Characteristic Analysis on Effects of High-Energy Pipe Wall Friction on Steam Jets

An analytical theory of heated duct flows in supersonic combustors

Wall Friction and its Effects on the Density Distribution in the Compaction of Pharmaceutical Excipients

In a previous paper, we reported the development of CFD-DECOM, a Computational Fluid Dynamics (CFD) model based on the Arbitrary Lagrangian Eulerian (ALE) approach and the Homogeneous Equilibrium Method (HEM) for simulating multi-phase flows, to predict the transient flow following the rupture of pipelines conveying rich gas or pure carbon dioxide (CO2). The use of CFD allows the effect of pipe wall heat transfer and friction to be quantified. Here, the former is considered through the implementation of a conjugate heat transfer model while the two-phase pipe wall friction is computed using established correlations. The model was previously validated for rich gas and to a limited extent dense phase CO2 decompression against the available shock tube test data. This paper describes the extension of the model to the decompression of both gaseous and dense phase CO2 with impurities. The Peng-Robinson-Stryjek-Vera Equation Of State (EOS), which is capable of predicting the real gas thermodynamic behaviour of CO2 with impurities, has been implemented in addition to the Peng-Robinson and Span and Wagner EOSs. The liquid-vapour phase equilibrium of a multi-component fluid is determined by flash calculations. The predictions are compared with the measurements of some of the recent gaseous and dense phase CO2 shock tube tests commissioned by National Grid. The detailed comparison is presented showing reasonably good agreement with the experimental data. Further numerical study has also been carried out to investigate the effects of wall friction and heat transfer, different EOSs and impurities on the decompression behaviour.

Multi-dimensional numerical simulations were performed to study the interactions between shock wave and premixed flame. The three-dimensional (3D) fully-compressible, reactive Navier–Stokes equations were solved using a high-order numerical method on a dynamically adapting mesh. The effect of wall friction on the shock–flame interaction was examined by varying wall boundary condition on sidewall. The simulations agree with previous experiment in terms of flame perturbation and flame evolution. The results show two effects of wall friction on flame–shock interaction: (1) flame stretching and (2) damping of local flame perturbation very close to the no-slip wall. The stretch effect leads to non-uniform development of the perturbated flame and consequently a significantly higher growth rate in both global flame perturbation and averaged pressure in the no-slip case compared to the free-slip case. By contrast, the damping effect locally moderates the flame perturbation in close proximity to the no-slip wall because less vorticity is deposited on this part of flame during shock–flame interaction. Quantitative analysis of vortex dynamics suggests that vorticity generation that is produced by baroclinic torque and enhanced by the dilation term during shock–flame interaction causes a growth of flame perturbation via Richtmyer–Meshkov instability. Nevertheless, the vorticity generation is greatly weakened in close proximity to the no-slip wall by the viscous torque and viscous dissipation terms due to friction.

In this work, granular flow rheology is investigated by means of discrete numerical simulations of a torsional, cylindrical shear cell. Firstly, we focus on azimuthal velocity profiles and study the effect of (i) the confining pressure, (ii) the particle-wall friction coefficient, (iii) the rotating velocity of the bottom wall and (iv) the cell diameter. For small cell diameters, azimuthal velocity profiles are nearly auto-similar, i.e. they are almost linear with the radial coordinate. Different strain localization regimes are observed : shear can be localized at the bottom, at the top of the shear cell, or it can be even quite distributed. This behavior originates from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. Then we study the effective friction at the cylindrical wall, and point out the strong link between wall friction, slip and fluctuations of forces and velocities. Even if the system is globally below the sliding threshold, force fluctuations trigger slip events, leading to a nonzero wall slip velocity and an effective wall friction coefficient different from the particle-wall one. A scaling law was found linking slip velocity, granular temperature in the main flow direction and effective friction. Our results suggest that fluctuations are an important ingredient for theories aiming to capture the interface rheology of granular materials.

Extrusion of solid-liquid particulate pastes is a well-established process in industry for continuously forming products of defined cross-sectional shape. At low extrusion velocities, the solids and liquid phases can separate due to drainage of liquid through the interparticle pores, termed liquid phase migration (LPM). The effect of wall friction, die shape and extrusion speed on LPM in a cylindrically axisymmetric ram extruder is investigated using a two-dimensional finite element model of paste extrusion based on soil mechanics principles (modified Cam-Clay). This extends the smooth walled model reported by Patel et al. (2007) to incorporate a simplified Tresca wall friction condition. Three die entry angles (90°, 60° and 45°) and two extrusion speeds are considered. The extrusion pressure is predicted to increase with the Tresca friction factor and the extent of LPM is predicted to increase with decreasing ram speed (both as expected). The effects of wall friction on LPM are shown to be dictated by the die shape and ram displacement: there are few general rules relating extruder design and operating conditions to extent of LPM, so that finite element-based simulation is likely to be needed to predict the onset of LPM accurately.

We report numerical simulations on granular shear flows confined between two flat but frictional sidewalls. Novel regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the flow. The effective friction at sidewalls is characterized (effective friction coefficient and orientation of the friction force) for each regime, and its interdependence with slip and force fluctuations is pointed out. We propose a simple scaling law linking the slip velocity to the granular temperature in the main flow direction which leads naturally to another scaling law for the effective friction.

The total pressure drop in horizontal wells is considered to consist of reversible (acceleration) and irreversible (wall friction, perforation roughness, mixing effects) pressure drop. The fundamental equations for pressure drop are presented along with relationships used for pipe junction flow. Experiments on a perforated pipe with 144 perforations, geometrically similar with wellbore casing (12 SPF, 60° phasing), are presented and analyzed. The results are applied to a typical horizontal oil well in the North Sea. It was found that the total pressure drop consists typically of 80 percent wall friction, IS percent mixing effects (including perforation roughness) and 5 percent pressure drop due to acceleration.

Elastic modulus of powder beds—the effects of wall friction: a model compared to experimental data

Effect of wall friction on variation of formwork pressure over time in self-consolidating concrete

The effects of wall friction and solid acceleration on the mal-distribution of gas–solid flow in double identical parallel cyclones

This paper performed the direct shear test for a green sand mold to construct the Mohr–Coulomb (MC) model as a mechanical model of the green sand mold, which is essential to predict the casting deformation by computer simulation. It is generally known that the pressure loaded on the test piece is not fully transmitted to its shear plane in the direct shear test because of the friction between the test piece and the shear box. A previous study estimated the vertical stress on the shear plane from the pressure transmission coefficient measured when the test piece was not sheared. However, this method ignored the change in the value and direction of the wall friction due to the dilatancy of the test piece during shearing. The present paper determines the values of the material constants in the MC model by two methods: by eliminating the effect of the wall friction during shearing and by ignoring that effect. In the prior method, the vertical stress on the shear plane is directly measured throughout the test by the load cell attached below the test piece. As a result, when the wall friction effect during shearing is not eliminated, the strength of the test piece was evaluated to be twice as large as that obtained eliminating the wall friction effect. With the MC model ignoring the wall friction, the computer simulation to predict the casting deformation will estimate the unrealistically high strength of the mold, leading to an erroneous prediction of the casting deformation.

Study and application of boiling water reactor jet pump characteristic

A mathematical model and computational algorithm are derived for the prediction of natural gas pipeline flow. Non-isothermal and compressible steady-state flow is considered. Heat transfer between gas flow and surroundings is taken into account together with the heat generation due to the gas friction on the inner pipeline wall. The computational algorithm is based on the marching procedure with defined initial conditions. The predicted thermal effect of the wall friction is validated by the simulation of a case that is available in the open literature. The influence of heat generation by gas wall friction in the long transmission pipeline on gas pressure and temperature is evaluated. Differences between results obtained with and without the heat generation due to gas wall friction are analysed. The heat generation due to gas friction on the pipeline inner wall has an influence on the gas temperature change along the pipeline, while its influence on the pressure drop is negligible. These detailed results are novel since most of the previously published results on non-isothermal gas flow did not take into account the thermal effect of the gas wall friction or the influence of this effect was not evaluated. The presented results are a support to the gas pipeline design methods and operational analyses.

The effects of wall friction on the ejection of pressed ceramic parts