Porous Wall Boundary Research Articles

Validation of a novel numerical model to predict regionalized blood flow in the coronary arteries.

Ischaemic heart disease results from insufficient coronary blood flow. Direct measurement of absolute flow (mL/min) is feasible, but has not entered routine clinical practice in most catheterization laboratories. Interventional cardiologists, therefore, rely on surrogate markers of flow. Recently, we described a computational fluid dynamics (CFD) method for predicting flow that differentiates inlet, side branch, and outlet flows during angiography. In the current study, we evaluate a new method that regionalizes flow along the length of the artery. Three-dimensional coronary anatomy was reconstructed from angiograms from 20 patients with chronic coronary syndrome. All flows were computed using CFD by applying the pressure gradient to the reconstructed geometry. Side branch flow was modelled as a porous wall boundary. Side branch flow magnitude was based on morphometric scaling laws with two models: a homogeneous model with flow loss along the entire arterial length; and a regionalized model with flow proportional to local taper. Flow results were validated against invasive measurements of flow by continuous infusion thermodilution (Coroventis™, Abbott). Both methods quantified flow relative to the invasive measures: homogeneous (r 0.47, P 0.006; zero bias; 95% CI -168 to +168 mL/min); regionalized method (r 0.43, P 0.013; zero bias; 95% CI -175 to +175 mL/min). During angiography and pressure wire assessment, coronary flow can now be regionalized and differentiated at the inlet, outlet, and side branches. The effect of epicardial disease on agreement suggests the model may be best targeted at cases with a stenosis close to side branches.

Homogenized Flux-Body Force Treatment of Compressible Viscous Porous Wall Boundary Conditions

A homogenization approach is proposed for the treatment of porous wall boundary conditions in the computation of compressible viscous flows. Like any other homogenization approach, it eliminates the need for pore-resolved fluid meshes, and therefore enables practical flow simulations in computational fluid domains with porous wall boundaries. Unlike alternative approaches, however, it does not require prescribing a mass flow rate and does not introduce in the computational model a heuristic discharge coefficient. Instead, it models the inviscid flux through a porous wall surrounded by the flow as a weighted average of the inviscid flux at an impermeable surface and that through pores. It also introduces a body force term in the governing equations to account for friction loss along the pore boundaries. The source term depends on the thickness of the porous wall and the concept of an equivalent single pore. The feasibility of the latter concept is demonstrated using low-speed permeability test data for the fabric of the Mars Science Laboratory parachute canopy. The overall homogenization approach is illustrated with a series of supersonic flow computations through the same fabric and verified using supersonic pore-resolved numerical simulations.

The effects of exothermic catalytic reactions upon combined transport of heat and mass in porous microreactors

Microreactors for chemical synthesis and combustion have already attracted significant attention. Exothermic catalytic activity features heavily in these devices and thus advective-diffusive transport is of key importance in their analyses. Yet, thermal modelling of the heat generated by catalytic reactions on the internal surfaces of porous microreactors has remained as an important unresolved issue. To address this, the diffusion of heat of catalytic reactions into three phases including fluid, porous solid and solid walls is investigated by extending an existing interface model of porous media under local thermal non-equilibrium. This is applied to a microchannel fully filled with a porous material, subject to a heat flux generated by a catalytic layer coated on the porous-wall boundary. The finite wall thickness and viscous dissipation of the flow kinetic energy are considered, and a two-dimensional analytical model is developed, examining the combined heat and mass transfer and thermodynamic irreversibilities of the system. The analytical solution is validated against the existing theoretical studies on simpler configurations as well as a computational model of the microreactor in the limit of very large porosity. In keeping with the recent findings, the wall thickness is shown to strongly influence the heat and mass transport within the system. This remains unchanged when the symmetricity of the microchannel is broken through placing walls of unequal thicknesses, while deviation from local thermal equilibrium is significantly intensified in this case. Importantly, the Nusselt number is shown to have a singular point, which remains fixed under various conditions.

Analytical model for steady flow through a finite channel with one porous wall with arbitrary variable suction or injection

This paper presents an exact solution of two-dimensional laminar flow through a finite length channel with one porous wall. It improves upon previous solutions by (1) satisfying the no-slip boundary condition at the channel dead end, (2) adding a turbulent term to the porous wall boundary condition, (3) allowing for arbitrary variable suction or injection across the porous wall, and (4) model validation against new cryogenic liquid hydrogen and oxygen experimental data. Of particular interest in the current work is the modeling of cryogenic propellant flow through a porous liquid acquisition device (LAD) screen and channel inside a propellant tank. First, a detailed review of the literature is presented for previously attempted solutions to channel flow with one porous wall. Next, the governing equations, boundary conditions, and model assumptions are used to derive the analytical flow solution and present general model results for pressure and velocity fields within the channel. Then, the model solution is compared with horizontal LAD channel flow data in liquid oxygen as well as vertical LAD channel flow data in an inverted outflow configuration in liquid hydrogen. Model results are used to update the static cryogenic bubble point pressure model with a dynamic bubble point term which factors in enhanced convection and cooling at the screen during propellant outflow. Convective heat transfer at the LAD screen during outflow is also quantified by comparing model and data. The new analytical flow solution with the dynamic bubble point model is shown to compare well with available cryogenic experimental data.

Navier-Stokes Analysis of Wind-Tunnel Interference on Transonic Airfoil Flutter

A time-domain numerical method is used for the simulation and investigation of the transonic two-degree-offreedom bending/torsion e utter characteristics of the National Aerospace Laboratory 7301 section measured in a wind-tunnelexperiment.Animplicit, time-accurate, two-dimensional,compressible,thin-layerNavier ‐Stokeseow solver is coupled with a two-degree-of-freedom structural model. The wind-tunnel walls are included to model the experimental e ow conditions more closely and to obtain accurate aerodynamic predictions in the computations. A three-block grid is used for the discretization of the domain, including the airfoil and wind-tunnel walls. Solid and porous wall boundary conditions are implemented and tested for the domain boundaries representing the tunnel walls. Computations of the steady transonic aerodynamic characteristics show good agreement with the experimental results when a 50% porosity wall boundary condition is assumed for the wind-tunnel walls. Including the wall effectsimproved theagreementoftheaeroelasticcomputations,which predicted limit-cyclee utter amplitudes in closer agreement with the experiment compared to the unbounded e ow calculations.

Numerical Analysis of Passive Control of Pseudo-Shock.

Oscillation of the pseudo-shock in the rectangular duct with the porous wall was investigated numerically. In the simulation, 2nd-order accurate, Harten-Yee's upwing TVD scheme was used for high resolution and numerical stability, and Chien's κ-ε two equation model was used as the turbulence model. To simulate the effect of the blowing and suction on the porous wall, Darcy's law was used on the porous wall boundary. The boundary layer thickness under the first shock wave oscillates due to the shock oscillation, which changes the strength of the first shock wave, so that it suppresses the pressure fluctuation downstream of the first shock wave. The effects of some parameters of the passive control on the pseudo-shock oscillation were investigated.

Numerical Analysis of Passive Control of Pseudo-Shock.

Oscillation of the pseudo shock in the rectangular duct with the porous wall was investigated numerically. In the simulation, 2nd order accurate, Harten Yee's upwind TVD scheme was used for high resolution and numerical stability, and Chien's κ-e two equation model was used as the turbulence model. To simulate the effect of the blowing and suction on the porous wall, Darcy's law was used on the porous wall boundary. The boundary layer thickness under the first shock wave oscillates due to the shock oscillation, which changes the strength of the first shock wave changes, so that it suppresses the pressure fluctuation downstream of the first shock wave. The effects of some parameters of the passive control on the pseudo-shock oscillation were investigated.

Computational Method for Describing Porous Wall Boundary Conditions Based on Experimental Data

A computational and experimental study has been undertaken to investigate methods of modeling solid and porous wall boundary conditions in computational fluid dynamics (CFD) codes. The procedure utilizes experimental pressure measurements at the walls to develop a flow-fleld solution based on the method of singularities. This solution is then imposed as a pressure boundary condition in a CFD simulation of the internal flowfield. The effectiveness of this method in describing the boundary conditions at the wind-tunnel walls using only sparse experimental measurements has been investigated. Verification of the approach using computational studies has been carried out using an incompressible flow solver. The current work demonstrates this technique for low-speed flows and compares the result with experimental data obtained from a heavily instrumented variable porosity test section. Position and refinement of experimental measurements required to describe porous wall boundary conditions has also been considered for application to other porous wall wind tunnels. The approach deveioped is simple, is computationally inexpensive, and does not require extensive or intrusive measurements. It may be applied to both solid and porous wall wind-tunnel tests.

Computational method for describing porous wall boundary conditions based on experimental data

Computational method for describing porous wall boundary conditions based on experimental data