A formulation methodology for multicomponent distillation sequences based on stochastic optimization

Based on stochastic optimization strategy, a formulation methodology is proposed for synthesizing distillation column sequences, allowing more than one middle component as the distributing components between a pair of key components in the non-sharp split. In order to represent and manipulate the distillation configuration structures, a new coding procedure is proposed in the form of one-dimensional array. Theoretically, an array can represent any kind of split(non-sharp and sharp). With the application of a binary sort tree approach, a robust flow sheet encoding and decoding procedure is developed so that the problem formulation and solution becomes tractable. In this paper,the synthesis problem is formulated as a mixed-integer nonlinear programming(MINLP) problem and an improved simulated annealing approach is adopted to solve the optimization problem. Besides, a shortcut method is applied to the evaluation of all required design parameters as well as the total function.

Numerical study of separation on the trailing edge of a symmetrical airfoil at a low Reynolds number

This study focuses on the trailing-edge separation of a symmetrical airfoil at a low Rey-nolds number. Finite volume method is adopted to solve the unsteady Reynolds-averaged Navier-Stokes （RANS） equation. Flow of the symmetrical airfoil SD8020 at a low Reynolds number has been simulated. Laminar separation bubble in the flow field of the airfoil is observed and process of unsteady bubble burst and vortex shedding from airfoil surfaces is investigated. The time-dependent lift coefficient is characteristic of periodic fluctuations and the lift curve varies nonlinearly with the attack of angle. Laminar separation occurs on both surfaces of airfoil at small angles of attack. With the increase of angle of attack, laminar separation occurs and then reattaches near the trailing edge on the upper surface of airfoil, which forms laminar separation bubble. When the attack of angle reaches certain value, the laminar separation bubble is unstable and produces two kinds of large scale vortex, i.e. primary vortex and secondary vortex. The periodic processes that include secondary vortex production, motion of secondary vortex and vortex shedding cause fluctuation of the lift coefficient. The periodic time varies with attack of angle. The secondary vortex is relatively stronger than the primary vortex, which means its influence is relatively stronger than the primary vortex.

Numerical analysis of flow separation zone in a confluent meander bend channel

The flow pattern in the confluent meander bend channel under the conditions of different discharge ratios and junction angles is numerically simulated by means of the large eddy simulation（LES）, and the characteristics of the flow separation zone are analyzed. Numerical results are well validated by experimental data with a good agreement. Analysis of the vertical confinement shows that the turbulence within the separation zone can be characterized as quasi-2-D. Details of the separation zone characteristics are revealed as shown by mean velocity isolines. According to the analysis of numerical results, the length and the width of the separation zone generally increase with the increase of the discharge ratio and the junction angle. However, the width of the separation zone keeps substantially constant when the junction angle increases from 60 o to90o. The dimensionless shape of the separation zone is nearly the same for three discharge ratios and three junction angles. The formulas of the relative width and the relative length of the separation zone are obtained by means of the polynomial fit method.

Passive Control of Laminar Separation Bubble with Spanwise Groove on a Low-speed Highly Loaded Low-pressure Turbine Blade

LES (Large-Eddy Simulation) computations were preformed to investigate the mechanisms of a kind of spanwisegroove for the passive control of laminar separation bubble on the suction surface of a low-speed highly loadedlow-pressure turbine blade at Re = 50,000 (Reynolds number, based on inlet velocity and axial chord length).Compared with the smooth suction surface, the numerical results indicate that: (1) the groove is effective toshorten and thin the separation bubble, which contributes the flow loss reduction on the groove surface, by thinningthe boundary layer behind the groove and promoting earlier transition inception in the separation bubble; (2)upstream movement of the transition inception location on the grooved surface is suggested being the result of thelower frequency at which the highest amplification rate of instability waves occurs, and the larger initial amplitudeof the disturbance at the most unstable frequency before transition; and (3) the viscous instability mode ispromoted on the grooved surface, due to the thinning of the boundary layer behind the groove.

APPLICATION OF VORTEX-IN-CELL METHOD IN THE RANDOM DISCRETE VORTEX SIMULATION FOR THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER

The vortex-in-cell method in the discrete vortex simulation for the separated flow around a bluff body is discussed,Some improvements are made.The separated flow around a circular cylinder in oscillatory flow is investigated.