Parametric studies of the aerodynamic excitation in high pressure turbines

Numerical and experimental studies are performed on the influence of several key parameters on the aerodynamic exitation of a high-pressure turbine rotor blade row due to the upstream stator row. In order to change the vane passing frequency two stators with similar vane shapes and identical exit Mach number and exit flow angle are used. To be able to separate subsonic and transonic stator induced flow distortions data is recorded at two different flow regimes. The axial gap between stator and rotor is varied as well. Experiments were run in a closed loop high speed annular wind tunnel. Unsteady velocity data were measured with a three-dimensional Laser-Two-Focus anemometer between stator and rotor and downstream of the rotor. The unsteady part of the instantaneous velocity, the gust, is split into streamwise, transverse and radial components and harmonically decomposed. This data is compared to numerical results obtained with a quasi 3D method (UNSFLO) and analysed regarding two aspects: the dependency of the gust on the changed parameters and the impact of the gust on the forcing function (blade excitation pressures)

Comparison of Models to Predict Low Engine Order Excitation in a High Pressure Turbine Stage

The paper compares three numerical strategies to predict the aerodynamic rotor excitation sources of "Low Engine Order" (LEO) in a high-pressure turbine stage. Main focus is laid on methods to compute the stator exit flow. The aim is to evaluate computationally cheap approaches to avoid modelling the whole circumference of the stator. A single passage viscous strategy, a single passage inviscid linear blade movement strategy and a viscous multi passage sector strategy are compared and evaluated. The assessment of the prediction quality is made by comparison of the computed stator exit flow to experimental data. The main result is that only the global behaviour of the stator exit flow is estimated right, both level and amplitude of Mach number and pressure are computed with poor agreement to experiments. Future evaluations of the resulting rotor excitation pressure are needed to estimate the level of necessary agreement to give acceptable predictions of the low engine order forced response

Aerodynamic Performance of Two Isolated Turbine Stators in Transonic Annular Cascade Flow

The objectives of the present work are to investigate experimentally the steady aerodynamic characteristics of two isolated turbine stators and the development of the wakes at transonic flow conditions in an annular turbine facility. The steady three-dimensional flow field was measured at several axial downstream positions and three radial positions using a three-dimensional Laser-Two-Focus anemometer and a total pressure probe. Steady vane surface pressure distributions were recorded on the vane surfaces. A trailing edge shock propagating in the stator downstream flow field was found to have a significant influence on the volocity and turbulence intensity distribution. In the wake strong radial velocity components were obtained. Close to the trailing edge they are directed towards the hub, further downstream the flow is directed towards the tip. At midspan the experimental vane surface data and wake flow data are compared with predictions from two different numerical models: Firstly a 2D/Q3D code solving the viscous terms only in the boundary layer region of the vanes (k-1 turbulence model) and elsewhere the Euler equations, secondly a fully viscous 3D code using a Baldwin-Lomax type turbulence model. Fairly good agreement between numerical results and experimental data were achieved. Differences, which are mainly observed in the wake flow predictions, are assumed to be due to turbulence modeling and a possible grid resolution influence. Furthermore, three dimensional flow contributions were observed in the 3D predictions, especially in the wake region, which could partly lead to the differences between VOLSOL and UNSFLO results. Different trends for the 3D effects have been found in the experiments and for VOLSOL. The data will serve as part of a database for further experimental and numerical investigations of stator-rotor interactions in a turbine configuration. It is assumed that the presented data describe key parameters determining the forced response of a downstream rotor blade row

A Snapshot of the Emerging Tomato Genome Sequence

The genome of tomato (Solanum lycopersicum L.) is being sequenced by an international consortium of 10 countries (Korea, China, the United Kingdom, India, the Netherlands, France, Japan, Spain, Italy, and the United States) as part of the larger \u201cInternational Solanaceae Genome Project (SOL): Systems Approach to Diversity and Adaptation\u201d initiative. The tomato genome sequencing project uses an ordered bacterial artificial chromosome (BAC) approach to generate a high-quality tomato euchromatic genome sequence for use as a reference genome for the Solanaceae and euasterids. Sequence is deposited at GenBank and at the SOL Genomics Network (SGN). Currently, there are around 1000 BACs finished or in progress, representing more than a third of the projected euchromatic portion of the genome. An annotation effort is also underway by the International Tomato Annotation Group. The expected number of genes in the euchromatin is 3c40,000, based on an estimate from a preliminary annotation of 11% of finished sequence. Here, we present this first snapshot of the emerging tomato genome and its annotation, a short comparison with potato (Solanum tuberosum L.) sequence data, and the tools available for the researchers to exploit this new resource are also presented. In the future, whole-genome shotgun techniques will be combined with the BAC-by-BAC approach to cover the entire tomato genome. The high-quality reference euchromatic tomato sequence is expected to be near completion by 2010

The Medicago genome provides insight into the evolution of rhizobial symbioses

Legumes (Fabaceae or Leguminosae) are unique among cultivated plants for their ability to carry out endosymbiotic nitrogen fixation with rhizobial bacteria, a process that takes place in a specialized structure known as the nodule. Legumes belong to one of the two main groups of eurosids, the Fabidae, which includes most species capable of endosymbiotic nitrogen fixation(1). Legumes comprise several evolutionary lineages derived from a common ancestor 60 million years ago (Myr ago). Papilionoids are the largest clade, dating nearly to the origin of legumes and containing most cultivated species(2). Medicago truncatula is a long-established model for the study of legume biology. Here we describe the draft sequence of the M. truncatula euchromatin based on a recently completed BAC assembly supplemented with Illumina shotgun sequence, together capturing similar to 94% of all M. truncatula genes. A whole-genome duplication (WGD) approximately 58 Myr ago had a major role in shaping the M. truncatula genome and thereby contributed to the evolution of endosymbiotic nitrogen fixation. Subsequent to the WGD, the M. truncatula genome experienced higher levels of rearrangement than two other sequenced legumes, Glycine max and Lotus japonicus. M. truncatula is a close relative of alfalfa (Medicago sativa), a widely cultivated crop with limited genomics tools and complex autotetraploid genetics. As such, the M. truncatula genome sequence provides significant opportunities to expand alfalfa's genomic toolbox