Correlation analysis of cavitation-induced pressure pulsation and vibration in a bulb turbine

Cavitation is one of the main causes of deteriorating stability of bulb turbines.To enhance their stability,this study examines the effects of runner cavitation on draft tube pressure fluctuation and vibration in bulb turbine through experimental methods.With varying cavitation coefficients,a synchronous test system,including a high-speed camera,vibration acceleration sensors and pressure pulsation sensors,is applied to obtain cavitation images of the runner,vibration and internal fluid pressure pulsation data of the draft tube.The results show that the correlated component of pressure pulsation signals during the cavitation process is the synchronous pressure pulsation of 16f_(n)With the development of cavitation,the amplitude of synchronous pressure pulsation increases first and then decreases.Cavitation enhances the high-frequency vibration on the wall of runner chamber.The root mean square(rms)of the vertical vibration component IMF3,the horizontal vibration components IMF2,IMF4 are linearly negatively correlated with the cavitation coefficient.The associated component between cavitation-induced vibration and pressure pulsation signal is 16f_(n)and its harmonics.In the process of cavitation,pressure pulsation plays a leading role in vibration.

Brominated Butyl Rubber Anticorrosive Coating and its Self-healing Behaviors

Self-healing anticorrosive coatings in extreme environment have attracted considerable interest from researchers.In this work,4-tert-butylpyridine(TBP)was incorporated into brominated butyl rubber(BIIR)polymer networks to form a reversible ionic bond with the highly reactive bromine anion.Based on the low glass transition temperature of the BIIR polymer and the electrostatic effects,a robust self-healing anticorrosive coating of TBP-BIIR was prepared.TBP-BIIR coating showed a maximum protection efficiency(PE)of more than 94%(TBP-BIIR-acid,94.37%;TBP-BIIR-alkali,94.95%;TBP-BIIR-salt,95.49%)when treated with a strong acid(HNO_(3),pH=2),strong base(NaOH,pH=12)and high salt solution(3.5 wt%NaCl).In addition,the PE of coating repaired exceed 89%,and the maximum PE value was approximately 95%in different solutions,which demonstrated its extinguished self-healing abilities.These results indicated that the TBP-BIIR anticorrosive coating could provide excellent safety and durability in special environment,which would be extremely beneficial to improve the working life of metal parts used in aviation and shipping,oil and gas and related industries.

C型槽参数对NACA0009翼型间隙流动的影响

间隙流动广泛存在于流体机械转子位置,其存在会直接影响内部流态的稳定性,降低效率的同时降低水力机械的寿命。该文采用数值计算方法研究了C型槽对NACA0009翼型叶顶间隙泄漏涡的抑制机理,并使用正交试验法对C型槽的槽数、槽宽、槽深和内侧面偏斜角度对翼型的影响进行了研究。研究结果表明:C型槽产生低速涡流,有效降低了间隙位置泄漏流的流速,从而抑制高速泄漏流的产生,且C型槽深度和偏斜角度的选取对于翼型的水动力性能影响较大。并借助正交试验结果提出了两种最优C型槽设置方法,有效抑制了间隙泄漏涡。

叶顶间隙对气液混输泵水力性能的影响研究

该文以气液两相三级混输泵为研究对象,基于数值模拟研究了不同含气率下叶顶间隙对混输泵外特性、内流场、载荷分布及气相分布的影响,并通过与实验对比验证了数值模拟是可靠的。主要结果表明:随着叶顶间隙增大,混输泵扬程和效率均呈现下降趋势,纯水工况相较20%含气率工况下降幅度更加显著;虽然叶顶泄漏现象随着间隙值的增大逐渐加剧,但20%含气率时大间隙下叶顶间隙内流动比小间隙模型更加平稳;叶顶间隙使得叶片表面压力分布发生变化,含气率小于10%时,随着间隙值的增大叶片表面静压逐渐降低。当含气率大于10%以后,其变化较为混乱;合理的叶顶间隙能有效改善叶轮内的气相分布。就该文所研究的混输泵而言,叶顶间隙小于0.28%D(叶轮直径)时,随着间隙值增大叶轮内的气相分布越均匀。

Ice Crystal Growth Mechanism and Structure-activity Relationships of Graphene Oxide/Poly(vinyl alcohol)Aerogels

Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure remains an academic challenge.Herein,by employing graphene oxide(GO)as the aerogel skeleton and utilizing poly(vinyl alcohol)(PVA)to regulate the ice crystal growth,we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method.We demonstrate that due to the hydrogen bond formed between PVA and water molecules,resulting in the initial crystallization temperature being reduced from-12.60℃(GO/PVA-0.01)to-16.21℃(GO/PVA-0.1).Meanwhile,the strong hydrogen bond between PVA and GO limits the diffusion of water molecules,thereby inhibiting the growth of ice crystals,decreasing the pore size of the GO/PVA aerogel from 9.96 nm(GO/PVA-0.01)to 7.19 nm(GO/PVA-0.3),and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13MPa.Overall,the finding of this study can be extended to other aerogel precursors,and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.

Numerical investigation of the effect of T-shaped blade on the energy performance improvement of a semi-open centrifugal pump

The tip leakage flow formed by the tip clearance of a semi-open centrifugal pump adversely affects the energy performance and the energy waste. A T-shaped blade is proposed to be used to improve the energy characteristics. The internal flow field is simulated via the shear stress transport turbulence model to analyze the influence of the T-shaped blade on the performance of a centrifugal pump. It is shown that with the T-shaped blade, the hydraulic loss can be reduced, the Euler head can be increased, and the external characteristics can be improved. The maximum head and efficiency improvements are 3% and 1.6%, respectively. The relative flow angle near the tip clearance of the T-shaped blade decreases, and the strength of the backflow region is remarkably weakened. The area of the high entropy production region decreases, and the trend of the upstream diffusion is restrained under the design condition. The T-shaped blade can help to inhibit the diffusion of the high entropy production region to the hub under the low flow rate condition, but the entropy production and the mixing losses at the tip clearance are slightly increased. This research provides a new method for improving the energy performance of the semi-open centrifugal pump.