Airflow Disturbances Research Articles

Using the Torque Characteristics of Dampers to Measure Airflow, Part II: Analysis and Testing

This paper describes the analysis and testing of a method of measuring airflow from position and torque (APT) measurements of dampers. The method is based on a newly developed mathematical model of the aerodynamic torque characteristics of dampers. An uncertainty analysis demonstrates that the APT method can outperform a pitot tube over a wide range of conditions, but that it cannot outperform a pitot tube when the damper is nearly open. Tests on an offset-blade damper and a commercially available airflow station confirm the results of the uncertainty analysis and demonstrate that the APT technology is also insensitive to upstream airflow disturbances when the damper is less than 70% open.

Release of lead-containing particles from a wall enclosure.

The 1995 Department of Housing and Urban Development (HUD) Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing discusses using interior and exterior wall enclosures for lead hazard control. Leaded dust may be aerosolized inside enclosures and released through gaps and cracks into a room. The effects of airflow and mechanical disturbances on dust release were studied using a laboratory wall enclosure model with dust collected from homes with lead-based paint hazards. Airflows relevant to residences were blown down the enclosure and out a 4-, 6-, or 8-mm horizontal gap at its bottom, simulating potential enclosure failure. Then, low-frequency mechanical vibrations also were applied to the enclosure. No significant dust release was found when blowing air down the enclosure even at 37 cm/sec (representing extremely high flow); release occurred only with this high flow and 3 Hz mechanical disturbances. Dust was released primarily from the floor area immediately adjacent to the enclosure gap; the release rate fluctuated over time. Most dust initially settled near the enclosure. Dust release for 1 hour at extreme conditions (high airflow with vibration) yields lead loading above the 1995 HUD clearance level of 100 microg/ft2 only within 3-4 cm of the wall; for the HUD standard (1 ft2) sampling area, the lead loading does not exceed 30 microg/ ft2. Redistributing dust over the room's 16 m2 floor space yields average extreme-condition loading rate of 2 microg/ft2/hour. At less-than-extreme conditions, dust would have to be released for years without cleaning to yield a hazard.

Diabetes, sleep disorders, and male sexual function

The prevalence and role of sleep disorders in the sexual problems of diabetic patients remain unexplored. This study was conducted on 40 diabetic men carefully screened to exclude the confounding effects of other medical illnesses or drugs likely to impair sexual function and 40 age-matched healthy volunteers. They underwent an extensive psychosexual interview, medical and psychiatric evaluations, and three recorded nights in a sleep laboratory. Electroencephalogram, eye movements, muscle tone, and nocturnal penile tumescence were monitored continouusly. Respiratory airflow and bilateral anterior tibialis recordings were obtained during the first sleep session. Diabetic men had significantly higher prevalences of respiratory and periodic leg movement disturbances during sleep. There was clinical, although not nocturnal penile tumescence, evidence suggesting that respiratory abnormalities during sleep are associated with erectile difficulties in diabetic men. Future studies should include blood oxygenation and respiratory effort measures to clarify the significance of sleep-related airflow disturbances in diabetic patients.

Three-Dimensional Numerical Simulation of Plume Downwash with ak–ϵ Turbulence Model

Abstract Plume downwash at a large oil-gathering facility in the Prudhoe Bay, Alaska oil-field reservation was simulated in a series of numerical experiments. The purpose of this study was to investigate the potential of the numerical model as a means of assessing the impact of pollutants emitted from buoyant sources influenced by complex aerodynamic wakes. The model is a three-dimensional, Cartesian coordinate, finite difference code that solves the nonhydrostatic, time-averaged equations for the conservation of momentum and energy. The code uses a modified form of the standard first-order, two-equation (k–ϵ) engineering turbulence closure model. Wind tunnel and field investigations of dispersion at this arctic industrial complex indicate that dispersion is significantly influenced by building-generated airflow disturbances. We have used the numerical model to simulate directly the mean features of the flow field and dispersion from a buoyant source at an industrial site. The flow features varied dependi...

Building wake dispersion at an Arctic industrial site: Field tracer observations and plume model evaluations

Ten multi-hour atmospheric dispersion SF 6 tracer experiments were conducted during October and November of 1987 near a large oil gathering facility in the Prudhoe Bay, Alaska, oilfield reservation. The purpose of this study was to investigate dispersion under arctic conditions and in situations where building-generated airflow disturbances dominate downwind distributions of ground level pollutant concentrations. This was accomplished with a network of micrometeorological instruments, portable syringe tracer samplers, continuous tracer analyzers, and infrared visualization of near source plume behavior. Atmospheric stability and wind speed profiles at this arctic site are influenced by the smooth (surface roughness = 0.03 cm), snow covered tundra surface which receives negligible levels of solar isolation in winter. The dispersion of pollutants emitted from sources within the oil gathering facility, however, is dominated by the influence of nearby buildings when high winds generate elevated ground level concentrations. An order of magnitude increase in maximum ground level concentration was observed as wind speeds increased from 5 to 8 m s −1 and another order of magnitude increase was observed as winds increased from 8 to 16 m s −1. Variation in maximum concentrations was also observed with changes in wind direction. Vertical plume diffusion ( σ z ) near the buildings was a factor of 2–3 greater than that observed in open terrain and was dependent on both wind speed and the projected building width and location of nearby buildings. Wind tunnel tracer distributions for east winds agree with field observations but also indicate that a significant increase in plume downwash occurs with other wind directions. Concentration distributions were calculated using several versions of the Industrial Source Complex (ISC) model. Model estimates of ground level concentrations were within a factor of three depending on wind direction. The model predictions are extremely sensitive to the ratio of plume height to vertical plume diffusion which is significantly influenced by a complex aerodynamic wake in the field.

Application of quadratic optimization to supersonic inlet control

This paper describes the application of linear stochastic optimal control theory to the design of the control system for the air intake, the inlet, of a supersonic air-breathing propulsion system. The controls must maintain a stable inlet shock position in the presence of random airflow disturbances and prevent inlet unstart. Two different linear time invariant controllers are developed. One is designed to minimize a nonquadratic index, the expected frequency of inlet unstart, and the other is designed to minimize the mean square value of inlet shock motion. The quadratic equivalence principle is used to obtain a linear controller that minimizes the nonquadratic index. The two controllers are compared on the basis of unstart prevention, control effort requirements, and frequency response. It is concluded that while controls designed to minimize unstarts are desirable in that the index minimized is physically meaningful, computation time required is longer than for the minimum mean square shock position approach. The simpler minimum mean square shock position solution produced expected unstart frequency values which were not significantly larger than those of the nonquadratic solution.

Rain gage catch variation due to airflow disturbances around a standard rain gage

Although the spatial position has an important influence on the performance of a rain gage, the physical presence of the gage itself must be considered a hindrance to its operation. An obstruction to airflow in the vicinity of the gage, owing to the presence of the gage, results in disturbances in the local precipitation pattern in which the rainfall measurement is made. The airflow pattern data obtained in a study of a wind tunnel model and aerodynamic drag characteristics of water drops are used to perform a computer simulation on the movements of the drops as they approach the gage. These drop paths are analyzed to establish the effectiveness of the gage in measuring precipitation. If we use drop sizes of 1–5 mm in diameter, we find that the gage catches from 103 to 11% of the drops as the free stream velocity increases from 10 to 50 feet per second. In general, the decrease in catch is less pronounced as the drop size is increased.

Application of Quadratic Optimization to Supersonic Inlet Control

This paper describes the application of linear stochastic optimal control theory to the design of the control system for the air intake (inlet) of a supersonic air-breathing propulsion system. The controls must maintain a stable inlet shock position in the presence of random airflow disturbances and prevent inlet unstart. Two different linear time invariant control systems are developed. One is designed to minimize a nonquadratic index, the expected frequency of inlet unstart, and the other is designed to minimize the mean square value of inlet shock motion. The quadratic equivalence principle is used to obtain the best linear controller that minimizes the nonquadratic performance index. The two systems are compared on the basis of unstart prevention, control effort requirements, and sensitivity to parameter variations. It is concluded that while controls designed to minimize unstarts are desirable in that the index minimized is a physically meaningful quantity, computation time required is longer than for the minimum mean square shock position approach. In addition, the simpler minimum mean square shock position solution produced expected unstart frequency figures which were not significantly worse than those of the non-quadratic solution.