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The Study of Flow Phenomena

The Study of Flow Phenomena May, 1932 AIRCRAFT ENGINEERING 127 A Special Small Wind Tunnel of High Accuracy Built in France Described H E small wind tunnel of the Service des Recherches de 1'Aéronautiquc was begun in 1926 and completed early in 1928. Its equipmen t has been designed with a view to pro­ vidin g a highly accurate installation for scientific research on flow phenomena, the most note­ worth y feature being a special system of recording dynamometer s on the electrometric principle, designed by M. Villey, allowing of continuous recordin g of the forces measured. Th e wind tunnel is of the Eiffel type with closed tes t chamber and open jet. The installation allows of a maximum air speed of 50 m./sec. Th e entrance cone is a convergent cone with progressively decreasing cross-section, with a diameter , D., of 1·8 m . (5 ft. 11 in.) at the throat, an d of 4·5 m. (14 ft. 9 in.) (2·5 D.) at the entrance, th e length being 3·1 m. (10 ft. 2 in.) (1·72 D.). I t is made of sheet steel and built-in in the test chamber . A honeycomb, constituted by cells of meta l sheet the lines of which are truncated pyramid s with apices coincident with the axis of th e tunnel, is fitted at the entrance to the cone. Th e test chamber is of reinforced concrete. It ha s two stories above the ground floor. Space for the recording instruments is provided in part of the ground floor, the remainder being fitted u p as a small workshop for the mounting of the models. The cones open into the first floor space. Th e open jet, free on all sides, has a length of 1·7 m. (5 ft. 7 in.) (0·95 D.). The aerodynamic balanc e and the control board for the fan are on thi s floor. The second floor is devoted to the suspension system. Th e exit, also of sheet steel, is in the form of a cone with an included angle of 8 deg. It is flared at the entrance at an angle of 45 deg. to which has a diameter of 3·9 m. (12 ft. 9½ in.) th e air speed as a function of time, continuous th e air stream. The diameter at the entrance is fluctuations amounting to ±1 per cent, with (2·17 D.) the total length is brought up to 13·3 m. th e same as the throat diameter of the entrance occasional increases up to 2 per cent for short (43 ft. 7½ in.). The exit cone is carried on a metal cone, whilst the diameter at the exit is 3·45 m. periods, were revealed in certain tests. Investiga­ framework. (11 ft. 4 in.) (1·9 D.). The length of the cone tion of the angularity of the air flow showed that Th e distribution of the velocity across the jet prope r is 12 metres (39 ft. 4 in.) (6·7 D.) excluding th e stream undergoes a downward deflection wa s investigated in three planes along two dia­ th e flare a t th e entrance and the expanded section of about 0·40 deg. No figure is given for the meter s for velocities of 30 and 45 m./sec . with a t the end to take the fan. With this section, turbulence . ver y satisfactory results, an average uniformity over th e main section of th e je t (excluding a margin Th e excellent working of the electrometric * This description of the French wind tunnel is taken from of about 20 cm. at the periphery) to within 1 per dynamomete r system and, in particular, the high Publication Scientifique et Technique No. 5 of the Service des cen t being obtained. As regards uniformity of efficiency of the bridge voltage regulator, specially Recherches de l'Aéronautique du Ministère de l'Air. developed on a new principle by M. Vernotte, regulatin g the E.M.F. passed to the dynamometers wit h extraordinary accuracy, ensures an accuracy of the recording system to within rather less than 5 per cent. Adding to this error those due to th e fluctuations of velocity, turbulence, mutual interference of the suspension system, stretch of wires, etc., the maximum total error, except in exceptiona l cases, may reach 2 per cent. As a rule , however, the total error does not exceed 1 per cent, as in most cases some of the errors cancel out. Th e power factor of th e Petite Soufflerie is rather low, being about 1·4 for the usual range of air velocities. This is ascribed to the unusual length of the test section and to the unsatisfactory con­ ditions for the return flow due to the shape of the buildin g in which the tunnel is located. Th e efficiency of the tunnel, expressed as the rati o of the pressure H, generating the velocity in the jet, to the difference between the pressure outsid e the tunnel and the pressure in front of th e fan, is practically independent of the velocity. Th e investigation yielded 2·37 as the true mean efficiency of th e tunnel. Th e pressure losses in the entrance cone vary betwee n 2 and 3 per cent of H according to the velocity. Those in the exit cone amount to 58 per cent, instead of the theoretical value, according t o Bernouilli's law, of 93 per cent, the difference bein g ascribed to losses due to the effect of the tes t chamber and to friction and viscosity effects in the cone. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

The Study of Flow Phenomena

Aircraft Engineering and Aerospace Technology , Volume 4 (5): 1 – May 1, 1932

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb029547
Publisher site
See Article on Publisher Site

Abstract

May, 1932 AIRCRAFT ENGINEERING 127 A Special Small Wind Tunnel of High Accuracy Built in France Described H E small wind tunnel of the Service des Recherches de 1'Aéronautiquc was begun in 1926 and completed early in 1928. Its equipmen t has been designed with a view to pro­ vidin g a highly accurate installation for scientific research on flow phenomena, the most note­ worth y feature being a special system of recording dynamometer s on the electrometric principle, designed by M. Villey, allowing of continuous recordin g of the forces measured. Th e wind tunnel is of the Eiffel type with closed tes t chamber and open jet. The installation allows of a maximum air speed of 50 m./sec. Th e entrance cone is a convergent cone with progressively decreasing cross-section, with a diameter , D., of 1·8 m . (5 ft. 11 in.) at the throat, an d of 4·5 m. (14 ft. 9 in.) (2·5 D.) at the entrance, th e length being 3·1 m. (10 ft. 2 in.) (1·72 D.). I t is made of sheet steel and built-in in the test chamber . A honeycomb, constituted by cells of meta l sheet the lines of which are truncated pyramid s with apices coincident with the axis of th e tunnel, is fitted at the entrance to the cone. Th e test chamber is of reinforced concrete. It ha s two stories above the ground floor. Space for the recording instruments is provided in part of the ground floor, the remainder being fitted u p as a small workshop for the mounting of the models. The cones open into the first floor space. Th e open jet, free on all sides, has a length of 1·7 m. (5 ft. 7 in.) (0·95 D.). The aerodynamic balanc e and the control board for the fan are on thi s floor. The second floor is devoted to the suspension system. Th e exit, also of sheet steel, is in the form of a cone with an included angle of 8 deg. It is flared at the entrance at an angle of 45 deg. to which has a diameter of 3·9 m. (12 ft. 9½ in.) th e air speed as a function of time, continuous th e air stream. The diameter at the entrance is fluctuations amounting to ±1 per cent, with (2·17 D.) the total length is brought up to 13·3 m. th e same as the throat diameter of the entrance occasional increases up to 2 per cent for short (43 ft. 7½ in.). The exit cone is carried on a metal cone, whilst the diameter at the exit is 3·45 m. periods, were revealed in certain tests. Investiga­ framework. (11 ft. 4 in.) (1·9 D.). The length of the cone tion of the angularity of the air flow showed that Th e distribution of the velocity across the jet prope r is 12 metres (39 ft. 4 in.) (6·7 D.) excluding th e stream undergoes a downward deflection wa s investigated in three planes along two dia­ th e flare a t th e entrance and the expanded section of about 0·40 deg. No figure is given for the meter s for velocities of 30 and 45 m./sec . with a t the end to take the fan. With this section, turbulence . ver y satisfactory results, an average uniformity over th e main section of th e je t (excluding a margin Th e excellent working of the electrometric * This description of the French wind tunnel is taken from of about 20 cm. at the periphery) to within 1 per dynamomete r system and, in particular, the high Publication Scientifique et Technique No. 5 of the Service des cen t being obtained. As regards uniformity of efficiency of the bridge voltage regulator, specially Recherches de l'Aéronautique du Ministère de l'Air. developed on a new principle by M. Vernotte, regulatin g the E.M.F. passed to the dynamometers wit h extraordinary accuracy, ensures an accuracy of the recording system to within rather less than 5 per cent. Adding to this error those due to th e fluctuations of velocity, turbulence, mutual interference of the suspension system, stretch of wires, etc., the maximum total error, except in exceptiona l cases, may reach 2 per cent. As a rule , however, the total error does not exceed 1 per cent, as in most cases some of the errors cancel out. Th e power factor of th e Petite Soufflerie is rather low, being about 1·4 for the usual range of air velocities. This is ascribed to the unusual length of the test section and to the unsatisfactory con­ ditions for the return flow due to the shape of the buildin g in which the tunnel is located. Th e efficiency of the tunnel, expressed as the rati o of the pressure H, generating the velocity in the jet, to the difference between the pressure outsid e the tunnel and the pressure in front of th e fan, is practically independent of the velocity. Th e investigation yielded 2·37 as the true mean efficiency of th e tunnel. Th e pressure losses in the entrance cone vary betwee n 2 and 3 per cent of H according to the velocity. Those in the exit cone amount to 58 per cent, instead of the theoretical value, according t o Bernouilli's law, of 93 per cent, the difference bein g ascribed to losses due to the effect of the tes t chamber and to friction and viscosity effects in the cone.

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: May 1, 1932

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