scholarly journals Retrieval of Urban Boundary Layer Structures from Doppler Lidar Data. Part I: Accuracy Assessment

2008 ◽  
Vol 65 (1) ◽  
pp. 3-20 ◽  
Author(s):  
Quanxin Xia ◽  
Ching-Long Lin ◽  
Ronald Calhoun ◽  
Rob K. Newsom
Keyword(s):  
Boundary Layer ◽  
Radial Velocity ◽  
Eddy Viscosity ◽  
Velocity Fields ◽  
Urban Boundary Layer ◽  
Flow Structures ◽  
Lidar Data ◽  
Velocity Data ◽  
Beam Direction ◽  
The Cross

Abstract Two coherent Doppler lidars from the U.S. Army Research Laboratory (ARL) and Arizona State University (ASU) were deployed in the Joint Urban 2003 atmospheric dispersion field experiment (JU2003) held in Oklahoma City, Oklahoma. The dual-lidar data were used to evaluate the accuracy of a four-dimensional variational data assimilation (4DVAR) method and to identify the coherent flow structures in the urban boundary layer. The objectives of the study are threefold. The first objective is to examine the effect of eddy viscosity models on the quality of retrieved velocity data. The second objective is to determine the fidelity of single-lidar 4DVAR and evaluate the difference between single- and dual-lidar retrievals. The third objective is to inspect flow structures above some geospatial features on the land surface. It is found that the approach of treating eddy viscosity as part of the control variables yields better results than the approach of prescribing viscosity. The ARL single-lidar 4DVAR is able to retrieve radial velocity fields with an accuracy of 98% in the along-beam direction and 80%–90% in the cross-beam direction. For the dual-lidar 4DVAR, the accuracy of retrieved radial velocity in the ARL cross-beam direction improves to 90%–94% of the ASU radial velocity data. By using the dual-lidar-retrieved data as a reference, the single-lidar 4DVAR is able to recover fluctuating velocity fields with 70%–80% accuracy in the along-beam direction and 60%–70% accuracy in the cross-beam direction. Large-scale convective roll structures are found in the vicinity of the downtown airport and parks. Vortical structures are identified near the business district. Strong up- and downdrafts are also found above a cluster of restaurants.

scholarly journals Measurements of wind turbulence parameters by a conically scanning coherent Doppler lidar in the atmospheric boundary layer

2017 ◽  
Author(s):  
Igor N. Smalikho ◽  
Viktor A. Banakh
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Radial Velocity ◽  
Dissipation Rate ◽  
Stream Line ◽  
Lidar Data ◽  
Doppler Lidar ◽  
Integral Scale ◽  
Coherent Doppler Lidar ◽  
Turbulence Parameters

Abstract. The method and results of lidar studies of spatiotemporal variability of wind turbulence in the atmospheric boundary layer are reported. The measurements were conducted by a Stream Line pulsed coherent Doppler lidar with the use of conical scanning by a probing beam around the vertical axis. Lidar data are used to estimate the kinetic energy of turbulence, turbulent energy dissipation rate, integral scale of turbulence, and momentum fluxes. The dissipation rate was determined from the azimuth structure function of radial velocity within the inertial subrange of turbulence. When estimating the kinetic energy of turbulence from lidar data, we took into account the averaging of radial velocity over the sensing volume. The integral scale of turbulence was determined on the assumption that the structure of random irregularities of the wind field is described by the von Karman model. The domain of applicability of the used method and the accuracy of estimation of turbulence parameters were determined. Turbulence parameters estimated from Stream Line lidar measurement data and from data of a sonic anemometer were compared.

scholarly journals Measurements of wind turbulence parameters by a conically scanning coherent Doppler lidar in the atmospheric boundary layer

2017 ◽  
Vol 10 (11) ◽  
pp. 4191-4208 ◽  
Author(s):  
Igor N. Smalikho ◽  
Viktor A. Banakh
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Radial Velocity ◽  
Dissipation Rate ◽  
Stream Line ◽  
Lidar Data ◽  
Doppler Lidar ◽  
Integral Scale ◽  
Coherent Doppler Lidar ◽  
Turbulence Parameters

Abstract. The method and results of lidar studies of spatiotemporal variability of wind turbulence in the atmospheric boundary layer are reported. The measurements were conducted by a Stream Line pulsed coherent Doppler lidar (PCDL) with the use of conical scanning by a probing beam around the vertical axis. Lidar data are used to estimate the kinetic energy of turbulence, turbulent energy dissipation rate, integral scale of turbulence, and momentum fluxes. The dissipation rate was determined from the azimuth structure function of radial velocity within the inertial subrange of turbulence. When estimating the kinetic energy of turbulence from lidar data, we took into account the averaging of radial velocity over the sensing volume. The integral scale of turbulence was determined on the assumption that the structure of random irregularities of the wind field is described by the von Kármán model. The domain of applicability of the used method and the accuracy of the estimation of turbulence parameters were determined. Turbulence parameters estimated from Stream Line lidar measurement data and from data of a sonic anemometer were compared.

Shock wave–boundary layer interaction in supersonic flow over a forward-facing step

2016 ◽  
Vol 807 ◽  
pp. 258-302 ◽  
Author(s):  
Jayaprakash N. Murugan ◽  
Raghuraman N. Govardhan
Keyword(s):  
Boundary Layer ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Velocity Fields ◽  
Recirculation Region ◽  
Velocity Data ◽  
Flow Area ◽  
Piv Measurements ◽  
Shock Position ◽  
Forward Facing Step

We study in the present work a Mach 2.5 flow over a forward-facing step. The focus of the work is the flow ahead of the step, in particular, the unsteady interactions between the shock, the boundary layer and the separation bubble. The primary geometrical parameter in the problem is the ratio of the step height to the incoming boundary layer thickness, $h/\unicode[STIX]{x1D6FF}$, which is kept fixed at 2. Results are presented from detailed particle image velocimetry (PIV) measurements in two orthogonal planes to obtain a reasonable picture of the whole flow field. The mean velocity field in the central cross-stream or wall-normal ($x$–$y$) plane shows that the incoming boundary layer separates upstream of the step forming a large separation bubble ahead of the step, which can be relatively well resolved in PIV measurements compared to the compression ramp cases. Wall pressure fluctuation spectra close to the separation location show a dominant frequency ($f$) that is two orders of magnitude smaller than the characteristic frequency of the incoming boundary layer ($U_{\infty }/\unicode[STIX]{x1D6FF}$), consistent with low-frequency motions of the shock that have received a lot of recent attention ($U_{\infty }$ $=$ free-stream velocity, $\unicode[STIX]{x1D6FF}$ $=$ boundary layer thickness). PIV measurements in the wall-normal plane show large variations in shock position with time. The shock position measured from velocity data outside the boundary layer is found to be well correlated with the reverse flow area ahead of the step, and weakly correlated to structures in the incoming boundary layer. In contrast, the shock foot, determined from velocity data within the boundary layer, is found to be well correlated to the low- and high-speed streaks in the incoming boundary layer, in addition to the reverse flow area ahead of the step. Instantaneous velocity fields in the spanwise ($x$–$z$) plane parallel to the lower wall show that the shock is broadly two-dimensional with small spanwise ripples, while the recirculation region has very large spanwise variations. The spanwise-averaged shock location is found to be well correlated to the most upstream location of the recirculation region over a spanwise length ($x_{r,min}^{sp}$). Instantaneous velocity fields show that when some part of the recirculation region is far upstream, the corresponding nearly two-dimensional shock is also far upstream. On the other hand, when $x_{r,min}^{sp}$ is relatively downstream, the resulting shock is also found to be downstream. Hence, the present results suggest that for the forward-facing step configuration, the large-scale streamwise motions of the shock are mainly correlated to the most upstream point of the recirculation region, which has large spanwise variations.

scholarly journals Retrieval of Urban Boundary Layer Structures from Doppler Lidar Data. Part II: Proper Orthogonal Decomposition

2008 ◽  
Vol 65 (1) ◽  
pp. 21-42 ◽  
Author(s):  
Ching-Long Lin ◽  
Quanxin Xia ◽  
Ronald Calhoun
Keyword(s):  
Boundary Layer ◽  
Proper Orthogonal Decomposition ◽  
Coherent Structures ◽  
Inversion Layer ◽  
Urban Boundary Layer ◽  
Orthogonal Decomposition ◽  
Data Matrix ◽  
Lidar Data ◽  
Roll Vortices ◽  
Proper Orthogonal

Abstract The proper orthogonal decomposition technique is applied to 74 snapshots of 3D wind and temperature fields to study turbulent coherent structures and their interplay in the urban boundary layer over Oklahoma City, Oklahoma. These snapshots of data are extracted from single-lidar data via a four-dimensional variational data assimilation technique. The total velocities and fluctuating temperature are used to construct the data matrix for the decomposition; thus the first eigenmode represents the temporal mean of these data. Roll vortices with a wavelength–height ratio of 3.2 are identified in the first, most energetic eigenmode and are attributed to the inflection-point instability. The second and third spatial eigenmodes also exhibit roll characteristics with different time and length scales, resulting in clockwise- and counterclockwise-rotating roll vortices above the airport and the central business districts. Their positive correlation with temperature fluctuation suggests that those roll structures are driven by thermal as well as wind shear. Their limited horizontal extent seems to coincide with the path of the Oklahoma River. With decreasing rank, coherent structures undergo a transition from roll to polygon patterns. A localized downdraft or updraft located above a cluster of restaurants is captured by the fourth eigenmode. In the capping inversion layer, gravity wave eigenmodes are observed and may be attributed to convection waves. The representation of instantaneous snapshots by high-ranking eigenmodes is then examined by reconstruction of reduced-order fields. It is found that the first four eigenmodes are sufficient to capture the overall characteristics of the 74 snapshots of data.

A vertically oscillating plate disturbing the development of a boundary layer

1995 ◽  
Vol 298 ◽  
pp. 1-22 ◽  
Author(s):  
J. J. Miau ◽  
C. R. Chen ◽  
J. H. Chou
Keyword(s):  
Boundary Layer ◽  
Momentum Equation ◽  
Flow Structures ◽  
Pressure Measurements ◽  
Flux Rate ◽  
Velocity Data ◽  
Fibre Probe ◽  
The Mean ◽  
Vorticity Flux ◽  
Oscillating Plate

A vertically oscillating plate in a boundary layer regulates the vorticity flux rate with respect to time and displaces the vorticity away from the wall. These phenomena are discussed for non-dimensional frequencies of the oscillating plate K = 0, 0.006, 0.01 and 0.02. The velocity data obtained by a split-fibre probe near the wall in the region immediately downstream of the oscillating plate lead to a discussion on the behaviour of the flow structures with respect to the non-dimensional frequency. The physical understanding deduced is complementary to the findings of a smoke-wire flow visualization conducted in this study. An integral analysis of the momentum equation indicates that the mean vorticity flux rate of the present flow is composed of contributions from both the parallel shear layer and the curving streamline. This analysis further suggests that the mean vorticity flux rate can be obtained through a combination of pressure measurements at the wall and in the irrotational region of the flow.

scholarly journals The impact of a foehn wind on PM10 concentrations and the urban boundary layer in complex terrain: a case study from Kraków, Poland

Tellus B ◽  
2021 ◽  
Vol 73 (1) ◽  
pp. 1-26
Author(s):  
Piotr Sekuła ◽  
Anita Bokwa ◽  
Zbigniew Ustrnul ◽  
Mirosław Zimnoch ◽  
Bogdan Bochenek
Keyword(s):  
Boundary Layer ◽  
Complex Terrain ◽  
Urban Boundary Layer ◽  
The Impact

scholarly journals Kinematics of Disk Stars in the Solar Neighbourhood

1998 ◽  
Vol 11 (1) ◽  
pp. 574-574
Author(s):  
A.E. Gómez ◽  
S. Grenier ◽  
S. Udry ◽  
M. Haywood ◽  
V. Sabas ◽  
...  
Keyword(s):  
Dispersion Relation ◽  
Radial Velocity ◽  
Velocity Dispersion ◽  
Tangential Velocity ◽  
Thin Disk ◽  
The Other ◽  
Proper Motions ◽  
Velocity Data ◽  
Kinematic Data ◽  
Radial Velocity Data

Using Hipparcos parallaxes and proper motions together with radial velocity data and individual ages estimated from isochones, the velocity ellipsoid has been determined as a function of age. On the basis of the available kinematic data two different samples were considered: a first one (7789 stars) for which only tangential velocities were calculated and a second one containing 3104 stars with available U, V and W velocity components and total velocities ≤ 65 km.s-1. The main conclusions are: -Mixing is not complete at about 0.8-1 Gyr. -The shape of the velocity ellipsoid changes with time getting rounder from σu/σv/σ-w = 1/0.63/0.42 ± 0.04 at about 1 Gyr to1/0.7/0.62 ±0.04 at 4-5 Gyr. -The age-velocity-dispersion relation (from the sample with kinematical selection) rises to a maximum, thereafter remaining roughly constant; there is no dynamically significant evolution of the disk after about 4-5 Gyr. -Among the stars with solar metallicities and log(age) > 9.8 two groups are identified: one has typical thin disk characteristics, the other is older than 10 Gyr and lags the LSR at about 40 km.s-1 . -The variation of the tangential velocity with age(without selection on the tangential velocity) shows a discontinuity at about 10 Gyr, which may be attributed to stars typically of the thick disk populations for ages > 10 Gyr.

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