No abstract

The design of most aerodynamic surfaces, as for example the helicopter rotor, is based essentially on quasi-steady theories. However, the dynamics of a rotating blade introduce unexpected fluctuations and overshoots of properties like lift, drag, etc. The phenomenon of unsteady stall is intimately connected with the development of an oscillating boundary layer and separation. Experimental investigation of such flows was undertaken by a method of visualization developed especially for the study of laminar or turbulent boundary layers and separation. The method captures the instantaneous two-dimensional flow field, including regions of separated flow, and provides accurate quantitative information. Laser-doppler anemometer measurements complement the optically obtained data. Results reveal that separation responds with time-lag to external disturbances, in agreement with unsteady stall data. Oscillating outer flows result in displacement of the point of separation and, under certain conditions, the Despard & Miller (1971) criterion was found to hold. Earlier theoretical models of separation are confirmed qualitatively and for the early stages of the transient phenomena. The findings provide physical insight and quantitative data that may help explain the phenomenon of unsteady stall and unsteady separation.

No abstract

No abstract

The scope of paper is to examine whether the recent financial crisis has had any impact on international capital markets and more precisely on the 4 primary international stock markets of England, France, Japan, the United States and Greece. The research is based on the use of the Financial Stress Index (FSI) from July 2005 until December 2008 and August 2009. Research results showed that the recent financial crisis has had a negative impact on all examined markets, with the Tokyo stock exchange being the one mostly affected. It was, also, found increased variability of performances following the start of the financial crisis, a fact that is indicative of the presence of conditional heteroscedasticity. As far as the Greek market is concerned, the recent financial crisis has not affected in general the credit expansion towards enterprises and households; however, it has affected the credit expansion to enterprises and households on a case-to-case basis