The effect of polyethyleneoxide (Polyox grade WSR 301) on grid-generated turbulence was investigated using laser anemometry and flow-visualization techniques. It was found that the polymer additive reduced both the turbulent intensity and the rate of decay behind the grid. At typical drag-reducing concentrations, turbulent energy spectra were qualitatively the same as those in water, in agreement with the results of other investigations. However, at higher additive concentrations, the dissipation-range spectra showed noticeable attenuation. This seemed to be a threshold effect with onset at a polymer concentration between 100 and 250 ppm. This result was supported by photographs of dye-injection tracer but in this case the onset concentration for small-eddy suppression was between 50 and 100 ppm.
A laser-Doppler anemometer was used to measure the radial variation of axial turbulent velocity in the flow of water and aqueous polymer solution through a round pipe. Results were obtained for the mean velocity the turbulent intensity, and the one-dimensional energy spectrum. The polymers used were polyacrylamide (Separan AP 273; in a concentration range 25-200 WPPM). Both polymers are well known as effective additives to reduce turbulent drag, when dissolved in water to give a solution concentration of a few PPM. The mean velocity and turbulent intensity were both found to be increased by the polymer additives, with the magnitude of the effect depending on the polymer concentration This was in agreement with the results of other investigations. At low additive concentrations, the energy spectra were found to be identical to those for water flows; this also was in agreement with previous results. At higher concentrations, energy spectra showed noticeable attenuation in the largest (dissipation) range of wavenumbers. There was a corresponding enhancement of the small-wavenumber (energy-containing) range. This seemed to be a threshold effect with onset at a concentration of between 50 PPM and 100 PPM for Polyox WSR 301 and between 25 PPM and 50 PPM for Separan AP 273.
A headward fluid shift occurs during microgravity exposure, which causes the cardiovascular adaptive syndrome. Different countermeasures have been proposed to decrease its symptomatology, like the application of lower body negative pressure (LBNP). A LBNP box with an environment control system was developed, aiming to improve features of LBNP boxes used worldwide. It consists of five carbon steel ribs in the shape of a cylinder, which is wrapped with high pressure resistant and transparent vinyl. Inner and outer-wheeled trolleys can comfortably and easily move the subject in and out of the box. A custom-made skirt is secured around the subject's waist by an adjustable belt. The other end is secured between two window-type wooden structures, which seal the LBNP box. Inlet and an outlet valves connect the external to the internal environment of the chamber and tube system allows air to circulate gently. Electronic sensors are used to adjust the airflow keeping a pre-set negative pressure without changing humidity and temperature inside the box. Structural, pressure profile and leaking tests were performed with successful results. The improvements of the present LBNP box have substantially decreased the undesirable side effects of uncontrolled environment conditions during rapid pressure changes, and increased test subjects' comfort.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.