Unified Treatment of Flow Instabilities of Turbomachines

The relationship among four flow instabilities of turbomachines, namely, surge, rotating stall, cavitation surge, and rotating cavitation, is elucidated, using a unified or common model for their analysis. The simplest unifying model was employed in the analysis to focus on the characteristic features of each instability. Moreover, the concentration is on the stability criteria, and hence, the amplitudes are assumed small. Of course, the instabilities often grow to amplitudes comparable with the average value of the flow variable. Flows upstream and downstream of the impeller were assumed to be one dimensional for surge and cavitation surge and to be two dimensional for rotating stall and rotating cavitation, respectively. Viscous effects were taken into consideration in the form of cascade loss. Impeller blade geometry was incorporated in the assumption that the flow is perfectly guided. The peripheral wavelength of the disturbance was assumed to be much larger than the blade pitch

Urinary Level of Liver-Type Fatty Acid Binding Protein Reflects the Degree of Tubulointerstitial Damage in Polycystic Kidney Disease

Background/Aims: Polycystic kidney disease (PKD) is a common, progressive, and heritable type of kidney disease. Although certain imaging modalities are useful for the diagnosis and staging of PKD, they cannot adequately monitor the severity of interstitial inflammation and fibrosis. Therefore, the present study evaluated the urinary level of liver-type fatty acid binding protein (L-FABP) as a marker of interstitial inflammation and fibrosis in PKD. Methods: Male PCK/CrljCrl-Pkhd1pck/Crl (PCK) rats (n = 34) were used as an animal model of the PKD. Age-and sex-matched Sprague–Dawley rats (SD) (n = 34) were used as controls. Urine samples were obtained from the rats at 8, 12, 16, 20, and 24 weeks of age, and the sera and kidney tissues were obtained at 8, 16, 20, and 24 weeks of age. Results: All PCK rats developed cysts, and the degrees of tubular epithelial cell proliferation and interstitial inflammation increased linearly with age in these model rats relative to the controls. Interstitial fibrosis tended to increase in the PCK rats from 8 to 20 weeks of age, and revealed a peak level at 20 weeks. The urinary L-FABP levels increased linearly with age in the PCK rats, and the levels at 12, 16, 20, and 24 weeks were significantly higher than those in the controls. The urinary levels of L-FABP in the PCK rats correlated significantly with the severity of tubulointerstitial damage; specifically, we observed a significant correlation of the urinary levels at 16 weeks of age with the total kidney volume at 20 weeks. In contrast, both PCK and SD rats exhibited similar serum levels of L-FABP. Conclusion: Urinary L-FABP reflects the progression of tubulointerstitial damage, and therefore, may be a useful marker for monitoring the progression of PKD

Observation of Helium Two-Phase Flows in a Pipe

Applications using cryogenic fluid generally encounter obstacles or complex pipe shapes such as an orifice or a converging-diverging nozzle. Therefore, a flow visualization study on two-phase cryogenic flow passing through a convergent-divergent nozzle or an orifice nozzle installed in a horizontal pipe is carried out to clarify the fundamental characteristics of the transient growth process of helium cloud cavitation. The pipe is filled with pressurized cryogenic liquid and flow immediately occurs when the on-off valve is opened. The transient growth process of the cloud cavitation induced by flow through the throat is observed from high-speed video images. Comparisons between the high-speed observations and the pressure measurements indicates that the transient growth process can be divided into two different steps by taking into account the transition point based on the observational results. Furthermore, it is confirmed that there are two types of the pressure instability in blowdown tests: one is the instability induced by density wave oscillation and the other is that induced by acoustic wave oscillation

Molecular Dynamics Study of the Nucleation of Bubble

In this paper the effect of internal degrees of freedom on the limit of metastability is analyzed by the Molecular Dynamics (MD) method. Oxygen is assumed as the liquid and oxygen molecules are assumed as both monatomic and diatomic molecules. The Lennard{Jones (LJ) potential is used as the intermolecular potential for monatomic molecules and 2 Center Lennard{Jones (2CLJ) potential is used as the intermolecular potential for diatomic molecules. These parameters are determined so that the averaged potentials of the respective molecules are consistent with each other. Simulations are performed at various states and an Equation of State (EOS) of each liquid is obtained. The spinodal lines obtained from the respective EOSs are compared with each other and the effect of molecular orientation in diatomic liquid on the thermodynamic limit of metastability is investigated. Moreover, the kinetic limit of metastability is also investigated and the difference between the monatomic and diatomic liquid oxygen is analyzed