The Effects of the Width of an Isolated Valley on Near-Surface Turbulence

With the aim of ascertaining the effects of the widths (A) of valleys on near-surface turbulence, flows over an isolated symmetric three-dimensional valley of constant depth (H) and slopes are characterized in a large-boundary-layer wind tunnel. Starting at A = 4H, valley widths were systematically varied to A = 12H with constant increments of 2H. High-resolution laser-Doppler velocimetry measurements were made at several equivalent locations above each of the resulting valley geometries and compared with data from undisturbed flows over flat terrain. Flow separation caused by the first ridges generated inner-valley recirculation bubbles with lengths dependent on the valley widths. Secondary recirculation zones were also observed downstream from the crests of the second ridges. Results show that the width modifications exert the strongest effects on turbulence within the valleys and the vicinities of the second ridges. Above these locations, maximal magnitudes of turbulence are generally found for the larger width geometries. Furthermore, lateral turbulence overpowers the longitudinal counterparts nearest to the surface, with maximal gains occurring for the smaller widths. Our data indicate that valley widths are impactful on near-surface flows and should be considered together with other more established geometric parameters of influence.

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The Influence of Slopes of Isolated Three-Dimensional Valleys on Near-Surface Turbulence

Boundary-Layer Meteorology ◽

10.1007/s10546-021-00648-8 ◽

2021 ◽

Author(s):

Sylvio Freitas ◽

Frank Harms ◽

Bernd Leitl

Keyword(s):

Boundary Layer ◽

Longitudinal Velocity ◽

Three Dimensional ◽

Boundary Layer Flows ◽

Homogeneous Surface ◽

Near Surface ◽

Surface Turbulence ◽

Stable Atmospheric Boundary Layer ◽

Recirculation Zones ◽

Layer Flow

AbstractMotivated by a limited understanding of how valleys affect near-surface turbulence, characterizations of neutrally stable atmospheric-boundary-layer flows over isolated valleys are presented. In particular, the influence of the slopes of the three-dimensional ridges that form the idealized valleys are investigated. Flows over three distinct symmetric valley geometries were modelled in a large boundary-layer wind tunnel. For each valley geometry, the high-resolution measurements from the crests of each of the ridges and the midpoint between them are compared with an undisturbed moderately rough classed boundary-layer flow over flat terrain with homogeneous surface roughness. Flow separation originates above the crests of the first ridges of all geometries and generates recirculation zones. These are characterized by slope-dependent increases in three-dimensional near-surface turbulence when compared with the attached flows further upstream. The recirculation zones longitudinally extend to roughly half the valley width. Above the crests of the second ridges, the longitudinal velocity component decreases and turbulence intensity increases when compared with the flows above the crests of the first ridges. Results also exhibit significant increases of turbulence above the inner-valley regions of all geometries.

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The Effect of Vane Clocking on the Unsteady Flowfield in a One and a Half Stage Transonic Turbine

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-27848 ◽

2007 ◽

Author(s):

O. Schennach ◽

R. Pecnik ◽

B. Paradiso ◽

E. Go¨ttlich ◽

A. Marn ◽

...

Keyword(s):

Laser Doppler Velocimetry ◽

Three Dimensional ◽

Fast Response ◽

Navier Stokes ◽

Doppler Velocimetry ◽

Pressure Transducers ◽

Wake Interactions ◽

Transonic Turbine ◽

Response Pressure ◽

Vane Clocking

The current paper presents the results of numerical and experimental clocking investigations performed in a high-pressure transonic turbine with a downstream vane row. The objective was a detailed analysis of shock and wake interactions in such a 1.5 stage machine while clocking the vanes. Therefore a transient 3D-Navier Stokes calculation was done for two clocking positions and the three dimensional results are compared with Laser-Doppler-Velocimetry measurements at midspan. Additionally the second vane was equipped with fast response pressure transducers to record the instantaneous surface pressure for 20 different clocking positions at midspan.

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The Interaction of Rolling Vortices With a Turbulent Boundary Layer

Journal of Fluids Engineering ◽

10.1115/1.2817302 ◽

1995 ◽

Vol 117 (4) ◽

pp. 564-570

Author(s):

M. J. Donnelly ◽

O. K. Rediniotis ◽

S. A. Ragab ◽

D. P. Telionis

Keyword(s):

Boundary Layer ◽

Kinetic Energy ◽

Turbulent Boundary Layer ◽

Life Span ◽

Turbulent Kinetic Energy ◽

Laser Doppler Velocimetry ◽

Doppler Velocimetry ◽

Turbulence Level ◽

Periodic Field ◽

Entire Boundary

Laser-Doppler velocimetry is employed to measure the periodic field created by releasing spanwise vortices in a turbulent boundary layer. Phase-averaged vorticity and turbulence level contours are estimated and presented. It is found that vortices with diameter of the order of the boundary layer quickly diffuse and disappear while their turbulent kinetic energy spreads uniformly across the entire boundary layer. Larger vortices have a considerably longer life span and in turn feed more vorticity into the boundary layer.

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Marine boundary layer cloud property retrievals from high-resolution ASTER observations: case studies and comparison with Terra MODIS

Atmospheric Measurement Techniques ◽

10.5194/amt-9-5869-2016 ◽

2016 ◽

Vol 9 (12) ◽

pp. 5869-5894 ◽

Cited By ~ 10

Author(s):

Frank Werner ◽

Galina Wind ◽

Zhibo Zhang ◽

Steven Platnick ◽

Larry Di Girolamo ◽

...

Keyword(s):

Boundary Layer ◽

High Resolution ◽

Marine Boundary Layer ◽

Thermal Emission ◽

Three Dimensional ◽

Correlation Coefficients ◽

Retrieval Algorithm ◽

Research Level ◽

Boundary Layer Cloud ◽

Layer Cloud

Abstract. A research-level retrieval algorithm for cloud optical and microphysical properties is developed for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra satellite. It is based on the operational MODIS algorithm. This paper documents the technical details of this algorithm and evaluates the retrievals for selected marine boundary layer cloud scenes through comparisons with the operational MODIS Data Collection 6 (C6) cloud product. The newly developed, ASTER-specific cloud masking algorithm is evaluated through comparison with an independent algorithm reported in [Zhao and Di Girolamo(2006)]. To validate and evaluate the cloud optical thickness (τ) and cloud effective radius (reff) from ASTER, the high-spatial-resolution ASTER observations are first aggregated to the same 1000 m resolution as MODIS. Subsequently, τaA and reff, aA retrieved from the aggregated ASTER radiances are compared with the collocated MODIS retrievals. For overcast pixels, the two data sets agree very well with Pearson's product-moment correlation coefficients of R > 0.970. However, for partially cloudy pixels there are significant differences between reff, aA and the MODIS results which can exceed 10 µm. Moreover, it is shown that the numerous delicate cloud structures in the example marine boundary layer scenes, resolved by the high-resolution ASTER retrievals, are smoothed by the MODIS observations. The overall good agreement between the research-level ASTER results and the operational MODIS C6 products proves the feasibility of MODIS-like retrievals from ASTER reflectance measurements and provides the basis for future studies concerning the scale dependency of satellite observations and three-dimensional radiative effects.

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The Namib Turbulence Experiment: Investigating surface-atmosphere heat transfer in three dimensions

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-20-0269.1 ◽

2021 ◽

Keyword(s):

Heat Transfer ◽

Surface Layer ◽

Temperature Field ◽

Heat Exchange ◽

High Resolution ◽

Three Dimensional ◽

Temperature Fluctuations ◽

Near Surface ◽

Turbulent Heat Exchange ◽

Wide Range

Abstract The Namib Turbulence EXperiment (NamTEX) was a multi-national micrometeorological campaign conducted in the Central Namib Desert to investigate three-dimensional surface layer turbulence and the spatio-temporal patterns of heat transfer between the sub-surface, surface, and atmosphere. The Namib provides an ideal location for fundamental research that revisits some key assumptions in micrometeorology that are implicitly included in the parameterizations describing energy exchange in weather forecasting and climate models: Homogenous flat surfaces, no vegetation, little moisture, and cloud-free skies create a strong and consistent diurnal forcing, resulting in a wide range of atmospheric stabilities. A novel combination of instruments was used to simultaneously measure variables and processes relevant to heat transfer: A three km fibre-optic distributed temperature sensor (DTS) was suspended in a pseudo-three-dimensional array within a 300 m x 300 m domain to provide vertical cross-sections of air temperature fluctuations. Aerial and ground-based thermal imagers recorded high resolution surface temperature fluctuations within the domain and revealed the spatial thermal imprint of atmospheric structures responsible for heat exchange. High-resolution soil temperature and moisture profiles together with heat flux plates provided information on near-surface soil dynamics. Turbulent heat exchange was measured with a vertical array of five eddy-covariance point measurements on a 21-m mast, as well as by co-located small- and large-aperture scintillometers. This contribution first details the scientific goals and experimental set-up of the NamTEX campaign. Then using a typical day, we demonstrate i) the coupling of surface layer, surface, and soil temperatures using high-frequency temperature measurements, ii) differences in spatial and temporal standard deviations of the horizontal temperature field using spatially distributed measurements, and iii) horizontal anisotropy of the turbulent temperature field.

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Development of LDV(Laser Doppler Velocimetry) for Measuring Three Dimensional Hull Wake of Ship Model in Large Cavitation Tunnel

Journal of the Society of Naval Architects of Korea ◽

10.3744/snak.2017.54.6.515 ◽

2017 ◽

Vol 54 (6) ◽

pp. 515-521 ◽

Cited By ~ 1

Author(s):

Bu-Geun Paik ◽

Jong-Woo Ahn ◽

Han-Shin Seol ◽

Young-Ha Park ◽

Ki-Sup Kim ◽

...

Keyword(s):

Laser Doppler Velocimetry ◽

Three Dimensional ◽

Laser Doppler ◽

Doppler Velocimetry ◽

Ship Model ◽

Cavitation Tunnel

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Laser Doppler Velocimetry (LDV) measurements of airfoil surface flow on a Horizontal Axis Wind Turbine in boundary layer

Energy ◽

10.1016/j.energy.2019.06.150 ◽

2019 ◽

Vol 183 ◽

pp. 341-357 ◽

Cited By ~ 2

Author(s):

Qing'an Li ◽

Jianzhong Xu ◽

Takao Maeda ◽

Yasunari Kamada ◽

Shogo Nishimura ◽

...

Keyword(s):

Boundary Layer ◽

Wind Turbine ◽

Laser Doppler Velocimetry ◽

Surface Flow ◽

Horizontal Axis ◽

Laser Doppler ◽

Doppler Velocimetry ◽

Horizontal Axis Wind Turbine ◽

Airfoil Surface

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Measurements of Enhanced Near-Surface Turbulence under Windrows

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0265.1 ◽

2020 ◽

Vol 50 (1) ◽

pp. 197-215

Author(s):

Seth F. Zippel ◽

Ted Maksym ◽

Malcolm Scully ◽

Peter Sutherland ◽

Dany Dumont

Keyword(s):

Boundary Layer ◽

Surface Flux ◽

Breaking Waves ◽

Surface Boundary ◽

Surface Boundary Layer ◽

Near Surface ◽

Surface Turbulence ◽

Order Of Magnitude ◽

Convergence Zones ◽

Shallow Bay

AbstractObservations of waves, winds, turbulence, and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of Rimouski, Québec. Water velocities measured from a forward-looking pulse-coherent ADCP mounted on a small zodiac show spanwise (cross-windrow) convergence, streamwise (downwind) velocity enhancement, and downwelling in the windrows, consistent with the view that windrows are the result of counterrotating pairs of wind-aligned vortices. The spacing of windrows, measured with acoustic backscatter and with surface imagery, was measured to be approximately twice the water depth, which suggests an aspect ratio of 1. The magnitude and vertical distribution of turbulence measured from the ADCP are consistent with a previous scaling and observations of near-surface turbulence under breaking waves, with dissipation rates larger and decaying faster vertically than what is expected from a shear-driven boundary layer. Measurements of dissipation rate are partitioned to within, and outside of the windrow convergence zones, and measurements inside the convergence zones are found to be nearly an order of magnitude larger than those outside with similar vertical structure. A ratio of time scales suggests that turbulence likely dissipates before it can be advected horizontally into convergences, but the advection of wave energy into convergences may elevate the surface flux of TKE and could explain the elevated turbulence in the windrows. These results add to a limited number of conflicting observations of turbulence variability due to windrows, which may modify gas flux, and heat and momentum transport in the surface boundary layer.

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The Three-Dimensional Structure and Evolution of a Tornado Boundary Layer

Weather and Forecasting ◽

10.1175/waf-d-13-00070.1 ◽

2013 ◽

Vol 28 (6) ◽

pp. 1552-1561 ◽

Cited By ~ 47

Author(s):

Karen A. Kosiba ◽

Joshua Wurman

Keyword(s):

Boundary Layer ◽

Three Dimensional ◽

Flow Region ◽

Ground Level ◽

Dimensional Structure ◽

Surface Boundary ◽

Surface Boundary Layer ◽

Near Surface ◽

Three Dimensional Structure ◽

Flow Swirl

Abstract The finescale three-dimensional structure and evolution of the near-surface boundary layer of a tornado (TBL) is mapped for the first time. The multibeam Rapid-Scan Doppler on Wheels (RSDOW) collected data at several vertical levels, as low as 4, 6, 10, 12, 14, and 17 m above ground level (AGL), contemporaneously at 7-s intervals for several minutes in a tornado near Russell, Kansas, on 25 May 2012. Additionally, a mobile mesonet anemometer measured winds at 3.5 m AGL in the core flow region. The radar, anemometer, and ground-based velocity-track display (GBVTD) analyses reveal the peak wind intensity is very near the surface at ~5 m AGL, about 15% higher than at 10 m AGL and 25% higher than at ~40 m AGL. GBVTD analyses resolve a downdraft within the radius of maximum winds (RMW), which decreased in magnitude when varying estimates for debris centrifuging are included. Much of the inflow (from −1 to −7 m s−1) is at or below 10–14 m AGL, much shallower than reported previously. Surface outflow precedes tornado dissipation. Comparisons between large-eddy simulation (LES) predictions of the corner flow swirl ratio Sc and observed tornado intensity changes are consistent.

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