Gap Flow Research Articles

Legitimate earnings inequality and national welfare commitment: Correspondence between economic institutions and the pay 80,000+ people in 30 nations think legitimate for ordinary jobs and for elite jobs

In formulating views of just reward for high-status and low-status work, do ordinary citizens take cues from their nation's public stance on income inequality as institutionally embedded in their welfare state, i.e. their social welfare and labor market policies, their "welfarism"? How large a morally correct earnings gap flows from that? Our multilevel analyses (fixed effects, random intercepts) replicate prior research on the impact of individual characteristics and socioeconomic development. They open new territory with the discovery that public opinion on legitimate/just earnings of high-status occupations aligns moderately strongly with welfarism, ceteris paribus, with welfare state citizens advocating lower pay for the elite but not higher pay for working-class occupations: The welfare state is not (or no longer) a matter of helping the poor but instead of bringing down the elite, "cutting down the tall poppies". Data: World Inequality Study v2.1: 30 countries, 71 surveys, and over 88,000 individuals.

3D simulation of gas-laden liquid flows in centrifugal pumps and the assessment of two-fluid CFD methods

An assessment of a two-fluid model assuming a continuous liquid and a dispersed gas phase for 3D computational fluid dynamics (CFD) simulations of gas/liquid flow in a centrifugal research pump is performed. A monodisperse two-fluid model, in conjunction with a statistical eddy-viscosity turbulence model, is utilized. By a comprehensive measurement database, a thorough assessment of model inaccuracies is enabled. The results on a horizontal diffuser flow reveal that the turbulence model is one main limitation of simulation accuracy for gas/liquid flows. Regarding pump flows, distinctions of single-phase and two-phase flow in a closed and semi-open impeller are figured out. Even single-phase flow simulations reveal challenging requirements on a high spatial resolution, e.g., of the rounded blade trailing edge and the tip clearance gap flow. In two-phase pump operation, gas accumulations lead to coherent gas pockets that are predicted partly at wrong locations within the blade channel. At best, a qualitative prediction of gas accumulations and the head drop towards increasing inlet gas volume fractions (IGVF) can be obtained. One main limitation of two-fluid methods for pump flow is figured out in terms of the violation of the dilute, disperse phase assumption due to locally high disperse phase loading within coherent gas accumulations. In these circumstances, bubble population models do not appear beneficial compared to a monodisperse bubble distribution. Volume-of-Fluid (VOF) methods may be utilized to capture the phase interface at large accumulated gas cavities, requiring a high spatial resolution. Thus, a hybrid model, i.e., a dispersed phase two-fluid model including polydispersity for flow regions with a dilute gas phase, should be combined with an interphase capturing model, e.g., in terms of VOF. This hybrid model, together with scale-resolving turbulence models, seems to be indispensable for a quantitative two-phase pump performance prediction.

Porosity distribution and mechanical response of laser-MIG hybrid butt welded 6082-T6 aluminum alloy joint

6082-T6 aluminum alloy with thickness of 6 mm were welded by laser-MIG hybrid welding. The effects of welding parameters on the porosity distribution, the correlations between the porosity distribution and mechanical properties were comprehensively investigated. The porosities mainly appeared near the fusion line of the arc zone when the arc current larger than 140 A, and which mainly existed in the center of the laser zone with other unsuitable parameters. Adopting low welding speed and setting heat source distance as around 3 mm were beneficial for the reduction of the porosity rate. The laser power, defocus distance, fit-up gap and gas flow rate had less effects on the porosity distribution. The average tensile strength of the joints without porosities was 260 MPa, which decreased to 224 MPa and 202 MPa as the porosity rate increased to 5.1% and 8.9%. The tensile specimens fractured at the heat affected zone or in the weld center when the porosity rates less or greater than 3%, and the fracture feature was diverted from ductile fracture to ductile and brittle mixed mode as the porosity rate increasing. The fatigue strength reduced from 113 MPa to 56 MPa when the porosity rate increased from 0% to 8.9%, while the porosity position had little effect on it. The fracture initiated in the weld surface when the joints without porosity, and which initiated near the porosity when the porosities existed in the joint.

Numerical investigation of the patterns of the flow past nine cylinders at low Reynolds number

Numerical investigations of the flow patterns around nine cylinders under the condition of Reynolds number around 200 are carried out. The change in the mean lift coefficient, the mean drag coefficient, Strouhal number, and mean streamwise velocity with the change in the pitch ratio is revealed. The Shannon entropy is calculated in the sample region to qualitatively measure the randomness of the velocity field in the region. It is shown that in flow regimes there are three patterns, including shield flow (1.1 < L/D < 2), reattachment of the shear layer (2 < L/D < 3.5), and vortex impact (3.5 < L/D < 5). The gap flow under different wake patterns has different effects on the change in hydrodynamic characteristics. The mean streamwise velocity is not strictly symmetrical about y/D when 2 < L/D < 3.5, and this asymmetry becomes more obvious as the pitch ratio increases. This asymmetry phenomenon is caused by deflection wake and instability of the shear layer falling from the surface of the upper and lower cylinders. The Shannon entropy of the velocity field decreases with an increase in the pitch ratio.

The influence of the angle between the secondary and primary cylinders on force coefficients and flow field characteristics at a low Reynolds number

Viscous flow around two unequal cylinders is simulated by solving the non-dimensional Navier–Stokes equations. A total of 13 two-dimensional numerical cases are carried out in this study for the flow fields around two adjacent cylinders at Re= 200. The ratio of d/D is equal to 0.25 (d and D are the diameters of the secondary and primary cylinders, respectively), the distance between two cylinders is kept as a constant (G = D), and the angle between them ranges from θ = 0° to θ = 180°. Firstly, six types of wake patterns are proposed and detailedly analyzed for the first time in this study. It is observed that the vortex shedding pattern is dependent on the position of the secondary cylinder. Secondly, this paper systematically analyzes the gap flow features between two cylinders for various angles, including the gap-flow strength, the deflection direction and the deflection mechanism. Additionally, this study also discusses in detail the variation characteristics of the drag coefficient, the lift coefficient, the Strouhal number and the time-averaged pressure. It is found that the drag and lift coefficients share a similar variation regularity, while the Strouhal number presents an opposite tendency with the change of the angle.

Flow-structure interactions of two tandem inverted flags in a water tunnel

The dynamic behaviors and vortex interaction modes of two tandem inverted flags at different gap distances and flow velocities are investigated experimentally in this paper. The results show that the straight, flapping, and deflected modes can still be observed with a successive increase in the flow velocity. The fixed-phase, different-frequency, changing-phase, alternating-phase, and aperiodic flapping modes are further found in the flapping mode. Considering the fixed phase difference and predominance of the fixed-phase mode, we mainly focus on this mode. The amplitude of the front flag is almost similar to that of an isolated flag due to the unaffected leading-edge vortex when they are both in the flapping mode, while it is smaller for the rear flag, indicating the great significance of the rear flag amplitude for studying the dynamic behaviors of two tandem inverted flags. First, the relation between the amplitude of the rear flag and the phase difference contains two linear segments with almost the same slope and a constant segment, fully demonstrating their strong correlation rather than the irrelevance. Second, the rear flag and the trailing-edge vortex (TEV) of the front flag are found to interact via the strong and weak interaction modes. Only in the strong interaction mode can the rear flag extract energy from the TEV of the front flag at lower critical flow velocity, resulting in a larger amplitude than that of the front flag. In general, a small gap distance is more conducive to energy harvesting at low flow velocity, while a large gap distance is more beneficial at high flow velocity.

Analysis and Optimization of Flow Field in Electrochemical Machining of the staggered groove on Gear Tooth Surface

Self-lubricating gears can better adapt to the bad lubrication conditions without oil or oil scarcity. Staggered groove can be produced by Electrochemical machining (ECM) on the gear tooth surface to fill solid lubricating materials. The cathode with and without flow slot has been designed. Three basin models have been established which are forward flow mode, reverse flow mode and side flow mode. The gap flow field of ECM has been analyzed. It is determined that positive flow is a suitable flow mode. By optimizing the structure of the flow slot in the cathode, the deficiency of the forward flow field is improved.

Linear stability investigations on the inward flow between closely spaced co-rotating disks

In order to identify transitional flow, the linear stability of inward flow in a narrow gap between co-rotating disks is studied. Two methods are developed. The local approach assumes periodic nature of the flow in radial and circumferential direction, whereas the computationally more expensive biglobal variant only requires periodicity in circumferential direction. Stability maps are provided for a single set of operating conditions spanning a range of Reynolds numbers at fixed rotor geometry and rotational speed. The theoretical findings are compared to a set of experimental velocity profiles that includes the transitional region according to profile shapes. Apart from some explainable inconsistencies, the determined stability limits agree with each other and with results from previous studies.

How do Social Networks Affect Intergenerational Income Flow

China’s income gap and intergenerational income flow are of great concern. This paper empirically studies the influence of social networks on intergenerational income flow. Using the correlation of intergenerational income percentile ranks between fathers’ and sons’ income to measure intergenerational income flow, and measuring social networks from three dimensions of scale, intensity and instrumentality, the study finds that social networks significantly promote intergenerational income flow, and the conclusion still holds after using fathers’ family composition as a tool variable to eliminate endogeneity in 1966−1976. This kind of influence is more obvious in the areas with low marketization, woman and low-income families. Further research shows that social networks promote intergenerational income flow by strengthening information sharing, reducing credit constraints and improving children’s employment, and the three dimensions of social networks play different roles in different channels.

Quantifying uncertainty in annual runoff due to missing data.

Long-term streamflow datasets inevitably include gaps, which must be filled to allow estimates of runoff and ultimately catchment water budgets. Uncertainty introduced by filling gaps in discharge records is rarely, if ever, reported. We characterized the uncertainty due to streamflow gaps in a reference watershed at the Hubbard Brook Experimental Forest (HBEF) from 1996 to 2009 by simulating artificial gaps of varying duration and flow rate, with the objective of quantifying their contribution to uncertainty in annual streamflow. Gaps were filled using an ensemble of regressions relating discharge from nearby streams, and the predicted flow was compared to the actual flow. Differences between the predicted and actual runoff increased with both gap length and flow rate, averaging 2.8% of the runoff during the gap. At the HBEF, the sum of gaps averaged 22 days per year, with the lowest and highest annual uncertainties due to gaps ranging from 1.5 mm (95% confidence interval surrounding mean runoff) to 21.1 mm. As a percentage of annual runoff, uncertainty due to gap filling ranged from 0.2–2.1%, depending on the year. Uncertainty in annual runoff due to gaps was small at the HBEF, where infilling models are based on multiple similar catchments in close proximity to the catchment of interest. The method demonstrated here can be used to quantify uncertainty due to gaps in any long-term streamflow data set, regardless of the gap-filling model applied.

Numerical model of two-phase mechanical face seal with shallow grooves based on finite volume method

Purpose By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, an effective method to study the flow field of the mechanical seal when both cavitation and boiling exist simultaneously is found. Design/methodology/approach Based on the finite volume method, a fluid model was developed to investigate a two-phase mechanical seal. The validity of the proposed model was verified by comparing with some classical models. Findings By modeling and analyzing the two-phase mechanical seal of the fan-shaped groove end face, which is prone to phase change, the analysis of the gap flow field of the mechanical seal was realized when cavitation and boiling existed simultaneously. Originality/value Based on the model proposed for different conditions, the pressure and phase states in the shallow groove sealing gap were compared. The phase change rate between the mechanical seal faces was also investigated. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2019-0537/

Computational study on synovial fluid flow behaviour in cartilage contact gap under osteoarthritic condition

This study numerically investigates the pathological changes of fluid flow in cartilage contact gap due to the changes in cartilage surface roughness and synovial fluid characteristics in osteoarthritic (OA) condition. First, cartilage surface topographies in both healthy and OA conditions are constructed using a numerical approach with consideration of both vertical and horizontal roughness. Then, constitutive equations for synovial fluid viscosity are obtained through calibration against previous experimental data. Finally, the roughness and synovial fluid information are input into the gap flow model to predict the gap permeability. The results show that the rougher surface of OA cartilage tends to decrease gap permeability by around 30%–60%. More importantly, with the reduction in gap size, the decrease in gap permeability becomes more significant, which could result in an early fluid ultrafiltration into the tissue. Moreover, it is demonstrated that the pathological synovial fluid has more deleterious effects on the gap permeability than the OA cartilage surface, as it could potentially increase the gap permeability by a few hundred times for pressure gradients less than 106 Pa/m, which could inhibit the fluid ultrafiltration into the tissue. The outcomes from this research indicate that the change in fluid flow behaviour in contact gap in OA condition could significantly affect the function of articular joints.

Viscous fluid flow in a wide annular gap of two rotating coaxial cylinders

The Couette-Taylor flow is considered in a wide gap between coaxial cylinders in the case when the outer cylinder is at rest and the inner one rotates at a constant speed. Unsteady motion of a viscous fluid is described by the system of Navier-Stokes equations. The problem is solved by the control volume method in the OpenFOAM software. Two stable states were obtained depending on the surface rotation speed: the cylindrical Couette flow and the Taylor vortex flow. The calculation results are compared with the known data of other authors. The dependence of the dimensionless shear rate on the Taylor number is obtained.

Rake impact on turboshaft compressors, a numerical study

PurposeTurboshaft engines usually include one centrifugal compressor due to its high-pressure ratio, stability and compactness. Many designers rely on positive raking to decrease tip gap flow and therefore losses. However recent optimization studies revealed geometries contradicting this canonic view. Hence, this paper aims to investigate how the rake angle alone can influence performance and to which extent.Design/methodology/approachA turboshaft representative impeller was chosen and altered for null and +/−30° rake angles. Menter's shear stress transport model is used for steady computational fluid dynamics simulations, sweeping the nominal speedline at various tip clearances. Backsweep distribution is identical in all cases, isolating rake influence.FindingsPressure ratio was lowered for the both positively and negatively raked blades, but through distinct aerodynamic mechanisms. Although the flow through the tip gap was lower for the positive rake, this is due to lower blade loading. Splitter comparison reveal that these effects are more pronounced in the radial regions.Practical implicationsSome of the findings may extend beyond turboshaft engines, into turbochargers, home appliances or industrial blowers. However, all extrapolations must consider specific differences between these applications. Turboshaft compressors designers can benefit from this study when setting up their free parameters and penalty functions in the early concept stages.Originality/valueOnly few similar studies can be found in the literature to date, none similar to turboshaft applications. Also, this impeller is designed to eliminate leading edge shocks and suction side boundary layer separation, which makes it easier to isolate the tip gap flow effects. The authors also provide a framework on which semi-empirical design equations can be further developed to incorporate rake into 1D design tools.

Exergy, economic, environmental and sustainability analyses of possible regenerative evaporative cooling device topologies

Due to the increase in cooling load globally, it needs to find an efficient, environment-friendly and sustainable cooling technology. The regenerative evaporative cooler is a better option in this direction. The regenerative evaporative cooler can be possible in different configurations depending on the primary air, secondary air and water flow directions, and it is required to select a thermodynamically, economically and environmentally best sustainable configuration. Hence, this paper numerically simulates exergy, economic and environmental parameters of regenerative evaporative cooler using the generalized model. All possible configurations of the regenerative evaporative cooler are compared based on exergy destruction, exergy efficiency, specific total cost, CO2 emission and sustainability index. The effect of the geometric and operating parameters on the performance of all configurations is investigated. The analysis concluded that lower channel gap, extraction ratio and air flow rate improve exergetic efficiency and sustainability index and reduce CO2 emission. Within studied configurations of the regenerative evaporative cooler, A and H are best in terms of higher exergy efficiency, lower specific total cost and higher sustainability index.

Wellbore trajectory control tool seal system leakage analysis based on steady gap flow

Lubricant leakage will inevitably occur during the working process of wellbore trajectory control tools. Even including the lubricant compensation system, serious leakage will still cause lacks lubrication of the internal mechanical structure as well as electronic system damaged by external infiltration fluid, especially when it comes to battery sub and other electronic equipment. Seal system leakage prediction method was presented based on the assumption of steady gap flow. It is assumed that there is a constant gap between the lip seal and the rotating shaft, the gap height is determined by oil film thickness, and the length of the gap was determined by the contact analysis using the Mooney–Rivlin constitutive model. The analysis results show that the contact length between the primary seal lip and the rotary shaft is about 0.1 mm under the condition of ensuring the contact between the deputy seal lip and the rotary shaft. The overall lubricant leakage finite element analysis model was established, and the relationship between the internal lubricant pressure of the tool and the total leakage was obtained. The results of analysis indicate that under the internal pressure of 0.03 MPa, the lubricant leakage is approximately 6 mL/h, which was verified by experiments.

Analysis of Leakage Model of All-Metal Screw Pump

Traditional rubber screw pumps use an interference method to engage. When the pressure is less than the breakdown pressure of the pump, there is no leakage in the pump. The all-metal screw pump stator and rotor are made of metal, and the stator and rotor adopt a gap-fitting engagement method, so even when the pump is working normally, the leakage is objective. Based on the concentric annular gap flow, the pressure drop leakage caused by the fluid inertia force is fully considered, and the calculation formula of the leakage of the all-metal screw pump is studied from the three aspects of transverse leakage, longitudinal leakage, and oblique leakage. This model was experimentally verified by a commercial all-metal screw pump produced by Shihong Petroleum Equipment Company. The model results show that the leakage of the all-metal screw pump is mainly affected by the structure parameters of the pump itself and the density of the pumped fluid, and the gap height is the main factor affecting the leakage.

Flow-induced vibration of one-fixed-one-free tandem arrangement cylinders with different mass-damping ratios using wind tunnel experiment

Flow-induced vibration (FIV) of an elastically mounted circular cylinder with four different mass-damping parameters m∗ζ (= 0.184, 0.288, 0.407, 0.719) placed in the wake of a fixed one has been studied in a wind channel at Reynolds number Re= 4000–48000. The spacing ratios S/D are from 1.1 to 8.0 (where S is the center-to-center spacing and D is the cylinder diameter). Two initial conditions, ‘from rest’ and ‘increasing velocity’, are used in the test. The vibration amplitude responses, oscillation frequency and vortex shedding frequency are analyzed and discussed. Based on the m∗ζ, S/D and initial conditions, results indicate that, for both ‘from rest’ and ‘increasing velocity’ cases, the downstream cylinder exhibits three regimes of vibration responses: pure VR (vortex resonance), separated VR and wake-induced galloping (WIG), and combined VR and WIG. However, the S/D for the occurrence of each regime will be changed depending on m∗ζ and initial conditions. Vortex resonance, gap flow and the unsteady vortex-structure interactions can contribute to the vibrations. When the spacing is small, an obvious hysteresis phenomenon can be observed for ‘from rest’ and ‘increasing velocity’. As S/D increases, the hysteresis can be negligible and the vibration characteristics are nearly the same for various initial conditions. By comparing with the results between high m∗ζ performed in wind tunnel at present and low m∗ζ in water tunnel, it can be found that, with the increasing of m∗ζ, the vibration amplitude and region are gradually decreasing. And the vibration regime, oscillation frequency and vortex shedding frequency are significantly different.

Fluid Dynamics of Flow Around Side-by-Side Arranged Cylinders

Flow past four side-by-side identical square cylinders arranged normal to the flow have been found to show interesting and important flow features which are very difficult to get through experiments. Lattice Boltzmann method (LBM) is used for numerical simulations of two-dimensional (2D) flow around four side-by-side arranged cylinders. In this study, the Reynolds number (Re) is chosen to be 60, 80, 100, 120 and 140 and the spacing ratio g* (= g/D, where D is the size of cylinder and g is the distance between the cylinders) is set at 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5 and 4. Based on the flow characteristics, seven distinct and unique flow regimes are identified for different ranges of Re and g*. Physical features of each flow regime such as wake structures, vortex dynamics, gap flow behavior, time histories of lift coefficients, shedding frequencies and hydrodynamic forces are thoroughly discussed. The Reynolds numbers strongly affect the flow, especially at 0 ≤ g* ≤ 2, in terms of vortex-shedding frequency. A significant secondary frequency is also found other than the primary frequency in the base-bleed and flip-flopping flow regimes. It is observed that for g* ≥ 2.5 primary shedding frequency strongly affects the flow dynamics and the mutual interaction of the wakes behind the cylinders decreases with an increase in the Reynolds number. The Strouhal value is same for the outer and inner cylinders in inphase–antiphase weak interaction flow regime and different for base-bleed and flip-flopping flow regimes. In inphase asynchronous weak interaction flow regime, the Strouhal number is same for all four cylinders.

Experimental study of the self-excited resonance effect on the dynamic lift and flow structure around inline cylinders

The excitation of acoustic resonance by air flow around a row of inline cylinders is investigated experimentally using phase-locked particle image velocimetry and direct measurements of the dynamic lift forces. The experiments are performed during self-excited acoustic resonance for arrangements of two, three, four, and five inline cylinders with a spacing ratio L∕D=2.0, where L is the center-to-center distance between the cylinders and D is the cylinder diameter, to clarify the effect of increasing the number of cylinders on the resonance mechanism and the characteristics of the periodic flow cycle. The PIV measurements show that increasing the number of cylinders results in weaker and distorted periodic flow structures around the most downstream cylinders. However, the phase and strength of the flow structures within the most upstream gap are minimally affected. Intrinsic flow features, such as gap flow that is observed in some cases, lead to the disruption of the shear layer impingement on downstream cylinders. Moreover, direct measurements of the dynamic lift forces on all cylinders simultaneously identified the upstream gap as the location where most of the energy exchange between the flow and the acoustic fields occurs. Decomposition of the dynamic lift force with respect to the acoustic pressure revealed that the distorted flow structures were accompanied by weaker, sometimes negative, contribution to the acoustic resonance excitation. The findings presented in this article explain the observation that for inline configurations of cylinders, as well as inline tube bundles, increasing the number of cylinders in the flow direction does not result in stronger resonance, and demonstrate that countermeasures for resonance excitation should target the most upstream rows of cylinders.