Constructions for cyclic 3‐designs and improved results on cyclic Steiner quadruple systems

This paper gives some recursive constructions for cyclic 3‐designs. Using these constructions we improve Grannell and Griggs's construction for cyclic Steiner quadruple systems, and many known recursive constructions for cyclic Steiner quadruple systems are unified. Finally, some new infinite families of cyclic Steiner quadruple systems are obtained. © 2010 Wiley Periodicals, Inc. J Combin Designs 19:178‐201, 2011     

Experimental and analytical investigation of liquid sheet breakup characteristics

The main objective of this research is to study analytically and experimentally the liquid sheet breakup of a flat fan jet nozzle resulting from pressure-swirling. In this study the effects of nozzle shape and spray pressure on the liquid sheet characteristics were investigated for four nozzles with different exit widths (1.0, 1.5, 2.0 and 2.5 mm). The length of liquid sheet breakup, liquid sheet velocity and the size of formed droplets were measured by a digital high speed camera. The breakup characteristics of plane liquid sheets in atmosphere are analytically investigated by means of linear and nonlinear hydrodynamic instability analyses. The liquid sheet breakup process was studied for initial sinuous and also varicose modes of disturbance. The results presented the effect of the nozzle width and the spray pressure on the breakup length and also on the size of the formed droplets. Comparing the experimental results with the theoretical ones for all the four types of nozzles, gives a good agreement with difference ranges from 4% to 12%. Also, the comparison between the obtained results and the results due to others shows a good agreement with difference ranged from 5% to 16%. Empirical correlations have been deduced describing the relation between the liquid sheet breakup characteristics and affecting parameters; liquid sheet Reynolds number, Weber number and the nozzle width.     

A study on the flow field and local heat transfer performance due to geometric scaling of centrifugal fans

Scaled versions of fan designs are often chosen to address thermal management issues in space constrained applications. Using velocity field and local heat transfer measurement techniques, the thermal performance characteristics of a range of geometrically scaled centrifugal fan designs have been investigated. Complex fluid flow structures and surface heat transfer trends due to centrifugal fans were found to be common over a wide range of fan aspect ratios (blade height to fan diameter). The limiting aspect ratio for heat transfer enhancement was 0.3, as larger aspect ratios were shown to result in a reduction in overall thermal performance. Over the range of fans examined, the low profile centrifugal designs produced significant enhancement in thermal performance when compared to that predicted using classical laminar flow theory. The limiting non-dimensional distance from the fan, where this enhancement is no longer apparent, has also been determined. Using the fundamental information inferred from local velocity field and heat transfer measurements, selection criteria can be determined for both low and high power practical applications where space restrictions exist.     

吸力面带凹窝轴流风扇内流分析与实验研究

本文采用Navier-Stokes方程和κ-ε两方程模型分别对空调用轴流风轮叶片吸力面设置凹窝和不设置凹窝的的内流特性进行了三维数值模拟,同时对两者的风量噪音特性进行了实验研究.结果表明,在叶片吸力面设置凹窝没有改善风轮的整体流量─压力特性,不能提高风扇的静压升,凹窝只能提高凹窝局部位置的静压升,且凹窝中心压力大,凹窝边缘压力低.小流量时,风扇吸力面设置凹窝反而增加风机噪音,大流量时,凹窝对风机的噪音没有影响.     

斜蜗舌对贯流风机内流的影响及降噪机制研究

本文提出采用一种新型的不等距蜗舌(这里统称为斜蜗舌)在提高风机的外特性性能的同时,相对降低噪声.通过试验与数值模拟,比较直叶片式,斜叶片式贯流风机分别用直蜗舌和斜蜗舌时内流、外特性及噪声频谱.采用三维Navier-Stokes方程和κ-ε两方程湍流模型对内部流场进行数值分析,发现与采用常规蜗舌的贯流风机不同的是斜蜗舌贯流风机偏心涡位置随着蜗舌间隙的变化而发生改变.本文旨在探讨斜蜗舌对贯流风机内流的影响及降噪的机制.