Paper 1: Measurement and Recording of Transient Pressures in Unsteady Flow

Abstract

The problems in developing satisfactory measuring techniques for studying pressure transients can best be considered under three headings. First, there are the problems concerned with obtaining a continuous electrical signal which represents the value of the pressure at any instant. Suitable devices include diaphragm-type instruments and piezo-electric types and these may have quite different characteristics. The former are generally more suitable for low pressure and low frequency applications, while the latter can be used for very short time transient measurements at higher pressures. The types of error which are most likely depend both on the application and the characteristics of the primary transducer unit chosen. A second group of problems is concerned with the recording or analysis of the electrical signals from the pressure transducer. These include errors associated with chart-type recordings, cathode-ray oscillograph recording, statistical sampling and filters, and for frequency analysis. The importance of various transient and steady-state recording errors and the type of application will again determine which is the most suitable equipment to choose. A final group of problems is associated with the calibration of the measuring system finally selected and the interpretation of the measurements. There are several difficulties and sources of error here since it is not always possible to perform basic calibration under the same conditions as the experimental measurements.