Results on scale effects for cavitation inception at small and large Reynoldsnumbers were compared, respectively. The empirical relation for scale effects suggested by Dr.Andreas Keller was checked, which showed that ...Results on scale effects for cavitation inception at small and large Reynoldsnumbers were compared, respectively. The empirical relation for scale effects suggested by Dr.Andreas Keller was checked, which showed that the comparison of results on cavitation inception atsmall Reynolds numbers below 1 x 10~6 was confirmed very well, but at larger Reynolds numbers abovethe magnitude of 1 x 10~6 was not clearly confirmed.展开更多
The tensile strength of test liquid affects the cavitation inception numbers very seriously, and the zero-tensile strength as a criterion for detection of the cavitation inception numbers can be used, in order to redu...The tensile strength of test liquid affects the cavitation inception numbers very seriously, and the zero-tensile strength as a criterion for detection of the cavitation inception numbers can be used, in order to reduce the influence of tensile strength. The scale effect on measuring zero-tensile strength of test liquid based on hydraulic methods must be considered. it is supposed that the zero-tensile strength can be defined by use of the comparative method, which unites the classical theory of cavitation inception with the modern one based on an identical criterion.展开更多
Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and ...Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and the insufficient reflection of the nuclei effects on cavitation in the numerical methods, the cavitating hydrodynamics and cavitation low frequency noise spectrum of three geometrically similar 7-bladed highly skewed propellers with non-uniform inflow are addressed. In this process, a numerical bridge from the multiphase viscous simulation of propeller cavitation hydrodynamics to its hydro-acoustics is built, and the scale effects on performances and the applicability of exist scaling law are analyzed. The effects of non-condensable gas(NCG) on cavitation inception are involved explicitly in the improved Sauer's cavitation model, and the cavity volume acceleration related to its characteristic length is used to produce the noise spectrum. Results show that, with the same cavitation number, the cavity extension on propeller blades increases with diameter associated with an earlier shift of the beginning point of thrust decline induced by cavitation, while the three decline slopes of thrust breakdown curves are found to be nearly the same. The power of the scaling law based on local Reynolds number around 0.9R section is determined as 0.11. As for the smallest propeller, the predominant tonal noise is located at blade passing frequency(BPF), whereas 2BPF for the middle and both 2BPF and 3BPF for the largest, which shows the cavitating line spectrum is fully related to the interaction between non-uniform inflow and fluctuated cavity volume. The predicted spectrum level exceedance from the middle to the large propeller is 6.65 dB at BPF and 5.94 dB at 2BPF. Since it just differs less than 2 dB to the increment obtained by empirical scaling law, it is inferred that the scale effects on them are acceptable with a sufficient model scale, and so do the scaling law. The numerical implementation of cavitating hydrodynamics and hydro-acoustics prediction of propeller in big scale in wake has been completed.展开更多
The phenomenon of discharge atomization occurs as hydraulic structures discharging,which influences the safety of power station,electrical equipment and produces environmental pollution.A series of physical model test...The phenomenon of discharge atomization occurs as hydraulic structures discharging,which influences the safety of power station,electrical equipment and produces environmental pollution.A series of physical model tests and feedback analysis are adapted to preliminarily study the scale effect of discharge atomization model by use of the field observation data of discharge atomization.The effect of Re and We numbers of flow on the atomization intensity is analyzed.A conversion relationship of atomization intensity between prototype and model results and the similarity criteria of the atomization range are developed. The conclusion is that the surface tension of discharge atomization model could be ignored when the Weber number is larger than 500.Some case studies are given by use of the similitude criteria of the atomization model.展开更多
文摘Results on scale effects for cavitation inception at small and large Reynoldsnumbers were compared, respectively. The empirical relation for scale effects suggested by Dr.Andreas Keller was checked, which showed that the comparison of results on cavitation inception atsmall Reynolds numbers below 1 x 10~6 was confirmed very well, but at larger Reynolds numbers abovethe magnitude of 1 x 10~6 was not clearly confirmed.
文摘The tensile strength of test liquid affects the cavitation inception numbers very seriously, and the zero-tensile strength as a criterion for detection of the cavitation inception numbers can be used, in order to reduce the influence of tensile strength. The scale effect on measuring zero-tensile strength of test liquid based on hydraulic methods must be considered. it is supposed that the zero-tensile strength can be defined by use of the comparative method, which unites the classical theory of cavitation inception with the modern one based on an identical criterion.
基金supported by National Natural Science Foundation of China(Grant No.51009144)
文摘Considering the lack of theoretical models and ingredients necessary to explain the scaling of the results of propeller cavitation inception and cavitating hydroacoustics from model tests to full scale currently, and the insufficient reflection of the nuclei effects on cavitation in the numerical methods, the cavitating hydrodynamics and cavitation low frequency noise spectrum of three geometrically similar 7-bladed highly skewed propellers with non-uniform inflow are addressed. In this process, a numerical bridge from the multiphase viscous simulation of propeller cavitation hydrodynamics to its hydro-acoustics is built, and the scale effects on performances and the applicability of exist scaling law are analyzed. The effects of non-condensable gas(NCG) on cavitation inception are involved explicitly in the improved Sauer's cavitation model, and the cavity volume acceleration related to its characteristic length is used to produce the noise spectrum. Results show that, with the same cavitation number, the cavity extension on propeller blades increases with diameter associated with an earlier shift of the beginning point of thrust decline induced by cavitation, while the three decline slopes of thrust breakdown curves are found to be nearly the same. The power of the scaling law based on local Reynolds number around 0.9R section is determined as 0.11. As for the smallest propeller, the predominant tonal noise is located at blade passing frequency(BPF), whereas 2BPF for the middle and both 2BPF and 3BPF for the largest, which shows the cavitating line spectrum is fully related to the interaction between non-uniform inflow and fluctuated cavity volume. The predicted spectrum level exceedance from the middle to the large propeller is 6.65 dB at BPF and 5.94 dB at 2BPF. Since it just differs less than 2 dB to the increment obtained by empirical scaling law, it is inferred that the scale effects on them are acceptable with a sufficient model scale, and so do the scaling law. The numerical implementation of cavitating hydrodynamics and hydro-acoustics prediction of propeller in big scale in wake has been completed.
基金supported by the National Natural Science Foundation of China and the Hydropower Development of Yalong River Foundation (Grant No.50579084)the National Key Technologies R&D Program of China(Grant No.2008BAB29B04-3-3)
文摘The phenomenon of discharge atomization occurs as hydraulic structures discharging,which influences the safety of power station,electrical equipment and produces environmental pollution.A series of physical model tests and feedback analysis are adapted to preliminarily study the scale effect of discharge atomization model by use of the field observation data of discharge atomization.The effect of Re and We numbers of flow on the atomization intensity is analyzed.A conversion relationship of atomization intensity between prototype and model results and the similarity criteria of the atomization range are developed. The conclusion is that the surface tension of discharge atomization model could be ignored when the Weber number is larger than 500.Some case studies are given by use of the similitude criteria of the atomization model.