K.H. Papadopoulos

On the combination of air velocity and flow measurements in single sided natural ventilation configurations

Abstract Single sided natural ventilation configurations are very frequent especially in buildings in urban environments. Four single sided ventilation experiments were carried out in a full scale outdoor Test Cell facility. Air velocity measurements were taken at various heights in the middle of the opening. The average air flow rate through the opening was derived using the tracer gas decay technique. This work presents the results of an investigation into the relationship between the air velocity at the opening and the bulk air flow rate measurements. The paper presents a description of the experimental set-up as well as a qualitative discussion of the results.

Predicting single sided natural ventilation rates in buildings

Natural ventilation contributes significantly in reducing the cooling load of buildings and in increasing thermal comfort. Single sided natural ventilation configurations are very frequent especially in urban environments. Fifty-two single sided natural ventilation configurations have been studied experimentally and are compared with the predictions of six different network ventilation models. The heat and mass transfer characteristics of the studied cases are analysed and discussed. Finally, a new model to predict air flow rates in single sided natural ventilation configurations is proposed.

A study of the near wake structure of a wind turbine comparing measurements from laboratory and full-scale experiments

Wake flow measurements have been performed using the technique of particle image velocimetry (PIV) at stations downstream from a model wind turbine rotor, and evaluated against experimental data from two full-scale machines. Comparisons include both mean velocity and turbulent intensity cross-wake profiles at a range of tip speed ratios. The application of PIV to the study of wind turbine wakes is described in detail, including the steps required to ensure appropriate and accurate simulation of the flow field conditions. The results suggest that the PIV method is a potentially useful tool in the investigation of detailed wake flow, though significant differences are observed between wake velocity deficits at full- and model scale. These are discussed with regard to scale effect, the influence of terrain, model similarity, and the phenomenon of wake meandering and effective cross-wake smoothing.

An experimental study of the near-wake structure of a wind turbine operating over complex terrain

Abstract Wind parks are often cited in complex terrain whose features determine the wind flow over the area. Results from a field experiment, comprising in-situ and remote sensing techniques (high-resolution acoustic sounders), concerning the upwind area and the near-wake region behind a single medium-sized wind turbine are presented. The experimental site is the Samos Island Wind Park installed on top of a 390 m-high saddle. Because of the topography, wind speed acceleration and channeling effects are expected; thus, the commonly used logarithmic profile is not valid, and the choice of a representative surface roughness length z o is difficult. Interesting features of the profiles of the standard deviation of the ambient wind speed are also presented. The obtained results reveal a nonlinear interaction of the near wake with the turbine-tower shadowing, while cross-wind wake profiles indicate a potential core structure. The effect of ambient turbulence is apparent, especially at lower wind speeds, even at a distance of one rotor diameter (1 D ) behind the turbine. The wake centerline at distances greater than 1 D is often observed at heights greater than the hub-height and attributed to the wind flow characteristics over the Wind Park. Finally, evidence of rotational motion inside the wake is identified.

Influence of background flow on evolution of saronic gulf sea breeze

Abstract Results from an experimental campaign at the coastline of the Saronic Gulf during the summer of 1992 are presented. The frontal intensity and the rotation of the wind hodograph at the shoreline during sea-breeze case:; are examined under different background flow conditions. The frontal intensity classification is based on the vertical velocities induced, as measured by a high resolution acoustic sounder. Three representative cases are presented. Conclusions are based on the analysis of all observed sea-breeze flows. Background off-shore or shore-parallel flows are more probable to create a strong or weak front, respectively. The development of frontal characteristics under background on-shore flow is attributed to off shore land features. The wind hodograph rotation is shown to be associated to the initial direction of the sea breeze, which is determined by the background flow direction. When the background flow possesses a westerly component the hodograph shows anticlockwise rotation, while an easterly background component causes the wind vector rotation to be clockwise.

Air mass exchange between the athens basin and the messogia plain of Attika, Greece

The present work investigates the interaction between the local and synoptic meteorology and the resultant air mass exchange between two major regions of the Athens Metropolitan Area (AMA); the Messogia Plain, a rural area under development and the Athens Basin which combines industrial and human activities. These are separated by the 1000 m-high Hymettos Mountain. Meteorological data from a 4-month experimental campaign are used to (a) identify and classify the principal synoptic types observed, based on past long-term observations, (b) determine the recurrent surface wind flow patterns over the Messogia Plain and the Athens Basin, (c) specify the effect of the local thermal flows on the meteorological coupling of the two areas in relation to the synoptic, background (large-scale) conditions, and (d) analyse the flow over the Hymettos Mountain and through the natural openings which link the two areas geographically.

Study of the turbulent characteristics of the near-wake field of a medium-sized wind turbine operating in high wind conditions

The near-wake turbulent structure that is downwind of a medium-sized, horizontal axis wind turbine at a distance of one rotor diameter is discussed. The experimental site is the Samos Island Wind Park comprising nine wind turbines installed on the top of a 400 m-high saddle. The analysis is based on experimental data obtained mainly under strong wind conditions by two masts erected upstream and downstream of a wind turbine. The field of wind turbulence is examined both in integral and spectral form. Consideration of the perturbation produced by the tower construction is crucial in the interpretation of results. Observations show that the turbulent field varies from the edge to the center of the wake and strongly depends on the incident wind speed. Increased turbulent levels are observed near the blade tips, with evidence of a similar trend around the hub height for all wind speeds. Decreases of wind turbulence are observed in mid frequencies inside the wake due to the reduced shear associated with the flat crosswind velocity profile. This effect seems to dominate in the variation of the integral values of the longitudinal wind component variance. The low frequency portion of wind spectra reverses behavior in high wind speeds, i.e., an increase in energy relative to background values is observed. This is probably due to the shape of the turbine characteristic power curve. Cross-wind profiles of turbulent shear stresses at the lower boundary of the wake are also discussed.

A hot-wire based, research atmospheric turbulence probe : design analysis and performance

The design details, constructional characteristics and performance of a research atmospheric turbulence probe based on the hot wire technique are presented. The presentation emphasizes issues related to the hot-wire calibration procedure and the effect of the data processing on the system reliability. The probe is capable of measuring the three wind components, the mean and fluctuating temperature.