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Caltech Authors (103,751 recursos)
Repository of works by Caltech published authors.

Type = Conference or Workshop Item

Mostrando recursos 1 - 20 de 485

1. Deformation of Drill Pipe Held in Rotary Slips - Vreeland, T., Jr.
This paper presents an analysis of measurements of drill-pipe deformation in the slip area. Drill pipe was loaded in excess of the load at the minimum yield strength with the pipe in VARCO Type SOL and Type SDXL slips. A VARCO Type MSS solid master bushing was used with the type SDL slips and the master bushing of a VARCO KMPC unit was used with the Type SDXL slips. Measurements were made on the reduction in pipe diameter in the slip area as a function of load. Values of load which caused inelastic deformation of the pipe are determined and compared to the values previously calculated from theory.

2. Examining the Abundance of Rare Elements in Solar Energetic Particle Events - Cohen, C. M. S.; Mewaldt, R. A.; Christian, E. R.; Cummings, A. C.; Leske, R. A.; Slocum, P. L.; Stone, E. C.; von Rosenvinge, T. T.; Wiedenbeck, M. E.
Using data accumulated with the Solar Isotope Spectrometer on ACE during 27 large solar energetic pa1ticle (SEP) events the effects of charge-to-mass (Q/M) fractionation on rare elements arc examined. In an attempt to correct for these fractionation effects and obtain preliminary estimates of the coronal abundances of K, Ti, Cr, Mn, Co, Ni, Cu, and Zn, the SEP events are classified according to their Fe/Si ratio. The data from all events within an Fe/Si category are summed and the rare element abundances extracted over an energy interval of 20 to 65 MeV/nucleon. We estimated the apparent Q/M fractionation, corrected for it, and...

3. Reynolds-number Dependence of Streamwise Velocity Fluctuations in Turbulent Pipe Flow - Morrison, Jonathan F.; Jiang, Weimin; McKeon, Beverley J.; Smits, Alexander J.
Statistics of the streamwise velocity component in fully-developed pipe flow are examined for Reynolds numbers in the range 5.5 x 10^4 < Re_D < 5.7 x 10^6. The second moment exhibits two maxima: one in the viscous sublayer is Reynolds-number dependent while the other, near the lower edge of the log region, is also Reynolds-number dependent and follows roughly the peak in Reynolds shear stress. The behaviour of both peaks is consistent with the concept of inactive motion which increases with increasing Reynolds number and decreasing distance from the wall. No simple scaling is apparent, and in particular, so-called "mixed"...

4. Stabilising Control Laws for the Incompressible Navier-Stokes Equations using Sector Stability Theory - Sharma, A. S.; Limebeer, D. J. N.; McKeon, B. J.; Morrison, J. F.
A method for nonlinear global stabilisation of the incompressible Navier-Stokes equations is presented and used to eliminate transient growth in linearly stable Poiseuille flow for the case of full-field actuation and sensing. In the absence of complete velocity field sensing and full actuation the controller synthesis procedure gives a controller that minimises the the attainable perturbation energy over all disturbances and thus maximises the disturbance threshold for transition to occur. The control laws are found using the theory of positive real systems, originating in the control systems community. It is found that a control law making the linearised part of the perturbed Navier-Stokes equations positive real, provides nonlinear...

5. Transition in incompressible boundary layers with two-dimensional excrescences - McKeon, B. J.; Bender, A. M.; Westphal, R. V.; Drake, A.
An experimental investigation of the transition process in boundary layers subjected to forward- or aft-facing two-dimensional step excrescences is described. The objective of the work was to characterize the variation of transition Reynolds numbers with measurable roughness and boundary layer parameters, with the specific goal of specifying new tolerance criteria for laminar flow airfoils, alongside a fundamental investigation of linear boundary layer stability mechanisms. Results from an ongoing program of increasing complexity on effects of pressure gradient on excrescence-induced transition are presented. Preliminary N-factor calculations are used to determine the effects of boundary layer stability and attempt to isolate the effect of the disturbance due to the excrescence.

6. Effect of sting size on the wake of a sphere at subcritical Reynolds numbers - Norman, A. K.; McKeon, B. J.
Vortex shedding and turbulent motion in the wake of a sphere that is supported using a streamwise-aligned cylindrical sting are investigated at a subcritical Reynolds number of Re=3800, using high speed particle image velocimetry. The mechanism by which the presence of a sting of increasing diameter relative to the diameter of the sphere influences the wake, in terms of both the small-scale shear instability and the larger wake instability, is explored and brie y compared with the two-dimensional analog of the splitter plate introduced into a cylinder wake. The difficulties associated with obtaining converged statistics, along with the effect of free stream turbulence and sphere...

7. Perturbation of a turbulent boundary layer by spatially-impulsive dynamic roughness - McKeon, B. J.; Jacobi, I.; LeHew, J.
First experimental measurements of manipulation of the structure of a canonical zero pressure gradient turbulent boundary layer using a low frequency (compared to the viscous frequency) mechanical dynamic roughness are presented. “Dynamic” (or time-dependent) surface roughness is proposed as a method for both control and diagnosis of turbulent boundary layers.

8. Forces on a Sphere in the Presence of Static and Dynamic Roughness Elements - Norman, A. K.; McKeon, B. J.
Though the effect of distributed roughness on flow over a sphere has been examined in detail, there have been few observations as to the effect of an isolated roughness element on the forces induced on a sphere that is in uniform flow. In this experimental study, we examine how the forces are altered due to both a stationary and dynamic three-dimensional roughness element in the Reynolds number range of 5 x 104 to 5 x 105. It is found that even a small change to the geometry of the sphere, by adding a cylindrical roughness element with a width and height...

9. An Approach to Measuring Step Excrescence Effects in the Presence of a Pressure Gradient - Bender, Anne M.; Elliott, J. Russell; Shinagawa, Yuto; Korntheuer, Andrea J.; Drake, Aaron; Westphal, Russell V.; Gerashchenko, Sergiy; McKeon, B. J.; Yoshioka, Shuya
An experimental study was undertaken to determine the effects of step excrescences on boundary layer transition using a unique ground test facility in which the test model was propelled though still air. The models used were designed to have a nominally constant pressure gradient so that the results would be relevant to laminar flow aircraft whose wings often have long runs of mildly favorable pressure gradient. The models had an integrated continuously adjustable two-dimensional step, which could be adjusted to be forward-facing or aft-facing. The large model was used to increase the Reynolds numbers examined so that the results are...

10. Hot-Wire Measurements of the Influence of Surface Steps on Transition in Favorable Pressure Gradient Boundary Layers - Gerashchenko, S.; McKeon, B. J.; Westphal, R. V.; Bender, A. M.; Drake, A.
An examination of the effects of surface step excrescences on boundary layer transition was performed, using a unique experimental facility. The objective of the work was to characterize the variation of transition Reynolds numbers with measurable step size and boundary layer parameters, with the specific goal of specifying new tolerance criteria for laminar flow airfoils, alongside a fundamental investigation of boundary layer transition mechanisms. This paper focuses on interpretation of hot-wire measurements, including supporting stability calculations, undertaken as part of the study. The results for both forward and aft-facing steps indicated a substantial stabilizing effect of favorable pressure gradient on...

11. Step Excrescence Effects for Manufacturing Tolerances on Laminar Flow Wings - Drake, Aaron; Bender, Anne M.; Korntheuer, Andrea J.; Westphal, Russell V.; McKeon, Beverley J.; Gerashchenko, Sergiy; Rohe, Wayne; Dale, Gary
Manufacturing tolerances for laminar flow wings can be significantly tighter than those of conventional aircraft. The tighter tolerances can significantly affect the assessment of the practicality of designing for laminar flow. However, existing data on the effects of excrescences typical of manufacturing process are limited. Further, information on the effects—often beneficial—of pressure gradient present on the laminar flow wings is not generally available. To address these concerns, a series of experiments has been undertaken to examine the effects of surface steps in the presence of pressure gradients. The step geometries were selected to represent those that result from actual aircraft...

12. Energetic Modes in Turbulent Pipe Flow From Resolvent Analysis - McKeon, B. J.; Sharma, A. S.
We describe a method to investigate the mode shapes in turbulent pipe flow at a given wavenumber pair that are most responsive to harmonic forcing in the sense that the they correspond to the largest singular value in a Schmidt decomposition of the linear Navier-Stokes operator using the turbulent mean profile as the base flow. The ideas follow logically from the work of Sharma & McKeon (2009), who considered a similar approach for laminar pipe flow.

13. Colloquium on Solid State Devices - Fisk, J. B.; Dacey, George C.; Mead, Carver A.; Humphrey, Floyd B.; Anderson, J. Reid; Jaumot, F. E.; Rose, Albert; Ittner, William B. III; Peterson, John W.; Hulm, John K.; Thomas, J. Earl; Tucker, Gardiner; Pierce, John R.; Oliver, Bernard M.
[no abstract]

14. A study of convection velocities in a zero pressure gradient turbulent boundary layer - LeHew, J.; Guala, M.; McKeon, B. J.
Time-resolved DPIV measurements performed in wall parallel planes at several wall normal locations in a turbulent boundary layer (TBL) are used to illuminate the distribution of wall parallel velocities in a three-dimensional energy spectrum over streamwise, spanwise, and temporal wavelengths. To our knowledge, this is the first time this type of spectral distribution has been reported. Slices of the 3D spectrum can give insight into the propagation of different scales in the ow as well as the streamwise and spanwise extent of dominant scales. Measurements were performed at three wall normal locations, y^+ = 34; 108; and 278, in a zero pressure...

15. Characteristics of a turbulent boundary layer perturbed by spatially-impulsive dynamic roughness - Jacobi, I.; Guala, M.; McKeon, B. J.
Statistical and spectral analyses of the manipulation of a canonical zero pressure gradient turbulent boundary layer using static roughness and low-frequency dynamic roughness patches are presented. A shift of spectral energy away from the wall downstream of the roughness patch is observed. The dynamic roughness is shown to disrupt the structure of the boundary layer, while embedding its periodic signature in an extensive stretch of the downstream flow field.

16. Open Access adoption at Caltech - Porter, George S.
Insights into OA adoptions and migrations from commercial publishers in several different fields of research by Caltech faculty.

17. On effectiveness of a rank-1 model of turbulent channels for representing the velocity spectra - Moarref, Rashad; Sharma, Ati S.; Tropp, Joel A.; McKeon, Beverley J.
We evaluate the efficacy of a gain-based rank-1 model, developed by McKeon & Sharma (J. Fluid Mech., 2010), for representing the energy spectra and the streamwise/wall-normal co-spectrum in a turbulent channel. This is motivated by our previous observation that the streamwise turbulent energy intensity is well approximated by the rank-1 model subject to a broadband forcing in the wall-parallel directions and a properly selected temporal intensity. In the present study, the evaluation is based on finding the optimal forcing spectrum that minimizes the deviation between the two-dimensional velocity spectra at different wall-normal locations obtained from direct numerical simulations at friction Reynolds...

18. A systems approach to modeling opposition control in turbulent pipe flow - Luhar, M.; Sharma, A. S.; McKeon, B. J.
Despite being one of the earliest - and most studied - active control techniques proposed for wall-bounded turbulent flows, the opposition control method of Choi et al., [J.Fluid Mech., Vol. 262, 1994, pp. 75-110] remains to be fully understood. In this paper, we develop a simple model for opposition control by extending the forcing-response analysis presented in McKeon and Sharma [J. Fluid Mech., Vol. 658, 2010, pp. 336-382]. Based on a gain analysis of the Navier-Stokes equations, the velocity field in turbulent pipe flow is decomposed into a series of highly-amplified response modes (i.e., propagating helical waves). Opposition control, introduced via...

19. Closing the loop: an explicit calculation of the nonlinearity in the resolvent formulation of wall turbulence - Sharma, A. S.; McKeon, B. J.
The resolvent-based analysis of wall turbulence (McKeon & Sharma 2010) is extended with an explicit treatment of the non-linearity in the Navier-Stokes equations. The equivalent of triadic interaction in the wall-normal direction is described, and it is found that the resulting forcing has a phase shift of π/2 in terms associated with symmetric spatial directions. Explicit forms for the nonlinearity in fully-developed pipe and channel flows, i.e. in cylindrical and Cartesian coordinate systems.

20. Dynamic separation on a pitching and surging airfoil as a model for flow over vertical axis wind turbine blades - Dunne, R.; McKeon, B. J.
Vertical axis wind turbine (VAWT) blades undergo dynamic separation due to the large angle of attack variation they experience during a turbine rotation. The flow over a single blade was modeled using a sinusoidally pitching and surging airfoil in a constant free stream flow at a mean chord Reynolds number of 10^5. Two-dimensional, time resolved velocity fields were acquired using particle image velocimetry (PIV). Vorticity contours were used to visualize shear layer and vortex activity. A low order model of dynamic separation was developed using Dynamic Mode Decomposition (DMD). A primary and secondary dynamic separation mode were identified as the critical...

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