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Showing papers by "Ephraim M Sparrow published in 1972"



Journal ArticleDOI
01 Jun 1972
TL;DR: In this paper, the effects of swirl on the rate of mass flow and on the velocity field in the throat region of axi-symmetric nozzles are studied analytically and experimentally.
Abstract: The effects of swirl on the rate of mass flow and on the velocity field in the throat region of axi-symmetric nozzles are studied analytically and experimentally. In the analytical phase, methods are developed for treating either the direct or the inverse problem for flow in de Lavai and annular nozzles, taking account of either weak or strong swirl. The experiments were performed in an annular nozzle, with swirl being imparted to the flow by adjustable vanes situated upstream of the test section.

23 citations


Journal ArticleDOI
TL;DR: In this article, the effects of fluid injection on the structure of an initially fully developed, low Reynolds number, turbulent pipe flow have been studied by means of a hot-film anemometer.
Abstract: The effects of fluid injection on the structure of an initially fully developed, low Reynolds number, turbulent pipe flow have been studied by means of a hot-film anemometer. Measurements were made of the axial turbulence intensity field and of the time-mean streamwise velocity distribution, both in the porous-walled pipe and in the solid-walled hydrodynamic development section. Oscilloscope traces showing the timewise pattern of the local velocity fluctuations were also monitored. The Reynolds number of the air flow at the inlet of the porous pipe was varied from 3090 to 6350, and the Reynolds number of the injected air ranged from 60 to 160.Near the tube wall, the initial effect of injection is a significant reduction of the axial turbulence level and an increase in the thickness of the viscous and buffer layers. The degree by which turbulence is reduced in this region is more or less proportional to the ratio of the injection to entrance Reynolds numbers. In the core region of the flow, which is centred about the tube axis, there is also an initial reduction in the magnitude of the axial component of turbulence which is thought to be due to injection-induced acceleration of the flow. There is also an annular region, which separates the wall and core regions, in which the turbulence intensity initially increases. In the downstream portion of the porous tube the entire flow undergoes a re-transition to fully developed turbulence.

20 citations


Journal ArticleDOI
TL;DR: In this article, a system consisting of a thin, transparent film on an absorbing metallic substrate can function as a reflection polarizer, and the performance of such a system is evaluated.
Abstract: A system consisting of a thin, transparent film on an absorbing metallic substrate can function as a reflection polarizer. For given optical constants, analysis yields the angles of incidence at which reflection of either component of polarization is extinguished. For each such polarizing angle, any one of a set of discrete film thicknesses can be employed to obtain polarized light. The polarizing characteristics of several illustrative film–substrate systems have been calculated. Criteria for evaluating the performance of a reflection polarizer included the magnitude of the reflectance of the unextinguished component, and the sensitivity of the extinguished component to departures from the polarizing angle and from the optimum film thicknesses. These criteria responded in a systematic manner to variation of the reflectance of the substrate and the refractive index of the film. High reflectance of the unextinguished component and low sensitivity of the extinguished component can be attained.

17 citations


Journal ArticleDOI
TL;DR: In this article, the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow was investigated using a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere.
Abstract: Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

14 citations


Journal ArticleDOI
TL;DR: In this article, the cross-sectional distributions of axial turbulence intensity and time-mean velocity in hydrodynamically developed pipe flows were made by means of a hot-film anemometer.

14 citations



Journal ArticleDOI
TL;DR: In this paper, a method for the successive determination of the refractive index, thickness, and extinction coefficient of a slightly absorbing thin film situated on a transparent substrate is presented. But the method does not require the magnitude of the reflectance as input.
Abstract: Methods are developed for the successive determination of the refractive index, thickness, and extinction coefficient of a slightly absorbing thin film situated on a slightly absorbing or transparent substrate. The refractive index is found from a measurement of the Brewster angle for the film–substrate interface. This Brewster angle, termed the second-surface Brewster angle, is shown to be highly insensitive to small values of the extinction coefficient. The film thickness is deduced from measurements of the angles at which maxima and minima occur in the measured distribution of reflectance vs angle of incidence. Thus, neither the refractive index nor the thickness determinations requires the magnitude of the reflectance as input. On the other hand, the extinction coefficient is deduced from the value of the reflectance at a maximum point in the distribution of reflectance vs incidence angle.

6 citations


Journal ArticleDOI
TL;DR: In this article, the authors determined the efficiency of solar absorption of honeycomb structure attached to collecting base surface on which incoming solar energy impinges directly on the base surface by using a honeycomb.
Abstract: Determination of efficiency of solar absorption of honeycomb structure attached to collecting base surface on which incoming solar energy impinges directly on base surface

2 citations