Computational methods for internal flows with emphasis on turbomachinery

Current computational methods for analyzing flows in turbomachinery and other related internal propulsion components are presented. The methods are divided into two classes. The inviscid methods deal specifically with turbomachinery applications. Viscous methods, deal with generalized duct flows as well as flows in turbomachinery passages. Inviscid methods are categorized into the potential, stream function, and Euler aproaches. Viscous methods are treated in terms of parabolic, partially parabolic, and elliptic procedures. Various grids used in association with these procedures are also discussed

Time-dependent transonic flow solutions for axial turbomachinery

Three-dimensional unsteady transonic flow through an axial turbomachine stage is described in terms of a pair of two-dimensional formulations pertaining to orthogonal surfaces, namely, a blade-to-blade surface and a hub-to-casing surface. The resulting systems of nonlinear, inviscid, compressible equations of motion are solved by an explicit finite-difference technique. The blade-to-blade program includes the periodic interaction between rotor and stator blade rows. Treatment of the boundary conditions and of the blade slipstream motion by a characteristic type procedure is discussed in detail. Harmonic analysis of the acoustic far field produced by the blade row interaction, including an arbitrary initial transient, is outlined. Results from the blade-to-blade program are compared with experimental measurements of the rotating pressure field at the tip of a high-speed fan. The hub-to-casing program determines circumferentially averaged flow properties on a meridional plane. Blade row interactions are neglected in this formulation, but the force distributions over the entire blade surface for both the rotor and stator are obtained. Results from the hub-to-casing program are compared with a relaxation method solution for a subsonic rotor. Results are also presented for a quiet fan stage which includes transonic flow in both the rotor and stator and a normal shock in the stator

Rossby wave instability does not require sharp resistivity gradients

Context. Rossby wave instability (RWI) at dead zone boundaries may play an important role in planet formation. Viscous hydrodynamics results suggest RWI is excited only when the viscosity changes over a radial distance less than two density scale heights. However in the disks around Solar-mass T Tauri stars, it is not viscosity but magnetic forces that provide the accretion stress beyond about 10 AU, where surface densities are low enough so stellar X-rays and interstellar cosmic rays can penetrate. Aims. We explore the conditions for RWI in the smooth transition with increasing distance, from resistive and magnetically-dead to conducting and magnetically-active. Methods. We perform 3D unstratified MHD simulations with the Pencil code, using static resistivity profiles. Results. We find that in MHD, contrary to viscous models, the RWI is triggered even with a gradual change in resistivity extending from 10 to 40 AU (i.e., spanning 15 scale heights for aspect ratio 0.1). This is because magneto-rotational turbulence sets in abruptly when the resistivity reaches a threshold level. At higher resistivities the longest unstable wavelength is quenched, resulting in a sharp decline of the Maxwell stress towards the star. The sharp gradient in the magnetic forces leads to a localized density bump, that is in turn Rossby wave unstable. Conclusions. Even weak gradients in the resistivity can lead to sharp transitions in the Maxwell stress. As a result the RWI is more easily activated in the outer disk than previously thought. Rossby vortices at the outer dead zone boundary thus could underlie the dust asymmetries seen in the outer reaches of transition disks

Using GIS for Selecting Trees for Thinning

Thinning removes trees within a stand to regulate the level of site occupancy and subsequent stand development. Before thinning is applied, foresters determine the amount of residual growing stock, the spatial distribution of the residual trees, and the criteria used to select trees to cut. In this study, a portion of a loblolly pine (Pinus taeda) plantation was surveyed through a complete tree tally with the coordinates of each individual tree recorded. The dataset was then processed in a GIS program composed in Arc Marco Language (AML) applying a moving circular quadrat system superimposed over the study area. In each quadrant, tree attributes including DBH (nearest 0.1 inch), basal area (sq ft per ac), and density (trees per unit area) were utilized as determining factors for tree selection. A 3D visualization before and after thinning was created with a goal of equal distribution of trees across the stand

No Rise in Incidence but Geographical Heterogeneity in the Occurrence of Primary Biliary Cirrhosis in North East England

In this study, we examined temporal changes in the incidence of primary biliary cirrhosis (PBC) and investigated associations between PBC incidence and sociodemographic factors and spatial clustering. We included 982 patients aged ≥40 years from North East England with incident PBC diagnosed during 1987–2003. Age-standardized incidence rates with 95% confidence intervals were calculated. Negative binomial regression was used to analyze incidence and socioeconomic deprivation. Clustering analysis was performed using point process methods, testing the null hypothesis that disease risk does not vary spatially and that PBC cases occur independently. The age-standardized incidence rate was 53.50 per million persons per year (95% confidence interval: 48.65, 58.35) in 1987–1994 and 45.09 per million persons per year (95% confidence interval: 41.10, 49.07) in 1995–2003. Risk of PBC increased in areas with higher levels of socioeconomic deprivation (P = 0.035). More specifically, risk increased in areas with higher levels of overcrowded homes (P = 0.040), higher levels of households without cars (P < 0.001), and higher levels of non-owner-occupied homes (P < 0.001). Overall, there was evidence of spatial clustering (P = 0.001). The findings confirm that overall incidence of PBC did not rise over time, but sociodemographic variations suggest that certain aspects of deprivation are involved in its etiology

Financial development and economic growth : long-run equilibrium and transitional dynamics

We analyze the impact of financial development on economic growth. Differently from previous studies that focus mainly on balanced growth path outcomes, we also analyze the transitional dynamics of our model economy by using a finance-extended Uzawa-Lucas framework where financial intermediation affects both human and physical capital accumulation. We show that, under certain rather general conditions, economic growth may turn out to be non-monotonically related to financial development (as suggested by the most recent empirical evidence) and that too much finance may be detrimental to growth. We also show that the degree of financial development may affect the speed of convergence, which suggests that finance may play a crucial role in determining the length of the recovery process associated with exogenous shocks. Moreover, in a special case of the model, we observe that, under a realistic set of parameters, social welfare decreases with financial development, meaning that even when finance positively affects economic growth the short term costs associated with financial activities more than compensate their long run benefits

Structural investigation of MOVPE-Grown GaAs on Ge by X-ray techniques

The selection of appropriate characterisation methodologies is vital for analysing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III-V layers. In this work we investigate the structural properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Ge substrates – (100) with 6⁰ offset towards – under various growth conditions. Synchrotron X-ray topography (SXRT) is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other X-ray techniques, such as reciprocal space mapping (RSM) and triple axis ω-scans of (00l)-reflections (l = 2, 4, 6) are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by X-ray diffraction (XRD), as well as atomic force microscopy (AFM), and transmission electron microscopy (TEM)