Accuracy of Sonic Anemometers: Laminar Wind-Tunnel Calibrations Compared to Atmospheric In Situ Calibrations Against a Reference Instrument

2004 ◽  
Vol 111 (1) ◽  
pp. 33-54 ◽  
Author(s):  
Ulf Högström ◽  
Ann-Sofi Smedman
Keyword(s):  
Wind Tunnel ◽  
Reference Instrument ◽  
Sonic Anemometers

scholarly journals Velocity-Based EDR Retrieval Techniques Applied to Doppler Radar Measurements from Rain: Two Case Studies

2019 ◽  
Vol 36 (9) ◽  
pp. 1693-1711 ◽  
Author(s):  
A. C. P. Oude Nijhuis ◽  
C. M. H. Unal ◽  
O. A. Krasnov ◽  
H. W. J. Russchenberg ◽  
A. G. Yarovoy
Keyword(s):  
Case Studies ◽  
Doppler Radar ◽  
Energy Dissipation Rate ◽  
Accurate Estimation ◽  
Retrieval Technique ◽  
Sonic Anemometers ◽  
Radar Measurements ◽  
Rain Events ◽  
Kolmogorov Constant

In this article, five velocity-based energy dissipation rate (EDR) retrieval techniques are assessed. The EDR retrieval techniques are applied to Doppler measurements from Transportable Atmospheric Radar (TARA)—a precipitation profiling radar—operating in the vertically fixed-pointing mode. A generalized formula for the Kolmogorov constant is derived, which gives potential for the application of the EDR retrieval techniques to any radar line of sight (LOS). Two case studies are discussed that contain rain events of about 2 and 18 h, respectively. The EDR values retrieved from the radar are compared to in situ EDR values from collocated sonic anemometers. For the two case studies, a correlation coefficient of 0.79 was found for the wind speed variance (WSV) EDR retrieval technique, which uses 3D wind vectors as input and has a total sampling time of 10 min. From this comparison it is concluded that the radar is able to measure EDR with a reasonable accuracy. Almost no correlation was found for the vertical wind velocity variance (VWVV) EDR retrieval technique, as it was not possible to sufficiently separate the turbulence dynamics contribution to the radar Doppler mean velocities from the velocity contribution of falling raindrops. An important cause of the discrepancies between radar and in situ EDR values is thus due to insufficient accurate estimation of vertical air velocities.

In situ study of volcanic ash resuspension using a portable wind tunnel.

2020 ◽  
Author(s):  
Jacopo Taddeucci ◽  
Elisabetta del Bello ◽  
Jonathan P Merrison ◽  
Keld R Rasmussen ◽  
Jens J Iversen ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
High Speed ◽  
Volcanic Ash ◽  
Field Experiments ◽  
Critical Parameters ◽  
Test Bed ◽  
High Definition ◽  
Sustained Activity

<p>The resuspension of volcanic ash deposits by wind is a well-known source of hazard following explosive eruptions. Besides the mail control exerted by the local wind field, ash resuspension is also influenced by: 1) atmospheric humidity; 2) features of the deposit (grain size distribution, sedimentary structures, etc.), and 3) features of the substrate (i.e. moisture, roughness). Ash resuspension is modeled using numerical simulations, which however require physical characterization and identification of the critical parameters controlling ash resuspension. Wind tunnel studies on volcanic particles are very limited and restricted to laboratory parameterizations, with in-situ effects not been parameterized. We tested field experiments of volcanic ash resuspension developing a portable wind tunnel and deploying on proximal (3 km) ash deposits from the semi-sustained activity of Sakurajima volcano (Japan) and from distal (250 km ca.) ash deposits from the 2011 Cordon Caulle eruption (Chile). The wind tunnel is calibrated with both LDA and pitot tubes measurements. The device allows generating a controlled wind profile within a 110x12x12 cm test section, which is placed directly on an untouched test bed of naturally deposited ash. Two types of experiments were performed: 1) ramp up speed experiments, where the wind speed is increased until reaching the threshold friction speed on four different substrates; 2) constant speed experiments, where three wind speed values where kept for 20 minutes using the same substrate. The threshold friction speed is measured with a hot wire anemometer, and the movement of resuspended ash is detected by means of multiple high speed and high definition digital camcorders. In-situ measured threshold friction speeds are compared to 1) in situ observed episodes of resuspension driven by local winds and 2) laboratory determination of threshold friction speed in controlled environmental conditions, and using the same ash deposited homogeneously.</p><p> </p>

Interferometry for in situ mass transfer measurements in a wind tunnel

1984 ◽  
Vol 2 (4) ◽  
pp. 203-203 ◽  
Author(s):  
B. L. Button ◽  
B. N. Dobbins
Keyword(s):  
Mass Transfer ◽  
Wind Tunnel

scholarly journals Three-dimensional in-situ imaging of cracks in concrete using diffuse ultrasound

2017 ◽  
Vol 17 (2) ◽  
pp. 279-284 ◽  
Author(s):  
Yuxiang Zhang ◽  
Eric Larose ◽  
Ludovic Moreau ◽  
Grégoire d’Ozouville
Keyword(s):  
Wind Tunnel ◽  
Multiple Scattering ◽  
Structural Changes ◽  
Imaging Technique ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Thick Wall ◽  
Pressure Changes ◽  
Diffuse Ultrasound

Locadiff, an innovative imaging technique based on diffuse waves, has recently been developed in order to image mechanical changes in heterogeneous, geological, or man-made materials. This manuscript reports the on-site application of Locadiff to locate several pre-existing cracks on an aeronautical wind tunnel made of pre-stressed concrete. Using 32 transducers working at ultrasonic frequencies (80–220 kHz) where multiple scattering occurs, we monitor during 15 min an area of 2.5 m×2.5 m of a 35-cm-thick wall. With the wind tunnel in its routine operation, structural changes around the cracks are detected, thanks to their closing or opening due to slight pressure changes. By mapping the density of such microstructure changes in the bulk of the material, locating three pre-existing cracks is properly performed in three dimensions.

Sailing Downwind: Aerodynamic Performance of the Velella Sail

1991 ◽  
Vol 158 (1) ◽  
pp. 117-132
Author(s):  
LISBETH FRANCIS
Keyword(s):  
Natural Selection ◽  
Wind Tunnel ◽  
Aspect Ratio ◽  
Hydrodynamic Force ◽  
Center Of Pressure ◽  
Aerodynamic Force ◽  
Aerodynamic Performance ◽  
Polar Plot ◽  
Low Aspect Ratio

Using a wind tunnel built over a shallow pool and methods devised for measuring the performance of yacht sails, I describe aerodynamic performance in situ for the sailor-by-the-wind, Velella velella. By contrast with designers of the modern yacht mainsail, natural selection has apparently favored stability and seaworthiness over performance to windward. The Velella sail is a low aspect ratio airfoil with an unusually flat polar plot. Primarily a drag-based locomotory structure, this thin, leaf-like sail generates maximum force when oriented at attack angles between 50° and 90°. In the wind tunnel, free-sailing animals spontaneously assumed stable orientations at attack angles ranging from 28° to 87° and sailed with their hulls approximately broadside to the apparent flow of oncoming water. At these angles, aerodynamic force on the sail is asymmetrical, with the center of pressure upwind of the sail midline. Since aerodynamic force on the sail is balanced at equilibrium by hydrodynamic force on the hull, this orientation must be caused by asymmetrical forces acting on surface and underwater parts as the wind drags the animal along the surface of the water.

scholarly journals In Situ Calibration of Hot-Film Probes Using a Collocated Sonic Anemometer: Implementation of a Neural Network

2010 ◽  
Vol 27 (1) ◽  
pp. 23-41 ◽  
Author(s):  
E. Kit ◽  
A. Cherkassky ◽  
T. Sant ◽  
H. J. S. Fernando
Keyword(s):  
Neural Network ◽  
Sonic Anemometer ◽  
Input Voltage ◽  
Calibration Method ◽  
Calibration Procedure ◽  
Approximation Technique ◽  
Sonic Anemometers ◽  
Standard Calibration ◽  
Hot Film

Abstract Although the integral quantities of atmospheric turbulence are conveniently measured using sonic anemometers, obtaining relevant finescale variables such as the kinetic energy dissipation using conventional hot-film/wire techniques remains a challenge because of two main difficulties. The first difficulty is the mean wind variability, which causes violation of the requirement that mean winds have a specific alignment with the hot-film/wire probe. To circumvent this problem, a combination of collocated sonic and hot-film anemometers, with the former measuring mean winds and aligning the latter in the appropriate wind direction via an automated platform, is successfully designed and implemented. The second difficulty is the necessity of frequent and onerous calibrations akin to hot-film anemometry that lead to logistical difficulties during outdoor (field) measurements. This is addressed by employing sonic measurements to calibrate the hot films in the same combination, with the output (velocity) to input (voltage) transfer function for the hot film derived using a neural network (NN) model. The NN is trained using low-pass-filtered hot-film and sonic data taken in situ. This new hot-film calibration procedure is compared with the standard calibration method based on an external calibrator. It is inferred that the sonic-based NN method offers great potential as an alternative to laborious standard calibration techniques, particularly in the laboratory and in stable atmospheric boundary layer settings. The NN approximation technique is found to be superior to the conventionally used polynomial fitting methods when used in conjunction with unevenly spaced calibration velocity data generated by sonic anemometers.

scholarly journals Estimation of turbulence parameters from scanning lidars and in-situ instrumentation in the Perdigão 2017 campaign

2019 ◽  
Author(s):  
Norman Wildmann ◽  
Nicola Bodini ◽  
Julie K. Lundquist ◽  
Ludovic Bariteau ◽  
Johannes Wagner
Keyword(s):  
Temporal Variability ◽  
Shear Zones ◽  
Spectral Width ◽  
Early Morning ◽  
Spatial And Temporal Variability ◽  
Atmospheric Conditions ◽  
Sonic Anemometers ◽  
Spatio Temporal ◽  
Lifting System

Abstract. The understanding of the sources, spatial distribution and temporal variability of turbulence in the atmospheric boundary layer (ABL) and improved simulation of its forcing processes require observations in a broad range of terrain types and atmospheric conditions. In this study, we estimate turbulence kinetic energy (TKE) dissipation rate using multiple techniques, including traditional in-situ measurements of sonic anemometers on meteorological towers, a hot-wire anemometer on a tethered lifting system (TLS), as well as remote-sensing retrievals from a vertically staring lidar and two lidars performing range-height indicator (RHI) scans. For the retrieval of ε from the lidar RHI scans, we introduce a modification of the Doppler Spectral Width (DSW) method. This method uses spatio-temporal averages of the variance of the line-of-sight (LOS) velocity and the turbulent broadening of the Doppler backscatter spectrum. We validate this method against the observations from the other instruments, also including uncertainty estimations for each method. The synthesis of the results from all instruments enables a detailed analysis of the spatial and temporal variability of ε across a valley between two parallel ridges at the Perdigão 2017 campaign. We find that the shear zones above and below nighttime low-level jets (LLJ) experience turbulence enhancements, as does the wake of a wind turbine (WT). We analyze in detail how ε varies in the early morning of 14 June 2017, when the turbulence in the valley, approximately eleven rotor diameters downstream of the WT, is still significantly enhanced by the WT wake.

scholarly journals Towards improved turbulence estimation with Doppler wind lidar VAD scans

2020 ◽  
Author(s):  
Norman Wildmann ◽  
Eileen Päschke ◽  
Anke Roiger ◽  
Christian Mallaun
Keyword(s):  
Theoretical Model ◽  
Dissipation Rate ◽  
Elevation Angle ◽  
Turbulence Measurement ◽  
Sonic Anemometers ◽  
Tke Dissipation Rate ◽  
Wind Lidar ◽  
Turbulence Parameters ◽  
Doppler Wind Lidar

Abstract. The retrieval of turbulence parameters with profiling Doppler wind lidars (DWL) is of high interest for boundarylayer meteorology and its applications. The DWL measurements extend beyond the observations with meteorological masts and are comparably flexible in their installation. Velocity-azimuth display (VAD) type scans can be used to retrieve turbulence kinetic energy (TKE) dissipation rate through a fit of measured azimuth structure functions to a theoretical model. At the elevation angle of 35.3° it is also possible to derive TKE. We show in this study how modifications to existing methods allow to retrieve TKE and its dissipation rate even with a small number of scans, how a simple correction for advection improves the results at low altitudes and that VAD scans at different elevation angles with the same instrument provide comparable results of TKE dissipation rate after all filters and corrections. For this purpose, data of two experiments are utilized: First, measurements at the Observatory Lindenberg – Richard-Aßmann Observatory (MOL-RAO) are used for validation of the DWL retrieval with sonic anemometers on a meteorological mast. Second, distributed measurements of three DWL during the CoMet campaign are analyzed and compared to in-situ measurements of the DLR Cessna Grand Caravan 208B. The comparison to in-situ instruments shows that the methods to improve turbulence retrievals from VAD scans introduced in this study are effective, especially at low altitudes and for narrow cone angles, but it also shows the limits of turbulence measurement with state-ofthe-art DWL in low turbulence regimes.

Sign in / Sign up

Export Citation Format

Share Document