Recursos de colección

Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

Group = Graduate Aeronautical Laboratories (Fluid Mechanics)

Mostrando recursos 1 - 20 de 78

  1. Large Structure Dynamics and Entrainment in the Mixing Layer at High Reynolds Number

    Dimotakis, Paul E.; Brown, Garry L.
    Observations were made on a turbulent mixing layer in a water channel at Reynolds numbers up to 3 x 10^6 . Flow visualization with dyes revealed (once more) large coherent structures and showed their role in the entrainment process; observations of the reaction of a base and an acid indicator injected on the two sides of the layer, respectively, gave some indication of where molecular mixing occurs. Autocorrelations of streamwise velocity fluctuations, using an LDV, revealed a fundamental periodicity associated with the large structures. The surprisingly long correlation times suggest time scales much longer than had been supposed; it is argued that...

  2. Transonic Limits of Linearized Theory

    Cole, J. D.
    The transonic regime, extending from Mach numbers at which shock waves first appear with the associated drag rise to Mach numbers at which the head shock wave is firmly attached to the nose of the body, is well known. Not so well known, perhaps, is the reason for the failure of linearized theory to describe the flow in this regime, in particular, to permit an accurate calculation of the pressure.

  3. Magnetohydrodynamic Waves

    Cole, J. D.
    The aim of this paper is to study some special magnetohydrodynamic waves and their connection with the methods of their production, that is, the boundary conditions. Possible wave motions of a fluid form the underlying structure of the mathematical description; hence a knowledge of their behavior leads to a deeper understanding of fluid dynamical problems. Furthermore there is some evidence that these waves can be produced in the laboratory and may occur in nature. These waves occur in a model fluid which is an ordinary gas dynamic fluid endowed with a scalar electrical conductivity σ. In practice there is a fairly direct...

  4. Expansion Procedures and Similarity Laws for Transonic Flow Part I. Slender Bodies at Zero Incidence

    Cole, J. D.; Messiter, A. F.
    The purpose of this report is to provide a detailed and comprehensive account of a transonic approximation as applied to flows past wings and bodies. It is mainly concerned with the derivation of approximate equations, boundary conditions, etc., rather than with the more difficult problem of the solution of transonic flow problems. Thus the report contains for the most part a re-examination of the basic ideas, as presented for example, in Ref. 1. The essential new point of view introduced here is to regard the approximate transonic equations as part of a systematic expansion procedure. Thus, it becomes possible, in principle, to...

  5. Acceleration of Slender Bodies of Revolution through Sonic Velocity

    Cole, J. D.
    [see PDF for abstract]

  6. Multidisciplinary Study of Pulse Detonation Engines

    Shepherd, J. E.
    Research at the Explosion Dynamics Laboratories at Caltech over the past three years under an ONR contract has examined many issues critical to Pulse Detonation Engine (PDE) development. These include: fundamental and applied studies of detonation initiation; detonation cell width measurements to characterize fuels, including JP10; visualization of the reaction zone structure of propagating detonations; direct measurements and analytical modeling of impulse from a detonation tube, including the effects of partial fill and exit geometry; studies of detonation diffraction; and the structural response of tubes to detonation loading, including fracture and failure. Each of these aspects of our program is discussed and key results are presented.

  7. A Study of Wakes Behind a Circular Cylinder at M = 5.7

    McCarthy, J. F.; Kubota, T.
    The flow field behind a circular cylinder was investigated experimentally at a nominal Mach number of 5.7, over a range of Reynolds numbers from 4500 to 66,500, based on the cylinder diameter. Pitot pressure, static pressure, and total temperature were measured at various distances behind cylinders of three different diameters in order to determine the flow properties in the wake. To correlate data at different Reynolds numbers and to discriminate turbulent wakes from laminar wakes, a linearized theory for the laminar far wake was developed, which included the effects of axial pressure gradient. The transition from laminar flow to turbulent flow was also determined by computing diffusion coefficients from the velocity profiles. The transition...

  8. Laser Doppler Velocity & Vorticity Measurements in Turbulent Shear Layers

    Lang, Daniel B.; Dimotakis, Paul E.
    A Laser Doppler Velocimeter (LDV) system was developed to measure the instantaneous spanwise vorticity, - ω_z, in a turbulent shear layer. It was necessary to design and fabricate the LDV optics and processing electronics, as no commercially available LDV systems met the specifications of measuring the velocity at four closely spaced points to the requisite accuracy. Measurements were also made of the instantaneous u, v, u', v' and - u'v'. The instantaneous vorticity was processed to obtain an estimate of its probability density function, from which the mean and rms values were estimated. It was also possible to separate the irrotational...

  9. Hydroacoustic Testing of a NACA-66 (MOD) Hydrofoil in the GALCIT High Speed Water Tunnel

    Dimotakis, Paul E.
    The work described in this report represents a primarily exploratory effort to assess the feasibility of performing accurate hydroacoustic measurements at high signal-to-noise ratios, in the GALCIT High Speed Water Tunnel (HSWT), hereafter referred to as the Tunnel, to characterize the hydroacoustic environment in the HSWT 2-D test section, and to complement the force and flow visualization measurements that were performed using the two-dimensional, NACA 66 (MOD) hydrofoil in the recent past. See Baloga (1982), Dimotakis et al. (1988), Shen & Dimotakis 1989a, and Shen &. Dimotakis 1989b. This work was also a sequel to earlier hydroacoustic measurements that were performed by S. Barker...

  10. Equations of Electrogasdynamics and Applications

    Demetriades, Anthony; Hill, Jack H.
    This report presents in summary work done in the period from 1959 to 1963 at the Hypersonic Research Project, Graduate Aeronautical Laboratories California Institute of Technology, on some theoretical aspects of the dynamics of ionized gases. The objective of this work was to set up a system of conservation equations when no magnetic field or complicated chemical effects are present. Emphasis is placed on the gross exchange processes among species at a point, rather than the gradient transport mechanisms (e. g. , viscosity and heat conduction); in the past this point of view was often called "Gaseous Electronics". In subordinatipg the magnetic field...

  11. The Supersonic Hydrogen-Fluorine Combustion Facility Design Review Report Version 4.0

    Hall, Jeffery; Dimotakis, Paul
    This version (4.0) of the report is intended to provide a general overview of the facility and its capabilities. It includes brief descriptions of all major components, including those elements of the fluorine gas delivery system that were ignored in the previous versions. More detailed information on the facility can be found in the appendices, including engineering drawings, device data sheets and sample calculations.

  12. Characterization of gravity current formation for the use in detonation refraction experiments

    Wolf, M. L.; Lieberman, D. H.; Shepherd, J. E.
    Detonation propagation through an interface is being studied at Caltech. In these experiments, the interface shape is determined by the gravity currents. This report presents an experimental study of the formation and the development of these gravity currents by an analog system in a water channel using water and salt water to simulate the density differences in detonation experiments. The major parameters such as the Reynolds number and the density difference were matched in both experiments to be able to compare the gravity current in the water channel and the gravity current in the Galcit detonation tube. In the present study, the gravity current was generated by the...

  13. Pulse Detonation Engines: Initiation, Propagation, and Performance

    Shepherd, J. E.
    Research carried out from 2003-2005 at the Explosion Dynamics Laboratories at Caltech under an ONR contract has examined many issues critical to Pulse Detonation Engine (PDE) development. These include: detonation structure imaging using OH PLIF; a narrow channel facility for examining regular and irregular detonations; detonation diffraction; mechanism of soot track generation; fundamental and applied studies of detonation initiation; direct measurements and analytical modeling of impulse from a detonation tube, including the effects of partial fill and nozzles; models of detonation engine performance; thermodynamic analysis of unsteady and steady propulsion systems. Each of these aspects of our program is discussed and key results are presented.

  14. Detonation Initiation by Annular Jets and Shock Waves

    Shepherd, Joseph E.
    The objective of this research is to experimentally determine the feasibility of initiating detonation in fuel-air mixtures using only the energy in hot, compressed air. The existing 6-inch shock tube at Caltech was used to create hot, high-pressure air behind a reflected shock wave. The hot air created an imploding annular shock wave when it jetted through an annular orifice into a 76-mm-diameter, 1-m-long tube attached to the end of the shock tube. A special test section with an annular opening covered by a diaphragm is attached to the end wall of the shock tube. The test section is filled...

  15. Design Considerations and Structural Analysis of the Narrow Channel Facility

    Grunthaner, M. P.; Austin, J. M.
    The narrow channel (NC) facility design is based on the GALCIT Detonation Tube (GDT) test section design of Mike Kaneshige [3]. The main differences are 1) the design of the longitudinal bolted joint was simplified and 2) the keys for the flanges are not designed to assist with shear loading. The GDT side windows and PLIF window may be used in the NC facility. 304 SS was chosen for its excellent corrosion resistance. The yield strength is 275 MPa. 304 SS is non-magnetic and is therefore more difficult to grind on a table with magnetic locking. All four plates were blanchard...

  16. Structural Response of Shells to Shock and Detonation Loading

    Beltman, W. M.; Shepherd, J. E.
    Part I: theory. Part II: shock loading of a thin aluminum tube. Part III: the GALCIT detonation tube.

  17. Combustion within Porous Waste

    Pfahl, Ulrich; Shepherd, Joseph E.; Unal, Cetin
    Flammable gases (primarily hydrogen and nitrous oxide but also ammonia and methane) are continuously being generated within the waste contained in the tank farms at Hanford Site. Some portions of the waste are porous and conceivably, a combustion event could occur within the waste due to accidental ignition. This has been postulated as a potential hazard since deflagrations and detonations are observed in laboratory experiments to propagate through combustible gases in porous materials, or through interconnected flammable gas voids. The waste in Hanford storage tanks are mainly in three different forms, a: salt cake, b: sludge, c: supernatant. Formation of...

  18. Flammability, Ignition Energy and Flame Speeds in NH_3-H_2-CH_4-N_2O-O_2-N_2 Mixtures

    Pfahl, Ulrich; Shepherd, Joseph E.
    This report describes studies on flammability and flame propagation in mixtures of interest to the Flammable Gas Safety Issue for the waste tank farms at the Hanford site. Flammability limits, pressure histories, ignition energy, and flame speeds have been measured for selected mixtures of hydrogen–nitrous oxide–air, methane–nitrous oxide–air, ammonia–nitrous oxide and hydrogen–nitrous oxide–ammonia–nitrogen–methane–air mixtures at initial pressures of 100 kPa. These investigations were accompanied by reactant and product gas-analysis using gas chromatography and Fourier transform infrared spectrometry.

  19. User Guide for Detonation Cell Size Measurement using Photoshop and Matlab

    Hébral, J.-P.; Shepherd, J. E.
    Detonation cells are a characteristic feature of detonation shots, and their size is a very valuable experiment parameter to know. To reduce the uncertainty in this variable that is used to being related to manual measuring, a computational processing has been developed, based on Fourier analysis of digital pictures. The objective is to highlight the relevant frequencies present in the cellular pattern, and thus get the most encountered spatial wave length, which would turn out to be the cell size. This guide is aimed to provide with the tools, knowledge, and advice needed to compute cell size measurements using the Photoshop procedures...

  20. Shock and detonation modeling with the Mie-Grüneisen equation of state

    Arienti, M.; Morano, E.; Shepherd, J. E.
    We consider the numerical simulation of inviscid reactive flows with application to high density explosive detonation. The numerical model is based on the Euler equations and the Mie-Grüneisen equation of state extended to treat chemical energy release and expanded states. The equations are computed with a Roe-Glaister solver on a Cartesian mesh. We present results for two substances, a binder and an explosive. Our solution method is verified against the exact solution of the shock tube problem for solid materials. We show under what conditions a "physical" expansion shock can appear in this example. We then address the problem of modeling expanded...

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