Safe off-design operation of compressors is limited to the region in which the flow is stable. Flow instabilities can be of two types, rotating stall and surge. The first of these subjects the blading to high oscillating stresses while the second may also have a disastrous effect on the whole system of which the compressor is a component. In this paper, the properties of these two types of instability are discussed and some simple criteria for determining system stability are presented.

A one-dimensional analysis of air-lift pump performance in shallow water has been developed which includes the effects of friction and slip between the gas and the liquid. The theory predicts the performance characteristics of these devices successfully, and explains the empirical design rules recommended in earlier publications.

Although uniform inlet conditions are highly desirable and system designers attempt to insure distortion-free flow entering compressors, situations frequently arise in which substantial total pressure, velocity, and angle variations exist at the compressor inlet. Aircraft gas turbines are particularly prone to inlet distortion problems due to changes in aircraft attitude and the effect of the airframe on the inlet flow conditions, but industrial insallations may also suffer from inlet distortion in cases where poorly designed bends have been installed upstream of the compressor. In this paper, problems associated with inlet distortion are discussed and some of the simpler techniques for analyzing the effects of circumferential inlet distortion are presented.

A study has been made of the effects of free stream oscillations on laminar boundary layers of the Howarth type. Detailed measurements of oscillations have been made for the two conditions of Blasius flow and a Howarth flow fairly near separation. It has been found that there are three types of behavior, corresponding to low, intermediate, and high frequencies. Low and very high frequency oscillations are shown to be well described by existing approximate solutions. However, an intermediate frequency region required a new analytic treatment, the results of which do in fact account for the measured flow behavior in that region.

In this paper a vertical downward flow map and a vertical upward flow map are presented. A comparison of the two flow maps shows that significant differences exist between the two directions of flow. The experimental work was performed with an air-water flow in a 11/2-in inside diameter transparent tube.