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rss_1.0 Recursos de colección

Caltech Authors (93,451 recursos)
Repository of works by Caltech published authors.

Type = Report or Paper

Mostrando recursos 1 - 20 de 2,552

1. A model for “dynamic roughness” in turbulent channel flow - McKeon, B. J.
A simple model for roughness elements with a time-varying height was used to investigate the effect of time-dependent, “dynamic” roughness on wall-bounded flow. Temporally varying wall velocities were specified in a turbulent channel flow simulation in order to model the effect of introducing a roughness time scale in addition to a distribution of roughness length scales.

2. Strichartz inequality for orthonormal functions - Frank, Rupert L.; Lewin, Mathieu; Lieb, Elliott H.; Seiringer, Robert
We prove a Strichartz inequality for a system of orthonormal functions, with an optimal behavior of the constant in the limit of a large number of functions. The estimate generalizes the usual Strichartz inequality, in the same fashion as the Lieb-Thirring inequality generalizes the Sobolev inequality. As an application, we consider the Schrödinger equation in a time-dependent potential and we show the existence of the wave operator in Schatten spaces.

3. Some issues on turbulent mixing and turbulence - Dimotakis, Paul E.
Recent data on turbulent mixing suggest that the mixing transition, previously documented to occur in shear layers, also occurs in jets, as well as many other flows, and can be regarded as a universal phenomenon. The resulting, fully-developed turbulent flow requires a minimum Reynolds number of Re_T ≈ 10^4, or a Taylor Reynolds number of Re_T ≈ 10^2 to be sustained. Turbulent mixing in this fully-developed state does not appear to be universal, however, with a qualitatively different behavior between shear layers and jets.

4. Measurements of scalar power spectra in high Schmidt number turbulent jets - Miller, Paul L.; Dimotakis, Paul E.
Single-point, jet-fluid concentration measurements obtained from high Schmidt number (Sc ≃ 1.9 x 10^3) turbulent jets permit an investigation of temporal scalar power spectra, for jet Reynolds numbers in the range of 1.25 ≤ Re x 10^(-4)≤ 7.2. At intermediate scales, we find a spectrum with a logarithmic derivative (slope) that is increasing with Reynolds number, in absolute value, but less than 5/3 at the highest Reynolds number in our experiments. At the smallest scales, our spectra exhibit no k^(-1) power-law behavior, possessing a log-normal region over a range of scales exceeding a factor of 40, in some cases.

5. Image correlation velocimetry - Tokumaru, P. T.; Dimotakis, P. E.
This paper focuses on the correlation of two successive scalar images for the purpose of measuring imaged fluid motions. A method is presented for deforming, or transforming, one image to another. Taylor series expansions of the Lagrangian displacement field are used, in conjunction with an integral form of the equations of motion, to approximate this transformation. The proposed method locally correlates images for displacements, rotations, deformations, and higher order displacement gradient fields, and applies a global minimization procedure to insure a global consistency in the results. An integral form of the equations of motion is employed and, as a consequence, no spatial or temporal...

6. Chemical Reactions in Turbulent Mixing Flows - Dimotakis, Paul E.; Leonard, Anthony
The purpose of this research is to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic and supersonic flows. The program during this reporting period was comprised of several parts: a. an experimental effort, b. a numerical simulation effort, and c. an effort to develop instrumentation and diagnostics; flow and combustion facilities; and data-acquisition systems. The latter as dictated by the specific needs of the experimental part of the program. Our approach in this research has been to carry out a series of detailed theoretical and experimental studies of turbulent mixing in primarily in two, well-defined, fundamentally important flow fields: free-shear layers and...

7. The Effects of Damkohler Number on a Turbulent Shear Layer - Experimental Results - Mungal, M. G.; Frieler, C. E.
A chemical reaction for which the reaction rate can be varied is studied in a fully developed, two-dimensional, turbulent mixing layer. The layer is formed between two nitrogen streams, one carrying low concentrations of fluorine and the other hydrogen and nitric oxide. For fixed concentrations of fluorine and hydrogen and for nitric oxide concentrations that are small fractions of the fluorine concentration, the heat release is fixed but the overall reaction rate is controlled by the nitric oxide concentration. Therefore, for fixed flow conditions, the nitric oxide concentration determines the ratio of the reaction rate to the mixing rate. For large values of...

8. The Effects of Damköhler Number in a Turbulent Shear Layer - Broadwell, J. E.; Mungal, M. G.
A simple model describing chemical reaction in a turbulent shear layer is put in quantitative form and the model predictions compared with experiment. The reactants are not pre-mixed and the flow is two-dimensional. The dependence of the amount of product in the layer on the Schmidt, Reynolds, and Damköhler numbers and on the stoichiometric ratio is exhibited explicitly in the model. The first two parameters appear as the product (ScRe) and influence that part of the reaction taking place in strained laminar flames. In the limit ScRe → = (for Sc > 1 and Re >> 1) the molecular mixing becomes independent...

9. Chemical Reactions in Turbulent Mixing Flows - Dimotakis, Paul E.; Broadwell, James E.; Leonard, Anthony
The purpose of this research has been to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic and supersonic flows. Progress in this effort thus far has uncovered important deficiencies in conventional modeling of these phenomena, and offered alternative suggestions and formulations to address some of these deficiencies. This program is comprised of an experimental effort, an analytical modeling effort, a computational effort, and a diagnostics development and data-acquisition effort, the latter as dictated by specific needs of our experiments. Our approach has been to carry out a series of detailed theoretical and experimental studies primarily in two,...

10. Chemical Reactions in Turbulent Mixing Flows - Dimotakis, P. E.; Broadwell, J. E.; Leonard, A.
Work is continuing primarily in gas phase turbulent mixing and chemical reactions. The liquid phase work to date is in its final stages of being analyzed and documented for dissemination in the form of archival publications. In the gas phase shear layer work, our investigations are concentrating on shear layer free stream density ratio effects, finite kinetic rate (Damköhler number) effects, and a design effort in support of the planned extension of the work to supersonic flows. In jet flows, progress has been made in the gas phase laser Rayleigh scattering techniques developed for conserved scalar measurements down to diffusion space and...

11. Designer non-Abelian anyon platforms: from Majorana to Fibonacci - Alicea, Jason; Stern, Ady
The emergence of non-Abelian anyons from large collections of interacting elementary particles is a conceptually beautiful phenomenon with important ramifications for fault-tolerant quantum computing. Over the last few decades the field has evolved from a highly theoretical subject to an active experimental area, particularly following proposals for trapping non-Abelian anyons in `engineered' structures built from well-understood components. In this short overview we briefly tour the impressive progress that has taken place in the quest for the simplest type of non-Abelian anyon---defects binding Majorana zero modes---and then turn to similar strategies for pursuing more exotic excitations. Specifically, we describe how interfacing...

12. Chemical Reactions in Turbulent Mixing Flows - Dimotakis, Paul E.; Broadwell, James E.; Leonard, Anthony
The purpose of this research is to conduct fundamental investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic and supersonic flows. Our program is comprised of several parts: a. an experimental effort, b. an analytical effort, c. a computational effort, d. a modeling effort, and e. a diagnostics development and data-acquisition effort, the latter as dictated by specific needs of the experimental part of the overall program. Our approach has been to carry out a series of detailed theoretical and experimental studies of turbulent mixing in primarily in two, well-defined, fundamentally important flow fields: free shear layers and axisymmetric jets. To elucidate molecular transport effects, experiments and theory...

13. A new probe of magnetic fields in the pre-reionization epoch: I. Formalism - Venumadhav, Tejaswi; Oklopčić, Antonija; Gluscevic, Vera; Mishra, Abhilash; Hirata, Christopher M.
We propose a method of measuring extremely weak magnetic fields in the inter galactic medium prior to and during the epoch of cosmic reionization. The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition. The resulting change in the brightness temperature fluctuations encodes information about the magnetic field the atoms are immersed in. The method is most suited to probing fields that are coherent on large scales. Due to the long lifetime of the triplet state of the 21-cm transition, this technique is naturally sensitive to extremely weak field strengths, of order 10^(-19)...

14. An Instrument for the Direct Measurement of Skin Friction in High Speed Flow - Dhawan, Satish
In recent years the development of high speed aircraft and missiles has shown the importance of the effects of compressibility and heat transfer on boundary layer flow and hence on drag. The general problem is a highly complex one and involves processes like turbulence and shock waves in a real fluid. Such phenomena pose formidable theoretical difficulties for an analytical solution of the drag problem (for theoretical work on the subject see Refs. 1 and 2). in the case of shock free laminar flow the mechanism of the resistance experienced by a given body is fairly well understood and the...

15. Nonlinear Behavior of Acoustic Waves in Combustion Chambers - Culick, F. E. C.
This report is concerned with the general problem of the nonlinear growth and limiting amplitude of acoustic waves in a combustion chamber. The analysis is intended to provide a formal framework within which practical problems can be treated with a minimum of effort and expense. There are broadly three parts. First, the general conservation equations are expanded in two small parameters, one characterizing the mean flow field and one measuring the amplitude of oscillations, and then combined to yield a nonlinear inhomogeneous wave equation. Second, the unsteady pressure and velocity fields are expressed as syntheses of the normal modes of the chamber,...

16. Measurements of Energy Losses Associated with Interactions Between Acoustic Waves and a Steady Flow Field - Culick, F. E. C.; Magiawala, K.
An experimental program has been conducted to study interactions between acoustic waves and non-uniform flow fields. Data have been taken in an impedance tube, modified to accommodate an average flow, and in a resonance tube. Results are given for the influence of flow through a subsonic exhaust vent on an acoustic field. Measurements for circular and slot vents of several sizes and for two frequencies show that the flow through the vent causes a transfer of energy from the average flow field to the acoustic field: The vent acts as a source or gain of acoustic energy.

17. Magnetohydrodynamic Simple Waves - Cole, J. D.; Lynn, Y. M.
The simple wave solutions, which in ordinary gas dynamics correspond lo expansion flows or Prandtl-Meyer flows are generalized here to ideal magnetohydrodynamic flows. The one-dimensional unsteady (x, t) case is considered. Due to magnetic effects more than one component of field and velocity must be considered, To carry out the simple wave formalism the equations of motion (continuity, momentum, induction) are written in terms of flow velocities (u_1, u_2), Alfvén velocities (b_1, b_2) and sound speed (a), These velocities are then functions only of the phase ξ = x_1 - U(ξ)t; each phase line can be thought of as an infinitesimal wave propagating...

18. Blunt Body Theory for Hypersonic Flow - Hida, K.
A systematic analysis of Newtonian flow past an axi-symmetrical blunt body is developed by expanding various physical quantities in power series of λ = (γ-l)/(γ+l), where γ stands for the ratio of specific heats of a gas. Some general results such as stand-off distance, pressure distribution along the axis of symmetry are given, provided that the shock is detached and has finite curvature at its nose. More extensive calculations are made for the flow past a flat-faced disc and power-law bodies.

19. A Parimutuel-like Mechanism from Information Aggregation: A Field Test Inside Intel - Plott, Charles R.; Gillen, Benjamin J.; Shum, Matthew
Field tests of a new Information Aggregation Mechanism (IAM) developed via laboratory experimental methods were implemented inside Intel Corporation for sales forecasting. The IAM, which incorporates selected features of parimutuel betting, is uniquely designed to collect and quantize as probability distributions any dispersed, subjectively held information that might exist. The tests demonstrate the robustness of experimental results and the practical usefulness of the IAM. The IAM yields predicted distributions of future sales that are very accurate at short horizons; indeed, more accurate than Intel's official in-house forecast 59% of the time. A symmetric game model suggests why the IAM works.

20. Theoretical and Experimental Investigations of Axial Flow Compressors. Part 3: Progress Report on Loss Measurements In Vortex Blading - Alsworth, Charles C.; Iura, Toru
This report gives the results of extensive and detailed measurements of the flow pattern in a single stage axial flow compressor with free vortex blading. Considerable information is given on the location and magnitude of losses through the various blade rows. Some of the measurements are repetitions of those given in an earlier report, but the new data is more detailed and presumably more accurate. Preliminary results are presented on the investigation of the radial distribution of work input by measuring the rise of stagnation temperature along a stream line.

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