Numerical Analysis of Labyrinth Seal Performance for the Impeller Backface Cavity of a Supercritical CO_(2) Radial Inflow Turbine

For a radial inflow turbine(RIT),leakage flow in impeller backface cavity has critical impacts on aerodynamic performance of the RIT and axial force acting on the RIT impeller.In order to control this leakage flow,different types of labyrinth seals are numerically studied in this paper based on a supercritical carbon dioxide(S-CO_(2))RIT.The effects of seal clearance and cavity outlet pressure are first analyzed,and the impacts of seal design parameters,including height,number and shape of seal teeth,are evaluated.Results indicate that adding labyrinth seal can improve cavity pressure and hence adequately inhibits leakage flow.Decreasing the seal clearance and increasing the height of seal teeth are beneficial to improve sealing performance,and the same effect can be obtained by increasing the number of seal teeth.Meanwhile,employing seals can reduce leakage loss and improve RIT efficiency under a specific range of cavity outlet pressure.Finally,the influences of seal types on the flow field in seal cavity are numerically analyzed,and results demonstrate that isosceles trapezoidal type of seal cavity has better sealing performance than triangular,rectangular and right-angled trapezoidal seal cavities.

Control Effect and Cost Evaluation of Different Sex Pheromones and Trapping Lamps against Spodoptern litura,Helicoverpa assulta and Helicoverpa armigera in Tobacco

[ Objective] The aim was to study the control effect of different sex pheromones and trapping lamps against main pests in tobacco. [ Method] Control effect of sex pheromone of different matrix lures and Jiaduo trapping lamp against Spodoptern litura, Helicoverpa assulta and Helicoverpa armigera in tobacco in Teng- chong of Yunnan were determined and compared, and the control cast was evaluated. [Result] The use of insect sex pheromones and insecticidal light traps had certain effect against S. litura and H. armiger. The trapping effect of sex pheromone traps was better than that of Jiaduo trapping lamp, and the PVC matrix lure had better performance than rubber matrix lure, which had strongest capturing capacity, continuous control effect and significant effort against S. litura. The traps with different settled densities and hanging heights also had different trapping effect against S. litura and H. armiger, and the hanging height of 100 - 150 cm from ground was the best; as the cost was considered, the cast of the area with low density of traps was the lowest, which was reduced by over 44% than conventional chemical control area. [ Conclusion] It is safe and effective to use sex pheromone and insecticidal light traps to control S. litura and H. armigera, and it is a green environmental protection biological physical control technology, having extended application prospect in large area.

Stator re-stagger optimization in multistage axial compressor

As a widely applied technique in multistage axial compressors,variable stator vanes(VSV)can flexibly rematch the blade rows to fulfil a variety of aerodynamic performance requirements,such as high efficiency and wide surge margin.The purpose of this paper is to develop an optimization method to quickly determine VSV settings during the preliminary design phase.A mean-line method with a model calibration procedure is adopted to evaluate compressor performance,and the NSGA-II algorithm is employed for automatic optimization.The developed optimization system is then employed to determined re-stagger arrangement in a multistage compressor.A single-speed optimization with performance constraints of specific operating point and a multi-speed optimization with different control laws are conducted.Results are compared with available experimental re-stagger scheme,which verifies the effectiveness of the re-stagger optimization method.Moreover,method is proposed to determine operating parameters of a working point with a user-defined pressure ratio or mass flow rate after variable geometry.

The development and application of an inviscid inverse method

A two-dimensional inviscid inverse method is developed,verified and applied inthis paper.The method solves the Euler equation in absolute reference frame by a cell-centeredfinite volume method,and the hybrid Runge-Kutta method ls used for time integration.Different from the direct method,the inverse method imposes a unique"transpiration"boundary condition on the blade surfaces.The inputs of inverse method are pressure loadingand blade tangential thickness distribution along the blade chord.During the time marchingprocess,the blade shape is periodically updated.When the solution is converged,the bladeshape will be stabled.In the paper,the principle of the inverse method is described in detail.Then the developed inverse method is verified against a consistence test:recover an axialcompressor cascade from a different start.Finally,to demonstrate the powerful capability ofthe method,it is used to redesign the cascade,and final results give an improved aerodynamicperformance.