From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from a document discussing fluid dynamics, pressure in nozzles, and the calculation of mass discharge.
| Identifier | ExFiles\Box 36\1\ scan 022 | |
| Date | 1st February 1919 guessed | |
| Contd. -10- forces a pressure in the vena contracta greater than the external pressure, and equal in fact to the throat pressure in the ideal nozzle. In other words, the expansion down to the external pressure is not completed at the vena contracta, but the cross section of the stream at which it is completed, is greater than that of the vena contracta and may even be greater than that of the orifice: The jet takes the form:- Hence under these circumstances the discharge is the same as if the external pressure were equal to the throat pressure in the ideal nozzle (which is a definite fraction of the internal pressure) and cannot be increased by reducing the external pressure. Making the substitution D = { 2 / (n + 1) } ^ (n / (n-1)) in the first expression for W, we obtain W = CA * sqrt( gn. * (P1 / V1) * { 2 / (n + 1) } ^ ( (n+1) / (n-1) ) ) for the mass of discharge per second when the external pressure bears to the internal pressure a lesser ratio than .527 (i.e. for air) This assumes adiabatic expansion. On substituting n = 1.405 this reduces to W = CA * sqrt( 15.1 * (P1 / V1) ) and since P1 V1 = 53.2 T1 | ||