Single Flow Regime Research Articles

Generalization Limits of Data-Driven Turbulence Models

AbstractMany industrial applications require turbulent closure models that yield accurate predictions across a wide spectrum of flow regimes. In this study, we investigate how data-driven augmentations of popular eddy viscosity models affect their generalization properties. We perform a systematic generalization study with a particular closure model that was trained for a single flow regime. We systematically increase the complexity of the test cases up to an industrial application governed by a multitude of flow patterns and thereby demonstrate that tailoring a model to a specific flow phenomenon decreases its generalization capability. In fact, the accuracy gain in regions that the model was explicitly calibrated for is smaller than the loss elsewhere. We furthermore show that extrapolation or, generally, a lack of training samples with a similar feature vector is not the main reason for generalization errors. There is actually only a weak correlation. Accordingly, generalization errors are probably due to a data-mismatch, i.e., a systematic difference in the mappings from the model inputs to the required responses. More diverse training sets unlikely provide a remedy due to the strict stability requirements emerging from the ill-conditioned RANS equations. The universality of data-driven eddy viscosity models with variable coefficients is, therefore, inherently limited.

Analysis of Mixed Convection on Two-Phase Nanofluid Flow Past a Vertical Plate in Brinkman-Extended Darcy Porous Medium with Nield Conditions

The rapid advancement in technology in recent years has shown that nanofluids are very vital to further development in science and technology. Moreover, many industrial specifications cannot be met by allowing natural convection only, hence the need to incorporate forced convection and natural convection into a single flow regime. The research aims to quantify the mixed convective two-phase flow past a vertical permeable surface in a Brinkman-Extended Darcy porous medium (BEDPM) induced by nanofluid, with heat and mass transfer. In addition, the Nield condition is also incorporated. The model of the problem was initially constructed in the vital form of leading governing equations (LGEs). These LGEs are specifically called partial differential equations (PDEs) (because of two or more independent variables) which were later converted into a set of the single independent variable of ordinary differential equations (ODEs) by implementing the similarity transformations. The set of single independent ODEs was numerically solved via the boundary value problem of fourth-order (bvp4c) technique. The bvp4c is one of the most frequently recommended built-in MATLAB subroutines based on the three-stage Labatto formula. The impact of several physically embedded influential parameters on the fluid flow, along with mass and thermal properties of the nanofluid in a Brinkman-Extended Darcy porous medium for the cases of buoyancy assisting flow (BAF) and buoyancy opposing flow (BOF), were investigated and argued. The numerical outcomes clarify that the porosity parameter reduces the velocity, whereas the concentration and the temperature enhance in the case of the buoyancy assisting and buoyancy opposing flows. In addition, the wall drag force elevates for the larger value of the dimensionless permeability parameter K1 and the buoyancy ratio parameter N, while it declines for the modified porosity parameter ε1.

Bayesian probabilistic dual-flow-regime decline curve analysis for complex production profile evaluation

Decline curve analysis (DCA) has been broadly applied in the oil and gas industry to predict future production and estimate reserves. The Arps decline model is one of the most popular DCA models used by the oil and gas industry. This model was designed for boundary dominated flow in conventional reservoirs. In practice, it has also been widely applied to both transient flow and boundary dominated flow in conventional reservoirs. Applied to a complex production profile involving dual flow regime from artificially enhanced tight/shale reservoir, each production segment needs to be analyzed separately. Although several analytical decline curve models have been developed in recent years to address the problem, none of them is flexible enough to model both production profiles from a single flow regime and a dual flow regime.In this study, we introduce a new production decline analysis model that can fit both production profiles from single flow regime and dual flow regime without the need to separate the production segments. We also introduce a probabilistic measure using Bayesian Markov Chain Monte Carlo simulation to determine the existence of dual flow regimes, the location of the regime switch, and uncertainties in parameter estimations with the new model. The proposed Probabilistic Dual Regime Decline Curve Analysis (PDR-DCA) method is tested on 344 horizontal Northern Montney gas wells.This proposed Bayesian approach provides a workflow to generate probabilistic decline curve for both single and dual segment production profile, probabilistic type well curve for a well group, and production prediction for well with very short production history.

Flow Regimes and Transition Criteria during Passage of Bubbles through a Liquid-Liquid Interface.

The passage of a single bubble or a stream of bubbles through a liquid-liquid interface is a highly dynamic process that can result in a number of different outcomes. Previous studies focused primarily on a single bubble and single flow regime, and very few investigations have considered bubble streams. In the present work, six different liquid combinations made up of water, ethanol, a perfluorocarbon liquid, PP1, and one of three different viscosity silicone oils are tested with air bubbles from 2 to 6 mm in diameter rising between 5 and 55 cm/s. Both single bubbles and bubble streams varying in frequency from 5 to 40 bubbles/s are tested. High-speed imaging is used to capture and classify the flow regimes associated with each flow type. Four different flow regimes are identified for single-bubble passage, and six are found for bubble stream passage. On the basis of theoretical considerations, nondimensional numbers are developed for characterizing the flow regimes and maps are generated that distinguish them and define flow regime transitions.

Comparison of fluidized bed flow regimes for steam methane reforming in membrane reactors: A simulation study

An important decision in the design of fluidized bed reactors is which of several flow regimes to choose. Almost all fluidized bed reactor models are restricted to a single flow regime, making comparison difficult, especially near the regime boundaries. This paper examines the performance of fluidized bed methane reformers with three models—a simple equilibrium model and two kinetic distributed models, based on different assumptions of varying sophistication. Membranes are incorporated to improve reactor performance. Eighteen cases are simulated for different flow regimes and membrane configurations. Predictions for the fast fluidization and turbulent flow regimes show that the rate-controlling step is permeation through the membranes. Bubbling regime simulations predict somewhat less hydrogen production than for turbulent and fast fluidization, due to the effects of interphase crossflow and mass transfer. Overall reactor performance is predicted to be best under turbulent fluidization operation. Practical considerations also affect the advantages, shortcomings and ultimate choice of flow regime.

Quasimonoenergetic ion bunches from exploding microstructured targets

An analytic model is proposed for generating bunches of light ions up to relativistic energies via Coulomb explosion (CE) of symmetric microstructured targets in plane, cylindrical, and spherical geometries, and the conditions under which CE can exist in a single-flow regime are derived. The time evolution of the mean velocity, density distribution, and energy spectra for accelerated ions is studied, and the CE-driven quasimonoenergetic light ions from bilayered microstructured targets are reported.

Fluidized bed catalytic reactor modeling across the flow regimes

AbstractFluidized bed reactor models are generally specific to a single flow regime resulting in ambiguities and discontinuities at the regime boundaries. In practice, only the bubbling, turbulent and fast fluidization regimes are of industrial significance for catalytic reactions. The turbulent fluidization regime is especially advantageous because of improved interphase mass transfer, resulting in improved selectivities and conversions. It is shown that some of the difficulties in modeling can be resolved by means of the probabilistic‐averaging model, recently published by Thompson et al. (1999). This model interpolates between the Grace (1984) two‐phase bubbling bed model at low velocities and single phase axially dispersed flow for fully established turbulent fluidization conditions, leading to improved predictions of conversion and selectivity for catalytic fluidized bed reactors operated at flow rates covering the full range between bubbling and fully turbulent fluidization. An analogous approach should be useful for beds operated at higher gas velocities as fast fluidization conditions are approached.

Time of Concentration Formula for Sheet Flow of Varying Flow Regime

For an overland plane with rainfall as the lateral inflow, the flow regime is complicated by the varying flow depth and velocity along the plane. The flow regime becomes variable. For a plane that is sufficiently long, from the upstream to the downstream end of the plane, the flow regime may change from laminar through transitional to turbulent. In this paper, by coupling the kinematic wave equations with the Darcy-Weisbach friction formula, a time of concentration formula for a portion of a plane subject to uniform rainfall excess and a constant upstream inflow is derived. This formula is applicable to a portion of plane with a single flow regime only. For practical application, this formula is further developed for a plane of uniform slope subject to uniform rainfall excess, with flow regime varying from laminar through transitional to turbulent. An application of the formula for varying flow regime shows that its time of concentration estimate is longer than those based on a single flow regime covering...

The coexistence of the froth and liquid phases in a flotation column

Froth flotation is widely used in the mineral processing industry to concentrate the valuable components of mineral feedstock. The operation of flotation cells and columns relies on the coexistence of distinct froth and pulp or liquid phases in the flotation vessel. A one-dimensional two-phase flow analysis has revealed that the froth and liquid phases can be treated as coexisting flow regimes at the froth-liquid interface. By modelling the froth phase adjacent to the froth-liquid interface as an expanded bubble bed, a quantitative diagram for predicting the transition from froth-liquid coexistence to a single flow regime was developed. The analysis also revealed the limiting condition for countercurrent flow in flotation vessels which is particularly relevant to the operation of flotation columns and the application of washwater to the froth. The predictions were confirmed experimentally using a laboratory flotation column.

A Cyclone for Size-Selective Sampling of Ambient Air

A cyclone with a 47 mm after-filter has been developed for ambient air size-selective monitoring. It has been extensively evaluated with laboratory-generated aerosol. Variation of the pressure drop and 50% cut point with flow rate show that the cyclone operates in a single flow regime with a vortex in the outlet flow. The particle size cutoff curve is comparable in sharpness to a cascade impactor and is the same for solid or liquid particles. At 21.7 L/min, D 50 is 2.5μm and at 15.4 L/min, D 50 is 3.5 μm. Collection efficiency data for flow rates from 8 to 27 L/min fit a universal curve when plotted vs. the normalized particle diameter, (D-D 50)/D 50 Reentrainment of previously deposited particles is less than 1 % of the loading per day. In field tests the cyclone has proved to be a very satisfactory size-selective sampler.