Leeward Face Research Articles

Effect of leeward orientation, adiabatic framing surfaces, and eaves on solar-collector-related heat transfer coefficients

Wind tunnel experiments were carried out to determine forced convection heat transfer coefficients for the leeward face of a roof-like structure. The experiments encompassed a variety of surface configurations, including: (a) a leeward face which transfers heat to the airflow over its entire surface, (b) a leeward face on which a thermally active zone is flanked by an adiabatic frame, and (c) eaves positioned along the lateral edges of the windward and leeward faces. Heat transfer coefficients were also measured on the windward face. It was found that in the operating range of flat plate collectors, the leeward-face heat transfer coefficients exceed those for the windward face. For a leeward face where adiabatic framing surfaces are situated along the lateral edges of a thermally active zone, the heat transfer coefficients are higher than those for the unframed case. On the other hand, framing adjacent to either the upper or lower edge of the face has little effect. Eaves situated along the lateral edges of the windward and leeward faces bring about only a slight increase in the leeward-face transfer coefficients. A flow visualization study revealed that the flow pattern adjacent to the leeward face is shaped by fluid which wells up from the sides of the roof-like structure.

Distribution and Steepness of Ripples on Carrier Waves

The slopes of ripples and the profiles of their carrier waves were simultaneously measured in a wind-wave tank with winds of various velocities blowing over preexisting, long, regular surface waves. The results include the apportionment and the slope distributions (and therefore the mean-square slopes) of ripples located on various portions of the carrier-wave profile. At low wind velocities, the surface-tension governing regime of wind-wave interaction, the leeward face of the carrier wave was found to contain more ripples than the windward face. The parasitic capillaries are concentrated on the upper half of the leeward face, and move along the leeward face toward the trough of carrier waves as the wind velocity increases. At high wind velocities, the gravity governing regime of wind-wave interaction, the ripples become more evenly distributed on the leeward and on the windward faces. How ever, the ripples on the windward face are concentrated near the carrier-wave crest, and the ripples on the leeward face are concentrated near the carrier-wave trough. At all wind velocities, the rms slope of ripples on the windward face of the carrier waves is greater than that on the leeward face.

Forced convection accompanying wind waves

Wind-wave tunnel experiments reveal, by use of techniques of the flow visualization, that wind waves are accompanied by the wind drift surface current with large velocity shear and with horizontal variation of velocity relative to the wave profile. The surface current converges from the crest to a little leeward face of the crest, making a downward flow there, even though the wave is not breaking. Namely, wind waves are accompanied by forced convections relative to the crests of the waves. Since the location of the convergence and the downward flow travels on the water surface as the crest of the wave propagates, the motion as a whole is characterized by turbulent structure as well as by the nature of water-surface waves. In this meaning, the term of real wind waves is proposed in contrast with ordinary water waves. The study of real wind waves will be essential in future development of the study of wind waves.

Nonlinear Panel Response to Nonstationary Wind Forces

The vibration of a flexible elastic panel to nonstationary wind surface pressures is investigated by a Monte Carlo technique. The nonlinear glass panel response is performed in time domain by simulating resulting generalized random forces on a digital computer. Equations of motion are solved in a Galerkin sense by developing a modal solution. Stress and deflection response calculations are performed for panels located on windward, leeward and side faces of the building. Aeroelastic panel instability with respect to static divergence and dynamic flutter is also investigated.

Pressure fluctuations on a large building and along-wind structural loading

Measurements of pressure fluctuations on the windward and leeward faces of a 43-m-high building situated in a relatively exposed location are described. Velocity fluctuation measurement were also made upstream and on top of the building. Correlations and spectra are presented. Comparison is made with quasi-steady linear theory as used in current design methods for along-wind building response. At high frequencies the theory is found to break down due to distortion of the turbulent fluctuations.