Range Of Wind Speed Conditions Research Articles

Sectional Leading Edge Vortex Lift and Drag Coefficients of Autorotating Samaras

Autorotating samaras such as Sycamore seeds are capable of descending at exceptionally slow speeds and the secret behind this characteristic is attributed to a flow mechanism known as the leading edge vortex (LEV). A stable LEV is known to increase the maximum lift coefficient attainable at high angles of attack and recent studies of revolving and flapping wings have proposed suitable lift and drag coefficient models to characterise the aerodynamic forces of the LEV. For the samara, however, little has been explored to properly test the suitability of these low-order lift and drag coefficient models in describing the aerodynamic forces produced by the samara. Thus, in this paper, we aim to analyse the use of two proposed aerodynamic models, namely, the normal force and Polhamus models, in describing the sectional aerodynamic lift of a samara that is producing a LEV. Additionally, we aim to quantify the aerodynamic parameters that can describe the lift and drag of the samara for a range of wind speed conditions. To achieve this, the study first examined the samara flight data available in the literature, and from it, the profiles of the lift coefficient curves were investigated. Subsequently, a numerical Blade Element-Momentum model (BEM) of the autorotating samara encompassing different lift profiles was developed and validated against a comprehensive set of samara flight data, which were measured from wind tunnel experiments conducted at the University of Bristol for three different Sycamores. The results indicated that both the normal force and Polhamus lift models combined with the normal force drag can be used to describe the two-dimensional lift characteristics of a samara exhibiting an LEV. However, the normal force model appeared to be more suitable, since the Polhamus relied on many assumptions. The results also revealed that the aerodynamic force parameters can vary with windspeed and with the samara wing characteristics, as well as along the span of the samara wing. Values of the lift curve slope, zero-lift drag coefficient, and maximum lift coefficient are predicted and presented for different samaras. The study also showed that the low-order BEM model was able to generate a good agreement with the experimental measurements in the prediction of both rotational speed and thrust. Such a validated BEM model can be used for the initial design of bio-inspired rotors for micro-air vehicles.

Ensemble estimates of the wave state related parameters in a sea spray parameterization scheme

Uncertainties of the wave state parameters in a sea spray parameterization scheme can be a major source of errors for air-sea turbulent (momentum, sensible and latent) fluxes parameterizations resulting in biases in numerical ocean simulations and forecasts. In this study, we explore applications of the ensemble adjustment Kalman filter (EAKF) data assimilation method to optimize the wave states parameters the 1-D POM ocean model for a full range of wind speed conditions. Thus, we assimilate sea surface temperature (SST) synthesized observations to improve our estimates of the SST analysis and prediction skill from low to high winds. Two types of experiments are conducted. In the first type, in a “twin” experiment framework, the SST “observations” generated by a “truth” model are assimilated into an imperfect, biased model to investigate the extent to which the parameters are able to be optimized, with respect to the “truth” values based on data from Station Papa and the Kuroshio Extension Observatory (KEO). In the second type, real SST observations from KEO are assimilated to obtain optimized parameters. With these optimized parameters, the SST analysis and prediction errors are significantly reduced, especially for high wind conditions.

New Geophysical Model Function for Ocean Emissivity at 89 GHz Over Arctic Waters

New empirical geophysical model functions (GMFs) have been developed to interpret 89-GHz brightness temperature measurements over cold Arctic seas. Careful data screening is applied to the Advanced Microwave Scanning Radiometer 2 (AMSR2) multifrequency measurements to exclude atmospheric scattering and large absorption impacts, to estimate the 89-GHz sea surface emissivity and its relative changes with surface wind speed (SWS). Matched-up wind speeds are directly derived from the AMSR2 low-frequency measurements. The GMFs are obtained from the AMSR2 level 1R 89 GHz measurements corrected for the atmospheric impact with physical models and atmospheric parameters derived from the AMSR2 data. A carefully selected database encompasses mostly cold sea conditions (<4 °C) and a large range of wind speed conditions, including extratropical cyclone and polar low high-wind events over the Nordic Seas. Resulting GMFs contrast with previously proposed ones manifesting larger SWS signal at horizontal and positive SWS signal at vertical polarization.

Estimation of Wind Vector Profile Using a Hexarotor Unmanned Aerial Vehicle and Its Application to Meteorological Observation up to 1000 m above Surface

AbstractSmall unmanned aerial vehicles (UAVs), also known as drones, have recently become promising tools in various fields. We investigated the feasibility of wind vector profile measurement using an ultrasonic anemometer installed on a 1-m-wide hexarotor UAV. Wind vectors measured by the UAV were compared to observations by a 55-m-high meteorological tower, over a wide range of wind speed conditions up to 11 m s−1, which is a higher wind speed range than those used in previous studies. The wind speeds and directions measured by the UAV and the tower were in good agreement, with a root-mean-square error of 0.6 m s−1 and 12° for wind speed and direction, respectively. The developed method was applied to field meteorological observations near a volcano, and the wind vector profiles, along with temperature and humidity, were measured by the UAV for up to an altitude of 1000 m, which is a higher altitude range than those used in previous studies. The wind vector profile measured by the UAV was compared with Doppler lidar measurements (collected several kilometers away from the UAV measurements) and was found to be qualitatively similar to that captured by the Doppler lidar, and it adequately represented the features of the atmospheric boundary layer. The feasibility of wind profile measurement up to 1000 m by a small rotor-based UAV was clarified over a wide range of wind speed conditions.

Online monitoring of a power slip-ring on the shaft of a wind power generator

The experimental results obtained from an online monitoring study of out-of-round defects in the slip-rings of wind turbine generators are presented. Five defects were involved, in which the slip-ring diameter varied from the normal value of 224 mm over large ranges of polar angle. The angular dependence of the radius changes was different for each defect and the amplitudes of the changes varied from 0.035 mm to 0.110 mm over the five defects. The defect detection sensor was a shock accelerometer embedded in the brush contacting the slip-ring and connecting the rotating and static parts of the generator. The time dependences of the brush acceleration produced by each defect, and also by a perfect slip-ring, were measured over continuous time intervals of 10 s for 11 slip-ring rotation speeds varying from 370 to 3827 rlmin. This covers the practical range of wind speed conditions. Fast Fourier transforms (FFTs) of this data were performed in order to present the acceleration data in the frequency domain, especially because such presentations promise rapid identification of sharp changes in the defect profiles with angle. Plots of the Fourier coefficients (acceleration amplitudes) as a function of the ring rotation speed are presented for the first four harmonics. These curves contain one or two maxima or show evidence of an approach to a maximum at higher revolution speeds. A qualitative explanation of these maxima is proposed and an outline is also presented of a quantitative model of the measured acceleration data, which is to be the subject of further work. In the first analysis of data, a strong and systematic dependence of these maximum acceleration amplitudes on the defect amplitudes was found. This result holds promise that the embedded accelerometer can form a suitable basis for an online alarm system in which an automatic warning is issued when the acceleration amplitude for any harmonic exceeds a level previously decided upon and set by the turbine operators. Further analysis of the data combined with modelling is in progress in order to investigate the possibility of obtaining the detailed profile of out-of-round defects in slip-rings from online time-dependent brush acceleration measurements.

An approach to parameterization of the oceanic turbulent boundary layer in the western Pacific warm pool

Vertical profiles of zonal velocity and the dissipation rate ε of the turbulent kinetic energy obtained during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (COARE) are analyzed in the context of planetary boundary layer relationships previously derived from atmospheric measurements. The presence of a barrier layer and the striking effect of increased dimensionless shear and ε at the bottom of the surface mixed layer of the ocean, features often observed in the western Pacific warm pool area, are consistent with the boundary layer laws. The gradient Richardson number Ri is found to be a convenient parameter for scaling the nonstationary and horizontally heterogeneous mixed layer in the warm pool area. The approach to parameterization of the turbulent eddy coefficient within the mixed layer as a function of Ri is tested as part of a one‐dimensional model. A comparison between the observed and modeled upper ocean temperatures for two COARE examples shows a reasonable agreement over a wide range of wind speed conditions.

Measurements of the wind stress, heat flux, and turbulence intensity during storm conditions over the North Sea

During the first two weeks of December 1985, measurements of the wind stress, the three‐component wind speed variances, and the vertical flux of sensible heat were collected from a research platform in the North Sea. Obtained using a sonic anemometer, the turbulence data represent an extensive range of wind speed conditions (5–30 m/s), and the air‐sea temperature difference was observed to span from −3° to +3°C. The data were collected from a boom extending 17 m to the west of the North Sea Platform at 33 m above the water surface. The results indicated that the 10‐m‐height neutral drag coefficient, CDN, exhibited a strong dependence on wave age, i.e., CDN was larger for growing waves than for steady state or decaying sea. The normalized turbulence statistics were found to corroborate the results of Smith (1980) and Large and Pond (1981).