Minimal Performance Penalty Research Articles

Methods for Enhanced Turbulence Mixing in Supersonic Shear Flows

Supersonic shear layers have inherent low mixing rates due to compressibility effects. Their mixing rate relative to subsonic shear layers can be up to 5 times lower. Several important technological applications which require intense mixing of supersonic flows gave impetus to research aimed to develop methods to enhance mixing in compressible flows with minimal performance penalty. This paper reviews some of these methods applied to both planar shear layers and jets. The methods are arranged in several categories: passive and active control of shear layer instabilities, three dimensional jets, generation of axial vorticity and shock interaction with shear layers. The paper concludes by discussing the importance of the wide range of length-scales in which turbulent mixing occurs.

Small centrifugal pumps for low-thrust rockets

This paper presents the results of a combined analytical and experimental investigation of low specific speed pumps for potential use as components of propellant feed systems for low thrust rocket engines. Shrouded impellers and open face impellers were tested in volute type and vaned diffuser type pumps. Full- and partial-emission diffusers and full- and partial-admission impellers were tested. Axial and radial loads, head and efficiency versus flow, and cavitation tests were conducted. Predicted performance of two pumps are compared when pumping water and liquid hydrogen. Detailed pressure loss and parasitic power values are presented for two pump configurations. Partial-emission diffusers were found to permit use of larger impeller and diffuser passages with a minimal performance penalty. Normal manufacturing tolerances were found to result in substantial power requirement variation with only a small pressure rise change. Impeller wear ring leakage was found to reduce pump pressure rise to an increasing degree as the pump flowrate was decreased.

The distributed V kernel and its performance for diskless workstations

The distributed V kernel is a message-oriented kernel that provides uniform local and network interprocess communication. It is primarily being used in an environment of diskless workstations connected by a high-speed local network to a set of file servers. We describe a performance evaluation of the kernel, with particular emphasis on the cost of network file access. Our results show that over a local network: 1. Diskless workstations can access remote files with minimal performance penalty. 2. The V message facility can be used to access remote files at comparable cost to any well-tuned specialized file access protocol. We conclude that it is feasible to build a distributed system with all network communication using the V message facility even when most of the network nodes have no secondary storage.