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Notes: The equations for the higher-order moments of turbulent velocity fluctuations are considered. These are derived utilizing truncated, cumulant expansions as an approximation for the probability density distributions of the corresponding turbulence properties. By applying different degrees of truncations to these expansions, an alternative set of equations for the moments is formulated that contains only velocity correlations. From these equations, interrelations between the higher-order moments are deduced and are experimentally verified using data available in the literature and also data measured by the authors.

Notes: The bifurcation structure of two-dimensional, pressure-driven flows through a rectangular duct that is rotating about an axis perpendicular to its own is examined at a fixed Ekman number (Ek=ν/b2Ω) of 0.01. The solution structure for flow through a square duct (aspect ratio γ=1) is determined for Rossby numbers (Ro=U/bΩ) in the range of 0–5 using a computational scheme based on the arclength continuation method. The structure is much more complicated than reported earlier by Kheshgi and Scriven [Phys. Fluids 28, 2968 (1985)]. The primary branch with two limit points in Rossby number and a hysteresis behavior between the two- and four-cell flow structure that was computed by Kheshgi and Scriven is confirmed. An additional symmetric solution branch, which is disconnected from the primary branch (or rather connected via an asymmetric solution branch), is found. This has a two-cell flow structure at one end, a four-cell flow structure at the other and three limit points are located on the path. Two asymmetric solution branches emanating from symmetry breaking bifurcation points are also found for a square duct. Thus even within a Rossby number range of 0–5 a much richer solutions structure is found with up to five solutions at Ro=5. An eigenvalue calculation indicates that all two-dimensional solutions develop some form of unstable mode by the time Ro is increased to 5.0. In particular, the four-cell solution becomes unstable to asymmetric perturbations as found in a related problem of flow through a curved duct. The paths of the singular points are tracked with respect to variation in the aspect ratio using the fold following algorithm. A transcritical point is found at an aspect ratio of 0.815 and below which the four-cell solution is no longer on the primary branch. When the channel cross section is tilted even slightly (1°) with respect to the axis of rotation, the bifurcation points unfold and the two-cell solution evolves smoothly as Rossby number is increased. The four-cell solutions then become genuinely disconnected from the primary branch. The uniqueness range in Rossby number increases with increasing tilt.

Notes: Flow visualization studies and laser-Doppler anemometry (LDA) measurements have been performed on the flow field generated at a sudden expansion in a cylindrical pipe during the intake stroke of a piston. The range of piston Reynolds numbers investigated, based on piston diameter and velocity, was 18–125 and covered a laminar and a transition-to-turbulence regime. A detailed study of the parameters influencing the structure of the flow, i.e., the clearance volume and the piston velocity, was carried out and is presented, and the mechanism for the creation of flow instabilities at low Reynolds numbers is outlined. One of the striking features of the flow relates to the formation of vortex structures during the intake flow. It is found that under some circumstances these structures become unstable, despite the relatively low Reynolds number of the flow.

Notes: Higher-order correlations were measured in a turbulent boundary layer using the LDA measuring technique. In the paper, comparisons are made between the measured and predicted correlations obtained by utilizing the properties of truncated Gram–Charlier series expansions. Several theoretically derived relationships between correlations of different orders were confirmed by the experimental data. The experimental and theoretical results support the applicability of truncated Gram–Charlier series expansions for a refined statistical analysis of the conservation equations for higher-order moments of turbulent property fluctuations.

Notes: A numerical study of the viscous supersonic flow past a flat plate is presented. The objective is to investigate the supersonic flow at high angles of incidence where large flow gradients occur. The effect of the angle of incidence and the Reynolds number (Re) in the flow structure especially in the formation of the separation region is investigated. The study is based on the solution of the full Navier–Stokes equations by high resolution schemes, and it focuses on the supersonic flow over the plate at Re≤105. Results on fine computational grids are presented for flow angles up to 20°. The calculations reveal that the flow remain attached for angles of incidence less than a=5°. For a=5° and Re=105, separation of the flow at the trailing edge appeared. Increasing the flow angle (a(approximately-greater-than)5°) moves the separation point upstream while a reverse flow region forms for the entire range of the Reynolds numbers used in this study. The results reveal that for large angles of incidence, the variation of the Reynolds number has significant effects on the variation of the flow variables. The flow behind the trailing edge is also affected from the flow angle as well as from the Reynolds number. Comparisons are also presented between viscous and inviscid solutions. The comparisons show that the viscous effects are dominant on the upper surface of the plate as well as behind the trailing edge. These effects become stronger when the flow angle is a=20°.

Notes: A two-dimensional numerical study on the laminar flow past a circular cylinder rotating with a constant angular velocity was carried out. The objectives were to obtain a consistent set of data for the drag and lift coefficients for a wide range of rotation rates not available in the literature and a deeper insight into the flow field and vortex development behind the cylinder. First, a wide range of Reynolds numbers (0.01≤Re≤45) and rotation rates (0≤α≤6) were considered for the steady flow regime, where α is the circumferential velocity at the cylinder surface normalized by the free-stream velocity. Furthermore, unsteady flow calculations were carried out for one characteristic Reynolds number (Re=100) in the typical two-dimensional (2D) vortex shedding regime with α varying in the range 0≤α≤2. Additionally, the investigations were extended to very high rotation rates (α≤12) for which no data exist in the literature. The numerical investigations were based on a finite-volume flow solver enhanced by multi-grid acceleration and the local grid refinement technique to achieve efficient computations and accurate numerical results. The predictions show that the rotation of the cylinder suppresses the vortex development in both the steady and the unsteady flow regimes and significantly changes the flow field close to the cylinder. For very low Reynolds numbers, the drag force is not affected by rotation and the lift force is a linear function of α. For higher Re in the steady flow regime, the drag force decreases with increasing rotational velocities even leading to negative values. The lift force is almost a linear function of the rotational velocity and nearly independent of Re for low rotational speeds of α〈2. However, for higher α values and larger Reynolds numbers (Re〉1), a progressive increase in the lift force is observed. A very interesting phenomenon was found in the unsteady flow regime at Re=100. For low rotation rates (α≤2) the flow exhibits the behavior known from the literature, e.g., a linear increase of the mean lift coefficient with increasing α and the suppression of vortex shedding beyond a critical α value of about αL(approximate)1.8. However, for α(approximate)5, an unsteady periodic flow motion was found in the wake which is characterized by a frequency much lower than that known for normal vortex shedding. The change in the flow structure also leads to a distinct change in the mean lift coefficients which exhibits a linear relation of very high rotations rates and asymptotically converges to the values known from the potential flow theory. © 2002 American Institute of Physics.

Notes: The continuity and momentum equations do not imply a Reynolds number dependence of turbulence data when wall variables are used for normalization. However, experimental and numerical results show a Reynolds number dependence of turbulence intensity very close to the wall. The cause of this is explained. It results from the behavior of a sink term in the dissipation rate equation which shows a Reynolds number dependence in the limit of two-component two-dimensional turbulence as it exists close to walls. Away from the near-wall region the Reynolds number dependence originates from the streamwise pressure gradient which enters into the equations for the turbulent kinetic energy and turbulent dissipation rate through the gradient production processes. The low-Reynolds number effects in turbulent channel flow were investigated experimentally using the laser Doppler anemometry (LDA) measuring technique. A new method was used to eliminate the influence of the limited spatial resolution of the LDA measuring control volume. Results are presented for the limiting behavior of the turbulent intensity near the wall and its variation with the Reynolds number. The present LDA measurements confirm the trend in the data of direct numerical simulations. © 2001 American Institute of Physics.

Notes: O-Dealkylation of two series of fluorescent 7-alkoxy-coumarins and 7-alkoxyphenoxazones by plant cytochrome P450s was investigated in Helianthus tuberosus tuber tissues treated with prototype P450 inducers, environmental pollutants or agrochemicals. Methoxy-, ethoxy-, propoxy-and butoxycoumarins and methoxy- and ethoxyresorufins were metabolized by fplant microsomes. Dealkylation of pentoxy- and benzyloxyresorufins was not detected. All dealkylating activities were enhanced by aging plant tissues in the presence of xenobiotics, in some cases up to 20-fold relative to the activities detected in control tissues. Increases in total P450 in the same tissues never exceeded 3-fold. The isozymes induced by prototype P450 inducers clearly differed from those in mammalian liver. That multiple P450s with overlapping substrate specificities were involved in the metabolism of both alkoxycoumarins and alkoxyresorufins was demonstrated by (1) the differential induction of the activities in response to exposure to xenobiotics, (2) the differential inhibition of the activities by clotrimazole, paclobutrazole and tetcyclacis in aminopyrine and benzo(a)pyrene-treated tissues, and(3) the selective inhibition observed with antibodies raised against purified ethoxycoumarin deethylase fractions. Our results suggest that the measurement of the dealkylation of such fluorescent substrates in plants might be useful to monitor environmental pollution.

Notes: Growth responses of wheat plants to combined treatments of four mixed function oxidase (MFO) inhibitors and chlortoluron were determined. Analysis of interactions showed that piperonyl-butoxide and especially ABT (1-aminobenzotriazole) increased the toxicity of chlortoluron. Metyrapone and 2,4-dichlorophenoxypropyne were phytotoxic and did not exert any clear interaction. ABT also increased the toxicity of isoproturon to wheat.Our results suggest that ABT Strongly inhibits the breakdown of chlortoluron and isoproturon in wheat. Since ABT is known to act as a suicide substrate for plant cytochrome P-450, wheat enzymes involved in the metabolism of these two herbicides are likely to belong to this class. It thus appears that compounds designed to inhibit plant cytochrome P-450 enzymes may interact with herbicide metabolism and are potential synergists of herbicide activity.

Notes: Notes that, in a full-scale application of the Monte Carlo method for combined heat transfer analysis, problems usually arise from the large computing requirements. Here the method to overcome this difficulty is the parallel execution of the Monte Carlo method in a distributed computing environment. Addresses the problem of determination of the temperature field formed under the assumption of radiative equilibrium in an enclosure idealizing an industrial furnace. The medium contained in this enclosure absorbs, emits and scatters anisotropically thermal radiation. Discusses two topics in detail: first, the efficiency of the parallelization of the developed code, and second, the influence of the scattering behavior of the medium. The adopted parallelization method for the first topic is the decomposition of the statistical sample and its subsequent distribution among the available processors. The measured high efficiencies showed that this method is particularly suited to the target architecture of this study, which is a dedicated network of workstations supporting the message passing paradigm. For the second topic, the results showed that taking into account the isotropic scattering, as opposed to neglecting the scattering, has a pronounced impact on the temperature distribution inside the enclosure. In contrast, the consideration of the sharply forward scattering, that is characteristic of all the real combustion particles, leaves the predicted temperature field almost undistinguishable from the absorbing/emitting case.