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Volume 79 - February 1975

Contents

Page 4 of 9

Technical notes

  • Vortex shedding characteristics of eccentrically mounted prisms

  • A. S. Ramamurthy, K. Subramanya, N. Souriyal
  • Published online by Cambridge University Press:
    04 July 2016, pp. 42-44

  • Vortex shedding is an important factor in the design of structural elements subject to flow induced vibrations. Several reviews have appeared on this topic. However, in model testing, the vortex shedding frequency of a bluff body may change when the model mounting is eccentric (Fig. 1). This has not been studied in detail. Available information in this regard is restricted to the data of Shaw whose tests were conducted in a towing tank.

    This technical note presents experimental data on the vortex shedding characteristics of equiangular prisms (Fig. 2) mounted eccentrically in a wind tunnel. Explanations for the possible flow behaviour are also presented.

Reviews

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Technical note

  • The choked jet flowing into a stationary atmosphere

  • J. C. Gibbings
  • Published online by Cambridge University Press:
    04 July 2016, pp. 368-370

  • A previous discussion of the expanding flow of a choked axi-symmetric jet into a stationary atmosphere drew attention to the differences between various existing sets of observations and between observation and analysis. One reason advanced for these discrepancies was the influence of the mixing region at the edge of the jet while another was the degree of uniformity and steadiness of the flow at exit from the nozzle.

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Technical Notes

  • The effect of secondary flow velocity profile on the static performance of low speed ejector thrust augmenters

  • C. N. Jones
  • Published online by Cambridge University Press:
    04 July 2016, pp. 510-517

  • Jet thrust at low speeds is notoriously inefficient, and ejectors have often been proposed as thrust augmenters in the hope of increasing the mass flow and momentum flux for a given expenditure of energy. Henri Coanda reported the development of a successful thrust augmenter (the Coanda nozzle) for the propulsion of ambulance sledges in Russia during the Second World War, and useful thrust augmentations with this were reported by Sproule and Robinson and Reba. These reports raised interest in the technical press, and large scale experimental programmes have been mounted by Lockheed Aircraft, Cornell Aeronautical Laboratory, Hiller Aircraft and others. However, no clear conclusions seem to have resulted. Although recent published analyses of the performance of ideal ejector thrust augmenters stress the importance of size and energy input, no detailed analysis of the many different definitions of thrust augmentation which appear in the literature, or of their practical implications, seems to be available.

Technical note

  • Some measurements of the dynamic properties of mixed, carbon fibre reinforced, plastic beams and plates

  • R. G. White
  • Published online by Cambridge University Press:
    04 July 2016, pp. 318-325

  • The search for new materials for use in high performance structures, such as aircraft, has resulted in the development of carbon fibre reinforced plastics, CFRP. Parts of aircraft have been manufactured from CFRP, particularly in areas where high acoustic loads are experienced. The acoustic fatigue resistance of fibre reinforced structures is therefore of considerable interest. If the acoustic fatigue problem is to be studied, the response of such structures to acoustic excitation must be predicted and for this, knowledge of material characteristics is essential.

    The first stage in the investigation of structural materials is to obtain measured values of the dynamic properties. Data of interest to structural dynamicists are moduli of elasticity and damping information.

Reviews

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Technical notes

  • On the stability of a dirigible body

  • P. C. Rath, S. M. Sharma
  • Published online by Cambridge University Press:
    04 July 2016, pp. 179-182

  • When the Magnus effects are completely absent the oscillatory motion of a dirigible body is said to be plane-yawing. Such bodies are stabilised by attaching fins or control vanes at their rear ends. Initial choice of the fin-size is made, depending on a static stability condition: JM < O, where JM is the normalised overturning aerodynamic moment coefficient. A proper fin-size requirement should normally be found from an appropriate dynamic stability condition. Under the very severe aerodynamic restriction stipulated above, one would expect, if the static stability condition is liberally satisfied by attaching over calibre fins, perhaps dynamic stability requirements could be met. This, however, may considerably reduce the ballistic range of the body. One would, therefore, need some sort of an upper majorant for JM consistent with the dynamic stability of the body and this should be a function of the other associated aerodynamic forces. In the present note a suitable majorant function for JM has been worked out. For this purpose, the aerodynamic coefficients are assumed to be slowly ranging functions of the path length as is usually stipulated. The stability problem has been solved using certain known results in the oscillation theory of differential equations.

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Page 4 of 9