We investigate the stability of a Helmholtz velocity profile in a stably stratified fluid when a lower boundary is present. In addition to the traditional Kelvin-Helmholtz interfacial instability we find an infinitude of unstable internal gravity waves, the most unstable of which bear a close resemblance to disturbances observed in connection with clear air turbulence. It is shown that the grav...

The ability to obtain meteorological measurements in the planetary boundary layer for quantification of clear-air turbulence is investigated using the Small Multifunction Research and Teaching Sonde (SMARTSonde). With an instrumented unmanned aircraft, a series of flights were conducted in the spring of 2013 to obtain meteorological variables at Kessler Atmospheric and Ecological Field Station ...

Overview In free-surface flows the turbulence in the liquid may be sufficient to disturb the surface to the point of entraining air into the flow. This process is important, for example, in water treatment where air is needed to sustain microorganisms for water purification and in rivers and streams for sustaining a healthy fish population. Air entrainment is typically engineered into spillways...

Room air distribution in hospital operating rooms (OR) is critical to the effective functioning of surgical procedures, but the air distribution patterns are governed by complex physics that are currently not well understood. Both qualitative and quantitative flow visualization techniques were used to evaluate the room air distribution in a full-scale chamber designed to simulate a hospital ope...

People spend approximately one third of their life sleeping. Exposure to pollutants in the sleep environment often leads to a variety of adverse health effects, such as development and exacerbation of asthma. Avoiding exposure to these pollutants by providing a sufficient air quality in the sleep environment might be a feasible method to alleviate these health symptoms. We performed full-scale ...

Andersson, A. 2017. Air-sea exchange of O2 and CO2. Processes controlling the transfer efficiency. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1471. 42 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 9789155498061. World oceans cover more than 70% of the earth surface and constitutes a major sink of atmospheric CO2. Two of the most impor...

Shell and tube heat exchangers are widely being used in many of industrial and power engineering applications. Different techniques have been employed in order to enhance the performance of the heat exchanger. Air bubble injection is one method to increase the turbulence of the flowing fluids which in turn enhance the heat transfer performance. Injecting air bubbles is one of the promising tech...

A finite element flow solver based on unstructured grids is employed for studying the aerodynamic characteristics of Micro Air Vehicles. Inviscid and viscous flow simulations were performed for two different Micro Air Vehicles developed at NRL. Lift and drag force variations were computed for a range of flow angles and control surface angles. The Baldwin-Lomax turbulence model was employed for ...

Knowledge about the mechanisms of mass transfer across the aqueous boundary layer is still marginal because of the lack of suitable experimental techniques. We present a new technique to measure the air-water gas transfer rate and the spatial structure of the micro turbulence at the ocean surface using passive thermography. We make use of the fact that due to radiative cooling, latent and sensi...

Optical turbulence (OT) acts to distort light in the atmosphere, degrading imagery from large astronomical telescopes and possibly reducing data quality of air to air laser communication links. Some of the degradation due to turbulence can be corrected by adaptive optics. However, the severity of optical turbulence, and thus the amount of correction required, is largely dependent upon the turbu...