The development of turbulent pipe flow

Whilst turbulence still remains one of the great mysteries of classical physics, its reputation for a chaotic lack of structure is under intense scrutiny. Research now points to the existence of highly organized large-scale structures within turbulent flows. Much of this research have almost exclusively been carried out within a so called fully-developed region of flow. This region is downstream of a point beyond which the flow field’s behavior is invariant. However, it has not been conclusively proven that a fully developed region actually exists. A literature survey found that most facilities are cited as being ‘sufficiently long’, yet no formal definition or documentary evidence of the fully developed condition is widely accepted. The aim of the study is to produce a detailed analysis of the flow from the uniform inlet conditions through to the fully-developed turbulent state, along with an accurate definition of what constitutes fully developed flow. This investigation concerns the affect of both the growth of large-scale structures and their role in the evolution of the flow to the fully-developed condition. With the increasing acceptance of the turbulent large-scale structures model, previous research has not yet shown how large-scale structures affect this development length. These aims were achieved by the design, development and deployment of a carriage to transport hot-wires within the pipe allowing measurements at any stream wise point within the working sectio

A study of convection velocities in a zero pressure gradient turbulent boundary layer

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 gradient TBL at Re_τ = 470 . Two high speed cameras placed side-by-side in the streamwise direction give a 10δ streamwise field of view with a time step of Δt^+ = 0:5 between consecutive fields. Far from the wall the convection velocities of all scales are very close to the local mean velocity in agreement with the work of Dennis and Nickels, while at y^+ = 34 it was found that all measured scales in the flow convect faster than the local mean in agreement with Krogstad et. al. The variation of the convection velocity with scale and distance from the wall will be discussed

Oil film interferometry in high Reynolds number turbulent boundary layers

There is continuing debate regarding the validity of skin friction measurements that are dependent on the functional form of the mean velocity profile, for example, the Clauser chart method. This has brought about the need for independent and direct measures of wall shear stress, tw. Of the independent methods to measure tw, oil film interferometry is the most promising, and it has been extensively used recently at low and moderately high Reynolds number. The technique uses interferometry to measure the thinning rate of an oil film, which is linearly related to the level of shear stress acting on the oil film. In this paper we report on the use of this technique in a high Reynolds number boundary layer up to Rq = 50,000. Being an independent measure of tw, the oil film measurement can be used as a means to validate more conventional techniques, such as the Preston tube and Clauser chart at these high Reynolds numbers. The oil-film measurement is validated by making comparative measurements of tw in a large-scale fully-developed channel flow facility where the skin friction is known from the pressure gradient along the channe

Instrumentation for Millimeter-wave Magnetoelectrodynamic Investigations of Low-Dimensional Conductors and Superconductors

We describe instrumentation for conducting high sensitivity millimeter-wave cavity perturbation measurements over a broad frequency range (40-200 GHz) and in the presence of strong magnetic fields (up to 33 tesla). A Millimeter-wave Vector Network Analyzer (MVNA) acts as a continuously tunable microwave source and phase sensitive detector (8-350 GHz), enabling simultaneous measurements of the complex cavity parameters (resonance frequency and Q-value) at a rapid repetition rate (approx. 10 kHz). We discuss the principal of operation of the MVNA and the construction of a probe for coupling the MVNA to various cylindrical resonator configurations which can easily be inserted into a high field magnet cryostat. We also present several experimental results which demonstrate the potential of the instrument for studies of low-dimensional conducting systems.Comment: 20 pages including fig

Does the Repressor Coping Style Predict Lower Posttraumatic Stress Symptoms?

We tested whether a continuous measure of repressor coping style predicted lower posttraumatic stress disorder (PTSD) symptoms in 122 health care professionals serving in Operation Iraqi Freedom. Zero-order correlational analyses indicated that predeployment repressor coping scores negatively predicted postdeployment PTSD symptoms, $r_s = -0.29, p = 0.001$, whereas predeployment Connor-Davidson Resilience Scale (CD-RISC) scores did not predict postdeployment PTSD symptoms, $r_s = -0.13, p = 0.14$. However, predeployment trait anxiety was chiefly responsible for the association between repressor coping and PTSD symptom severity, $r_s = 0.38, p = 0.001$. Four percent of the subjects qualified for a probable PTSD diagnosis. Although service members with relatively higher PTSD scores had lower repressor coping scores than did the other subjects, their level of predeployment anxiety was chiefly responsible for this relationship. Knowing someone's predeployment level of trait anxiety permits better prediction of PTSD symptoms among trauma-exposed service members than does knowing his or her level of repressive coping.Psycholog

Методическая работа в дошкольной образовательной организации как условие повышения информационно-коммуникационной компетентности педагогов

Тема работы актуальна. В ВКР представлены условия, способствующие развитию компонентов ИКК педагогов. Работа имеет практическую значимост