Effects of swirl on flow separation and performance of wide angle diffusers

Experimental investigations have been carried out to determine whether the introduction of a circumferential velocity component can produce worthwhile improvements in the performance of, and eliminate flow separation in, wide angle conical diffusers. The swirl generator is a 24 flat-bladed, radial intake type. Systematic experimentation has been carried out for one diffuser configuration fitted with a tailpipe (16.5° and 4.4 area ratio) using varying strengths of inlet swirl and introducing the dissipated mechanical energy as the main criterion of diffuser performance. The best inlet swirl strength produced about 60% reduction of the total diffuser losses in swirl-free flow. The analysis of these results, together with information obtained from flow visualisation experiments, suggests that increasing the swirl beyond an observed threshold completely eliminated flow separation, but it also gave rise to a central zone of recirculating flow and hence additional dissipative losses. We conclude that the optimum improvement achievable in wide angle diffuser performance using swirl does not require the addition of more energy than it saves     

Computation of Internal and External Compressible Flows Using EDICT

Results are presented for finite element computations involving high speed, viscous compressible internal and external flows. The stabilized finite-element formulations for the Navier-Stokes equations in the conservation law form are solved using the conservation variables. To improve the accuracy of the base method, especially in the regions of flow that are associated with shocks, boundary-layers and their interactions, the Enhanced-Discretization Interface-Capturing Technique (EDICT) is utilized. An error indicator is employed to identify the regions in the computational domain that need enhanced discretization for increased accuracy. The method is implemented on a shared-memory parallel computer and is used to study complex flows, that involve shock-wave/boundary-layer interactions, in supersonic diffusers and wind-tunnels. The start-up problem in supersonic wind-tunnels, caused by a narrow second throat in the diffuser section, is simulated. This computation brings out some of the very interesting features of the unsteady dynamics of the start-up shock.     

Development of an Optical Fiber Fluorescence Setup for in situ PAHs Detection in Porous Media. Application to Pyranine Transport in Sand Columns

Abstract

An optical method based on fluorescence spectroscopy was developed for in-situ non-destructive, real time, organic pollutant detection and quantification in soil. Optical fiber-based light-induced fluorescence probes allowing in-situ specific chemical detection were constructed. Pyranine was chosen as a model fluorescent Polycyclic Aromatic Hydrocarbon (PAH). The effect of sand particles on fluorescence measurements was established: the fluorescence intensity in water-saturated sand was eight times lower than in aqueous solutions, due to light scattering by the sand particles. To adapt the method to dynamic pollutant concentration measurements in soil, two different designs of light diffusers were constructed and compared. A light distributor with a quartz window was chosen for its higher sensitivity and reproducibility. The probes were introduced into two different columns: short ones used to study the effect of the measurement location in the column and longer ones to study pyranine transport. It was shown that, in columns, the measurement location plays an important role; measurements near the walls, in particular, were different from those performed more towards the center of the column in a given section. As a consequence, one should avoid measurements near the circumference. Preliminary results were successfully compared to a chemical transport model and revealed that the methodology is a powerful tool to measure in-situ concentration changes; on the other hand, fluorescent measurements can be used efficiently to determine transport parameters and give results comparable with those obtained with classical breakthrough curve fittings.     

燃气透平末级叶片及扩压器的联合优化

本文基于iSIGHT优化软件包以及叶轮机械三维粘性CFD数值模拟软件包,采用包括全局探索式、梯度搜索 式优化算法以及近似模型的组合优化策略,对某燃气透平的末级叶型和扩压器外形进行了联合优化。优化后的透平末级与 扩压器部分的CFD预测效率提高了2.8％,同时扩压器的长度缩短了30.1％。     

The fabrication of novel optical diffusers based on UV-cured polymer dispersed liquid crystals

Polymer dispersed liquid crystals (PDLCs) with different sizes of the LC droplets are prepared based on the ultraviolet (UV) light curable acrylate monomers/LCs composites to fabricate the optical diffuser films. To acquire light diffusers with high optical performance, the effects of the monomer structure and the UV light intensity on the micro-structure of the PDLC films are studied. Results show that the PDLC films could exhibit a strong light scattering at the premise of maintaining high transmittance in the visible region. As the LC droplets are spherically dispersed in the polymer networks, when the size of LC droplets is about 3.0 μm, the haze can reach 88.5% and the transmittance is nearly 90.0%, which can be used as a bottom diffuser film. While when the size of LC droplets is about 10.0 μm, the haze and transmittance are 39.2% and 90.2%, respectively; hence, it can be a good choice for a top diffuser film. With the advantages of simple preparation, roll-to-roll industrial production and tunable optical properties, it is supported that the films based on UV-cured PDLC films can be applied as outstanding optical diffuser films in the liquid crystal display industry.