Fluid Dynamic Mechanisms Research Articles

An Investigation of a Strong Shock-Wave Turbulent Boundary Layer Interaction in a Supersonic Compressor Cascade

Experiments have been performed in a supersonic cascade facility to elucidate the fluid dynamic phenomena and loss mechanism of a strong shock-wave turbulent boundary layer interaction in a compressor cascade. The cascade geometry is typical for a transonic fan tip section that operates with a relative inlet Mach number of 1.5, a flow turning of about 3 deg, and a static pressure ratio of 2.15. The strong oblique and partly normal blade passage shock-wave with a preshock Mach number level of 1.42 to 1.52 induces a turbulent boundary layer separation on the blade suction surface. The free-stream Reynolds number based on chord length was about 2.7 × 106. Cascade overall performance, blade surface pressure distributions, Schlieren photographs, and surface visualizations are presented. Detailed Mach number and flow direction profiles of the interaction region (lambda shock) and the corresponding boundary layer have been determined using a Laser-2-Focus anemometer. The obtained results indicated that the axial blade passage stream sheet contraction (axial velocity density ratio) has a significant influence on the mechanism of strong interaction and the resulting total pressure losses.

Multiple normal shock wave/turbulent boundary-layer interactions

A multiple normal shock/turbulent boundary-layer interaction in a rectangular duct has been investigated experimentally using a two-component laser Doppler velocimeter (LDV). Just upstream of the normal shock system the Mach number was 1.61, the unit Reynolds number was 30 x 106 m ', and the confinement level as characterized by the ratio of the boundary-layer thickness to the duct half height was 0.32. The results presented here identify the fluid dynamic mechanisms involved in the reacceleration process following each shock in the multiple shock system. Two distinct expansion processes occur following each shock in the system: acceleration through a supersonic expansion fan originating near the wall and acceleration through an aerodynamic converging-diverging nozzle in the core flow.

Guidelines for Efficient Design and Operation of Opposed Swirl Nozzles

Guidelines are presented for efficient design and application of opposed swirl internal mix nozzles. Associated fluid dynamic mechanisms are briefly discussed.

Computational analysis of unsteady supersonic cavity flows driven by thick shear layers

AbstractSupersonic cavity flows driven by a thick shear layer at Mach 1·5 and 2·5 are studied by solving the two-dimensional unsteady compressible Navier-Stokes equations in terms of mass-averaged variables. The length to depth ratio of the rectangular cavity is three. The numerical scheme used is the finite-difference algorithm by Brailovskaya. A two-layer eddy-viscosity turbulence model is used. The results are compared with experimental data. The computations show the self-sustained oscillations at Mach 1·5 and 2·5. The continuous formation and downstream shedding of leading edge vortices is demonstrated. The oscillatory modes are correctly predicted. The first mode is attributed to a large unsteady trailing edge vortex moving in the transverse direction. Based on the analysis, it is considered that the oscillation in the length to depth ratio three cavity is a longitudinal one and is controlled by a fluid dynamic mechanism rather than a purely acoustic one.

Source mechanism of volcanic tremor

Low‐frequency (<10 Hz) volcanic earthquakes originate at a wide range of depths and occur before, during, and after magmatic eruptions. The characteristics of these earthquakes suggest that they are not typical tectonic events. Physically analogous processes occur in hydraulic fracturing of rock formations, low‐frequency icequakes in temperate glaciers, and autoresonance in hydroelectric power stations. We propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low‐frequency volcanic earthquakes (tremor). The fluid dynamic source mechanism explains low‐frequency earthquakes of arbitrary duration, magnitude, and depth of origin, as unsteady flow is independent of physical properties of the fluid and conduit. Fluid transients occur in both low‐viscosity gases and high‐viscosity liquids. A fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid, material properties, geometry and roughness of the conduit, and boundary conditions. To demonstrate the analytical potential of the fluid dynamic theory, we consider a single‐phase fluid, a melt of Mount Hood andesite at 1250°C, in which significant pressure and velocity variations occur only in the longitudinal direction. Further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations. For a simple, constant pressure reservoir‐conduit orifice fluid system, a change in orifice size can cause the source signal duration due to a single disturbance to change from several seconds to in excess of an hour. Fluid kinematic viscosity (0.412 m2/s) is both included and neglected in the analysis to illustrate its effect upon system damping. Tremor magnitude is related to the magnitude of the conduit wall motion occurring in response to oscillating fluid pressures. The entire volcanic fluid system does not generally experience a transient flow condition at a given time. Closed end and constant pressure fluid system boundaries reflect pressure waves and isolate components of the fluid system. Total fluid movement may not be accurately monitored by tremor data alone, since steady state and slowly changing flows are aseismic.

Studies on the adrenergic systems of the eye at the Wilmer Institute

The study of the ocular adrenergic systems at the Wilmer Institute over the last 40 years began with the examination of the formation and outflow of aqueous humor by Jonas Friedenwald and his co-workers in the early 1940's. At that time, researchers were attempting to understand the mechanisms of fluid dynamics in the eye, with the idea of altering these mechanisms to alleviate glaucoma only a distant goal. In the late 1950's, Langham and others reported on the effect of superior cervical ganglionectomy on intraocular pressure, following this work with a succession of papers on the relationship between alpha and beta adrenergic substances and aqueous humor dynamics. Sears, in collaboration with Bárány, described the effects of alpha and beta adrenergic substances on outflow resistance. Eakins, in 1963, suggested a mechanism of action for isoproterenol in the lowering of intraocular pressure. Work on timolol at Wilmer began with a report from Radius, Diamond, Pollack and Langham covering experimental studies with rabbits and clinical studies of the drug's ocular hypotensive effects on glaucoma patients. Richter and others also studied a small number of patients on maximal therapy and found further intraocular pressure reduction with added timolol.

Einfluß thermodynamischer und fluiddynamischer Vorgänge auf die Notentspannung chemischer Reaktoren

AbstractInfluence of thermodynamic and fluid dynamic mechanisms upon the emergency pressure relief of chemical reactors. The cross‐sectional areas of pressure relief devices for storage tanks and reactor vessels containing liquids under vapour pressure, which might undergo dangerous heating up, have so far been estimated on the basis of physically questionable procedures. This report analyses the pressure relief process using several extreme assumptions with regard to momentum and heat transfer in two phase flow. A conservative method of estimation is found under the assumptions of homogeneous flow and vapour‐liquid equilibrium. Using this procedure, a parametric study of the pressure relief process for a runaway polymerisation reaction has been carried out. Finally, recommendations are given concerning design of the vent line and control of the atmospheric dispersion of the relief stream via the jet exit momentum.

Mechanism of Closure of the Aortic Valve

THE human aortic valve consists of three cusps made of relatively inelastic, muscle-free material about 0.15 mm thick. It opens and shuts about once a second, and withstands a pressure difference of 100 mm of mercury when closed. It usually functions for 70 yr without failure, and works so efficiently that very little blood is regurgitated at each pulse. In order to support this large pressure difference, the cusps must close simultaneously in all operating conditions and should not touch the wall of the aorta, for considerable reversed flow would then be required to close the valve. This action suggests a fluid dynamic control mechanism which positions the cusps away from the wall of the aorta, so that the slightest reversed flow will close the valve.

Fluid Dynamic Mechanisms Which Regulate Tooth Movement

Fluid Dynamic Mechanisms Which Regulate Tooth Movement

A fluid-dynamic mechanism of meteorite pitting

A fluid-dynamic mechanism of meteorite pitting

A Comparison of Regenerative-Pump Theories Supported by New Performance Data

Abstract Several theories of the fluid-dynamic mechanism of a regenerative pump have been presented in the literature. The author has compared these theories and believes that in principle they are compatible. The differences occur in the assumptions made. Experimental data show that, although each assumption is useful for a limited operating condition and geometry, none covers a wide enough range for a complete analysis of the phenomenon. In addition, he presents a series of experimental data concerning the geometry of the pumping channel. Although the influence of the geometry of the pumping channel on performance is complicated, consistent tendencies are found. These tendencies and experimental data are available not only as an aid to design but also may serve as a guide for the improvement of any simple semiempirical theory of the regenerative pump as well as for testing any complete theories.

Closure to “Discussions of ‘A Theory of the Fluid-Dynamic Mechanism of Regenerative Pumps’” (1955, Trans. ASME, 77, pp. 1311–1315)

Closure to “Discussions of ‘A Theory of the Fluid-Dynamic Mechanism of Regenerative Pumps’” (1955, Trans. ASME, 77, pp. 1311–1315)