High-intensity Flow Research Articles

Simulation and assessment of long-term stormwater basin performance under real-time control retrofits

ABSTRACT The use of real-time control (RTC) as an adaptation technique for improving stormwater systems has been gaining attention in recent years for its ability to enhance water quality treatment and quantity management. An RTC retrofit of seven existing detention basins was simulated for a small (162 ha), an urbanized watershed in Blacksburg, VA. Two heuristic, reactive control algorithms were tested for their ability to improve hydraulic conditions at each facility and the watershed outlet through manipulation of an actuated valve. For 24-hour design storms, RTC only reduced peak flows at certain facilities for events with a return period of 2 years or less. For larger design storms, RTC maintained or increased peak flow rates. During a 15-year historic rainfall simulation, RTC retrofitting reduced the total duration of erosive flows for most facilities; however, the duration of high intensity flows increased, or remained unchanged. This result was also reflected at the watershed outlet.

Optimized Design of a Swirler for a Combustion Chamber of Non-Premixed Flame Using Genetic Algorithms

Recirculation in a combustion chamber is required for stabilizing the flame and reducing pollutants. The swirlers can generate recirculation in a combustion chamber, inducing a swirling flow that breaks vorticity and improves the mixing of air and fuel. The swirl number (Sn) is related to the formation of recirculation in conditions of high-intensity flows with Sn > 0.6. Thus, the optimized design of a swirler is necessary to generate enough turbulence that keeps the flame stable. We present the optimized design of a swirler considering the main parameters for a non-premixed combustion chamber. This optimization is made with genetic algorithms to ensure the generation of a recirculation zone in the combustion chamber. This recirculation phenomenon is simulated using computational fluid dynamics (CFD) models and applying the renormalization group (RNG) k-ε turbulence method. The chemistry is parameterized as a function of the mixture fraction and dissipation rate. A CFD comparison of a baseline swirler model and the proposed optimized swirler model shows that a recirculation zone with high intensity and longer length is generated in the primary zone of the combustion chamber when the optimized model is used. Furthermore, the CFD models depict swirling effects in the turbulent non-premixed flame, in which the stabilization is sensitive to the recirculation zone. The temperature results obtained with the CFD models agree well with the experimental results. The proposed design can help designers enhance the performance of combustion chambers and decrease the generation of CO and NOx.

РОЗПОДІЛ РЕСУРСІВ БАГАТОФАЗНОЇ СИСТЕМИ ОБРОБКИ ВЕЛИКИХ ДАНИХ ПРИ ВИСОКОІНТЕНСИВНОМУ ВХІДНОМУ ПОТОЦІ

Завдання оптимального проектування багатофазної системи обробки великих даних (БФСОВД) при високоінтенсивному вхідному потоці потребують застосування сучасних математичних і комп'ютерних методів та засобів. Предметом дослідження є ресурси багатофазної системи обробки великих даних. Мета дослідження – розроблення методу оптимального розподілу ресурсів БФСОВД при високоінтенсивному вхідному потоці, котрий враховує як можливість проведення аналізу даних у режимі реального часу, так і особливостей високоінтенсивного потоку вхідних даних із багатьох джерел. Результати. Визначено особливості високоінтенсивних потоків вхідних даних та показана можливість апроксимації його з достатньою точністю гауссівським розподілом. Також визначені особливості функціонування багатофазних систем та запропонована схема функціонування багатофазної системи обробки великих даних. Базуючись на отриманих результатах розроблена математична модель процесу оптимізаціі розподілу ресурсів багатофазної системи обробки великих даних при високоінтенсивному вхідному потоці. Для цього використано метод динамічного програмування. Висновок. В результаті отримана мінімальна кількість каналів в кожній фазі БФСОВД, при якій середній час аналізу даних в системі буде мінімальним.

Measurement of turbulent spatial structure and kinetic energy spectrum by exact temporal-to-spatial mapping

We present a method for converting a time record of turbulent velocity measured at a point in a flow to a spatial velocity record consisting of consecutive convection elements. The spatial record allows computation of dynamic statistical moments such as turbulent kinetic wavenumber spectra and spatial structure functions in a way that completely bypasses the need for Taylor’s hypothesis. The spatial statistics agree with the classical counterparts, such as the total kinetic energy spectrum, at least for spatial extents up to the Taylor microscale. The requirements for applying the method are access to the instantaneous velocity magnitude, in addition to the desired flow quantity, and a high temporal resolution in comparison to the relevant time scales of the flow. We map, without distortion and bias, notoriously difficult developing turbulent high intensity flows using three main aspects that distinguish these measurements from previous work in the field: (1) The measurements are conducted using laser Doppler anemometry and are therefore not contaminated by directional ambiguity (in contrast to, e.g., frequently employed hot-wire anemometers); (2) the measurement data are extracted using a correctly and transparently functioning processor and are analysed using methods derived from first principles to provide unbiased estimates of the velocity statistics; (3) the exact mapping proposed herein has been applied to the high turbulence intensity flows investigated to avoid the significant distortions caused by Taylor’s hypothesis. The method is first confirmed to produce the correct statistics using computer simulations and later applied to measurements in some of the most difficult regions of a round turbulent jet—the non-equilibrium developing region and the outermost parts of the developed jet. The proposed mapping is successfully validated using corresponding directly measured spatial statistics in the fully developed jet, even in the difficult outer regions of the jet where the average convection velocity is negligible and turbulence intensities increase dramatically. The measurements in the developing region reveal interesting features of an incomplete Richardson-Kolmogorov cascade under development.

Effects of tip streaming on the prediction of droplet size distribution in the presence of dispersants during subsea blowouts

Abstract (2017-193) With the presence of surfactants in the fluid mixture, tip streaming phenomenon often occurs where daughter droplets of micron or sub-micron size are ejected from thin threads of the droplet poles. Recent experimental and modeling studies of tip streaming phenomenon have been focusing on the formation of individual droplets. However, effects of tip streaming on the prediction of droplet formation during subsurface oil blowouts have not been thoroughly investigated. Due to the high intensity flow in the blowout, the amount of micron or sub-micron size droplets resulting from tip streaming could be substantial and cannot be ignored. In this study, a new empirical-numerical scheme is developed in the thoroughly-validated droplet formation model, VDROP-J, to account for the tip streaming phenomenon when dispersants are presence. Calibration of the new scheme and model validations are performed in association with the underwater oil jet experiments. The new model development improves the capability of VDROP-J model in application to the cases when dispersants are used, which would provide valuable information of droplet formation during subsea blowouts for decision makers and research groups.

Dramatic Effect of Vibrations on Dynamics of Rotating Hydrodynamic Systems

The results of theoretical and experimental investigation of the average dynamics of inhomogeneous systems in rotating cavity in the presence of oscillating force field are highlighted and analyzed. Average behavior of nonisothermal liquid as well as different multiphase systems (two liquids, liquid and gas, solid in liquid, granular matter in liquid) in quickly rotating horizontal cylinder subjected to vibrations of different direction is described. The specificity of dynamics of all the systems is determined by the Coriolis force which defines not only the average flows but the fluid oscillations also. The resonant excitation of inertial oscillations of liquid results in generation of intensive mean flows. The structure of vibrational streams is essentially determined by the type of inertial waves. So, excitation of an azimuthal wave generates azimuthal streams (outrunning or lagging, depending on frequency of the wave), three-dimensional standing waves (in the systems with deformable interface) generate regular spatial flows of high intensity. Under the resonant conditions the influence of vibrations appears to be very strong, the speed of mean streaming can achieve the values comparable with the speed of rotation of the container.

Cooperative effects in an ensemble of flows with a virtual cathode

Coherent effects in an ensemble of high-intensity flows with a virtual cathode are analyzed by means of simulation. It is demonstrated that, in the system under study, synchronization may result in the formation of coherent pulses.

A “Mickey Mouse” Coronary Anomaly

A 58-year-old asymptomatic man with a heart murmur underwent routine Doppler stress echocardiography that detected abnormal high-intensity flow from the aorta to the left atrium. Coronary angiography with a 6-French Amplatz left catheter (Scimed/Boston Scientific) and MEDRAD (MEDRAD Inc) power injections of radiographic contrast revealed a large aorto-left atrial fistula originating anteriorly from the aorta above the sinotubular junction. The fistula …

新潟県の丘陵山間地域における積雪環境特性

Snow environments were observed continuously for eleven years from 1988 to 1999 at a meteorological station located in the snowy mountains of Niigata prefecture. Observation data showed that annual mean precipitation was approximately 2, 990 mm, half of which appeared to be snowfall. Total annual precipitation was greatly influenced by the amount of snowfall, which fluctuated much more than that of rainfall. Although no remarkable upward trend in annual mean air temperature was observed, the annual range of air temperature trended to increase slightly. This region was covered with a thick snow accumulation of 360 cm in mean maximum depth for an average of 141 days per year. The water flow from snow accumulation increased in snowmelting periods and high intensity flows were recorded under rainy or foehn weather.

The measurement of Reynolds stresses with a pulsed-wire anemometer

An investigation of the errors arising in pulsed-wire anemometer measurements of the Reynolds stresses in turbulent flows is described. Attention is concentrated first on a theoretical approach, in which an idealized yaw response and an assumed form for the joint velocity probability-density distribution are used to determine the errors in measurements of, principally, UV and 3 when the probe is used like an ordinary single slanted hot wire. Actual pulsed-wire measurements in a range of turbulent shear flows are then compared with crossed-hot-wire results and with the theoretically simulated pulsed-wire response obtained from calculations and the crossed-wire data. It is shown that whilst pulsed-wire measurements of lateral intensity and shear stress are inevitably rather unsatisfactory in regions of low intensity (less than lo%, say) they agree reasonably well with crossed-wire measurements in flows where the intensities are higher, but do not exceed those for which sensible corrections to cross-wire data are possible (up to, say, 30 yo). In this medium-intensity range, however, the pulsed-wire errors are found to be critically dependent on the finite limit of the pulsed wire's yaw response; it seems that acceptable measurements can only be made if this exceeds about 75. Beyond an intensity of about 30 the errors in 3 measurements (which are usually much higher than those for UV) become less dependent on the exact nature of the yaw response and invariably decrease with increasing intensity. They can, with care, be made as low as 15 yo. It is concluded that pulsed-wire measurements of the Reynolds stresses can be made with an accuracy similar to that of crossed-wire measurements in medium-intensity flows. Such measurements are certainly adequate for many practical purposes in high-intensity flows where hot-wire techniques are useless.