S.J. Gumley

Doctor of Philosophy, Oxford University, October 1981

Tubing Systems for the Measurement of Fluctuating Pressures in Wind Engineering

Summary

An analysis is presented for the design of pneumatic tubing networks incorporated in systems for the measurement of flatting pressures. Such networks should satisfy the dual requirements of unity amplitude transfer function and linear phase transfer function between the pressures at the surface being tested and the remote pressure transducer. The results of the analysis are used in a computer program to aid the design of tubing systems for application to experimental wind engineering. The principle practical limitation is that the wind tunnel reference should be less than about 35 metres per second, although modifications to the analysis are suggested to enable design of tubing systems for the higher tunnel speeds characteristic of gas dynamics and other aerodynamic studies.

The design methods concentrate on single tube systems using restrictors to damp resonant peaks, and on pneumatic averaging systems using manifolds and restrictors. The analysis confirms that such devices can be used to control acoustic resonance's and the computer program enables tube dimensions to be chosen for optimum performance.

Other considerations essential to good design are defined and studied. These include the calibration of networks, the calculation of settling time of pneumatic systems after transients, design of surface tappings, effects of bends in tubing, effects of non-symmetry of averaging manifolds, and the higher frequency behaviour of tubing systems.

Experiments performed both in the Oxford 4m x 2m low speed wind tunnel and by other investigators elsewhere, and extensive literature survey, and numerical work all support the validity of the analysis. It is shown that the dimensions of all tubing elements (including tappings, manifolds, transducer volume and internal pathways in the pressure switch) along with relevant ambient conditions must be included as parameters in the design of tubing systems for the transmission of fluctuating pressures from a wind tunnel model to a remote pressure transducers. If not, large and unquantified errors will appear in experimental tests, especially at higher frequencies.

(No thesis available)