368,436 research outputs found
Model-based scaling of the streamwise energy density in high-Reynolds-number turbulent channels
Full text linkWe study the Reynolds number scaling of a gain-based, low-rank approximation to turbulent channel flows, determined by the resolvent formulation of McKeon & Sharma (2010), in order to obtain a description of the streamwise turbulence intensity from direct consideration of the Navier-Stokes equations. Under this formulation, the velocity field is decomposed into propagating waves (with single streamwise and spanwise wavelengths and wave speed) whose wall-normal shapes are determined from the principal singular function of the corresponding resolvent operator. We establish that the resolvent formulation admits three classes of wave parameters that induce universal behavior with Reynolds number on the low-rank model, and which are consistent with scalings proposed throughout the wall turbulence literature. For the rank-1 model subject to broadband forcing, the integrated streamwise energy density takes a universal form which is consistent with the dominant near-wall turbulent motions. When the shape of the forcing is optimized to enforce matching with results from direct numerical simulations at low turbulent Reynolds numbers, further similarity appears. Representation of these weight functions using similarity laws enables prediction of the Reynolds number and wall-normal variations of the streamwise energy intensity at high Reynolds numbers (Re ? ? 10³-10¹?). Results from this low rank model of the Navier-Stokes equations compare favorably with experimental results in the literature
Counter-gradient diffusion of Reynolds stress in turbulent Couette flow with forward-facing step
No full textThe turbulent Couette flow with a forward-facing step (sudden contraction) is investigated experimentally and numerically. The particle image velocimetry (PIV) measurement and direct numerical simulation (DNS) prove peculiar turbulence behavior, the counter-gradient diffusion of the Reynolds stress, near the front part of the corner separation on the forward step. The negative turbulence production which follows the counter-gradient diffusion is then evaluated through quadrant analysis. The negative contribution of Q1 and Q3 events inside the shear layer increases with decreasing the Reynolds number. The effect makes the counter-gradient diffusion rather pronounced in lower Reynolds number flows
Letter from T. M. Reynolds to S. B. Simmons
No full textLetter from T. M. Reynolds to S. B. Simmons, concerning scheduling for quartets at NFA convention
Wellcome Witnesses to Twentieth Century Medicine: Volume 1
No full textAnnotated and edited transcript of four Witness Seminars. Introduction by E M Tansey First published by the Wellcome Trust, 1997. ©The Trustee of the Wellcome Trust, London, 1997.In Volume One (Occasional Publication no. 4, 1997).All volumes are freely available online at: www.history.qmul.ac.uk/research/modbiomed/wellcome_witnesses/Annotated and edited transcript of four Witness Seminars. Introduction by E M Tansey.Annotated and edited transcript of four Witness Seminars. Introduction by E M Tansey.Annotated and edited transcript of four Witness Seminars. Introduction by E M Tansey.Annotated and edited transcript of four Witness Seminars. Introduction by E M Tansey.Four Witness Seminar transcripts of meetings held between 1993 and 1996: ‘Technology Transfer in Britain: The case of Monoclonal Antibodies’ (E M Tansey and P P Catterall, eds); ‘Self and Non-Self: A History of Autoimmunity’ (E M Tansey, S V Willhoft and D A Christie, eds); ‘Endogenous Opiates’ (E M Tansey and D A Christie, eds); ‘The Committee on Safety of Drugs’ (E M Tansey and L A Reynolds, eds). Introduction by E M Tansey, ‘What is a Witness Seminar’, separate index for each meeting. Tansey E M, Catterall P P, Christie D A, Willhoft S V, Reynolds L A. (eds) (1997) Wellcome Witnesses to Twentieth Century Medicine, volume 1. London: The Wellcome Trust.The Wellcome Trust is a registered charity, no. 210183
Experimental characterisation of large scale structures in a high Reynolds number turbulent boundary layer
No full textA very large field of view (4δ x 1δ) with a good spatial resolution owing to the use of four 2k x 2k pixel cameras was conducted in a flat plate boundary layer at two Reynolds numbers (Reθ ≈7,500 and 20,000). Comparing the flow statistics with previously obtained hot-wire data under similar flow conditions show good agreement. The goal of this experiment is to detect and characterise the large scale motions which develop in the log region of a high Reynolds number turbulent boundary layer
Letter from T. M. Reynolds to S. B. Simmons
No full textLetter from T. M. Reynolds to S. B. Simmons, concerning chorus rehearsal at convention
Numerical and statistical analyses of aerodynamic characteristics of low Reynolds number airfoils using Xfoil and JMP
No full textLow Reynolds number aerodynamics has become a promising topic of interest in various commercial utilizations such as wind turbines. Airfoils employed for this type of application usually experience performance degradation due to separation bubble formation. This study intends to investigate the behavior and effect of such phenomena and analyze the interrelationship among the contributive factors affecting its existence using JMP, a statistical analysis tool, with numerical data generated from Xfoil, a collective program applicable for low-speed airfoils. Numerical results were validated against published experimental data and exhibited favorable agreement more specifically within the upper limits of the given Reynolds number range. Surface pressure and skin friction drag coefficient plots show that the bubble length tends to decrease as angle of attack, Reynolds number and turbulence intensity are increased. The abridgement of the bubble extent due to enhancement of flow instabilities is associated with increase lift-to-drag ratio which is more pronounced in the attached flow regions. The statistical technique yielded predictive models for multiple outcome variables and it was learned that the main effects had more significant influence on the aerodynamic properties of airfoils and chordwise extent of separation bubble. © 2017 Author(s)
Effects of Damping and Reynolds Number on Vortex-Induced Vibrations
Full text linkVortex-induced vibrations have been studied experimentally with emphasis on damping and Reynolds number effects. Our system was an elastically-mounted rigid circular cylinder, free to oscillate only transverse to the flow direction, with very low inherent damping. We were able to prescribe the mass, damping, and elasticity of the system over a wide range of values, with the damping controlled by a custom-made variable magnetic eddy-current damping system.
Special emphasis is put on a nontraditional parameter formulation. The advantages of this formulation are explained, and an important new parameter, effective stiffness, is introduced. Using this new formulation, the amplitude and frequency responses are only a function of damping, Reynolds number, and effective stiffness. We show the effects that damping and Reynolds number each have on the amplitude and frequency response profiles and make the interesting observation that changes in damping or Reynolds number have similar effects.
The maximum amplitudes of our systems are studied in detail. We theoretically show that they should be functions of both damping and Reynolds number. This allows us to create constant-Reynolds-number curves of maximum amplitude over a large range of damping values, which we call a "generalized" Griffin plot. We also define maximum amplitudes in the case of zero damping as limiting amplitudes, and show that they are only a function of Reynolds number. We experimentally determine our limiting amplitude dependence on Reynolds number over the range 200 < Reynolds number < 5050.
Discontinuities in the amplitude response profile are also investigated. The discontinuity between the initial branch and the large-amplitude, upper branch is studied in two ways. First, the time-averaged behavior is examined to understand what controls the discontinuity and look for damping and Reynolds number effects. Second, we track the cycle-by-cycle transient response through this discontinuous amplitude change, induced either by changes in the tunnel velocity or system damping. Finally, we also find a new discontinuity hysteresis region between the lower branch and the desynchronized region, which appears to be a low Reynolds number effect and is only seen in systems with Reynolds number < 1000.</p
H. S. Reynolds Residence, architectural drawings, 1911
No full textArchitectural drawings for a residence commissioned by H. S. Reynolds Esq. and created by George Mills, an architect of Toledo, Ohio. The drawings are ink on linen, the commission number for the project is 1727, and they were created in 1911. The drawings include front and rear exterior elevations, numerous interior design details, as well as drawings for two chandeliers in the home. As of 2021 this building has not been demolished
Explicit algebraic and differential Reynolds stress model application to homogeneously sheared and compressed turbulence
No full textAn explicit algebraic and differential Reynolds stress models (EARSM and DRSM) are used to investigate the influence of homogeneous shear and compression on the behaviour of turbulence in the limit of rapid distortion theory (RDT). EARSM is shown to give realizable results and to preserve RDT regime, unlike the eddy-viscosity model (EVM). The DRSM version of our model is in reasonable agreement with RDT theory
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