In this paper, we design and experimentally validate an auxetic nonlinear piezoelectric energy harvester. This harvester combines a clamp-clamp beam and auxetic structures, which can improve the efficiency and bandwidth of the energy harvesting based on a pure mechanical structure without outer magnets or stoppers. Finite element analysis is performed to analyse the effects of the auxetic structures on the efficiency and nonlinearity of the energy harvester. The lumped parameter model is utilized to predict the performance of the energy harvester, which well matches the experimental results. In the experimental validation, under 0.1g base excitation, the power output of the two types of auxetic energy harvesters is 173% and 94% higher than the conventional nonlinear energy harvester. Besides, the bandwidths of the two types of auxetic energy harvesters are broadened by 1556% and 2142% compared with the linear systems.

The low-speed rectangular exit wind tunnel with sectioned contraction is widely used. The secondary flow vortices are found at contraction exit, which would lead to the non-uniform boundary layer and influence the aerodynamic experiment accuracy. In this paper, experimental and numerical approaches are adopted so as to clarify reasons for the formation of the secondary crossflow occurring at contraction exit and take measures to control it. The conclusions can be gotten as: the secondary crossflow is formed and developed in the second (rectangular-to-rectangular) contraction, and the first (circular-to-rectangular) contraction promote the secondary flow vortices to migrate to the middle of flow field to a certain extent; the formation of the secondary crossflow is related to the static pressure gradient in the contraction. Based on the mechanism analysis results, several methods aimed to control the secondary crossflow are proposed and verified, the results can be concluded as: in terms of the rectangular-to-rectangular contraction that contracts along one direction, it is difficult to effectively control the secondary crossflow just by optimizing contraction curves and contraction ratios, while adopting the boundary layer suction can significantly improve the boundary layer uniformity; if the rectangular-to-rectangular contraction contracts in two directions, such secondary crossflow can be well controlled.

The numerical investigation of the flow and heat transfer characteristics from arrays of impinging jets with the roughed target surface is presented in this paper. Three novel streamlined roughness elements are proposed: similar round protuberance, similar trapezoidal straight rib, and similar trapezoidal curved rib. The jet Reynolds number ranges from 15000 to 30000, the protuberance height is h/H = 0.36, the rib height is h/H = 0.3, 0.5, and 0.7 respectively. The results show that the protuberance can shorten the nozzle to the stagnation point distance, increasing the heat transfer at the stagnation point by nearly 40%. The rib has a remarkable effect of guiding the flow in span-wise direction and away from the target surface, weakening the cross-flow effect. The straight rib gets a better guidance performance, the curved rib provides a larger surface area. An appropriate increase of rib height can improve local heat transfer, continuing to increase mainly enlarge heat transfer area. The decent aerodynamic shape decreases the flow discharge coefficient by only 2% at the rib height of 0.3H.

Jet impingement cooling is an important way to cool turbine blades. Ribbed channels are widely used in the chord region of turbine blades and are an important internal cooling structure. In the design process of the internal cooling structure of the conventional turbine blade, it is the primary consideration of the designer to improve the heat transfer coefficient at the surface of the inner cooling passage. With the development of the design of the inner cooling structure of the turbine blade, the pressure loss caused by the inner cooling passage has been paid more and more attention. Therefore, many studies have begun to comprehensively consider the potential of various rib structures in enhancing heat transfer and reducing flow resistance. In the design process of the internal cooling structure of the conventional turbine blade, the rib is placed on the blade, which increases the blade burden. In this paper, the classic rib structure is changed, and the rib is placed on the impingement plate to research its heat transfer characteristics. In this study, the effects of ribs of different structures on heat transfer were tested. Calculate the working conditions of Reynolds number Re = 15000, 20000, 25000, 30000. The numerical calculation of the SST k-w model is used to evaluate the average Nusselt number of the target plate and the flow coefficient of the channel, and the heat transfer distribution and flow field are analyzed. This study is expected to achieve better coordination between improved heat transfer and reduced flow resistance.

To investigate their in-plane dynamic response, a rigid plate with mass was given an initial velocity to impact (square) honeycombs in the X 1 and X 2 directions, respectively. Firstly, the impact model was built and validated. Then, impact resistance capacity research was conducted. Results showed that each honeycomb performed similarly in X 1 and X 2 directions, and the reentrant honeycomb usually used smaller displacement and time to absorb the same amount of kinetic energy. Thus, it is better for application if these factors were the main concerns. After that, the nominal stress at the proximal and distal ends were discussed under various impact velocities. It is shown that, under impact loading, the reentrant honeycomb generally showed higher initial peak stress as well as lower plateau stress at both proximal and distal ends. In addition, combining these with the deformation process of honeycombs, it was concluded that the formation of the plateau area of the nominal stress curve is related to the crushing displacement of the impact plate as well as the collapse of cells.

In this paper, a class of axisymmetric thin-walled tubes with two types of geometries (straight and tapered) and four kinds of cross-sections (square, rectangle, circle, ellipse) are considered as energy absorbing components under oblique impact loading. The crash behavior of these tubes are first investigated by nonlinear finite element analysis through LS-DYNA. It is found that the tapered tubes has the better crashworthiness performance than the straight ones under oblique impact regarding both specific energy absorption (SEA) and peak crushing force (PCF). Among the tapered tubes, the tapered ellipse tube (TET) has the best crashworthiness performance. Then by calculating the overall SEA considering load angle uncertainty effect, it is found that the weighting factors for different load angles are critical for evaluating the crashworthiness performance of the tubes.

This paper describes the development of a compact engineering simulator of Pebble-bed Modular High Temperature Gas-cooled Reactor (HTR-PM) by embedding THERMIX code into the vPower simulation environment. The compact engineering simulator consists of modules for two reactors, two steam generators and entire secondary loop system for power generation with a water-steam Rankin cycle. Two THERMIX modules are employed to simulate the two primary loops corresponding to the two reactors in the HTR-PM respectively. Then, the vPower synchronizes the two THERMIX modules in executing simulation to such two reactor module-structures of HTR-PM. The simulation modules for secondary loop and human machine interface are mainly developed with intrinsic models of vPower simulation platform. Current simulation results are in good agreement with the design values and safety analysis results of HTR-PM. The compact HTR-PM engineering simulator will be improved and validated for safe analysis, procedure development and design change verification.

Normal and steady bed temperature provides a basis for the stabilization and safe operation of the circulating fluidized bed boiler (CFBB) unit. Because the bed temperature is affected by many operating factors, it often fluctuates unexpectedly. The bed temperature auto-control system seldom could be put into service during the operation of large capacity CFBB unit. On the basis of operation data of a commercial 450t/h CFBB, which is the first biggest CFBB made in China, the authors systematically analyze the main factors which influence the changes of bed temperature, such as fuel supply rate, air supply rate, oxygen concentration, dense zone height and the unit load et al. The record of the operation data show that the lag of the bed temperature is common phenomenon while fuel supply is changed, and the lag time varies with the fuel supply time, fuel supply operating mode and fuel supply rate; Coal quality and its grain diameter spectrum also have notable influence on bed temperature; Primary air rate has different influences on bed temperature at different operating conditions, and its adjustment range on bed temperature is limited while it is used to bed temperature control; The change of oxygen concentration can reflect combustion conditions in the furnace; The change of dense zone height will result in the change of bed temperature, so the adjustment of fluidization air rate is necessary; Bed temperature is one of the main factors which lead to the change of boiler load. At last, regulating rules on bed temperature control are analyzed and summarized. The conclusions can provide references for the design of control system and safe operation of CFBB unit.