort for the Wind-US code. They also provide an example case to aid engineers in learning to use the Wind-US software.

Wind flow in an urban environment.

PubMed

Dutt, A J

1991-10-01

The wind environment at ground leven in built-up areas is influenced by the extremely complex interaction amongst incident wind, mean vertical velocity gradient, turbulence and the shapes, sizes and layouts of building. Random layout of buildings could generate zones of overspeed and vortices in the connecting passage way between buildings, terraces, opensided shelters, courtyards, which could potentially cause unpleasantness, hazard from resuspended particulates, and airborne rain penetration into the buildings. The paper presents the results of two case studies comprising field measurements made within the Kent Ridge Campus, National University of Singapore, using DANTEC 54N10 Multichannel Flow Analyser and Probes. Results are presented in terms of non-dimensional windspeed coefficients. It is concluded that there is significant increase in windspeed due to channel and venturi effects. This information provides useful guidelines for building plans and layouts to the architects and engineers.

Gap Flows through Idealized Topography. Part I: Forcing by Large-Scale Winds in the Nonrotating Limit.

NASA Astrophysics Data System (ADS)

Gabersek, Sasa.; Durran, Dale R.

2004-12-01

Gap winds produced by a uniform airstream flowing over an isolated flat-top ridge cut by a straight narrow gap are investigated by numerical simulation. On the scale of the entire barrier, the proportion of the oncoming flow that passes through the gap is relatively independent of the nondimensional mountain height , even over that range of for which there is the previously documented transition from a “flow over the ridge” regime to a “flow around” regime.The kinematics and dynamics of the gap flow itself were investigated by examining mass and momentum budgets for control volumes at the entrance, central, and exit regions of the gap. These analyses suggest three basic behaviors: the linear regime (small ) in which there is essentially no enhancement of the gap flow; the mountain wave regime ( 1.5) in which vertical mass and momentum fluxes play a crucial role in creating very strong winds near the exit of the gap; and the upstream-blocking regime ( 5) in which lateral convergence generates the strongest winds near the entrance of the gap.Trajectory analysis of the flow in the strongest events, the mountain wave events, confirms the importance of net subsidence in creating high wind speeds. Neglect of vertical motion in applications of Bernoulli's equation to gap flows is shown to lead to unreasonable wind speed predictions whenever the temperature at the gap exit exceeds that at the gap entrance. The distribution of the Bernoulli function on an isentropic surface shows a correspondence between regions of high Bernoulli function and high wind speeds in the gap-exit jet similar to that previously documented for shallow-water flow.

Influence of upstream solar wind on thermospheric flows at Jupiter

NASA Astrophysics Data System (ADS)

Yates, J. N.; Achilleos, N.; Guio, P.

2012-02-01

The coupling of Jupiter's magnetosphere and ionosphere plays a vital role in creating its auroral emissions. The strength of these emissions is dependent on the difference in speed of the rotational flows within Jupiter's high-latitude thermosphere and the planet's magnetodisc. Using an azimuthally symmetric global circulation model, we have simulated how upstream solar wind conditions affect the energy and direction of atmospheric flows. In order to simulate the effect of a varying dynamic pressure in the upstream solar wind, we calculated three magnetic field profiles representing compressed, averaged and expanded ‘middle’ magnetospheres. These profiles were then used to solve for the angular velocity of plasma in the magnetosphere. This angular velocity determines the strength of currents flowing between the ionosphere and magnetosphere. We examine the influence of variability in this current system upon the global winds and energy inputs within the Jovian thermosphere. We find that the power dissipated by Joule heating and ion drag increases by ∼190% and ∼185% from our compressed to expanded model respectively. We investigated the effect of exterior boundary conditions on our models and found that by reducing the radial current at the outer edge of the magnetodisc, we also limit the thermosphere's ability to transmit angular momentum to this region.

New insights on the interaction between atmospheric flow and a full-scale 2.5 MW wind turbine

NASA Astrophysics Data System (ADS)

Chamorro, L. P.; Lee, S.; Olsen, D.; Milliren, C.; Marr, J.; Arndt, R.; Sotiropoulos, F.

2012-12-01

Power fluctuations and fatigue loads are among the most significant problems that wind turbines face throughout their lifetime. Atmospheric turbulence is the common driving mechanism that triggers instabilities on these quantities. Reducing the effects of the fluctuating flow on wind turbines is quite challenging due to the wide variety of length scales present in the boundary layer flow. Each group of these scales, which range from the order of a millimeter to kilometer and larger, plays a characteristic and distinctive role on the performance and structural reliability of wind turbines. This study seeks to contribute toward the understanding on the complex scale-to-scale interaction between wind turbine and flow turbulence. Novel insights into the physical mechanisms that govern the flow/turbine interaction will be discussed. To tackle the problem, we investigate the unsteady behavior of a full-scale 2.5 MW wind turbine under nearly neutral thermal stratification. The study is performed in the Eolos Wind Energy Research Field Station of the University of Minnesota. An instrumented 130 meter meteorological tower located upstream of a Clipper Liberty C96 wind turbine is used to characterize the turbulent flow and atmospheric conditions right upstream of the wind turbine. High resolution and synchronous measurements of the approach wind velocity at several heights, turbine power and strain at the tower foundation are used to determine the scale-to-scale interaction between flow and the wind turbine performance and its physical structure. The spectral distribution of the fluctuating turbine power and instantaneous stresses will be discussed in detail. Characteristic length scales playing a key role on the dynamics of the wind turbine as well as the distinctive effects of flow coherent motions and strong intermittent gusts will also be addressed. Funding was provided by the U.S. Department of Energy (DE-EE0002980) and Xcel Energy through the Renewable Development Fund

Numerical Investigation of the Turbulent Wind Flow Through Elevated Windbreak

NASA Astrophysics Data System (ADS)

Agarwal, Ashish; Irtaza, Hassan

2018-06-01

Analysis of airflow through elevated windbreaks is presented in this paper. Permeable nets and impermeable film increases considerable wind forces on the windbreaks which is susceptible to damage during high wind. A comprehensive numerical investigation has been carried out to analyze the effects of wind on standalone elevated windbreak clad with various permeable nets and an impermeable film. The variation of airflow behavior around and through permeable nets and airflow behavior around impermeable film were also been investigated. Computational fluid dynamics techniques using Reynolds Averaged Navier-Stokes equations has been used to predict the wind force coefficient and thus wind forces on panels supporting permeable nets and impermeable film for turbulent wind flow. Elevated windbreak panels were analyzed for seven different permeable nets having various solidity ratio, specific permeability and aerodynamic resistant coefficients. The permeable nets were modelled as porous jump media obeying Forchheimer's law and an impermeable film modelled as rigid wall.

Numerical Investigation of the Turbulent Wind Flow Through Elevated Windbreak

NASA Astrophysics Data System (ADS)

Agarwal, Ashish; Irtaza, Hassan

2018-04-01

Analysis of airflow through elevated windbreaks is presented in this paper. Permeable nets and impermeable film increases considerable wind forces on the windbreaks which is susceptible to damage during high wind. A comprehensive numerical investigation has been carried out to analyze the effects of wind on standalone elevated windbreak clad with various permeable nets and an impermeable film. The variation of airflow behavior around and through permeable nets and airflow behavior around impermeable film were also been investigated. Computational fluid dynamics techniques using Reynolds Averaged Navier-Stokes equations has been used to predict the wind force coefficient and thus wind forces on panels supporting permeable nets and impermeable film for turbulent wind flow. Elevated windbreak panels were analyzed for seven different permeable nets having various solidity ratio, specific permeability and aerodynamic resistant coefficients. The permeable nets were modelled as porous jump media obeying Forchheimer's law and an impermeable film modelled as rigid wall.

Wind flow through shrouded wind turbines

DTIC Science & Technology

2017-03-01

were so patient with me during this process, sometimes spending hours in the wind tunnel room with me while I performed what seemed like endless runs ...disorderly wind velocities that result from the rotating turbine blades . In 2011, a study conducted by the White House Office of Science and...targets, and scattering target returns” [4]. Furthermore, the shadowing effects from spinning wind turbine blades can adversely impact air-traffic

Differences and Similarities in MaCWAVE Summer and Winter Temperatures and Winds

NASA Technical Reports Server (NTRS)

Schmidlin, F. J.; Goldberg, R. A.

2008-01-01

Small meteorological rockets released inflatable falling spheres during the MaCWAVE Campaign. The Mountain and Convective Waves Ascending Vertically Experiment (MaCWAVE) was carried out in two parts, a summer sequence from Andoya Rocket Range (69N) during July 2002 to examine convective initiation of gravity waves and a winter sequence from ESRANGE (68N) during January 2003 to examine mountain-terrain initiated gravity waves. The sphere-tracked data provided significant information about the variation of temperature and wind from 70 km and above. The changes observed may be considered akin to tidal motion; unfortunately the launch activity was restricted to 12-hour periods, thus the observation of a full diurnal cycle was not possible. During summer, temperature variation was smaller than that observed during winter when peak to null differences reached 15-20 K at 80-85 km. Variation in the zonal winds varied up to 100+mps in summer and winter. Examination of the times of peak wind vs altitude showed that the peak zonal wind occurred approximately two hours ahead of the peak meridional wind. We provide details about the measurements and observed variations.

Development of Three-Dimensional Flow Code Package to Predict Performance and Stability of Aircraft with Leading Edge Ice Contamination

NASA Technical Reports Server (NTRS)

Strash, D. J.; Summa, J. M.

1996-01-01

In the work reported herein, a simplified, uncoupled, zonal procedure is utilized to assess the capability of numerically simulating icing effects on a Boeing 727-200 aircraft. The computational approach combines potential flow plus boundary layer simulations by VSAERO for the un-iced aircraft forces and moments with Navier-Stokes simulations by NPARC for the incremental forces and moments due to iced components. These are compared with wind tunnel force and moment data, supplied by the Boeing Company, examining longitudinal flight characteristics. Grid refinement improved the local flow features over previously reported work with no appreciable difference in the incremental ice effect. The computed lift curve slope with and without empennage ice matches the experimental value to within 1%, and the zero lift angle agrees to within 0.2 of a degree. The computed slope of the un-iced and iced aircraft longitudinal stability curve is within about 2% of the test data. This work demonstrates the feasibility of a zonal method for the icing analysis of complete aircraft or isolated components within the linear angle of attack range. In fact, this zonal technique has allowed for the viscous analysis of a complete aircraft with ice which is currently not otherwise considered tractable.

The performance & flow visualization studies of three-dimensional (3-D) wind turbine blade models

NASA Astrophysics Data System (ADS)

Sutrisno, Prajitno, Purnomo, W., Setyawan B.

2016-06-01

Recently, studies on the design of 3-D wind turbine blades have a less attention even though 3-D blade products are widely sold. In contrary, advanced studies in 3-D helicopter blade tip have been studied rigorously. Studies in wind turbine blade modeling are mostly assumed that blade spanwise sections behave as independent two-dimensional airfoils, implying that there is no exchange of momentum in the spanwise direction. Moreover, flow visualization experiments are infrequently conducted. Therefore, a modeling study of wind turbine blade with visualization experiment is needed to be improved to obtain a better understanding. The purpose of this study is to investigate the performance of 3-D wind turbine blade models with backward-forward swept and verify the flow patterns using flow visualization. In this research, the blade models are constructed based on the twist and chord distributions following Schmitz's formula. Forward and backward swept are added to the rotating blades. Based on this, the additional swept would enhance or diminish outward flow disturbance or stall development propagation on the spanwise blade surfaces to give better blade design. Some combinations, i. e., b lades with backward swept, provide a better 3-D favorable rotational force of the rotor system. The performance of the 3-D wind turbine system model is measured by a torque meter, employing Prony's braking system. Furthermore, the 3-D flow patterns around the rotating blade models are investigated by applying "tuft-visualization technique", to study the appearance of laminar, separated, and boundary layer flow patterns surrounding the 3-dimentional blade system.

Flow visualization around a rotating body in a wind tunnel

NASA Astrophysics Data System (ADS)

Hiraki, K.; Zaitsu, D.; Yanaga, Y.; Kleine, H.

2017-02-01

The rotational behavior of capsule-shaped models is investigated in the transonic wind tunnel of JAXA. A special support is developed to allow the model to rotate around the pitch, yaw and roll axes. This 3-DOF free rotational mounting apparatus achieves the least frictional torque from the support and the instruments. Two types of capsule models are prepared, one is drag type (SPH model) and the other is lift type (HTV-R model). The developed mounting apparatus is used in the wind tunnel tests with these capsule models. In a flow of Mach 0.9, the SPH model exhibits oscillations in pitch and yaw, and it rolls half a turn during the test. Similarly, the HTV-R model exhibits pitch and yaw oscillations in a flow of Mach 0.5. Moreover, it rolls multiple times during the test. In order to investigate the flow field around the capsule, the combined technique of color schlieren and surface tufts is applied. This visualization clearly shows the flow reattachment on the back surface of a capsule, which is suspected to induce the rapid rolling motion.

Distinct wind convergence patterns in the Mexico City basin due to the interaction of the gap winds with the synoptic flow

NASA Astrophysics Data System (ADS)

de Foy, B.; Clappier, A.; Molina, L. T.; Molina, M. J.

2006-04-01

Mexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A gap wind entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the gap wind. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The gap wind is found to occur on most days of the campaign and is the result of a temperature gradient across the southern basin rim which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the flow and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to both stronger gap flows due to channelling and winds over the southern and western basin rim. This results in a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere.

Calibration of the Flow in the Test Section of the Research Wind Tunnel at DST Group

DTIC Science & Technology

2015-10-01

calibration of the flow in the test section of the Research Wind Tunnel at DST Group. The calibration was performed to establish the flow quality and to...of the Flow in the Test Section of the Research Wind Tunnel at DST Group Executive Summary The Defence Science and Technology Group (DST

Production of oscillatory flow in wind tunnels

NASA Astrophysics Data System (ADS)

Al-Asmi, K.; Castro, I. P.

1993-06-01

A method for producing oscillatory flow in open-circuit wind tunnels driven by centrifugal fans is described. Performance characteristics of a new device installed on two such tunnels of greatly differing size are presented. It is shown that sinusoidal variations of the working section flow, having peak-to-peak amplitudes up to at least 30 percent of the mean flow speed and frequencies up to, typically, that corresponding to the acoustic quarter-wave-length frequency determined by the tunnel size, can be obtained with negligible harmonic distortion or acoustic noise difficulties. A brief review of the various methods that have been used previously is included, and the advantages and disadvantages of these different techniques are highlighted. The present technique seems to represent a significant improvement over many of them.

Monthly mean global climatology of temperature, wind, geopotential height, and pressure for 0 - 120 km

NASA Technical Reports Server (NTRS)

Fleming, Eric L.; Chandra, Sushil; Schoeberl, Mark R.; Barnett, John J.

1988-01-01

A monthly mean climatology is presented of temperature, wind, and geopotential height with nearly pole-to-pole coverage (80 S to 80 N) for 0 to 210 km, which can be used as a function of altitude and pressure. The purpose is to provide a reference for various atmospheric research and analysis activities. Data sources and methods of computation are described; in general, hydrostatic and thermal wind balance are maintained at all levels and latitudes. As observed in a series of cross-sectional plots, this climatology accurately reproduces most of the characteristic features of the atmosphere such as equatorial wind and the general structure of the tropopause, stratopause, and mesopause. A series of zonal wind profiles is also represented comparing this climatological wind with monthly mean climatological direct wind measurements in the upper mesosphere and lower thermosphere. The temperature and zonal wind climatology at stratospheric levels is compared with corresponding data from the National Meteorological Center, and general agreement is observed between the two data sets. Tables of the climatological values as a function of latitude and height for each month are contained in Appendix B, and are also available in floppy disk.

Theoretical and experimental study of flow-control devices for inlets of indraft wind tunnels

NASA Technical Reports Server (NTRS)

Ross, James C.

1989-01-01

The design of closed circuit wind tunnels has historically been performed using rule of thumb which have evolved over the years into a body of useful guidelines. The development of indraft wind tunnels, however, has not been as well documented. The design of indraft wind tunnels is therefore generally performed using a more intuitive approach, often resulting in a facility with disappointing flow quality. The primary problem is a lack of understanding of the flow in the inlet as it passes through the required antiturbulence treatment. For wind tunnels which employ large contraction ratio inlets, this lack of understanding is not serious since the relatively low velocity of the flow through the inlet treatment reduces the sensitivity to improper inlet design. When designing a small contraction ratio inlet, much more careful design is needed in order to reduce the flow distortions generated by the inlet treatment. As part of the National Full Scale Aerodynamics Complex Modification Project, 2-D computational methods were developed which account for the effect of both inlet screens and guide vanes on the test section velocity distribution. Comparisons with experimental data are presented which indicate that the methods accurately compute the flow distortions generated by a screen in a nonuniform velocity field. The use of inlet guide vanes to eliminate the screen induced distortion is also demonstrated both computationally and experimentally. Extensions of the results to 3-D is demonstrated and a successful wind tunnel design is presented.

Simulation of an Ice Giant-style Dynamo

NASA Astrophysics Data System (ADS)

Soderlund, K. M.; Aurnou, J. M.

2010-12-01

The Ice Giants, Uranus and Neptune, are unique in the solar system. These planets are the only known bodies to have multipolar magnetic fields where the quadrupole and octopole components have strengths comparable to or greater than that of the dipole. Cloud layer observations show that the planets also have zonal (east-west) flows that are fundamentally different from the banded winds of Jupiter and Saturn. The surface winds are characterized by strong retrograde equatorial jets that are flanked on either side by prograde jets at high latitudes. Thermal emission measurements of Neptune show that the surface energy flux pattern peaks in the equatorial and polar regions with minima at mid-latitudes. (The measurements for Uranus cannot adequately resolve the emission pattern.) The winds and magnetic fields are thought to be the result of convection in the planetary interior, which will also affect the heat flux pattern. Typically, it is implicitly assumed that the zonal winds are generated in a shallow layer, separate from the dynamo generation region. However, if the magnetic fields are driven near the surface, a single region can simultaneously generate both the zonal flows and the magnetic fields. Here, we present a novel numerical model of an Ice Giant-style dynamo to investigate this possibility. An order unity convective Rossby number (ratio of buoyancy to Coriolis forces) has been chosen because retrograde equatorial jets tend to occur in spherical shells when the effects of rotation are relatively weak. Our modeling results qualitatively reproduce all of the structural features of the global dynamical observations. Thus, a self-consistent model can generate magnetic field, zonal flow, and thermal emission patterns that agree with those of Uranus and Neptune. This model, then, leads us to hypothesize that the Ice Giants' zonal flows and magnetic fields are generated via dynamically coupled deep convection processes.

Venus winds from ultraviolet, visible and near infrared images from the VIRTIS instrument on Venus Express

NASA Astrophysics Data System (ADS)

Hueso, Ricardo; Garate-Lopez, I.; Peralta, J.; Bandos, T.; Sánchez-Lavega, A.

2013-10-01

After more than 6 years orbiting Venus the Venus Express mission has provided the largest database of observations of Venus atmosphere at different cloud layers with the combination of VMC and VIRTIS instruments. We present measurements of cloud motions in the South hemisphere of Venus analyzing images from the VIRTIS-M visible channel at different wavelengths sensitive to the upper cloud haze at 65-70 km height (dayside ultraviolet images) and the middle cloud deck (dayside visible and near infrared images around 1 μm) about 5-8 km deeper in the atmosphere. We combine VIRTIS images in nearby wavelengths to increase the contrast of atmospheric details and measurements were obtained with a semi-automatic cloud correlation algorithm. Both cloud layers are studied simultaneously to infer similarities and differences in these vertical levels in terms of cloud morphologies and winds. For both levels we present global mean zonal and meridional winds, latitudinal distribution of winds with local time and the wind shear between both altitudes. The upper branch of the Hadley cell circulation is well resolved in UV images with an acceleration of the meridional circulation at mid-latitudes with increasing local time peaking at 14-16h. This organized meridional circulation is almost absent in NIR images. Long-term variability of zonal winds is also found in UV images with increasing winds over time during the VEX mission. This is in agreement with current analysis of VMC images (Kathuntsev et al. 2013). The possible long-term acceleration of zonal winds is also examined for NIR images. References Khatuntsev et al. Icarus 226, 140-158 (2013)

The Wind-Scoured Lava Flows of Pavonis Mons

NASA Image and Video Library

2016-09-21

Click on the image for larger version This image shows a circular impact crater and an oval volcanic caldera on the southern flank of a large volcano on Mars called Pavonis Mons. The caldera is also the source of numerous finger-like lava flows and at least one sinuous lava channel. Both the caldera and the crater are degraded by aeolian (wind) erosion. The strong prevailing winds have apparently carved deep grooves into the terrain. When looking at the scene for the first time, the image seems motion blurred. However, upon a closer look, the smaller, young craters are pristine, so the image must be sharp and the "blurriness" is due to the processes acting on the terrain. This suggests that the deflation-produced grooves, along with the crater and the caldera, are old features and deflation is not very active today. Alternatively, perhaps these craters are simply too young to show signs of degradation. This deeply wind-scoured terrain type is unique to Mars. Wind-carved stream-lined landforms on Earth are called "yardangs," but they don't form extensive terrains like this one. The basaltic lavas on the flanks of this volcano have been exposed to wind for such a long time that there are no parallels on Earth. Terrestrial landscapes and terrestrial wind patterns change much more rapidly than on Mars. http://photojournal.jpl.nasa.gov/catalog/PIA21064

Differences and Similarities between Summer and Winter Temperatures and Winds during MaCWAVE

NASA Technical Reports Server (NTRS)

Schmidlin, F. J.; Goldberg, R. A.

2008-01-01

The Mountain and Convective Waves Ascending Vertically Experiment (MaCWAVE) was carried out in two sequences: one during the summer from the Andoya Rocket Range (69N) during July 2002 to examine convective initiation of gravity waves. The second was a winter sequence from ESRANGE (68N) during January 2003 to examine mountain-initiated waves. Inflatable falling spheres released from small meteorological rockets provided significant information about the variation of temperature and wind from 50 km and higher. The small rocket launch activity was restricted to 12-hour periods that inhibited observing a full diurnal cycle, nonetheless, the time-history of the measurements have provided information about tidal motion. During summer, temperature variation was smaller than observed during winter when peak differences reached 15-20 K at 80-85 km. variation in zonal winds varied up to more than 100 mps in summer and winter. Times of wind vs. altitude showed that the peak zonal component occurred approximately two hours ahead of the peak meridional wind. Measurement details and the observed variations are discussed.

Near-Surface Wind Predictions in Complex Terrain with a CFD Approach Optimized for Atmospheric Boundary Layer Flows

NASA Astrophysics Data System (ADS)

Wagenbrenner, N. S.; Forthofer, J.; Butler, B.; Shannon, K.

2014-12-01

Near-surface wind predictions are important for a number of applications, including transport and dispersion, wind energy forecasting, and wildfire behavior. Researchers and forecasters would benefit from a wind model that could be readily applied to complex terrain for use in these various disciplines. Unfortunately, near-surface winds in complex terrain are not handled well by traditional modeling approaches. Numerical weather prediction models employ coarse horizontal resolutions which do not adequately resolve sub-grid terrain features important to the surface flow. Computational fluid dynamics (CFD) models are increasingly being applied to simulate atmospheric boundary layer (ABL) flows, especially in wind energy applications; however, the standard functionality provided in commercial CFD models is not suitable for ABL flows. Appropriate CFD modeling in the ABL requires modification of empirically-derived wall function parameters and boundary conditions to avoid erroneous streamwise gradients due to inconsistences between inlet profiles and specified boundary conditions. This work presents a new version of a near-surface wind model for complex terrain called WindNinja. The new version of WindNinja offers two options for flow simulations: 1) the native, fast-running mass-consistent method available in previous model versions and 2) a CFD approach based on the OpenFOAM modeling framework and optimized for ABL flows. The model is described and evaluations of predictions with surface wind data collected from two recent field campaigns in complex terrain are presented. A comparison of predictions from the native mass-consistent method and the new CFD method is also provided.

Sensitivity of southern hemisphere westerly wind to boundary conditions for the last glacial maximum

NASA Astrophysics Data System (ADS)

Jun, S. Y.; Kim, S. J.; Kim, B. M.

2017-12-01

To examine the change in SH westerly wind in the LGM, we performed LGM simulation with sensitivity experiments by specifying the LGM sea ice in the Southern Ocean (SO), ice sheet over Antarctica, and tropical pacific sea surface temperature to CAM5 atmosphere general circulation model (GCM). The SH westerly response to LGM boundary conditions in the CAM5 was compared with those from CMIP5 LGM simulations. In the CAM5 LGM simulation, the SH westerly wind substantially increases between 40°S and 65°S, while the zonal-mean zonal wind decreases at latitudes higher than 65°S. The position of the SH maximum westerly wind moves poleward by about 8° in the LGM simulation. Sensitivity experiments suggest that the increase in SH westerly winds is mainly due to the increase in sea ice in the SO that accounts for 60% of total wind change. In the CMIP5-PMIP3 LGM experiments, most of the models show the slight increase and poleward shift of the SH westerly wind as in the CAM5 experiment. The increased and poleward shifted westerly wind in the LGM obtained in the current model result is consistent with previous model results and some lines of proxy evidence, though opposite model responses and proxy evidence exist for the SH westerly wind change.

Cross-shore variation of wind-driven flows on the inner shelf in Long Bay, South Carolina, United States

NASA Astrophysics Data System (ADS)

Gutierrez, Benjamin T.; Voulgaris, George; Work, Paul A.

2006-03-01

The cross-shore structure of subtidal flows on the inner shelf (7 to 12 m water depth) of Long Bay, South Carolina, a concave-shaped bay, is examined through the analysis of nearly 80 days of near-bed (1.7-2.2 m above bottom) current observations acquired during the spring and fall of 2001. In the spring and under northeastward winds (upwelling favorable) a two-layered flow was observed at depths greater than 10 m, while closer to the shore the currents were aligned with the wind. The two-layered flow is attributed to the presence of stratification, which has been observed under similar conditions in the South Atlantic Bight. When the wind stress was southwestward (downwelling favorable) and exceeded 0.1 N/m2, vertical mixing occurred, the two-layered flow pattern disappeared, and currents were directed alongshore with the wind at all sites and throughout the water column. In the fall, near-bed flows close to the shore (water depth <7 m) were often reduced compared to or opposed those measured farther offshore under southwestward winds. A simplified analysis of the depth-averaged, alongshore momentum balance illustrates that the alongshore pressure gradient approached or exceeded the magnitude of the alongshore wind stress at the same time that the nearshore alongshore current opposed the wind stress and alongshore currents farther offshore. In addition, the analysis suggests that the wind stress is reduced closer to shore so that the alongshore pressure gradient is large enough to drive the flow against the wind.

Evaluation of flow quality in two large NASA wind tunnels at transonic speeds

NASA Technical Reports Server (NTRS)

Harvey, W. D.; Stainback, P. C.; Owen, F. K.

1980-01-01

Wind tunnel testing of low drag airfoils and basic transition studies at transonic speeds are designed to provide high quality aerodynamic data at high Reynolds numbers. This requires that the flow quality in facilities used for such research be excellent. To obtain a better understanding of the characteristics of facility disturbances and identification of their sources for possible facility modification, detailed flow quality measurements were made in two prospective NASA wind tunnels. Experimental results are presented of an extensive and systematic flow quality study of the settling chamber, test section, and diffuser in the Langley 8 foot transonic pressure tunnel and the Ames 12 foot pressure wind tunnel. Results indicate that the free stream velocity and pressure fluctuation levels in both facilities are low at subsonic speeds and are so high as to make it difficult to conduct meaningful boundary layer control and transition studies at transonic speeds.

Incompressible viscous flow simulations of the NFAC wind tunnel

NASA Technical Reports Server (NTRS)

Champney, Joelle Milene

1986-01-01

The capabilities of an existing 3-D incompressible Navier-Stokes flow solver, INS3D, are extended and improved to solve turbulent flows through the incorporation of zero- and two-equation turbulence models. The two-equation model equations are solved in their high Reynolds number form and utilize wall functions in the treatment of solid wall boundary conditions. The implicit approximate factorization scheme is modified to improve the stability of the two-equation solver. Applications to the 3-D viscous flow inside the 80 by 120 feet open return wind tunnel of the National Full Scale Aerodynamics Complex (NFAC) are discussed and described.

A Zonal Approach for Prediction of Jet Noise

NASA Technical Reports Server (NTRS)

Shih, S. H.; Hixon, D. R.; Mankbadi, Reda R.

1995-01-01

A zonal approach for direct computation of sound generation and propagation from a supersonic jet is investigated. The present work splits the computational domain into a nonlinear, acoustic-source regime and a linear acoustic wave propagation regime. In the nonlinear regime, the unsteady flow is governed by the large-scale equations, which are the filtered compressible Navier-Stokes equations. In the linear acoustic regime, the sound wave propagation is described by the linearized Euler equations. Computational results are presented for a supersonic jet at M = 2. 1. It is demonstrated that no spurious modes are generated in the matching region and the computational expense is reduced substantially as opposed to fully large-scale simulation.

Dynamically Intuitive and Potentially Predicatable Three-Dimensional Structures in the Low Frequency Flow Variability of the Extratropical Northern Hemisphere

NASA Astrophysics Data System (ADS)

Wettstein, J. J.; Li, C.; Bradshaw, S.

2016-12-01

Canonical tropospheric climate variability patterns and their corresponding indices are ubiquitous, yet a firm dynamical interpretation has remained elusive for many of even the leading extratropical patterns. Part of the lingering difficulty in understanding and predicting atmospheric low frequency variability is the fact that the identification itself of the different patterns is indistinct. This study characterizes three-dimensional structures in the low frequency variability of the extratropical zonal wind field within the entire period of record of the ERA-Interim reanalysis and suggests the foundations for a new paradigm in identifying and predicting extratropical atmospheric low-frequency variability. In concert with previous results, there is a surprisingly rich three-dimensional structure to the variance of the zonal wind field that is not (cannot be) captured by traditional identification protocols that explore covariance of pressure in the lower troposphere, flow variability in the zonal mean or, for that matter, in any variable on any planar surface. Correspondingly, many of the pressure-based canonical indices of low frequency atmospheric variability exhibit inconsistent relationships to physically intuitive reorganizations of the subtropical and polar front jets and with other forcing mechanisms. Different patterns exhibit these inconsistencies to a greater or lesser extent. The three-dimensional variance of the zonal wind field is, by contrast, naturally organized around dynamically intuitive atmospheric redistributions that have a surprisingly large amount of physically intuitive information in the vertical. These conclusions are robust in a variety of seasons and also in intra-seasonal and inter-annual explorations. Similar results and conclusions are also derived using detrended data, other reanalyses, and state-of-the-art coupled climate model output. In addition to providing a clearer perspective on the distinct three-dimensional patterns of

Simulating flow around scaled model of a hypersonic vehicle in wind tunnel

NASA Astrophysics Data System (ADS)

Markova, T. V.; Aksenov, A. A.; Zhluktov, S. V.; Savitsky, D. V.; Gavrilov, A. D.; Son, E. E.; Prokhorov, A. N.

2016-11-01

A prospective hypersonic HEXAFLY aircraft is considered in the given paper. In order to obtain the aerodynamic characteristics of a new construction design of the aircraft, experiments with a scaled model have been carried out in a wind tunnel under different conditions. The runs have been performed at different angles of attack with and without hydrogen combustion in the scaled propulsion engine. However, the measured physical quantities do not provide all the information about the flowfield. Numerical simulation can complete the experimental data as well as to reduce the number of wind tunnel experiments. Besides that, reliable CFD software can be used for calculations of the aerodynamic characteristics for any possible design of the full-scale aircraft under different operation conditions. The reliability of the numerical predictions must be confirmed in verification study of the software. The given work is aimed at numerical investigation of the flowfield around and inside the scaled model of the HEXAFLY-CIAM module under wind tunnel conditions. A cold run (without combustion) was selected for this study. The calculations are performed in the FlowVision CFD software. The flow characteristics are compared against the available experimental data. The carried out verification study confirms the capability of the FlowVision CFD software to calculate the flows discussed.

Low-latitude zonal and vertical ion drifts seen by DE 2

NASA Technical Reports Server (NTRS)

Coley, W. R.; Heelis, R. A.

1989-01-01

Horizontal and vertical ion drift data from the DE 2 spacecraft have been used to determine average zonal and vertical plasma flow (electric field) characteristics in the +/- 26-deg dip latitude region during a time of high solar activity. The 'average data' local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time ((SLT) with a maximum westward velocity of 80 m/s in the early afternoon. There is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m/s. A secondary nighttime maximum exists at 0430 SLT preceeding the reversal to westward flow. This profile is in good agreement with Jicamarca, Peru, radar measurements made under similar solar maximum conditions. Haramonic analysis indicates a net superrotation which is strongest at lower apex altitudes. The diurnal term is dominant, but higher order terms through the quatradiurnal are significant.

Spatial structure of kinetic energy spectra in LES simulations of flow in an offshore wind farm

NASA Astrophysics Data System (ADS)

Fruh, Wolf-Gerrit; Creech, Angus

2017-04-01

The evolution of wind turbine and wind farm wakes was investigated numerically for the case of Lillgrund wind farm consisting of a tightly packed array of 48 turbines. The simulations for a number of wind directions at a free wind speed of just under the rated wind speed in a neutrally stable atmosphere were carried out using Large-Eddy Simulations with the adaptive Finite-Element CFD solver Fluidity. The results were interpolated from the irregularly spaced mesh nodes onto a regular grid with comparable spatial resolution at horizontal slices at various heights. To investigate the development of the wake as the flow evolves through the array, spectra of the kinetic energy in sections perpendicular to the wind directions within the wake and to the sides of the array were calculated. This paper will present the key features and spectral slopes of the flow as a function of downstream distance from the front turbine through and beyond the array. The main focus will be on the modification of the spectra as the flow crosses a row of turbines followed by its decay in the run-up to the next row, but we will also present to wake decay of the wind farm wake downstream of the array.

Wind-induced interannual variability of sea level slope, along-shelf flow, and surface salinity on the Northwest Atlantic shelf

NASA Astrophysics Data System (ADS)

Li, Yun; Ji, Rubao; Fratantoni, Paula S.; Chen, Changsheng; Hare, Jonathan A.; Davis, Cabell S.; Beardsley, Robert C.

2014-04-01

In this study, we examine the importance of regional wind forcing in modulating advective processes and hydrographic properties along the Northwest Atlantic shelf, with a focus on the Nova Scotian Shelf (NSS)-Gulf of Maine (GoM) region. Long-term observational data of alongshore wind stress, sea level slope, and along-shelf flow are analyzed to quantify the relationship between wind forcing and hydrodynamic responses on interannual time scales. Additionally, a simplified momentum balance model is used to examine the underlying mechanisms. Our results show significant correlation among the observed interannual variability of sea level slope, along-shelf flow, and alongshore wind stress in the NSS-GoM region. A mechanism is suggested to elucidate the role of wind in modulating the sea level slope and along-shelf flow: stronger southwesterly (northeastward) winds tend to weaken the prevailing southwestward flow over the shelf, building sea level in the upstream Newfoundland Shelf region, whereas weaker southwesterly winds allow stronger southwestward flow to develop, raising sea level in the GoM region. The wind-induced flow variability can influence the transport of low-salinity water from the Gulf of St. Lawrence to the GoM, explaining interannual variations in surface salinity distributions within the region. Hence, our results offer a viable mechanism, besides the freshening of remote upstream sources, to explain interannual patterns of freshening in the GoM.

Substorm-related thermospheric density and wind disturbances derived from CHAMP observations

NASA Astrophysics Data System (ADS)

Ritter, P.; Lühr, H.; Doornbos, E.

2010-06-01

The input of energy and momentum from the magnetosphere is most efficiently coupled into the high latitude ionosphere-thermosphere. The phenomenon we are focusing on here is the magnetospheric substorm. This paper presents substorm related observations of the thermosphere derived from the CHAMP satellite. With its sensitive accelerometer the satellite can measure the air density and zonal winds. Based on a large number of substorm events the average high and low latitude thermospheric response to substorm onsets was deduced. During magnetic substorms the thermospheric density is enhanced first at high latitudes. Then the disturbance travels at an average speed of 650 m/s to lower latitudes, and 3-4 h later the bulge reaches the equator on the night side. Under the influence of the Coriolis force the travelling atmospheric disturbance (TAD) is deflected westward. In accordance with present-day atmospheric models the disturbance zonal wind velocities during substorms are close to zero near the equator before midnight and attain moderate westward velocities after midnight. In general, the wind system is only weakly perturbed (Δvy<20 m/s) by substorms.

Observations of Martian surface winds at the Viking Lander 1 site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murphy, J.R.; Leovy, C.B.; Tillman, J.E.

1990-08-30

Partial failure of the wind instrumentation on the Viking Lander 1 (VL1) in the Martian subtropics (22.5{degree}N) has limited previous analyses of meteorological data for this site. The authors describe a method for reconstructing surface winds using data from the partially failed sensor and present and analyze a time series of wind, pressure, and temperature at the site covering 350 Mars days (sols). At the beginning of the mission during early summer, winds were controlled by regional topography, but they soon underwent a transition to a regime controlled by the Hadley circulation. Diurnal and semidiurnal wind oscillations and synoptic variationsmore » have been analyzed and compared with the corresponding variations at the Viking Lander 2 middle latitude site (48{degree}N). Diurnal wind oscillations were controlled primarily by regional topography and boundary layer forcing, although a global mode may have been influencing them during two brief episodes. Semidiurnal wind oscillations were controlled by the westward propagating semidiurnal tide from sol 210 onward. Comparison of the synoptic variations at the two sites suggests that the same eastward propagating wave trains were present at both sites, at least following the first 1977 great dust storm, but discordant inferred zonal wave numbers and phase speeds at the two sites cast doubt on the zonal wave numbers deduced from analyses of combined wind and pressure data, particularly at the VL1 site where the signal to noise ratio of the dominant synoptic waves is relatively small.« less

An experimental investigation of wind flow over tall towers in staggered form

NASA Astrophysics Data System (ADS)

Anwar, Proma; Islam, Md. Quamrul; Ali, Mohammad

2016-07-01

In this research work an experiment is conducted to see the effect of wind loading on square, pentagonal and Hexagonal shape cylinders in staggered form. The experiment is done in an open circuit wind tunnel at a Reynolds number of 4.23×104 based on the face width of the cylinder across the flow direction. The flow velocity has been kept uniform throughout the experiment at 14.3 m/s. The test has been conducted for single cylinders first and then in staggered form. Angle of attack is chosen at a definite interval. The static pressure at different locations of the cylinder is measured by inclined multi-manometer. From the surface static pressure readings pressure coefficients are calculated first, then drag and lift coefficients are calculated using numerical Integration Method. These results will surely help engineers to design buildings with such shapes more efficiently. All the results are expressed in non-dimensional form, so they can be applied for prototype buildings and determine the wind loading at any wind speed on structures of similar external shapes.

Large eddy simulation study of the kinetic energy entrainment by energetic turbulent flow structures in large wind farms

NASA Astrophysics Data System (ADS)

VerHulst, Claire; Meneveau, Charles

2014-02-01

In this study, we address the question of how kinetic energy is entrained into large wind turbine arrays and, in particular, how large-scale flow structures contribute to such entrainment. Previous research has shown this entrainment to be an important limiting factor in the performance of very large arrays where the flow becomes fully developed and there is a balance between the forcing of the atmospheric boundary layer and the resistance of the wind turbines. Given the high Reynolds numbers and domain sizes on the order of kilometers, we rely on wall-modeled large eddy simulation (LES) to simulate turbulent flow within the wind farm. Three-dimensional proper orthogonal decomposition (POD) analysis is then used to identify the most energetic flow structures present in the LES data. We quantify the contribution of each POD mode to the kinetic energy entrainment and its dependence on the layout of the wind turbine array. The primary large-scale structures are found to be streamwise, counter-rotating vortices located above the height of the wind turbines. While the flow is periodic, the geometry is not invariant to all horizontal translations due to the presence of the wind turbines and thus POD modes need not be Fourier modes. Differences of the obtained modes with Fourier modes are documented. Some of the modes are responsible for a large fraction of the kinetic energy flux to the wind turbine region. Surprisingly, more flow structures (POD modes) are needed to capture at least 40% of the turbulent kinetic energy, for which the POD analysis is optimal, than are needed to capture at least 40% of the kinetic energy flux to the turbines. For comparison, we consider the cases of aligned and staggered wind turbine arrays in a neutral atmospheric boundary layer as well as a reference case without wind turbines. While the general characteristics of the flow structures are robust, the net kinetic energy entrainment to the turbines depends on the presence and relative

Numerical Simulations of Laminar Air-Water Flow of a Non-linear Progressive Wave at Low Wind Speed

NASA Astrophysics Data System (ADS)

Wen, X.; Mobbs, S.

2014-03-01

A numerical simulation for two-dimensional laminar air-water flow of a non-linear progressive water wave with large steepness is performed when the background wind speed varies from zero to the wave phase speed. It is revealed that in the water the difference between the analytical solution of potential flow and numerical solution of viscous flow is very small, indicating that both solutions of the potential flow and viscous flow describe the water wave very accurately. In the air the solutions of potential and viscous flows are very different due to the effects of viscosity. The velocity distribution in the airflow is strongly influenced by the background wind speed and it is found that three wind speeds, , (the maximum orbital velocity of a water wave), and (the wave phase speed), are important in distinguishing different features of the flow patterns.

Transonic Navier-Stokes wing solution using a zonal approach. Part 1: Solution methodology and code validation

NASA Technical Reports Server (NTRS)

Flores, J.; Gundy, K.; Gundy, K.; Gundy, K.; Gundy, K.; Gundy, K.

1986-01-01

A fast diagonalized Beam-Warming algorithm is coupled with a zonal approach to solve the three-dimensional Euler/Navier-Stokes equations. The computer code, called Transonic Navier-Stokes (TNS), uses a total of four zones for wing configurations (or can be extended to complete aircraft configurations by adding zones). In the inner blocks near the wing surface, the thin-layer Navier-Stokes equations are solved, while in the outer two blocks the Euler equations are solved. The diagonal algorithm yields a speedup of as much as a factor of 40 over the original algorithm/zonal method code. The TNS code, in addition, has the capability to model wind tunnel walls. Transonic viscous solutions are obtained on a 150,000-point mesh for a NACA 0012 wing. A three-order-of-magnitude drop in the L2-norm of the residual requires approximately 500 iterations, which takes about 45 min of CPU time on a Cray-XMP processor. Simulations are also conducted for a different geometrical wing called WING C. All cases show good agreement with experimental data.

Zonal Acoustic Velocimetry in 30-cm, 60-cm, and 3-m Laboratory Models of the Outer Core

NASA Astrophysics Data System (ADS)

Rojas, R.; Doan, M. N.; Adams, M. M.; Mautino, A. R.; Stone, D.; Lekic, V.; Lathrop, D. P.

2016-12-01

A knowledge of zonal flows and shear is key in understanding magnetic field dynamics in the Earth and laboratory experiments with Earth-like geometries. Traditional techniques for measuring fluid flow using visualization and particle tracking are not well-suited to liquid metal flows. This has led us to develop a flow measurement technique based on acoustic mode velocimetry adapted from helioseismology. As a first step prior to measurements in the liquid sodium experiments, we implement this technique in our 60-cm diameter spherical Couette experiment in air. To account for a more realistic experimental geometry, including deviations from spherical symmetry, we compute predicted frequencies of acoustic normal modes using the finite element method. The higher accuracy of the predicted frequencies allows the identification of over a dozen acoustic modes, and mode identification is further aided by the use of multiple microphones and by analyzing spectra together with those obtained at a variety of nearby Rossby numbers. Differences between the predicted and observed mode frequencies are caused by differences in flow patterns present in the experiment. We compare acoustic mode frequency splittings with theoretical predictions for stationary fluid and solid body flow condition with excellent agreement. We also use this technique to estimate the zonal shear in those experiments across a range of Rossby numbers. Finally, we report on initial attempts to use this in liquid sodium in the 3-meter diameter experiment and parallel experiments performed in water in the 30-cm diameter experiment.

The transformation of vegetation vertical zonality affected by anthropogenic impact in East Fennoscandia (Russia)

NASA Astrophysics Data System (ADS)

Sidorik, Vadim; Miulgauzen, Daria

2017-04-01

birch crooked subshrub wood, which stretched to the north-east, proving the leading role of prevailing southwestern winds in pollution spreading in the area. As the anthropogenic impact decreases due to the Plant's emissions decline, there have been identified signs of ecosystem restoration. The beginning restoration helps parvifoliate forests to grow in barren lands, including the above-mentioned birch and aspen forest on Hangaslachdenvara upland. Reductive processes of soil formation are responsible for the development of soddy or raw humus horizons in the substrate overlaying the well-developed Podzols. Nevertheless, there is no restoration above 130 m on Hangaslachdenvara upland owing to the barrier effect, in other words, intensive deposition and accumulation of air pollutants on the upland's top. Thus, there has been defined that the anthropogenic impact led to total vegetation vertical zonality modification and physical disturbance of soil cover in East Fennoscandia. The typical taiga scheme of "coniferous forest - birch crooked wood - tundra subshrub and lichen communities" altitudinal belts was replaced by that of "parvifoliate forest - barren land" altitudinal belts. However, after the reduction of anthropogenic influence "zonal" plant communities begin to restore gradually and weak developed soils are forming.

Seasonal Variability of the 40-50 Day Oscillation in Wind and Rainfall in the Tropics.

NASA Astrophysics Data System (ADS)

Hartmann, Dennis L.; Gross, Jack R.

1988-10-01

Time spectral analysis is performed on long records of wind and precipitation from stations in the tropical Indian Ocean-Pacific Ocean are. The spectra are done separately for winter and summer half-years. Statistically significant spectral peaks in the 40-50 day period range show strong seasonal variability. The 40-50 day peaks in the 200 mb zonal wind spectra are stronger and more prevalent during the Northern Hemisphere winter half-year. Spectral peaks in the 850 mb wind show a preference for summer in the Northern Hemisphere.Precipitation spectra show significant 40-50 day peaks at selected locations in the Indonesian region and along the South Pacific convergence zone in the central Pacific during Southern Hemisphere summer. These oscillations in precipitation are coherent with nearby zonal wind oscillations. No significant oscillations in precipitation were found for stations significantly north of the equator during either half-year. In particular, no significant peaks in precipitation spectra were found for composites of stations on the Indian Peninsula during summer, where it has been proposed that the 40-50 day oscillation modulates monsoon precipitation.It is concluded that the 40-50 day oscillation is sustained by interactions between the large-scale flow and convective-scale processes and that these interactions take place in areas where intensely convective regions aye near the equator. The wind oscillation occupies a larger area, particularly at upper tropospheric levels, principally by horizontal wave propagation away from the excitation regions. Since the oscillation does not appear to be forced over India, it is conjectured that the seasonal variation in the intensity of the oscillation is attributable, in part, to the fact that the tropical convection is drawn away from the equator by the Indian summer monsoon. When the convection is drawn off the equator, the efficiency of the interaction with equatorially trapped modes declines, and hence the

On the vertical wind shear of Saturn's Equatorial Jet at cloud level

NASA Astrophysics Data System (ADS)

Sánchez-Lavega, A.; Pérez-Hoyos, S.

2005-08-01

With the aim of retrieving the altitude of cloud features used as zonal wind tracers in Saturn's atmosphere, we have reanalyzed three different sets of photometric and calibrated data corresponding to the Voyager epoch 1979-1981 (ground-based in 1979, Voyager 2 PPS and ISS observations in 1981), and we have analyze a new set of Hubble Space Telescope images for 2004. This analysis is put in the perspective of our previous HST study for 1994-2003 (Pérez-Hoyos et al., Icarus, 176, 155. 2005). A common result is found that the individual cloud tracers are embedded within a variable tropospheric haze. According to our models, the Voyager 2 ISS images locate the cloud tracers moving with zonal velocities of 455 to 465 (± 2) m/s at a pressure level of 360 ± 140 mbar. For HST observations, the cloud tracers moving with zonal wind speeds of 280 ± 10 m/s, locate at a pressure level of about 50 ± 10 mbar. All these values are calculated in the latitude 3 deg North. The speed difference, if interpreted as a vertical wind shear (Porco et al., Science, 307, 1226. 2005), requires a change of 90 m/s per scale height, two times greater than that estimated from Cassini CIRS data (Flasar et al., Science, 307, 1247, 2005). We also perform an initial guess on Cassini ISS vertical sounding levels, retrieving values compatible with the HST ones but not with Voyager wind measurements. We conclude that the wind speed velocity differences measured between 1979-81 and 2004 in the upper troposphere cannot be solely explained as a wind shear effect and demand dynamical processes. We discuss the possible action of Rossby waves or an intrinsic circulation change in the ammonia cloud layer and above, following a large period of equatorial storm activity. Acknowledgments: This work was supported by MCYT AYA2003-03216, FEDER, and Grupos UPV 15946/2004. S.P.-H. acknowledges a PhD fellowship from the Spanish MEC and R. H. a post-doc contract from Gobierno Vasco.

Climatology and inter-annual variability of the polar mesospheric winds inferred from meteor radar observations over Sodankylä (67N, 26E) during solar cycle 24

NASA Astrophysics Data System (ADS)

Lukianova, Renata; Kozlovsky, Alexander; Lester, Mark

2018-06-01

The inter-annual variability, climatological mean wind and tide fields in the northern polar mesosphere/lower thermosphere region of 82-98 km height are studied using observations by the meteor radar which has operated continuously during solar cycle 24 (from December 2008 onward) at the Sodankylä Geophysical Observatory (67N, 26E). Summer mean zonal winds are characterized by westward flow, up to 25 m/s, at lower heights and eastward flow, up to 30 m/s, at upper heights. In the winter an eastward flow, up to 10 m/s, dominates at all heights. The meridional winds are characterized by a relatively weak poleward flow (few m/s) in the winter and equatorward flow in the summer, with a jet core (∼15 m/s) located slightly below 90 km. These systematically varying winds are dominated by the semidiurnal tides. The largest amplitudes, up to 30 m/s, are observed at higher altitudes in winter and a secondary maximum is seen in August-September. The diurnal tides are almost a factor of two weaker and peak in summer. The variability of individual years is dominated by the winter perturbations. During the period of observations major sudden stratospheric warmings (SSW) occurred in January 2009 and 2013. During these events the wind fields were strongly modified. The lowest altitude eastward winds maximized up to 25 m/s, that is by more twice that of the non-SSW years. The poleward flow considerably increases (up 10 m/s) and extends from the lower heights throughout the whole altitude range. The annual pattern in temperature at ∼90 km height over Sodankyla consists of warm winters (up to 200 K) and cold summers (∼120 K).

Reattachment Zone Characterisation Under Offshore Winds With Flow Separation On The Lee Side Of Coastal Dunes

NASA Astrophysics Data System (ADS)

Delgado-Fernandez, I.; Jackson, D.; Cooper, J. A.; Baas, A. C.; Lynch, K.; Beyers, M.

2010-12-01

Airflow separation, lee-side eddies and secondary flows play an essential role on the formation and maintenance of sand dunes. Downstream from dune crests the flow surface layer detaches from the ground and generates an area characterised by turbulent eddies in the dune lee slope (the wake). At some distance downstream from the dune crest, flow separates into a reversed component directed toward the dune toe and an offshore “re-attached” component. This reattachment zone (RZ) has been documented in fluvial and desert environments, wind tunnel experiments and numerical simulations, but not yet characterised in coastal dunes. This study examines the extent and temporal evolution of the RZ and its implications for beach-dune interaction at Magilligan, Northern Ireland. Wind parameters were measured over a profile extending from an 11 m height dune crest towards the beach, covering a total distance of 65 m cross-shore. Data was collected using an array of nine ultrasonic anemometers (UAs) deployed in April-May 2010, as part of a larger experiment to capture airflow data under a range of incident wind velocities and offshore directions. UAs were located along the profile (5 m tower spacing) over the beach, which allowed a detailed examination of the RZ with empirical data. Numerical modelling using Computational Fluid Dynamics (CFD) software was also conducted with input data from anemometer field measurements, running over a surface mesh generated from LiDAR and DGPS surveys. Results demonstrate that there is a wind threshold of approximately 5-6 ms-1 under which no flow separation exists with offshore winds. As wind speed increases over the threshold, a flow reversal area is quickly formed, with the maximum extent of the RZ at approximately 3.5 dune heights (h). The maximum extent of the RZ increases up to 4.5h with stronger wind speeds of 8-10 ms-1 and remains relatively constant as wind speed further increases. This suggests that the spatial extent of the RZ is

Equatorial superrotation in a thermally driven zonally symmetric circulation

NASA Technical Reports Server (NTRS)

Mayr, H. G.; Harris, I.

1981-01-01

Near the equator where the Coriolis force vanishes, the momentum balance for the axially symmetric circulation is established between horizontal and vertical diffusion, which, a priori, does not impose constraints on the direction or magnitude of the zonal winds. Solar radiation absorbed at low latitudes is a major force in driving large scale motions with air rising near the equator and falling at higher latitudes. In the upper leg of the meridional cell, angular momentum is redistributed so that the atmosphere tends to subrotate (or corotate) at low latitudes and superrotate at high latitudes. In the lower leg, however, the process is reversed and produces a tendency for the equatorial region to superrotate. The outcome depends on the energy budget which is closely coupled to the momentum budget through the thermal wind equation; a pressure (temperature) maximum is required to sustain equatorial superrotation. Such a condition arises in regions which are convectively unstable and the temperature lapse rate is superadiabatic. It should arise in the tropospheres of Jupiter and Saturn; planetary energy from the interior is carried to higher altitudes where radiation to space becomes important. Upward equatorial motions in the direct and indirect circulations (Ferrel-Thomson type) imposed by insolation can then trap dynamic energy for equatorial heating which can sustain the superrotation of the equatorial region.

Wind Farm Flow Modeling using an Input-Output Reduced-Order Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Annoni, Jennifer; Gebraad, Pieter; Seiler, Peter

Wind turbines in a wind farm operate individually to maximize their own power regardless of the impact of aerodynamic interactions on neighboring turbines. There is the potential to increase power and reduce overall structural loads by properly coordinating turbines. To perform control design and analysis, a model needs to be of low computational cost, but retains the necessary dynamics seen in high-fidelity models. The objective of this work is to obtain a reduced-order model that represents the full-order flow computed using a high-fidelity model. A variety of methods, including proper orthogonal decomposition and dynamic mode decomposition, can be used tomore » extract the dominant flow structures and obtain a reduced-order model. In this paper, we combine proper orthogonal decomposition with a system identification technique to produce an input-output reduced-order model. This technique is used to construct a reduced-order model of the flow within a two-turbine array computed using a large-eddy simulation.« less

Numerical Simulation of Hot Accretion Flows. III. Revisiting Wind Properties Using the Trajectory Approach

NASA Astrophysics Data System (ADS)

Yuan, Feng; Gan, Zhaoming; Narayan, Ramesh; Sadowski, Aleksander; Bu, Defu; Bai, Xue-Ning

2015-05-01

Previous MHD simulations have shown that wind must exist in black hole hot accretion flows. In this paper, we continue our study by investigating the detailed properties of wind and the mechanism of wind production. For this aim, we make use of a 3D general relativistic MHD simulation of hot accretion flows around a Schwarzschild black hole. To distinguish real wind from turbulent outflows, we track the trajectories of the virtual Lagrangian particles from simulation data. We find two types of real outflows, i.e., a jet and a wind. The mass flux of wind is very significant, and its radial profile can be described by {{\\dot{M}}wind}≈ {{\\dot{M}}BH}≤ft( r/20 {{r}s} \\right), with {{\\dot{M}}BH} being the mass accretion rate at the black hole horizon and rs being the Schwarzschild radius. The poloidal wind speed almost remains constant once they are produced, but the flux-weighted wind speed roughly follows {{v}p,wind}(r)≈ 0.25{{v}k}(r), with vk(r) being the Keplerian speed at radius r. The mass flux of the jet is much lower, but the speed is much higher, {{v}p,jet} ˜ (0.3-0.4)c. Consequently, both the energy and momentum fluxes of the wind are much larger than those of the jet. The wind is produced and accelerated primarily by the combination of centrifugal force and magnetic pressure gradient, while the jet is mainly accelerated by the magnetic pressure gradient. Finally, we find that the wind production efficiency {{ɛ }wind}\\equiv {{\\dot{E}}wind}/{{\\dot{M}}BH}{{c}2}˜ 1/1000 is in good agreement with the value required from large-scale galaxy simulations with active galactic nucleus feedback.

The role of the winter residual circulation in the summer mesopause regions in WACCM

NASA Astrophysics Data System (ADS)

Sanne Kuilman, Maartje; Karlsson, Bodil

2018-03-01

High winter planetary wave activity warms the summer polar mesopause via a link between the two hemispheres. Complex wave-mean-flow interactions take place on a global scale, involving sharpening and weakening of the summer zonal flow. Changes in the wind shear occasionally generate flow instabilities. Additionally, an altering zonal wind modifies the breaking of vertically propagating gravity waves. A crucial component for changes in the summer zonal flow is the equatorial temperature, as it modifies latitudinal gradients. Since several mechanisms drive variability in the summer zonal flow, it can be hard to distinguish which one is dominant. In the mechanism coined interhemispheric coupling, the mesospheric zonal flow is suggested to be a key player for how the summer polar mesosphere responds to planetary wave activity in the winter hemisphere. We here use the Whole Atmosphere Community Climate Model (WACCM) to investigate the role of the summer stratosphere in shaping the conditions of the summer polar mesosphere. Using composite analyses, we show that in the absence of an anomalous summer mesospheric temperature gradient between the equator and the polar region, weak planetary wave forcing in the winter would lead to a warming of the summer mesosphere region instead of a cooling, and vice versa. This is opposing the temperature signal of the interhemispheric coupling that takes place in the mesosphere, in which a cold and calm winter stratosphere goes together with a cold summer mesopause. We hereby strengthen the evidence that the variability in the summer mesopause region is mainly driven by changes in the summer mesosphere rather than in the summer stratosphere.

Meso-beta scale numerical simulation studies of terrain-induced jet streak mass/momentum perturbations

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Kaplan, Michael L.

1993-01-01

The first section is on 3-D numerical modeling of terrain-induced circulations and covers the following: (1) additional insights into gravity wave generation mechanisms based on the control simulation; (2) ongoing nested-grid numerical simulations; (3) work to be completed during the remainder of FY-93; and (4) work objectives for FY-94. The second section is on linear theory and theoretical modeling and covers the following: (1) the free response of a uniform barotropic flow to an initially stationary unbalanced (ageostrophic) zonal wind anomaly; and (2) the free response of a uniform barotropic flow to an initially stationary balanced zonal wind anomaly.

Computational studies of horizontal axis wind turbines

NASA Astrophysics Data System (ADS)

Xu, Guanpeng

A numerical technique has been developed for efficiently simulating fully three-dimensional viscous fluid flow around horizontal axis wind turbines (HAWT) using a zonal approach. The flow field is viewed as a combination of viscous regions, inviscid regions and vortices. The method solves the costly unsteady Reynolds averaged Navier-Stokes (RANS) equations only in the viscous region around the turbine blades. It solves the full potential equation in the inviscid region where flow is irrotational and isentropic. The tip vortices are simulated using a Lagrangean approach, thus removing the need to accurately resolve them on a fine grid. The hybrid method is shown to provide good results with modest CPU resources. A full Navier-Stokes based methodology has also been developed for modeling wind turbines at high wind conditions where extensive stall may occur. An overset grid based version that can model rotor-tower interactions has been developed. Finally, a blade element theory based methodology has been developed for the purpose of developing improved tip loss models and stall delay models. The effects of turbulence are simulated using a zero equation eddy viscosity model, or a one equation Spalart-Allmaras model. Two transition models, one based on the Eppler's criterion, and the other based on Michel's criterion, have been developed and tested. The hybrid method has been extensively validated for axial wind conditions for three rotors---NREL Phase II, Phase III, and Phase VI configurations. A limited set of calculations has been done for rotors operating under yaw conditions. Preliminary simulations have also been carried out to assess the effects of the tower wake on the rotor. In most of these cases, satisfactory agreement has been obtained with measurements. Using the numerical results from present methodologies as a guide, Prandtl's tip loss model and Corrigan's stall delay model were correlated with present calculations. An improved tip loss model has been

Contribution of zonal harmonics to gravitational moment

NASA Technical Reports Server (NTRS)

Roithmayr, Carlos M.

1991-01-01

It is presently demonstrated that a recursive vector-dyadic expression for the contribution of a zonal harmonic of degree n to the gravitational moment about a small body's center-of-mass is obtainable with a procedure that involves twice differentiating a celestial body's gravitational potential with respect to a vector. The recursive property proceeds from taking advantage of a recursion relation for Legendre polynomials which appear in the gravitational potential. The contribution of the zonal harmonic of degree 2 is consistent with the gravitational moment exerted by an oblate spheroid.

Contribution of zonal harmonics to gravitational moment

NASA Astrophysics Data System (ADS)

Roithmayr, Carlos M.

1991-02-01

It is presently demonstrated that a recursive vector-dyadic expression for the contribution of a zonal harmonic of degree n to the gravitational moment about a small body's center-of-mass is obtainable with a procedure that involves twice differentiating a celestial body's gravitational potential with respect to a vector. The recursive property proceeds from taking advantage of a recursion relation for Legendre polynomials which appear in the gravitational potential. The contribution of the zonal harmonic of degree 2 is consistent with the gravitational moment exerted by an oblate spheroid.

Eastern Tropical Pacific Precipitation Response to Zonal SPCZ events

NASA Astrophysics Data System (ADS)

Durán-Quesada, A. M.; Lintner, B. R.

2014-12-01

Extreme El Niño events and warming conditions in the eastern tropical Pacific have been linked to pronounced spatial displacements of the South Pacific Convergence Zone known as "zonal SPCZ" events.. Using a global dataset of Lagrangian back trajectories computed with the FLEXPART model for the period 1980-2013, comprehensive analysis of the 3D circulation characteristics associated with the SPCZ is undertaken. Ten days history of along-trajectory specific humidity, potential vorticity and temperature are reconstructed for zonal SPCZ events as well as other states,, with differences related to El Niño intensity and development stage as well as the state of the Western Hemisphere Warm Pool. How zonal events influence precipitation over the Eastern Tropical Pacific is examined using back trajectories, reanalysis, TRMM precipitation, and additional satellite derived cloud information. It is found that SPCZ displacements are associated with enhanced convection over the Eastern Tropical Pacific in good agreement with prior work. The connection between intensification of precipitation over the eastern Tropical Pacific during zonal events and suppression of rainfall over the Maritime continent is also described.

Neutral winds in the polar thermosphere as measured from Dynamics Explorer

NASA Technical Reports Server (NTRS)

Killeen, T. L.; Hays, P. B.; Spencer, N. W.; Wharton, L. E.

1982-01-01

Remote sensing measurements of the meridional thermospheric neutral wind using the Fabry-Perot Interferometer on Dynamics Explorer have been combined with in-situ measurements of the zonal component using the Wind and Temperature Spectrometer on the same spacecraft. The two data sets with appropriate spatial phasing and averaging determine the vector wind along the track of the polar orbiting spacecraft. A study of fifty-eight passes over the Southern (sunlit) pole has enabled the average Universal Time dependence of the wind field to be determined for essentially a single solar local time cut. The results show the presence of a 'back-ground' wind field driven by solar EUV heating upon which is superposed a circulating wind field driven by high latitude momentum and energy sources.

Computational study: The influence of omni-directional guide vane on the flow pattern characteristic around Savonius wind turbine

NASA Astrophysics Data System (ADS)

Wicaksono, Yoga Arob; Tjahjana, D. D. D. P.

2017-01-01

Standart Savonius wind turbine have a low performance such as low coefficient of power and low coefficient of torque compared with another type of wind turbine. This phenomenon occurs because the wind stream can cause the negative pressure at the returning rotor. To solve this problem, standard Savonius combined with Omni Directional Guide Vane (ODGV) proposed. The aim of this research is to study the influence of ODGV on the flow pattern characteristic around of Savonius wind turbine. The numerical model is based on the Navier-Stokes equations with the standard k-ɛ turbulent model. This equation solved by a finite volume discretization method. This case was analyzed by commercial computational fluid dynamics solver such as SolidWorks Flow Simulations. Simulations were performed at the different wind directions; there are 0°, 30°,60° at 4 m/s wind speed. The numerical method validated with the past experimental data. The result indicated that the ODGV able to augment air flow to advancing rotor and decrease the negative pressure in the upstream of returning rotor compared to the bare Savonius wind turbine.

Remote Sensing of Complex Flows by Doppler Wind Lidar: Issues and Preliminary Recommendations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clifton, Andrew; Boquet, Matthieu; Burin Des Roziers, Edward

Remote sensing of winds using lidar has become popular and useful in the wind energy industry. Extensive experience has been gained with using lidar for applications including land-based and offshore resource assessment, plant operations, and turbine control. Prepared by members of International Energy Agency Task 32, this report describes the state of the art in the use of Doppler wind lidar for resource assessment in complex flows. The report will be used as input for future recommended practices on this topic.

Numerical simulation of transitional flow on a wind turbine airfoil with RANS-based transition model

NASA Astrophysics Data System (ADS)

Zhang, Ye; Sun, Zhengzhong; van Zuijlen, Alexander; van Bussel, Gerard

2017-09-01

This paper presents a numerical investigation of transitional flow on the wind turbine airfoil DU91-W2-250 with chord-based Reynolds number Rec = 1.0 × 106. The Reynolds-averaged Navier-Stokes based transition model using laminar kinetic energy concept, namely the k - kL - ω model, is employed to resolve the boundary layer transition. Some ambiguities for this model are discussed and it is further implemented into OpenFOAM-2.1.1. The k - kL - ω model is first validated through the chosen wind turbine airfoil at the angle of attack (AoA) of 6.24° against wind tunnel measurement, where lift and drag coefficients, surface pressure distribution and transition location are compared. In order to reveal the transitional flow on the airfoil, the mean boundary layer profiles in three zones, namely the laminar, transitional and fully turbulent regimes, are investigated. Observation of flow at the transition location identifies the laminar separation bubble. The AoA effect on boundary layer transition over wind turbine airfoil is also studied. Increasing the AoA from -3° to 10°, the laminar separation bubble moves upstream and reduces in size, which is in close agreement with wind tunnel measurement.

Numerical simulation on zonal disintegration in deep surrounding rock mass.

PubMed

Chen, Xuguang; Wang, Yuan; Mei, Yu; Zhang, Xin

2014-01-01

Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration phenomenon was confirmed and its mechanism is revealed. It is found to be the result of circular fracture which develops within surrounding rock mass under the high geostress. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The numerical results were in accordance with the model test findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic-plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks.

Numerical Simulation on Zonal Disintegration in Deep Surrounding Rock Mass

PubMed Central

Chen, Xuguang; Wang, Yuan; Mei, Yu; Zhang, Xin

2014-01-01

Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration phenomenon was confirmed and its mechanism is revealed. It is found to be the result of circular fracture which develops within surrounding rock mass under the high geostress. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The numerical results were in accordance with the model test findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic-plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks. PMID:24592166

The Role of Monsoon-Like Zonally Asymmetric Heating in Interhemispheric Transport

NASA Technical Reports Server (NTRS)

Chen, Gang; Orbe, Clara; Waugh, Darryn

2017-01-01

While the importance of the seasonal migration of the zonally averaged Hadley circulation on interhemispheric transport of trace gases has been recognized, few studies have examined the role of the zonally asymmetric monsoonal circulation. This study investigates the role of monsoon-like zonally asymmetric heating on interhemispheric transport using a dry atmospheric model that is forced by idealized Newtonian relaxation to a prescribed radiative equilibrium temperature. When only the seasonal cycle of zonally symmetric heating is considered, the mean age of air in the Southern Hemisphere since last contact with the Northern Hemisphere midlatitude boundary layer, is much larger than the observations. The introduction of monsoon-like zonally asymmetric heating not only reduces the mean age of tropospheric air to more realistic values, but also produces an upper-tropospheric cross-equatorial transport pathway in boreal summer that resembles the transport pathway simulated in the NASA Global Modeling Initiative (GMI) Chemistry Transport Model driven with MERRA meteorological fields. These results highlight the monsoon-induced eddy circulation plays an important role in the interhemispheric transport of long-lived chemical constituents.

Mean winds at the cloud top of Venus obtained from two-wavelength UV imaging by Akatsuki

NASA Astrophysics Data System (ADS)

Horinouchi, Takeshi; Kouyama, Toru; Lee, Yeon Joo; Murakami, Shin-ya; Ogohara, Kazunori; Takagi, Masahiro; Imamura, Takeshi; Nakajima, Kensuke; Peralta, Javier; Yamazaki, Atsushi; Yamada, Manabu; Watanabe, Shigeto

2018-01-01

Venus is covered with thick clouds. Ultraviolet (UV) images at 0.3-0.4 microns show detailed cloud features at the cloud-top level at about 70 km, which are created by an unknown UV-absorbing substance. Images acquired in this wavelength range have traditionally been used to measure winds at the cloud top. In this study, we report low-latitude winds obtained from the images taken by the UV imager, UVI, onboard the Akatsuki orbiter from December 2015 to March 2017. UVI provides images with two filters centered at 365 and 283 nm. While the 365-nm images enable continuation of traditional Venus observations, the 283-nm images visualize cloud features at an SO2 absorption band, which is novel. We used a sophisticated automated cloud-tracking method and thorough quality control to estimate winds with high precision. Horizontal winds obtained from the 283-nm images are generally similar to those from the 365-nm images, but in many cases, westward winds from the former are faster than the latter by a few m/s. From previous studies, one can argue that the 283-nm images likely reflect cloud features at higher altitude than the 365-nm images. If this is the case, the superrotation of the Venusian atmosphere generally increases with height at the cloud-top level, where it has been thought to roughly peak. The mean winds obtained from the 365-nm images exhibit local time dependence consistent with known tidal features. Mean zonal winds exhibit asymmetry with respect to the equator in the latter half of the analysis period, significantly at 365 nm and weakly at 283 nm. This contrast indicates that the relative altitude may vary with time and latitude, and so are the observed altitudes. In contrast, mean meridional winds do not exhibit much long-term variability. A previous study suggested that the geographic distribution of temporal mean zonal winds obtained from UV images from the Venus Express orbiter during 2006-2012 can be interpreted as forced by topographically induced

IEA-Task 31 WAKEBENCH: Towards a protocol for wind farm flow model evaluation. Part 2: Wind farm wake models

NASA Astrophysics Data System (ADS)

Moriarty, Patrick; Sanz Rodrigo, Javier; Gancarski, Pawel; Chuchfield, Matthew; Naughton, Jonathan W.; Hansen, Kurt S.; Machefaux, Ewan; Maguire, Eoghan; Castellani, Francesco; Terzi, Ludovico; Breton, Simon-Philippe; Ueda, Yuko

2014-06-01

Researchers within the International Energy Agency (IEA) Task 31: Wakebench have created a framework for the evaluation of wind farm flow models operating at the microscale level. The framework consists of a model evaluation protocol integrated with a web-based portal for model benchmarking (www.windbench.net). This paper provides an overview of the building-block validation approach applied to wind farm wake models, including best practices for the benchmarking and data processing procedures for validation datasets from wind farm SCADA and meteorological databases. A hierarchy of test cases has been proposed for wake model evaluation, from similarity theory of the axisymmetric wake and idealized infinite wind farm, to single-wake wind tunnel (UMN-EPFL) and field experiments (Sexbierum), to wind farm arrays in offshore (Horns Rev, Lillgrund) and complex terrain conditions (San Gregorio). A summary of results from the axisymmetric wake, Sexbierum, Horns Rev and Lillgrund benchmarks are used to discuss the state-of-the-art of wake model validation and highlight the most relevant issues for future development.

Time-varying zonal asymmetries in stratospheric nitrous oxide and methane

NASA Technical Reports Server (NTRS)

Gao, H.; Stanford, J. L.

1993-01-01

Previously analyses of Stratospheric And Mesospheric Sounder (SAMS) data of atmospheric constituent gases have dealt almost exclusively with zonal means (and mostly monthly means), owing perhaps to concern over data quality. The purpose of this note is to show that, with care, time-dependent zonally-asymmetric features may be recovered from the SAMS nitrous oxide and methane data. As an example, we demonstrate the existence of zonal wave-1 constituent perturbations with periods of a few weeks in the middle and upper stratosphere. When the perturbations are normalized by the constituent zonal-mean mixing ratio to compensate for the slowly varying (in both space and time) background concentration of constituents, wavepacket-like features are found over all latitudes and seasons in the three-year SAMS record. One specific low-latitude case discussed had features which appear to be consistent with constituent oscillations induced by episodic equatorial Kelvin waves. Further studies are needed to better identify the nature of the plethora of observed wave-like phenomena.

Near-Earth Solar Wind Flows and Related Geomagnetic Activity During more than Four Solar Cycles (1963-2011)

NASA Technical Reports Server (NTRS)

Richardson, Ian G.; Cane, Hilary V.

2012-01-01

In past studies, we classified the near-Earth solar wind into three basic flow types based on inspection of solar wind plasma and magnetic field parameters in the OMNI database and additional data (e.g., geomagnetic indices, energetic particle, and cosmic ray observations). These flow types are: (1) High-speed streams associated with coronal holes at the Sun, (2) Slow, interstream solar wind, and (3) Transient flows originating with coronal mass ejections at the Sun, including interplanetary coronal mass ejections and the associated upstream shocks and post-shock regions. The solar wind classification in these previous studies commenced with observations in 1972. In the present study, as well as updating this classification to the end of 2011, we have extended the classification back to 1963, the beginning of near-Earth solar wind observations, thereby encompassing the complete solar cycles 20 to 23 and the ascending phase of cycle 24. We discuss the cycle-to-cycle variations in near-Earth solar wind structures and l1e related geomagnetic activity over more than four solar cycles, updating some of the results of our earlier studies.

Experimental Study on the Wake Meandering Within a Scale Model Wind Farm Subject to a Wind-Tunnel Flow Simulating an Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Coudou, Nicolas; Buckingham, Sophia; Bricteux, Laurent; van Beeck, Jeroen

2017-12-01

The phenomenon of meandering of the wind-turbine wake comprises the motion of the wake as a whole in both horizontal and vertical directions as it is advected downstream. The oscillatory motion of the wake is a crucial factor in wind farms, because it increases the fatigue loads, and, in particular, the yaw loads on downstream turbines. To address this phenomenon, experimental investigations are carried out in a wind-tunnel flow simulating an atmospheric boundary layer with the Coriolis effect neglected. A 3 × 3 scaled wind farm composed of three-bladed rotating wind-turbine models is subject to a neutral boundary layer over a slightly-rough surface, i.e. corresponding to offshore conditions. Particle-image-velocimetry measurements are performed in a horizontal plane at hub height in the wakes of the three wind turbines occupying the wind-farm centreline. These measurements allow determination of the wake centrelines, with spectral analysis indicating the characteristic wavelength of the wake-meandering phenomenon. In addition, measurements with hot-wire anemometry are performed along a vertical line in the wakes of the same wind turbines, with both techniques revealing the presence of wake meandering behind all three turbines. The spectral analysis performed with the spatial and temporal signals obtained from these two measurement techniques indicates a Strouhal number of ≈ 0.20 - 0.22 based on the characteristic wake-meandering frequency, the rotor diameter and the flow speed at hub height.

Experimental Study on the Wake Meandering Within a Scale Model Wind Farm Subject to a Wind-Tunnel Flow Simulating an Atmospheric Boundary Layer

NASA Astrophysics Data System (ADS)

Coudou, Nicolas; Buckingham, Sophia; Bricteux, Laurent; van Beeck, Jeroen

2018-04-01

The phenomenon of meandering of the wind-turbine wake comprises the motion of the wake as a whole in both horizontal and vertical directions as it is advected downstream. The oscillatory motion of the wake is a crucial factor in wind farms, because it increases the fatigue loads, and, in particular, the yaw loads on downstream turbines. To address this phenomenon, experimental investigations are carried out in a wind-tunnel flow simulating an atmospheric boundary layer with the Coriolis effect neglected. A 3 × 3 scaled wind farm composed of three-bladed rotating wind-turbine models is subject to a neutral boundary layer over a slightly-rough surface, i.e. corresponding to offshore conditions. Particle-image-velocimetry measurements are performed in a horizontal plane at hub height in the wakes of the three wind turbines occupying the wind-farm centreline. These measurements allow determination of the wake centrelines, with spectral analysis indicating the characteristic wavelength of the wake-meandering phenomenon. In addition, measurements with hot-wire anemometry are performed along a vertical line in the wakes of the same wind turbines, with both techniques revealing the presence of wake meandering behind all three turbines. The spectral analysis performed with the spatial and temporal signals obtained from these two measurement techniques indicates a Strouhal number of ≈ 0.20 - 0.22 based on the characteristic wake-meandering frequency, the rotor diameter and the flow speed at hub height.

Wind circulation regimes at Venus' cloud tops: Ground-based Doppler velocimetry using CFHT/ESPaDOnS and comparison with simultaneous cloud tracking measurements using VEx/VIRTIS in February 2011

NASA Astrophysics Data System (ADS)

Machado, Pedro; Widemann, Thomas; Luz, David; Peralta, Javier

2014-11-01

We present new results based on ground-based Doppler spectroscopic measurements, obtained with the ESPaDOnS spectrograph at Canada-France-Hawaii telescope (CFHT) and simultaneous observations of velocity fields, obtained from space by the VIRTIS-M instrument on board the Venus Express spacecraft. These measurements are based on high-resolution spectra of Fraunhofer lines in the visible to NIR range (0.37-1.05 μm) acquired on February 19-21, 2011 at a resolution of about 80,000, measuring Venus' winds at 70 km, using incoming solar radiation scattered by cloud top particles in the observer's direction (Widemann, T., et al., [2007]. Planet. Space Sci. 55, 1741-1756; Widemann, T., et al., [2008]. Planet. Space Sci. 56, 1320-1334). The zonal wind field has been characterized by latitudinal bands, at a phase angle Φ = (68.7 ± 0.3) ° , between +10°N and 60°S, by steps of 10°, and from [ ϕ -ϕE ] = - 50 ° to sub-Earth longitude ϕE = 0 ° , by steps of 12°. From space, VIRTIS-M UV (0.38 μm) imaging exposures on the dayside were acquired simultaneously in orbit 1786, providing the first simultaneous cloud-tracking measurements with Doppler velocimetry. From the ground, we measured a zonal mean background velocity of v‾z = (117.3 ± 18.0) ms-1 on February 19, and v‾z = (117.5 ± 14.5) ms-1 on February 21. We detect an unambiguous poleward meridional flow on the morning dayside hemisphere of (18.8 ± 12.3) m s-1 on February 19/21. Latitudinal variations of the zonal and meridional winds are further compared with the simultaneous VIRTIS data. We discuss temporal variability as well as its statistical significance.

Assessment of a flow-through balance for hypersonic wind tunnel models with scramjet exhaust flow simulation

NASA Technical Reports Server (NTRS)

Huebner, Lawrence D.; Kniskern, Marc W.; Monta, William J.

1993-01-01

The purpose of this investigation were twofold: first, to determine whether accurate force and moment data could be obtained during hypersonic wind tunnel tests of a model with a scramjet exhaust flow simulation that uses a representative nonwatercooled, flow-through balance; second, to analyze temperature time histories on various parts of the balance to address thermal effects on force and moment data. The tests were conducted in the NASA Langley Research Center 20-Inch Mach 6 Wind Tunnel at free-stream Reynolds numbers ranging from 0.5 to 7.4 x 10(exp 6)/ft and nominal angles of attack of -3.5 deg, 0 deg, and 5 deg. The simulant exhaust gases were cold air, hot air, and a mixture of 50 percent Argon and 50 percent Freon by volume, which reached stagnation temperatures within the balance of 111, 214, and 283 F, respectively. All force and moment values were unaffected by the balance thermal response from exhaust gas simulation and external aerodynamic heating except for axial-force measurements, which were significantly affected by balance heating. This investigation showed that for this model at the conditions tested, a nonwatercooled, flow-through balance is not suitable for axial-force measurements during scramjet exhaust flow simulation tests at hypersonic speeds. In general, heated exhaust gas may produce unacceptable force and moment uncertainties when used with thermally sensitive balances.

A diagnostic model to estimate winds and small-scale drag from Mars Observer PMIRR data

NASA Technical Reports Server (NTRS)

Barnes, J. R.

1993-01-01

Theoretical and modeling studies indicate that small-scale drag due to breaking gravity waves is likely to be of considerable importance for the circulation in the middle atmospheric region (approximately 40-100 km altitude) on Mars. Recent earth-based spectroscopic observations have provided evidence for the existence of circulation features, in particular, a warm winter polar region, associated with gravity wave drag. Since the Mars Observer PMIRR experiment will obtain temperature profiles extending from the surface up to about 80 km altitude, it will be extensively sampling middle atmospheric regions in which gravity wave drag may play a dominant role. Estimating the drag then becomes crucial to the estimation of the atmospheric winds from the PMIRR-observed temperatures. An interative diagnostic model based upon one previously developed and tested with earth satellite temperature data will be applied to the PMIRR measurements to produce estimates of the small-scale zonal drag and three-dimensional wind fields in the Mars middle atmosphere. This model is based on the primitive equations, and can allow for time dependence (the time tendencies used may be based upon those computed in a Fast Fourier Mapping procedure). The small-scale zonal drag is estimated as the residual in the zonal momentum equation; the horizontal winds having first been estimated from the meridional momentum equation and the continuity equation. The scheme estimates the vertical motions from the thermodynamic equation, and thus needs estimates of the diabatic heating based upon the observed temperatures. The latter will be generated using a radiative model. It is hoped that the diagnostic scheme will be able to produce good estimates of the zonal gravity wave drag in the Mars middle atmosphere, estimates that can then be used in other diagnostic or assimilation efforts, as well as more theoretical studies.

Future Effects of Southern Hemisphere Stratospheric Zonal Asymmetries on Climate

NASA Astrophysics Data System (ADS)

Stone, K.; Solomon, S.; Kinnison, D. E.; Fyfe, J. C.

2017-12-01

Stratospheric zonal asymmetries in the Southern Hemisphere have been shown to have significant influences on both stratospheric and tropospheric dynamics and climate. Accurate representation of stratospheric ozone in particular is important for realistic simulation of the polar vortex strength and temperature trends. This is therefore also important for stratospheric ozone change's effect on the troposphere, both through modulation of the Southern Annular Mode (SAM), and more localized climate. Here, we characterization the impact of future changes in Southern Hemisphere zonal asymmetry on tropospheric climate, including changes to future tropospheric temperature, and precipitation. The separate impacts of increasing GHGs and ozone recovery on the zonal asymmetric influence on the surface are also investigated. For this purpose, we use a variety of models, including Chemistry Climate Model Initiative simulations from the Community Earth System Model, version 1, with the Whole Atmosphere Community Climate Model (CESM1(WACCM)) and the Australian Community Climate and Earth System Simulator-Chemistry Climate Model (ACCESS-CCM). These models have interactive chemistry and can therefore more accurately represent the zonally asymmetric nature of the stratosphere. The CESM1(WACCM) and ACCESS-CCM models are also compared to simulations from the Canadian Can2ESM model and CESM-Large Ensemble Project (LENS) that have prescribed ozone to further investigate the importance of simulating stratospheric zonal asymmetry.

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet

NASA Technical Reports Server (NTRS)

Simon-Miller, A. A.; Rogers, John H.; Gierasch, Peter J.; Choi, David; Allison, Michael; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-01-01

We have conducted a detailed study of the cloud features in the strong southern equatorial wind jet near 7.5 S planetographic latitude. To understand the apparent variations in average zonal wind jet velocity at this latitude [e.g.. 1,2,3], we have searched for variations iIi both feature latitude and velocity with longitude and time. In particular, we focused on the repetitive chevron-shaped dark spots visible on most dates and the more transient large anticyclonic system known as the South Equatorial Disturbance (SED). These small dark spots are interpreted as cloud holes, and are often used as material tracers of the wind field.

Numerical simulation of flows around deformed aircraft model in a wind tunnel

NASA Astrophysics Data System (ADS)

Lysenkov, A. V.; Bosnyakov, S. M.; Glazkov, S. A.; Gorbushin, A. R.; Kuzmina, S. I.; Kursakov, I. A.; Matyash, S. V.; Ishmuratov, F. Z.

2016-10-01

To obtain accurate data of calculation method error requires detailed simulation of the experiment in wind tunnel with keeping all features of the model, installation and gas flow. Two examples of such detailed data comparison are described in this paper. The experimental characteristics of NASA CRM model obtained in the ETW wind tunnel (Cologne, Germany), and CFD characteristics of this model obtained with the use of EWT-TsAGI application package are compared. Following comparison is carried out for an airplane model in the T-128 wind tunnel (TsAGI, Russia). It is seen that deformation influence on integral characteristics grows with increasing Re number and, accordingly, the dynamic pressure. CFD methods application for problems of experimental research in the wind tunnel allows to separate viscosity and elasticity effects.

The turbulence structure of katabatic flows below and above wind-speed maximum

NASA Astrophysics Data System (ADS)

Grachev, Andrey; Leo, Laura; Di Sabatino, Silvana; Fernando, Harindra; Pardyjak, Eric; Fairall, Christopher

2015-04-01

Measurements of atmospheric small-scale turbulence made over the complex-terrain at the US Army Dugway Proving Grounds in Utah during the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program are used to describe the turbulence structure of katabatic flows. Turbulent and mean meteorological data were continuously measured at multiple levels (up to seven) on four towers deployed along East lower slope (2-4 degrees) of Granite Mountain. The multi-level, multi-tower observations obtained during a 30-day long MATERHORN-Fall field campaign in September-October 2102 allow studying temporal and spatial structure of nocturnal slope flows in detail. In this study, we focus on the various statistics (fluxes, variances, spectra, cospectra, etc.) of the small-scale turbulence of katabatic winds. Observed vertical profiles of velocity, turbulent fluxes, and other quantities show steep gradients near the surface but in the layer above the slope jet these variables vary with height more slowly than near the surface. It is found that vertical momentum flux and horizontal heat (buoyancy) flux in a slope-following coordinate system change their sign below and above the wind maximum of a katabatic flow. The vertical momentum flux is directed downward (upward) whereas the horizontal heat flux is downslope (upslope) below (above) the wind maximum. Our study, therefore, suggests that a position of the jet speed maximum can be derived from linear interpolation between positive and negative values of the momentum flux (or the horizontal heat flux) and determination of a height where a flux becomes zero. It is shown that the standard deviations of all wind speed components (and therefore the turbulent kinetic energy) and the dissipation rate of turbulent kinetic energy have a local minimum, whereas the standard deviation of air temperature has an absolute maximum at the height of wind speed maximum. We report several cases when the destructive effect of vertical heat

Curved-flow, rolling-flow, and oscillatory pure-yawing wind-tunnel test methods for determination of dynamic stability derivatives

NASA Technical Reports Server (NTRS)

Chambers, J. R.; Grafton, S. B.; Lutze, F. H.

1981-01-01

Dynamic stability derivatives are evaluated on the basis of rolling-flow, curved-flow and snaking tests. Attention is given to the hardware associated with curved-flow, rolling-flow and oscillatory pure-yawing wind-tunnel tests. It is found that the snaking technique, when combined with linear- and forced-oscillation methods, yields an important method for evaluating beta derivatives for current configurations at high angles of attack. Since the rolling flow model is fixed during testing, forced oscillations may be imparted to the model, permitting the measurement of damping and cross-derivatives. These results, when coupled with basic rolling-flow or rotary-balance data, yield a highly accurate mathematical model for studies of incipient spin and spin entry.

On the fast zonal transport of the STS-121 space shuttle exhaust plume in the lower thermosphere

NASA Astrophysics Data System (ADS)

Yue, Jia; Liu, Han-Li; Meier, R. R.; Chang, Loren; Gu, Sheng-Yang; Russell, James, III

2013-03-01

Meier et al. (2011) reported rapid eastward transport of the STS-121 space shuttle (launch: July 4, 2006) main engine plume in the lower thermosphere, observed in hydrogen Lyman α images by the GUVI instrument onboard the TIMED satellite. In order to study the mechanism of the rapid zonal transport, diagnostic tracer calculations are performed using winds from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) simulation of July, 2006. It is found that the strong eastward jet at heights of 100-110 km, where the exhaust plume was deposited, results in a persistent eastward tracer motion with an average velocity of 45 m/s. This is generally consistent with, though faster than, the prevailing eastward shuttle plume movement with daily mean velocity of 30 m/s deduced from the STS-121 GUVI observation. The quasi-two-day wave (QTDW) was not included in the numerical simulation because it was found not to be large. Its absence, however, might be partially responsible for insufficient meridional transport to move the tracers away from the fast jet in the simulation. The current study and our model results from Yue and Liu (2010) explain two very different shuttle plume transport scenarios (STS-121 and STS-107 (launch: January 16, 2003), respectively): we conclude that lower thermospheric dynamics is sufficient to account for both very fast zonal motion (zonal jet in the case of STS-121) and very fast meridional motion to polar regions (large QTDW in the case of STS-107).

Unfolding the atmospheric and deep internal flows on Jupiter and Saturn using the Juno and Cassini gravity measurements

NASA Astrophysics Data System (ADS)

Galanti, Eli; Kaspi, Yohai

2016-10-01

In light of the first orbits of Juno at Jupiter, we discuss the Juno gravity experiment and possible initial results. Relating the flow on Jupiter and Saturn to perturbations in their density field is key to the analysis of the gravity measurements expected from both the Juno (Jupiter) and Cassini (Saturn) spacecraft during 2016-17. Both missions will provide latitude-dependent gravity fields, which in principle could be inverted to calculate the vertical structure of the observed cloud-level zonal flow on these planets. Current observations for the flow on these planets exists only at the cloud-level (0.1-1 bar). The observed cloud-level wind might be confined to the upper layers, or be a manifestation of deep cylindrical flows. Moreover, it is possible that in the case where the observed wind is superficial, there exists deep interior flow that is completely decoupled from the observed atmospheric flow.In this talk, we present a new adjoint based inverse model for inversion of the gravity measurements into flow fields. The model is constructed to be as general as possible, allowing for both cloud-level wind extending inward, and a decoupled deep flow that is constructed to produce cylindrical structures with variable width and magnitude, or can even be set to be completely general. The deep flow is also set to decay when approaching the upper levels so it has no manifestation there. The two sources of flow are then combined to a total flow field that is related to the density anomalies and gravity moments via a dynamical model. Given the measured gravitational moments from Jupiter and Saturn, the dynamical model, together with the adjoint inverse model are used for optimizing the control parameters and by this unfolding the deep and surface flows. Several scenarios are examined, including cases in which the surface wind and the deep flow have comparable effects on the gravity field, cases in which the deep flow is dominating over the surface wind, and an extreme

SPCZ zonal events and downstream influence on surface ocean conditions in the Indonesian Throughflow region

NASA Astrophysics Data System (ADS)

Linsley, Braddock K.; Wu, Henry C.; Rixen, Tim; Charles, Christopher D.; Gordon, Arnold L.; Moore, Michael D.

2017-01-01

Seasonal surface freshening of the Makassar Strait, the main conduit of the Indonesian Throughflow (ITF), is a key factor controlling the ITF. Here we present a 262 year reconstruction of seasonal sea-surface-salinity variability from 1742 to 2004 Common Era by using coral δ18O records from the central Makassar Strait. Our record reveals persistent seasonal freshening and also years with significant truncations of seasonal freshening that correlate exactly with South Pacific Convergence Zone (SPCZ) zonal events >4000 km to the east. During these events, the SPCZ dramatically rotates 15° north to near the equator and stronger westward flowing South Pacific boundary currents force higher-salinity water through the Makassar Strait in February-May halting the normal seasonal freshening in the strait. By these teleconnections, our Makassar coral δ18O series provides the first record of the recurrence interval of these zonal SPCZ events and demonstrates that they have occurred on a semiregular basis since the mid-1700s.

Nongeostrophic theory of zonally averaged circulation. I - Formulation

NASA Technical Reports Server (NTRS)

Tung, Ka Kit

1986-01-01

A nongeostrophic theory of zonally averaged circulation is formulated using the nonlinear primitive equations (mass conservation, thermodynamics, and zonal momentum) on a sphere. The relationship between the mean meridional circulation and diabatic heating rate is studied. Differences between results of nongeostropic theory and the geostrophic formulation concerning the role of eddy forcing of the diabatic circulation and the nonlinear nearly inviscid limit versus the geostrophic limit are discussed. Consideration is given to the Eliassen-Palm flux divergence, the Eliassen-Palm pseudodivergence, the nonacceleration theorem, and the nonlinear nongeostrophic Taylor relationship.

An overview of wave-mean flow interactions during the winter of 1978-79 derived from LIMS observations. [Limb Infrared Monitor of Stratosphere

NASA Technical Reports Server (NTRS)

Gille, J. C.; Lyjak, L. V.

1984-01-01

Gradient winds, Eliassen-Palm (EP) fluxes and flux divergences, and the squared refractive index for planetary waves have been calculated from mapped data from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment on Nimbus 7. The changes in the zonal mean atmospheric state, from early winter through 3 disturbances, is described. Convergence or divergence of the EP fluxes clearly produces changes in the zonal mean wind. The steering of the waves by the refractive index structure is not as clear on a daily basis.

Steady hydromagnetic flows in open magnetic fields. I - A class of analytic solutions. [for stellar winds

NASA Technical Reports Server (NTRS)

Low, B. C.; Tsinganos, K.

1986-01-01

In the case of an establishment of theoretical models of the hydromagnetic solar wind, the inclusion of the effects of the magnetic field in the solar wind makes it extremely dificult to solve the mathematical problem. This paper has the objective to present a set of particular analytic solutions. The general formulation of Tsinganos (1982) is used to identify a class of analytic solutions to the equations of steady hydromagnetic flows in spherical coordinates. Flow in an open magnetic field are studied, taking into account the problem in dimensionless form, the special case of radial flows with alpha = 0, general radial flows, illustrative examples for flows in which alpha is not equal to 0, a parametric study of nonradial flows in which alpha is not equal to zero, variations in the parameter nu, and variations in the initial speed eta.

A numerical simulation of the NFAC (National Full-scale Aerodynamics Complex) open-return wind tunnel inlet flow

NASA Technical Reports Server (NTRS)

Kaul, U. K.; Ross, J. C.; Jacocks, J. L.

1985-01-01

The flow into an open return wind tunnel inlet was simulated using Euler equations. An explicit predictor-corrector method was employed to solve the system. The calculation is time-accurate and was performed to achieve a steady-state solution. The predictions are in reasonable agreement with the experimental data. Wall pressures are accurately predicted except in a region of recirculating flow. Flow-field surveys agree qualitatively with laser velocimeter measurements. The method can be used in the design process for open return wind tunnels.

Computational Design and Analysis of a Transonic Natural Laminar Flow Wing for a Wind Tunnel Model

NASA Technical Reports Server (NTRS)

Lynde, Michelle N.; Campbell, Richard L.

2017-01-01

A natural laminar flow (NLF) wind tunnel model has been designed and analyzed for a wind tunnel test in the National Transonic Facility (NTF) at the NASA Langley Research Center. The NLF design method is built into the CDISC design module and uses a Navier-Stokes flow solver, a boundary layer profile solver, and stability analysis and transition prediction software. The NLF design method alters the pressure distribution to support laminar flow on the upper surface of wings with high sweep and flight Reynolds numbers. The method addresses transition due to attachment line contamination/transition, Gortler vortices, and crossflow and Tollmien-Schlichting modal instabilities. The design method is applied to the wing of the Common Research Model (CRM) at transonic flight conditions. Computational analysis predicts significant extents of laminar flow on the wing upper surface, which results in drag savings. A 5.2 percent scale semispan model of the CRM NLF wing will be built and tested in the NTF. This test will aim to validate the NLF design method, as well as characterize the laminar flow testing capabilities in the wind tunnel facility.

Flow-Visualization Techniques Used at High Speed by Configuration Aerodynamics Wind-Tunnel-Test Team