Finite difference methods for the solution of unsteady potential flows

Various problems which are confronted in the development of an unsteady finite difference potential code are reviewed mainly in the context of what is done for a typical small disturbance and full potential method. The issues discussed include choice of equations, linearization and conservation, differencing schemes, and algorithm development. A number of applications, including unsteady three dimensional rotor calculations, are demonstrated

Nucleoplasmic bridges and acrocentric chromosome associations as early markers of exposure to low levels of ionizing radiations in occupationally exposed hospital workers

Ionising radiation, with the contribution of telomere shortening, induces DNA double-strand breaks that result in chromosome end fusion, nucleoplasmic bridges (NPBs) and chromosome aberrations (ChAbs) as well as dicentric chromosomes. In order to investigate the chromosomal damage induced by occupational ionising radiation at low exposure levels, and to find early markers of health hazard, peripheral lymphocytes of occupationally exposed hospital workers were cytogenetically analysed. Results showed a significant difference in the frequency of ChAbs in exposed subjects relative to controls. A significant number of NPBs between nuclei of binucleated cultured lymphocytes from exposed subjects were also observed, as well as a consistent amount of acrocentric chromosomes with associations of their short arms. Excluding confounding factors, the frequencies of all these three biological endpoints differed significantly in exposed subjects from those in controls. Because the absence of telomeres and/or their short length could be a common root for both the findings, we utilised fluorescence in situ hybridisation technique with telomeric repeat as probe to demonstrate that, in exposed subjects, chromatin of short arms of involved acrocentric chromosomes did not exhibit a telomeric shortening but appeared strongly decondensed. This finding suggests that NPBs and telomeric acrocentric association should be regarded as early markers of exposure to low levels of ionising radiation and their increase should be seen as an early warning for the health of the involved workers

Experimental and analytical studies of a model helicopter rotor in hover

A benchmark test to aid the development of various rotor performance codes was conducted. Simultaneous blade pressure measurements and tip vortex surveys were made for a wide range of tip Mach numbers including the transonic flow regime. The measured tip vortex strength and geometry permit effective blade loading predictions when used as input to a prescribed wake lifting surface code. It is also shown that with proper inflow and boundary layer modeling, the supercritical flow regime can be accurately predicted

Full-potential modeling of blade-vortex interactions

A comparison is made of four different models for predicting the unsteady loading induced by a vortex passing close to an airfoil. (1) The first model approximates the vortex effect as a change in the airfoil angle of attack. (2) The second model is related to the first but, instead of imposing only a constant velocity on the airfoil, the distributed effect of the vortex is computed and used. This is analogous to a lifting surface method. (3) The third model is to specify a branch cut discontinuity in the potential field. The vortex is modeled as a jump in potential across the branch cut, the edge of which represents the center of the vortex. (4) The fourth method models the vortex expressing the potential as the sum of a known potential due to the vortex and an unknown perturbation due to the airfoil. The purpose of the current study is to investigate the four vortex models described above and to determine their relative merits and suitability for use in large three-dimensional codes

The development of CFD methods for rotor applications

The optimum design of the advancing helicopter rotor for high-speed forward flight always involves a tradeoff between transonic and stall limitations. However, the preoccupation of the rotor industry was primarily concerned with stall until well into the 1970s. This emphasis on stall resulted from the prevalent use of low-solidity rotors with rather outdated airfoil sections. The use of cambered airfoil sections and higher-solidity rotors substantially reduced stall and revealed the advancing transonic flow to be a more persistent limitation to high-speed rotor performance. Work in this area was spurred not only by operational necessity but also by the development of a tool for the prediction of these flows (the method of computational fluid dynamics). The development of computational fluid dynamics for these rotor problems was a major Army and NASA achievement. This work is now being extended to other rotor flow problems. The developments are outlined

A conservative implicit finite difference algorithm for the unsteady transonic full potential equation

An implicit finite difference procedure is developed to solve the unsteady full potential equation in conservation law form. Computational efficiency is maintained by use of approximate factorization techniques. The numerical algorithm is first order in time and second order in space. A circulation model and difference equations are developed for lifting airfoils in unsteady flow; however, thin airfoil body boundary conditions have been used with stretching functions to simplify the development of the numerical algorithm

Finite difference modeling of rotor flows including wake effects

Rotary wing finite difference methods are investigated. The main concern is the specification of boundary conditions to properly account for the effect of the wake on the blade. Examples are given of an approach where wake effects are introduced by specifying an equivalent angle of attack. An alternate approach is also given where discrete vortices are introduced into the finite difference grid. The resulting computations of hovering and high advance ratio cases compare well with experiment. Some consideration is also given to the modeling of low to moderate advance ratio flows

Value of polymorphisms and DNA methylation for the expression of CYP2E1 enzyme: implications in pharmacogenomics

Different individuals possess slightly different genetic information and show genetically-determined differences in several enzyme activities due to genetic variability. Following an integrated approach, we studied the polymorphisms and DNA methylation of the 5′ flanking region of the metabolizing enzyme CYP2E1 in correlation to its expression in both tumor and non-neoplastic liver cell lines, since to date little is known about the influence of these (epi)genetic elements in basal conditions and under induction by the specific inductor and a demethylating agent. In treated cells, reduced DNA methylation, assessed both at genomic and gene level, was not consistently associated with the increase of enzyme expression. Interestingly, the Rsa/Pst haplotype differentially influenced CYP2E1 enzyme expression. In addition, regarding the Variable Number of Tandem Repeats polymorphism, cells with A4/A4 genotype showed a greater expression inhibition (ranging from 20% to 30%) compared with others carrying the A2/A2 one, while those cells bringing A2/A3 genotype showed an increase of expression (of 25%, about). Finally, we demonstrated for the first time that the A2 and A3 CYP2E1 alleles play a more important role in the expression of the enzyme, compared with other (epi)genetic factors, since they are binding sites for trans-acting proteins. In conclusion our data contributes to define a hypothetical model of regulation of the expression of this enzyme. Clarifying the complex regulation of CYP2E1 enzyme expression, either by genetic or epigenetic elements, will give useful topics in pharmacogenomics, for typing people regarding its metabolizing capability and therapy response

An experimental investigation of the parallel blade-vortex interaction

A scheme for investigating the parallel blade vortex interaction (BVI) has been designed and tested. The scheme involves setting a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the blade at the forward azimuth. The method has revealed two propagation mechanisms: a type C shock propagation from the leading edge induced by the vortex at high tip speeds, and a rapid but continuous pressure pulse associated with the proximity of the vortex to the leading edge. The latter is thought to be the more important source. The effects of Mach number and vortex proximity are discussed

The structure of trailing vortices generated by model rotor blades

Hot-wire anemometry to analyze the structure and geometry of rotary wing trailing vortices is studied. Tests cover a range of aspect ratios and blade twist. For all configurations, measured vortex strength correlates well with maximum blade-bound circulation. Measurements of wake geometry are in agreement with classical data for high-aspect ratios. The detailed vortex structure is similar to that found for fixed wings and consists of four well defined regions--a viscous core, a turbulent mixing region, a merging region, and an inviscid outer region. A single set of empirical formulas for the entire set of test data is described