Non-uniform Velocity Distribution Research Articles

Scour around Bankline and Setback Abutments in Compound Channels

Prediction of bridge abutment scour is particularly difficult in compound channels because of the effects of the flow interaction between the floodplain and main channel superimposed on the flow obstruction, and contraction caused by the bridge abutment and highway embankment. Previous laboratory studies have focused on rectangular channels, although it is generally recognized that compound channels can have an additional geometric influence on the maximum clear-water scour depth. It is the purpose of this paper to integrate experimental results for clear-water abutment scour for different compound channel geometries by taking into account the flow redistribution that occurs between floodplain and main channel in the contracted section created by the bridge opening. In addition, sediment size, bridge backwater, abutment shape, and approach velocity and depth are included in a proposed scour depth relationship. Both setback and bankline abutments are considered. Experimental evidence is presented for the characteristic nonuniform lateral velocity distributions associated with compound channels in the bridge approach section as affected by backwater, and for the entrainment of floodplain flow into the main channel between the approach and bridge opening cross sections. Scour depth patterns are shown as remnants of the floodplain flow acceleration and entrainment process. It is demonstrated that a common relationship for scour depth can be developed for both setback and bankline abutments provided that a consistent definition of scour depth is utilized. The experimental results are applied successfully to a field case of measured abutment scour, but the need for additional high-quality, real-time field data is emphasized.

Flow Characteristic of a Porous System Employing Multi-hole Channels With or Without Surface Ceramics Layer

Flow behaviors in a porous system employing multi-hole channels with or without surface ceramics layer, which is commonly used for filtering process in industrial applications, are investigated by using Magnetic Resonance Imaging (MRI) for measuring axial velocity distribution inside the channels and numerical calculation for pressure distribution inside the porous filter. It is revealed that flow in the filter without surface ceramics layer shows non-uniform axial velocity distribution where channels nearest to the outside annulus only shows large axial velocity. On the other hand, in the case with surface ceramics layer, uniform axial velocity distribution is observed, because a ratio of flow resistance of surface layer to that of porous base dominates flow uniformity.

Intracluster stars tracing motions in nearby clusters

Cosmological simulations of structure formation predict that galaxies are dramatically modified by galaxy harassment during the assembly of galaxy clusters, losing a substantial fraction of their stellar mass which today must be in the form of intracluster stars. Simulations predict non-uniform spatial and radial velocity distributions for these stars. Intracluster planetary nebulae are the only abundant component of the intracluster light whose kinematics can be measured at this time. Comparing these velocity distributions with simulations will provide a unique opportunity to investigate the hierarchical cluster formation process as it takes place in the nearby universe.

125 混合潤滑状態におけるCMPプロセスの解析 : 摩擦抵抗に着目した解析モデルの実験的検証(OS-15 研磨技術)

An analytical approach to estimate the coefficient of friction (COF) in chemical mechanical polishing (CMP) process in mixed lubrication is developed in the present research. The Stribeck curve is calculated by experimental and analytical results of friction resistances. An analytical model, which can predict the distribution of contact stress and fluid pressure under the condition of nonuniform velocity distribution by utilizing the Stribeck curve, is developed. Polishing experiments are carried out for the verification of the model in terms of the friction resistance. It is confirmed that the effect of the wafer rotational speed on the friction resistance can be predicted successfully by the developed analytical model.

Effects of Entrance and Exit Shapes on a Uniform Flow in Regenerators

The flow loss in the regenerator mainly depends on fluid friction through the regenerator matrix, but it is also generated by sudden expansion and contraction flow at the regenerator ends. The entrance areas at the regenerator ends of typical Stirling cycle machines are smaller than the cross-sectional area of the regenerator matrix. So, the gas flow in the matrix becomes a flow field with non-uniform velocity distribution accompanying the expansion and contraction flow. In this paper, the geometry of a tapered flow passage between the regenerator ends and the matrix to produce more uniform flow in the matrix, is examined experimentally using steady single-blow equipment to model a regenerator with a narrow flow passage at the ends. Additionally, the effects of the flow passages are analyzed using CFD. The effect of the tapered flow passage, in producing more uniform flow, is greater than that of the gap.

An analytical study on heat transfer performance of radiators with non-uniform airflow distribution

Heat exchangers used in modern automobiles usually have a highly non-uniform air velocity distribution because of the complexity of the engine compartment and underhood flow fields; hence ineffective use of the core area has been noted. To adequately predict the heat transfer performance in typical car radiators, a generalized analytical model accounting for airflow maldistribution was developed using a finite element approach and applying appropriate heat transfer equations including the ε-NTU (effectiveness - number of heat transfer units) method with the Davenport correlation for the air-side heat transfer coefficient. The analytical results were verified against a set of experimental data from nine radiators tested in a wind tunnel and were found to be within +24 and −10 per cent of the experimental results. By applying the analytical model, several severe non-uniform velocity distributions were also studied. It was found that the loss of radiator performance caused by airflow maldistribution, compared with uniform airflow of the same total flowrate, was relatively minor except under extreme circumstances where the non-uniformity factor was larger than 0.5. The relatively simple set of equations presented in this paper can be used independently in spreadsheets or in conjunction with computational fluid dynamics (CFD) analysis, enabling a full numerical prediction of aerodynamic as well as thermodynamic performance of radiators to be conducted prior to a prototype being built.

On the errors associated with the use of large diameter SHPB, correction for radially non-uniform distribution of stress and particle velocity in SHPB testing

The large diameter (up to 100 mm) Split Hopkinson Pressure Bar (SHPB) setup is used throughout the world to test large-cell heterogeneous materials, small structures, etc. This paper proposes a correction method to take into account the non-uniform distribution of stress and particle velocity (non-plane wave effect) in large diameter setups, following the theory of wave propagation in an infinite cylindrical elastic or viscoelastic rod. Such a non-plane wave effect depends on the pressure bar diameter and the high-frequency components contained in the signals. This correction procedure can be performed together with the wave dispersion correction, which is already incorporated for many large diameter bars used. For the various metallic and Nylon viscoelastic bars (up to 60 mm diameter) available in our laboratory, the relative difference between the average values of the particle velocity (and stress) in a cross-section and that calculated with a standard one-dimensional analysis is found to be inferior to 5%. However, this difference increases with a higher impact velocity, because signals containing more important high-frequency components are generated by higher impact velocities. In order to find an upper limit of the potential error for bars of various diameters, the theoretical pulse signal for a perfect impact between two infinite cylindrical rods is used, which gives the highest signal spectrum. With this theoretical pulse, such an upper limit of the potential error for different bar diameters (up to 200 mm) is found. It shows that the potential average error can reach up to 12% for a 100-mm-diameter bar currently used in the world.

Bulk Compton Emission in the Gamma-Ray Burst Internal Shock Model

We investigate the role of the bulk Compton scattering process in the internal shock model. We numerically show that the radiation field created by internal shocks does not affect the efficiency of the energy conversion in the shocks even if fireball outflows have highly nonuniform velocity distributions. However, the bulk Compton scattering produces an additional high-energy component, especially when variability in the outflows arises because of a modulation of the mass injected into a constant energy flow. We show that an isotropic energy of 1050-1051 ergs could be radiated in the range of 100 MeV-GeV through the scattering process, provided that the shell's Lorentz factor varies between 10 and 104.

The Effect of Inlet Guide Vanes Wake Impingement on the Flow Structure and Turbulence Around a Rotor Blade

The flow structure and turbulence around the leading and trailing edges of a rotor blade operating downstream of a row of inlet guide vanes (IGV) are investigated experimentally. Particle image velocimetry (PIV) measurements are performed in a refractive index matched facility that provides unobstructed view of the entire flow field. Data obtained at several rotor blade phases focus on modification to the flow structure and turbulence in the IGV wake as it propagates along the blade. The phase-averaged velocity distributions demonstrate that wake impingement significantly modifies the wall-parallel velocity component and its gradients along the blade. Due to spatially non-uniform velocity distribution, especially on the suction side, the wake deforms while propagating along the blade, expanding near the leading edge and shrinking near the trailing edge. While being exposed to the nonuniform strain field within the rotor passage, the turbulence within the IGV wake becomes spatially nonuniform and highly anisotropic. Several mechanisms, which are consistent with rapid distortion theory (RDT) and distribution of turbulence production rate, contribute to the observed trends. For example, streamwise (in rotor frame reference) diffusion in the aft part of the rotor passage enhances the streamwise fluctuations. Compression also enhances the turbulence production very near the leading edge. However, along the suction side, rapid changes to the direction of compression and extension cause negative production. The so-called wall blockage effect reduces the wall-normal component.

Experiments on axisymmetric oscillating water jets: absorption of ammonia in presence of n-pentanol

The competing effects of pentanol adsorption and ammonia absorption on the shape of axisymmetric oscillating water jets are studied experimentally and interpreted qualitatively. While there is no significant influence of the absorption process on pure water jets, considerable change in jet length and deviation from sinusoidal evolution of surface oscillation in presence of n-pentanol is observed, accompanied by an increase in absorption rate. Hence dependence of jet shape on interfacial convection is shown. The effects of pentanol adsorption, surface elasticity of a pentanol surface film and nonuniform velocity distribution on jet stability are discussed quantitatively.

A New Design Method to Improve Flow Uniformity in a Reaction Injection Mold Entry

Abstract Reaction injection molding involves the injection of two or more kinds of liquid polymers into a mold at relative high speed. Such high inertia effect may result in air pocket inside the mold or non-uniform velocity distribution. How to design the mold entry geometry to provide uniform velocity distribution becomes one of the major topics in reaction injection molding process. Thus a new and simple method was developed in this work to optimize the reaction mold entry design. Several regulation islands were located in a fish tail entrance to help distribute the flow more even. Dimensions and locations of the islands will affect the flow uniformity and become the factors to be optimized. Taguchi's design of experiments coupled with computer flow simulation was used to achieve die geometry optimization. Effects of different dimensions of the islands on the flow uniformity can also be evaluated through statistical analyses in the flow simulation. Flow visualization technique was done by capturing flow images with high speed CCD. The experimental results showed very good agreements with the Fluent simulation results. The design methodology proposed here can help the molders in designing different reaction injection mold entries for better uniformity and performance.

Radial Distribution of Liquid Velocity in a Liquid-Solids Circulating Fluidized Bed

Local liquid velocity was measured in a liquid-solid circulating fluidized bed, with a Plexiglas riser column of 7.62 cm ID and 3.0 m in height, by a dual conductivity probe, with 508 micron glass beads. The results show that radial distribution of local liquid velocity in the LSCFB is nonuniform with higher liquid velocity at the axis and lower near the wall, compared to the more uniform radial profiles in both the conventional fluidization and the dilute liquid transport regimes. The radial nonuniformity increases with increasing liquid velocity and solids circulation rate in the LSCFB. A radial nonuniformity index, proposed by Zhu and Manyele (2001), was used to quantify the extent of the radial nonuniformity under different solids circulation rates and liquid flow rates. The radial nonuniformity index is used to qualify the radial distribution of liquid velocity. RNI values in the liquid-solid circulating fluidization regime are seen to be much higher than those in both the particulate fluidization regime and the dilute liquid transport regime, indicating the nonuniform radial distribution of local liquid velocity in the LSCFB. This illustrates the use of RNI as an effective measurement of the radial distribution of liquid velocity.

Reconstruction of the normal velocity distribution on the surface of an ultrasonic transducer from the acoustic pressure measured on a reference surface

In piezoceramic ultrasonic transducers, the thickness vibrations are usually accompanied by the excitation of Lamb waves, which are difficult to control. Therefore, the normal velocity distribution over the radiating surface is unknown. As a result, the ultrasonic field generated by the transducer cannot be predicted with the desired accuracy. The purpose of this study is to develop and experimentally validate a new method for evaluating the normal velocity distribution over the surface of an ultrasonic transducer. The method consists in measuring the amplitude and phase of the acoustic pressure field over a certain reference surface and then calculating the acoustic field at the transducer by using the Rayleigh integral. The accuracy and stability of the method are illustrated numerically. The method is tested experimentally with a focused piezoceramic transducer. In the experiment, the reference surface is represented by a plane perpendicular to the axis of the acoustic beam. The ultrasonic field is scanned by a needle hydrophone, which is moved by a micropositioner. The measurements show that the method provides an accurate prediction of the acoustic field generated by a source with an unknown nonuniform normal velocity distribution.

Numerical analysis of electrohydrodynamics in a round pipe

A numerical analysis on electrohydrodynamics (EHD) in a round pipe is presented based on the PISO (pressure-implicit with splitting of operators) scheme under a periodic boundary condition. The numerical results show that a vortex ring is generated between the electrodes due to the nonuniform distribution of velocity and charge density during the starting process. The increase of value of T (the ratio of electric stress to viscous stress) affects the developing process because of the unsteadiness repulsion among the charges will increase with T during this period. When the flow field finally reaches steady state, it becomes a fully developed pipe flow. The steady outlet velocity is in direct proportion to the square of the voltage imposed between electrodes. The spatial distribution of the pressure is similar to that of the electric potential between the electrodes because of the direct analogy between potential and pressure.

Review of Open Channel Hydraulics , by Terry W. Sturm

Despite the proliferation during recent years of textbooks on the topic of open channel hydraulics, many academics and professionals are still waiting for a book of the caliber of Henderson’s and Chow’s texts to use in the classroom or to modernize their reference library. In Sturm’s Open Channel Hydraulics, aimed at senior undergraduates and first-year graduate students, the author attempts to fill this niche by initially approaching open channel hydraulics from a fundamental perspective of fluid mechanics, and leading through to practical applications and computational solutions. He has provided chapters on introductory steady flow topics, unsteady flow theory, and numerical solutions. He also discusses flood routing and unsteady flow approximations, and the important practical consideration of flow in alluvial channels. Sturm opens with a very nice introduction that includes a brief history of our knowledge of open channel hydraulics. The introduction is followed by an overview of the topic, given in terms of definitions of the various flow approximations commonly applied in practice, placing them in their proper theoretical context. The overview is followed by a derivation of the fundamental equations of mass, momentum, and energy conservation, done reasonably, particularly with the explanation of momentum conservation, and derivation of Bernoulli’s equation and momentum’s ultimate link to the concept of energy conservation. He is perhaps a bit too succinct with the derivation of the equation of conservation of energy itself, though this is understandable given the complexity of this undertaking from a pedagogical perspective. The author takes this opportunity to impress upon the student some important fundamental concepts, including the significance of the kinetic energy and momentum correction coefficients for nonuniform velocity distributions, a highly favorable approach for an educational text, and the concepts of surface resistance versus form drag. He then provides the student with an excellent explanation and justification of the need for, and details of the application of, dimensional analysis techniques. Rather useful practice problems, particularly for the dimensional analysis technique, are provided. Following in the form of Henderson, the next two chapters introduce the reader to energy and momentum concepts. The author brings a fresh approach to these topics and presents them in an interesting manner, with immediate reference to specific examples. In addition, the complexities raised by overbank flows are introduced ~specifically in terms of multiple minimum specific energies!. The inclusion of weirs, stilling basins, and supercritical expansions and contractions in these chapters put the theory in context, and also challenges the student with complex, as well as simpler, applications of the fundamental theory. The next two chapters cover uniform and gradually varied flow, again working from a fundamental level including dimensional analysis and fluid mechanics in the case of uniform flow,

C01 入口形状が再生器マトリックス内流速分布に及ぼす影響

In Stirlig cycle machines, the regenerator entrance area is usually smaller than the cross-sectional area of matrix and the pressure drop loss increases due to a nonuniform velocity distribution in the matrix. This study measured and analyzed the effect of the small distance gap between the entrance and the matrix end on the pressure drop. In addition, the velocity distribution of a working gas flow was observed by the flow visualization methods using a smoke-wire and a hydrogen bubbling. The results show that the gap extends considerably the flow to radial direction, makes the velocity distribution uniform and is effective in decreasing the pressure drop loss across the regenerator matrix.

Axial liquid dispersion in a liquid–solid circulating fluidized bed

AbstractAlthough axial liquid dispersion has been studied extensively in particulate fluidized beds, no data has been reported previously in a liquid–solid circulating fluidized bed (LSCFb). In this work, the axial liquid dispersions at various radial positions were measured in an LSCFB of 76 mm in diameter and 3.0 m in height using a dual conductivity probe. The results reveal that the axial liquid dispersion is affected not only by the operating conditions but by the radial positions as well. A local axial dispersion model is proposed to describe the axial liquid dispersion at various radial positions. The local axial liquid dispersion coefficients determined by the proposed model are greater at the axis than near the wall region of the riser. This nonuniformity of axial liquid dispersion is believed to be caused by the radial nonuniform distribution of liquid velocity, and bed voidage in the LSCFB can significantly affect the axial liquid dispersion.

Optimizing the Hydraulic Characteristics and Thermal Performance of a Slabbing Mold for the High-Speed Continuous Casting of Steel

The most important component of continuous steel-casting machines is the mold, since it forms the skin of the ingot and removes 20‐25% of the heat of crystallization of the metal. The thermal performance of the mold affects its durability, the productivity of the continuous caster, and the number of surface defects on the slabs. Widespread use is being made of slabbing molds with walls of hot-rolled copper 70‐80 mm thick that contain drilled channels and a loop-type cooling system [1]. Such molds have shown satisfactory results with high-speed ingot withdrawal at 0.8‐1.0 m/min. At speeds greater than 1 m/min, there is an increase in the wear of the walls and a corresponding increase in the number of surface defects on the slabs ‐ defects such as spider-shaped cracks. Hydraulic calculations were performed for molds with a loop-type water supply system. Calculations were also performed to determine the temperature fields in the copper walls of the mold. It was proposed that a mold be designed with thin walls made of a cold-worked copper-silver (CS) alloy containing milled channels, a separate water feed for each surface, and high-speed water flow within the channels. Local water flow velocities and coefficients characterizing heat transfer from the copper wall to the water in each channel for ingot withdrawal speeds up to 1.4 m/min were calculated for a 250 〈 (1020‐1910) mm mold with a length of 1200 mm. The mold had a loop-type water supply system and drilled channels (water discharge 320 m 3 /h, average flow velocity 6 m/sec). Similar calculations were performed for a mold which had the same cross section and length and milled channels (water discharge 700 m 3 /h, average flow velocity 6 m/sec). In the hydraulic calculation, we assumed the existence of a parabolic distribution of water velocity across the water pipe and in the channels of the mold. In using the iteration method to perform calculations for a pipe when the channels are connected in series and parallel, we determined the hydraulic resistance of the system, water discharge, and average water flow velocity in each channel of the mold. The last quantity was subsequently used to calculate convective heat transfer between the copper wall and the water. The calculations showed that the hydraulic resistance of channels used with a loop-type feed system is nonuniform due to a difference in the losses caused by friction and the rotation of the flow. Such nonuniformity leads to a nonuniform distribution of velocity in the channels of the mold (Fig. 1). Nonuniformity of the velocity distribution can also be caused by a difference in geometric pressure in the channels that is related to a difference betwe en the temperatures of the copper walls. These problems do not exist in a scheme in which water is fed separately to the surfaces of the mold. We developed an algorithm to calculate the thermal performance of a mold for different slab withdrawal speeds. The algorithm makes it possible to determine the heat-transfer coefficients along the cooling channels, water temperature in the channels, and the temperature distribution in the wall. An evaluation was made to identify the regions of the working surface of the mold that might be weakened during service.

Jet mixing in a slot

Jet mixing inside a slot has the potential to be applied for cooling in various components in gas turbines. An experimental program was conducted to focus on investigating the flow mixing behavior inside the slots. Various parameters including orientation angle, inclination angle, slot width, effect of primary flow and slot depth were systematically examined. An array of seven jets with a jet-to-jet spacing of five diameters and velocity ratio of unity was used in the experiment. The results indicated that the flow distribution at the slot exit becomes more uniform as the orientation angle was increased from 0° to 60°. Wider slot width brought about high non-uniformity and was clearly undesirable. The optimum slot depth was found to range from 2 to 2.8 times the jet diameter. The flow field was the most uniform where the shear layers of the two adjacent jets met. Regions of low velocity and high pressure caused non-uniform velocity distribution downstream where the jets met, so deeper slots do not necessarily render better uniformity. When the orientation angle increased from 0 to 30° and 60°, the jets bent toward the wall in the inclined direction caused by the Coanda effect. The presence of the primary flow forced the jet to spread faster in the lateral direction and caused some non-uniform flow pockets at the slot exit. The compound angle configuration (60° jet orientation and 30° slot inclination angles) was discovered as the best choice.

Airflow maldistribution and the performance of a packaged air conditioning unit evaporator

The performance of an evaporator for a packaged air conditioning unit has been investigated. A heat transfer program ACOL5 validated in an earlier study, was used to predict the performance. Non-uniform velocity distribution measurements taken in a typical air conditioning unit were employed in the prediction of the evaporator performance. It was found that this maldistribution reduced the performance of an evaporator circuit, as compared to uniform flow. Circuits at the edges of the evaporator, where the velocity was low, did not perform well. With the refrigerants controlled by one thermostatic valve, the worst performing circuit affected the performance of the whole evaporator, the evaporator performance being reduced by as much as 35%. The performance of the evaporator, where the circuits had different numbers of passes, depended on the position of the circuit in the evaporator.