Mass Flow Components Research Articles

REGRESSION OF THE NAVIER-STOKES EQUATION SOLUTIONS FOR PULMONARY AIRWAY FLOW USING NEURAL NETWORKS.

Computerized fluid dynamics models of particle deposition in the human airways are used to characterize deposition patterns that enable the study of lung diseases like asthma and chronic obstructive pulmonary disease (COPD). Despite this fact, the influence of patient-specific geometry on the deposition efficiency and patterns is not well documented nor modeled. In part, this is due to the complexity of simulating the full Computational Fluid Dynamics (CFD) solution in patient-specific airway geometries, a factor that becomes a major hurdle for patient-specific studies given the complexity of the geometry of human lungs and their related airflow. In this paper, we present an approximation method based on neural networks to the Navier-Stokes equations that govern airway flow in a Physiologically Realistic Bifurcation (PRB) model for the conducting region of a single generation human airway branch. The flow distribution and deposition of tobacco particles have been simulated for the inspiratory regime using ANSYS Fluent and a neural network has been trained to regress the mean velocity and mass flow components. Our results show that the approximation works well under the modeled assumptions and the serial application of this model to a two-generation airway geometry provides reasonable approximations.

A Three-Zone Modeling Approach for Centrifugal Compressor Slip Factor Prediction

Accurate estimation of slip factor is of paramount importance to ensure centrifugal compressor work input is adequately predicted during the preliminary design process. However, variations in the flow field at impeller exit in both the pitchwise and spanwise directions complicate the evaluation procedure considerably. With the increasing implementation of engine downsizing technologies in the automotive sector, achieving a wide operating range has become a factor of prime importance for centrifugal compressors used in automotive turbocharging applications. As a result of the design features required to achieve this aim, modern impeller geometries have been shown to exhibit an approximately parabolic variation in slip factor across their respective operating maps. By comparison, traditional slip correlations typically exhibit a constant, or at best monotonic, relationship between slip factor and impeller exit flow coefficient. It is this lack of modeling fidelity which the current work seeks to address. In order to tackle these shortcomings, it is proposed that the impeller exit flow should be considered as being made up of three distinct regions: a region of recirculation next to the shroud providing aerodynamic blockage to the stage active flow, and a pitchwise subdivision of the active flow region into jet and wake components. It is illustrated that this hybrid approach in considering both spanwise and pitchwise stratification of the flow permits a better representation of slip factor to be achieved across the operating map. The factors influencing the relative extent of each of these three distinct regions of flow are numerous, requiring detailed investigations to successfully understand their sources and to characterize their extent. A combination of 3D computational fluid dynamics (CFD) data and gas stand test data for six automotive turbocharger compressor stages was employed to achieve this aim. Through application of the extensive interstage static pressure data gathered during gas stand testing at Queen's University Belfast, the results from the 3D CFD models were validated, thus permitting a more in-depth evaluation of the flow field in terms of locations and parameters that could not easily be measured under gas stand test conditions. Building on previous knowledge gained about the variation in shroud side recirculation with geometry and operating condition, the characteristic jet/wake flow structure emanating from the active flow region of the impeller was represented in terms of area and mass flow components. This knowledge allowed individual slip factor values for the jet and wake to be calculated and combined to give an accurate passage average value which exhibited the distinctive nonlinear variation in slip across the operating map which is frequently absent from existing modeling methods. Fundamental considerations of the flow phenomena in each region provided explanation of the results and permitted a modeling approach to be derived to replicate the trends observed in both the experimental data and the CFD simulations.

Blended Wing Body Thrust Reverser Cascade Feasibility Evaluation Through CFD

Airplane thrust reverser could significantly reduce the landing distance of a conventional civil turbofan. Control of the thrust reverser can be performed by a hydraulic and/or electric system. This study investigates whether this system can be used for blended wing body (BWB) civil airplanes as their engines are located over the wing body. Computational fluid dynamics (CFD) is used to analyze the feasibility of a thrust reverser cascade applied to BWB airplanes. This is selected because of its rapidity and low cost when compared to traditional wind tunnel tests. Analyses are performed on a 300-seating BWB (BWB300) landing configuration. The results show that the thrust reverser cascade can be applied to BWB300. Furthermore, the results also reveal that the probability of foreign object damage problems occurring during the BWB300 landing process when the thrust reverser cascade is working is low. Increasing the reverse mass flow component along the landing reverse direction can increase the thrust reverser efficiency. However, this would also increase the thrust reverser closing velocity. Therefore, when the thrust reverser design is performanced for BWB, a tradeoff between the efficiency and closing velocity should be considered.

Horsetails get the wind up

Horsetails get the wind up

Measurement of CO 2 flux above a tropical rain forest at Pasoh in Peninsular Malaysia

This paper reports on the results of a short-term observation of CO 2 flux above a tropical forest at Pasoh in Peninsular Malaysia, using the eddy covariance method with a closed-path CO 2 analyzer, in March 1998. CO 2 concentration profiles above and in a canopy were also measured. In the daytime, the time series of fluctuations in CO 2 concentration above the forest drew the ramp pattern with a period of 2 min. This suggests that large-scale turbulent motions contribute to CO 2 flux in the daytime. We obtained data on the CO 2 flux for 6 days and CO 2 storage flux under the flux measurement level for 3 days in this observation. The values of the CO 2 flux fell within −1.0 to 0.5 mg CO 2 m −2 s −1. Net ecosystem CO 2 exchange (NEE) was estimated as the sum of the CO 2 flux and the CO 2 storage flux. Compared with the CO 2 flux, the CO 2 storage flux was relatively large in the early morning and the nighttime, therefore, the storage flux became important to estimate the NEE in those periods. The daily values of the NEE ranged from −2.08 to −2.74 g C m −2 per day. The results suggest that this tropical forest was a CO 2 sink during the period. Although we tired to calculate the mass flow component proposed by Lee [Agric. For. Meteorol. 91 (1998) 39], the magnitudes of the mass flow obtained here were, from 5.20 to 12.55 g C m −2 per day, much larger than the magnitudes of the NEE.

On micrometeorological observations of surface-air exchange over tall vegetation

It is shown from the mass conservation and the continuity equations that the net ecosystem exchange (NEE) of a scalar constituent with the atmosphere should be NEE=∫ z r 0 ∂ c ̄ ∂t dz+( w′c′) r+ w ̄ r c ̄ r− 1 z r ∫ z r 0 c ̄ dz where the first term on RHS is the storage below the height of observation ( z r ), the second term is the eddy flux, and the third term is a mass flow component arising from horizontal flow convergence/divergence or a non-zero mean vertical velocity ( w ̄ r ) at height z r . The last term, unaccounted for in previous studies of surface-air exchanges, becomes important over tall vegetation and at times when the vertical gradient of the atmospheric constituent ( c ̄ r−(1/z r)∫ z r 0 c ̄ dz) is large, as is the case with CO 2 in forests at night. Experimental evidence is presented to support the postulation that the mass flow component is in large part responsible for the large run-to-run variations in eddy fluxes, the lack of energy balance closure and the apparent low eddy fluxes at night under stable stratifications. Three mechanisms causing the non-zero mean vertical velocity are discussed. Of these, drainage flow on undulating terrain is the most important one for long-term flux observations because only a small terrain slope is needed to trigger its occurrence. It is suggested from the data obtained at a boreal deciduous forest that without proper account of the mass flow component, the assessment of annual uptake of CO 2 could be biased significantly towards higher values. It is argued that quantifying the mass flow component is a major challenge facing the micrometeorological community.

TRANSLOCATION OF 11C‐PHOTOASSIMILATE IN THE BLADE OF MACROCYSTIS PYRIFERA (PHAEOPHYCEAE)1

ABSTRACTRadioactive bicarbonate was pulse fed to blades of Macrocystis pyrifera (L.) C. A. Ag. and the movement of the 11C‐labelled photoassimilates was monitored in vivo using an externally mounted array of Geiger‐Müller detectors. Results of experiments conducted in August 1982 and February 1983 showed kinetic transport profiles composed of short pulses of 11C (periods of two to three minutes and six to eight minutes) and a mass flow component travelling with a speed of 6–22 cm · h−1. The pulse‐like movement of 11C‐photoassimilates, revealed for the first time in a kelp, may be driven by an energy‐assisted transport mechanism. Light microscopy revealed a putative symplastic transport pathway from the photo synthetic meristoderm to the medullary sieve cells in the M. pyrifera blade. Of particular importance were the connections between the inner cortical cells and thin‐walled medullary sieve cells. Electron microscopy showed sieve plate pore diameters ranging between 35–60 nm in the cortex and ca. 40 nm in the end walls of the thin‐walled sieve cells.

The mechanism of water absorption by roots. I. Preliminary studies on the effect of hydrostatic pressure gradients.

During transpiration the hydrostatic tension which develops in the xylem conducting elements of the root draws water from the soil through the intervening tissues of the cortex, etc. It is uncertain whether this movement is entirely diffusional or in part a mass flow. To detect any such mass flow tomato plants grown in water culture were decapitated and placed in a canister through the lid of which the cut stem protruded and in which the pressure on the culture medium could be raised. The resulting rate of exudation (flux) was measured, and compared with the flux caused by an equivalent difference in osmotic potential obtained by measuring the ∆ f. p. of the medium and sap exuded. If these values of flux were equal, movement was by diffusion alone, but if pressure caused a greater flux, an additional mass flow was indicated. Preliminary experiments indicated a much greater flux in response to differences of pressure than osmotic potential, but accurate assessment of the effect was precluded by difficulties inherent in this straightforward approach. A less direct technique was therefore devised; the change in flux caused by changing the osmotic potential of the external medium (the hydrostatic pressure being maintained constant) was compared with the change in flux caused by changing the external pressure (the osmotic potential of the external medium being kept constant). The changes in flux were measured in such a way as to minimize changes in the osmotic potential in the xylem and in resistances to diffusion or mass flow respectively. In this way the change in flux per unit change in osmotic potential difference across the cortex (osmotic permeability coefficient,k0) and the change in flux per unit change in pressure difference across the cortex (pressure permeability coefficient,kp) could be compared under the same pressure gradient and in addition the effects of pressure gradients onk0could be studied. Thus, the effects of a pressure gradient on the diffusional movement of water could be assessed, as well as any mass flow component of the flux detected and measured.