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The constrained multi-objective multi-variable optimization of fans usually needs a great deal of computational fluid dynamics (CFD) calculations and is time-consuming. In this study, a new multi-model ensemble optimization algorithm is proposed to tackle such an expensive optimization problem. The multi-variable and multi-objective optimization are conducted with a new flexible multi-objective infill criterion. In addition, the search direction is determined by the multi-model ensemble assisted evolutionary algorithm and the feature extraction by the principal component analysis is used to reduce the dimension of optimization variables. First, the proposed algorithm and other two optimization algorithms which prevail in fan optimizations were compared by using test functions. With the same number of objective function evaluations, the proposed algorithm shows a fast convergency rate on finding the optimal objective function values. Then, this algorithm was used to optimize the rotor and stator blades of a large axial fan, with the efficiencies as the objectives at three flow rates, the high, the design and the low flow rate. Forty-two variables were included in the optimization process. The results show that compared with the prototype fan, the total pressure efficiencies of the optimized fan at the high, the design and the low flow rate were increased by 3.35%, 3.07% and 2.89%, respectively, after CFD simulations for 500 fan candidates with the constraint for the design pressure. The optimization results validate the effectiveness and feasibility of the proposed algorithm.

This paper presents an experimental study of the self-sustained transonic shock oscillating behaviors in a heavy-duty gas turbine compressor cascade under the inlet Mach number of 0.85, 0.90 and 0.95. The transonic shock patterns and the surface flow structures are captured by schlieren imaging and oil flow visualization. The time-averaged and instantaneous transonic shock oscillating behaviors at the near choke point and the near stall point are investigated by the Anodized Aluminum Pressure-Sensitive Paint (AA-PSP) surface pressure measurement. The normal passage shock dominant pattern and the detached bow shock dominant pattern at the near choke point and the near stall point are experimental characterized, respectively. The passage shock oscillation behaviors at the near choke point have been observed to undergo periodic pressure perturbations of the shock shift between the upstream λshock feet mode and the downstream λshock feet mode. The detached bow shock oscillation behaviors at the near stall point have been observed to undergo the pressure perturbations of the shock cycle movement between the upstream detached bow shock mode and the downstream detached bow shock mode. The differences between the shock shift mode and the shock cycle movement mode lead to the different streamwise oscillation travel ranges and different shock intensity variations under the same inlet Mach number.

Transonic tandem cascades can effectively increase the working load, and this feature conforms with the requirement of the large loads and pressure ratios of modern axial compressors. This paper presents an optimization strategy for a German Aerospace Center (DLR) transonic tandem cascade, with one front blade and two rear blades, at the inlet Mach number of 1.051. The tandem cascade profile was parameterized using 19 control parameters. Non-dominated sorting Genetic algorithm (NSGA-II) was used to drive the optimization evolution, with the computational fluid dynamics (CFD)-based cascade performances correction added for each generation. Inside the automatic optimization system, a pressure boundary condition iterative algorithm was developed for simulating the cascade performance with a constant supersonic inlet Mach number. The optimization results of the cascade showed that the deflection of the subsonic blade changed evidently. The shock wave intensity of the first blade row was weakened because of the reduced curvatures of the optimized pressure and suction sides of the front blade part and the downstream moved maximum thickness position. The total pressure losses decreased by 15.6%, 20.9% and 19.9% with a corresponding increase in cascade static pressure ratio by 1.3%, 1.8% and 1.7%, for the three cascade shapes in the Pareto solution sets under the near choke, the design and near stall conditions, respectively.

Experimental and numerical investigations were conducted to investigate the variations of shock-wave boundary layer interaction (SBLI) phenomena in a highly loaded transonic compressor cascade with Mach numbers. The schlieren technique was used to observe the shock structure in the cascade and the pressure tap method to measure the pressure distribution on the blade surface. The unsteady pressure distribution on blade surface was measured with the fast-response pressure-sensitive paint (PSP) technique to obtain the unsteady pressure distribution on the whole blade surface and to capture the shock oscillation characteristics caused by SBLI. In addition, the Reynolds Averaged Navier Stokes simulations were used to compute the three-dimensional steady flow field in the transonic cascade. It was found that the shock wave patterns and behaviors are affected evidently with the increase in incoming Mach number at the design flow angle, especially with the presence of the separation bubble caused by SBLI. The time-averaged pressure distribution on the blade surface measured by PSP technique showed a symmetric pressure filed at Mach numbers of 0.85, while the pressure field on the blade surface was an asymmetric one at Mach numbers of 0.90 and 0.95. The oscillation of the shock wave was closely with the flow separation bubble on the blade surface and could transverse over nearly one interval of the pressure taps. The oscillation of the shock wave may smear the pressure jump phenomenon measured by the pressure taps.

ABSTRACTIn this paper, a two-dimensional transonic cascade of German Aerospace Center (DLR) was redesigned with multi-objective optimization. The aerodynamic performance of the cascade was optimized with inlet Mach number of 1.1 by using the blade design method with thickness distribution superposed on the camber line. The non-dominated sorting genetic algorithm, (NSGA) II multi-objective optimization algorithm, was used to determine higher performance cascades. Cascade optimization was carried out within a unique inlet Mach number by varying the shapes of both the camber line and the thickness distribution curve. To enable the cascade to operate under specific conditions, we used an inlet Mach number control loop (IMCL) to regulate the outlet boundary conditions. Optimization was conducted to minimize the cascade total pressure loss coefficient under the three inlet conditions. The optimization results indicated that the total pressure loss coefficient can be reduced by 22% under the design condition, and the range of working conditions was widened.

In this paper, a cascade double-loop control (DLC) combined with modeling compensation methods is proposed to improve the tracking precision of the multiaperture imaging system (MAIS). The application of the flexible thin-wall ring mechanism in the coupling rotating prism (CRP) system causes a series of tracking and pointing challenges. Disturbances such as friction, shaft deformation, and model perturbation significantly deteriorate the tracking and pointing accuracy of the CRP. Two different modeling compensation methods that are interfaced with classical DLC are proposed to guarantee the tracking precision of the MAIS. Moreover, the disturbance observation and compensation performance of two different modeling compensation methods are analyzed and compared. Finally, simulation and experiment results indicate that the proposed control methods, especially model compensation based on speed close-loop control, obtain the best performance for disturbance rejection in the MAIS.

A novel covalently bonded Eu3+-based silica hybrid material was designed and its spectrophotometric anion sensing property was studied. The fluorescent receptor (europium complex) was covalently grafted to the silica matrix via a sol-gel approach. FTIR, UV-vis spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescent spectra were characterized, and the results revealed that the hybrid material with nanosphere structure displayed excellent photophysical property. In addition, the selective anion sensing property of the hybrid material was studied by UV-vis and fluorescence spectra. The results showed that the hybrid material exhibited a smart response with fluoride anions.

The success of stocking programs involving walleye Stizostedion vitreumhas frequently been judged by the contributions of the stocked walleye to the abundance of year-classes. But evaluation methods based only on contributions to the year-class augmented may be biased. We developed a method of estimating walleye year-class strength based on catch-at-age data from routine fish population assessments. We then examined the effect of walleye stocking on the stocked year-class and other year-classes by using catch-at-age data from walleyes in 200 Minnesota lakes. Although stocking increased the abundance of a year-class in lakes with natural walleye reproduction, stocking, especially of fingerlings, decreased the abundance of year-classes 1 year younger and 1 year older than the stocked year-class. In lakes without natural walleye reproduction, stocking did not affect adjacent year-classes significantly.

Data from Minnesota Department of Natural Resources lake surveys and stocking records were used to examine the effects of stocking programs involving walleye Stizostedion vitreumon the abundance and size of fish in walleye populations and to determine to what extent and under what conditions these effects occurred. We used data from 4,470 surveys in 1,924 lakes and from 20,634 walleye stocking records in 1,716 lakes. The analyses were conducted for various sizes of stocked fish and stocking frequencies and for lake groups with different walleye reproductive status. We reached the following conclusions. (1) Stocking in lakes without natural walleye reproduction increased walleye population abundance, but stocking in lakes where reproduction occurred had no effect on population abundance, (2) In lakes without walleye reproduction, walleye mean weight was reduced by stocking. In lakes with walleye reproduction, fry stocking decreased the mean weight of fish, but fingerling stocking had no effect on weight. The decrease in weight resulting from stocking was greater in lakes without natural walleye reproduction than in lakes with natural reproduction. (3) In situations where stocking affected population abundance or fish size, an increase in stocking frequency had diminishing effects. In general, where total population abundance increased as a result of stocking, the walleye mean weight decreased.