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).
Critique of a test rig's methodology for measuring water flow, air flow, air speed, and temperature.
| Identifier | ExFiles\Box 149a\2\ scan0257 | |
| Date | 6th November 1935 | |
| -2- Hs{Lord Ernest Hives - Chair}/Std.14/KW.6.11.35. Water flows are measured by means of a calibrated water meter. Air flows are measured in two ways - the actual air velocity at approx. the centre of the duct in front of the matrix is measured by means of a pitot head, while the "equivalent car speed" is measured by means of a gauge which records the sum of the dynamic and static heads at a similar position in the duct. The ducting, fan and matrix, are arranged so that there is a short length of duct between the matrix and the fan, the matrix being on the delivery side of the fan. Criticisms of Rig. (1) We do not think it is advisable to use a closed circuit system unless a large length of ducting and gauze screens or matrices are used to straighten out the air flow which will be very turbulent. (2) For the same reason we do not think that the matrix to be tested should be on the delivery side of the fan. Turbulent flow results and it is practically impossible to measure the air speed accurately. (3) The methods of measuring air speeds are satisfactory only if turbulence and unequal air disturbances are avoided. This applies more particularly to the measurement of actual air velocity. During the tests it was shown by moving the pitot head across the air stream that the air speed readings varied over a large range, even giving negative readings in some positions, due to swirl set up by the fan. (4) The range of air speeds obtainable is insufficient, the maximum being equivalent to a car speed of approximately 63 m.p.h. (5) The methods of measuring air and water temperatures are not sufficiently accurate. Remote reading thermometers of the type used are not sufficiently sensitive and are subject to errors which vary from time to time. | ||