Mechanisms of evolution of the propeller wake in the transition and far fields

In the present study the mechanisms of evolution of propeller tip and hub vortices in the transitional region and the far field are investigated experimentally. The experiments involved detailed time-resolved visualizations and velocimetry measurements and were aimed at examining the effect of the spiral-to-spiral distance on the mechanisms of wake evolution and instability transition. In this regard, three propellers having the same blade geometry but different number of blades were considered. The study outlined dependence of the wake instability on the spiralto- spiral distance and, in particular, a streamwise displacement of the transition region at the increasing inter-spiral distance. Furthermore, a multi-step grouping mechanism among tip vortices was highlighted and discussed. It is shown that such a phenomenon is driven by the mutual inductance between adjacent spirals whose characteristics change by changing the number of blades

Analysis of the propeller wake evolution by pressure and velocity phase measurements

In the present study an experimental analysis of the velocity and pressure fields behind a marine propeller, in non-cavitating regime is reported. Particle image velocimetry measurements were performed in phase with the propeller angle, to investigate the evolution of the axial and the radial velocity components, from the blade trailing edge up to two diameters downstream. In phase pressure measurements were performed at four radial and eight longitudinal positions downstream the propeller model at different advance ratios. Pressure data, processed by using slotting techniques, allowed reconstructing the evolution of the pressure field in phase with the reference blade position. In addition, the correlation of the velocity and pressure signals was performed. The analysis demonstrated that, within the near wake, the tip vortices passage is the most important contribution in generating the pressure field in the propeller flow. The incoming vortex breakdown process causes a strong deformation of the hub vortex far downstream of the slipstream contraction. This process contributes to the pressure generation at the shaft rate frequency

Analysis of the propeller wake by pressure and velocity correlation

In the present study an experimental analysis of the velocity and pressure fields behind a marine propeller, in non cavitating regime is reported. Velocity measurements were performed in phase with the propeller angle by using 2D Particle Image Velocimetry (2D-PIV). Measurements were carried out arranging the light sheet along the mid longitudinal plane of the propeller, to investigate the evolution of the axial and the radial velocity components, from the blade trailing edge up to 2 diameters downstream. The pressure measurements were performed at four radial and eight longitudinal positions downstream the propeller model. Measurements of the pressure field were performed at different advance ratios of the propeller. Pressure data, processed by using slotting techniques, allowed to reconstruct the evolution of the pressure field in phase with the reference blade position. In addition, the correlation of the velocity and pressure signals was performed. The analysis demonstrated that, within the near wake, the tip vortices passage is the most important contribution in generating the pressure field in the propeller flow. The incoming vortex breakdown process causes a strong deformation of the hub vortex far downstream the slipstream contraction. This process contributes to the pressure generation at the shaft rate frequency

Role of Pax2 in apoptosis resistance and proinvasive phenotype of Kaposi's sarcoma cells.

In this study, we found that Kaposi's sarcoma cells but not human microvascular endothelial cells expressed PAX2, a gene coding for a transcription factor involved both in organogenesis and tumorigenesis. Moreover, Pax2 was frequently expressed, on spindle-shaped cells, in Kaposi's sarcoma lesions. We cloned PAX2 from Kaposi's sarcoma cells and obtained antisense and sense DNA. Transfection of Kaposi's sarcoma cells with antisense DNA, which suppressed Pax2 protein expression, reduced cell growth and survival and enhanced the sensitivity of Kaposi's sarcoma cells to apoptosis induced by serum deprivation or vincristine treatment. In addition, antisense transfection inhibited the cell motility, the invasion of Matrigel, and the spindle shape morphology, which are characteristics of Kaposi's sarcoma cells. Moreover, the alphavbeta3 integrin, known to be involved in tumor invasion, was down-regulated. To evaluate the possible role of Pax2 expression in the endothelial origin of Kaposi's sarcoma cells, human microvascular endothelial cells were transfected with sense DNA. Endothelial cells transfected with sense PAX2 acquired spindle shape morphology, showed enhanced motility and Matrigel invasion, and displayed an enhanced expression of alphavbeta3 integrin. In conclusion, the expression of Pax2 by Kaposi's sarcoma cells correlated with an enhanced resistance against apoptotic signals and with the proinvasive phenotype. Moreover, PAX2-transfected endothelial cells acquired a phenotype resembling that of Kaposi's lesional cells, suggesting a role of this embryonic gene in tumorigenesis

An experimental investigation into the influence of installed chevron jet flows on wall-pressure fluctuations

Jet-surface interaction represents a significant community noise problem for the installation of modern ultra-high bypass ratio turbofan engines. The use of chevron nozzles is known to reduce low-frequency jet mixing noise by increasing the mixing rate close to the nozzle. It is currently unknown, however, to what extent such a nozzle lip treatment affects the Kelvin-Helmholtz instability, generated in the vicinity of the wing, which will modify the source of jet-surface interaction noise. To clarify the physics of the jet-surface interaction noise source, an extensive experimental investigation was conducted using the Flight Jet Rig in the anechoic chamber of the Doak Laboratory, at the University of Southampton. Various measurements were carried out on a round and a chevron single stream, unheated subsonic jet, both in an isolated configuration and installed beneath a 2D NACA4415 airfoil "wing". The wall-pressure field on the wing surface was investigated using a pair of miniature wall-pressure transducers and a set of ultra-thin precision microphones. These sensors were flush-mounted in both the stream-wise and span-wise directions on the pressure side of the wing and the unsteady wall-pressure data were analysed in the time and frequency domains. The far-field noise results show significant broadband noise reduction by the chevron jet. This is further evidenced by a reduction in the span-wise correlation length along the wing trailing edge over a wide range of frequencies. Significant reduction of the tonal trapped wave energy is also observed