Unsteady Simulations of a Film Cooling Flow from an Inclined Cylindrical Jet

Film cooling is extensively used to provide protection against the severe thermal environment in gas turbine engines. Most of the computational studies on film cooling flow have been done using steady Reynolds-averaged Navier–Stokes calculation procedures. However, the flowfield associated with a jet in a crossflow is highly unsteady and complex with different types of vortical structures. In this paper, a computational investigation about the unsteady phenomena of a jet in a crossflow is performed using detached eddy simulation. Detailed computation of a single row of 35 deg round holes on a flat plate has been obtained for a 1.0 blowing ratio and a 2.0 density ratio. First, time-step size, grid resolution, and computational domain tests for an unsteady simulation have been conducted. Comparison between the results of unsteady Reynolds-averaged Navier–Stokes calculation, detached eddy simulation, and large eddy simulation is also performed. Comparison of the time-averaged detached eddy simulation prediction with the measured film-cooling effectiveness shows that the detached eddy simulation prediction is reasonable. From present detached eddy simulations, the influential coherent vortical structures of a film cooling flow can be seen. The unsteady physics of jet in a crossflow interactions and a jet liftoff in film cooling flows have been explained.

Active use of DFIG based Wind Farms for Transient Stability Improvement during Grid Disturbances

The doubly-fed induction generator (DFIG) now represents the dominant technology in wind turbine design. One consequence of this is limited damping and inertial response during transient grid disturbances. A dasiadecoupledpsila strategy is therefore proposed to operate the DFIG grid-side converter (GSC) as a static synchronous compensator (STATCOM) during a fault, supporting the local voltage, while the DFIG operates as a fixed-speed induction generator (FSIG) providing an inertial response. The modeling aspects of the decoupled control strategy, the selection of protection control settings, the significance of the fault location and operation at sub- and super-synchronous speeds are analyzed in detail. In addition, a case study is developed to validate the proposed strategy under different wind penetrations levels. The simulations show that suitable configuration of the decoupled strategy can be deployed to improve system voltage stability and inertial response for a range of scenarios, especially at high wind penetration. The conclusions are placed in context of the practical limitations of the technology employed and the system conditions.

Binaural Reproduction of Finite Difference Simulations Using Spherical Array Processing

Due to its efficiency and simplicity, the finite-difference time-domain method is becoming a popular choice for solving wideband, transient problems in various fields of acoustics. So far, the issue of extracting a binaural response from finite difference simulations has only been discussed in the context of embedding a listener geometry in the grid. In this paper, we propose and study a method for binaural response rendering based on a spatial decomposition of the sound field. The finite difference grid is locally sampled using a volumetric array of receivers, from which a plane wave density function is computed and integrated with free-field head related transfer functions, in the spherical harmonics domain. The volumetric array is studied in terms of numerical robustness and spatial aliasing. Analytic formulas that predict the performance of the array are developed, facilitating spatial resolution analysis and numerical binaural response analysis for a number of finite difference schemes. Particular emphasis is placed on the effects of numerical dispersion on array processing and on the resulting binaural responses. Our method is compared to a binaural simulation based on the image method. Results indicate good spatial and temporal agreement between the two methods.

Channelled Waves in Anisotropic Mesh Metamaterials

Channelled waves in 2-D periodic anisotropic L-C mesh metamaterials have been investigated. Circuit simulation and the newly developed analytical model of a unit cell have demonstrated full qualitative agreement for both lossless and lossy cases. Isofrequencies for a lattice unit cell and the circuit simulations of finite meshes have shown that propagating waves are channelled from a point source as pencil beams which can travel only along specific trajectories. The beam direction varies with frequency, and at the resonance frequency, the phase and group velocities of the travelling wave are orthogonal. The effect of losses was explored, and it was shown that losses cause qualitative changes of the channelled wave type. It was proven that the channelled waves do not follow the laws of geometrical optics (Snell's law, specular reflection, etc.) at the interfaces of L-C meshes but are governed by the conditions of phase synchronism and impedance matching. Only in the special case of dual L-C and C-L meshes with the interface parallel to the axis of rectangular grid excited at the resonance frequency (X=1) do the channels follow the trajectories of optical rays. A planar mesh test cell has been designed and used for retrieving the unit cell L-C parameters from the S-parameter measurements.

An investigation into the use of atomic datasets in simulations of the Ni-like gadolinium x-ray laser

The effect of differing the datasets used in the modelling of the Ni-like Gd x-ray laser (XRL) is examined through the 1.50 hydro-atomic code, EHYBRID. Two atomic datasets, including energy levels and radiative and collisional excitation rates, are used as input data for the code. It is found that the behaviour of the XRL is somewhat different than might be expected from superficial examination of the atomic data. The similarities in the gain profiles at low densities are found to have encouraging implications. in our attempts to model XRLs.