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The Berlin oil channel for drag reduction research 总被引:3,自引:0,他引:3
D. W. Bechert G. Hoppe J. G. Th. van der Hoeven R. Makris 《Experiments in fluids》1992,12(4-5):251-260
For drag reduction research an oil channel has been designed and built. It is also well suited for investigations on turbulent flow and in particular on the dynamics of the viscous sublayer near the wall. The thickness of the viscous sublayer (y
+= 5) can be varied between 1 and 4 mm. Surfaces with longitudinal ribs (riblets), which are known to reduce drag, can have fairly large dimensions. The lateral spacing of the ribs can lie between 3 and 10 mm, as compared to about 0.5 mm spacing for conventional wind tunnels. It has been proved by appropriate tests that the oil channel data are completely equivalent to data from other facilities and with other mean flow geometries. However, the shear stress data from the new oil channel are much more accurate than previous data due to a novel differential shear force balance with an accuracy of ±0.2%. In addition to shear stress measurements, velocity fluctuation measurements can be carried out with hot wire or hot film probes. In order to calibrate these probes, a moving sled permits to emulate the flow velocities with the fluid in the channel at rest. A number of additional innovations contribute to the improvement of the measurements, such as, e.g., (i) novel adjustable turbulators to maintain equilibrium turbulence in the channel, (ii) a bubble trap to avoid bubbles in the channel at high flow velocities, (iii) a simple method for the precision calibration of manometers, and (iv) the elimination of (Coulomb) friction in ball bearings. This latter fairly general invention is used for the wheels of the calibration unit of the balance. The channel has a cross section of 25 × 85 cm and is 11 m long. It is filled with about 4.5 metric tons of baby oil (white paraffine oil), which is transparent and odorless like water. The kinematic viscosity of the oil is v = 1.2×10–5 m2/s, and the highest (average) velocity is 1.29 m/s. Thus, the Reynolds number range (calculated with the channel width, 0.25 m) lies between 5,000 and 26,800 for fully established turbulent flow.The material of this paper has been partly presented at the 5th European Drag Reduction Working Meeting 15th and 16th November 1990, London 相似文献
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Felix Hoppe 《Fresenius' Journal of Analytical Chemistry》1863,2(1):454-456
Ohne Zusammenfassung 相似文献
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Using single crystal data the occurence of the K2NaCrF6 type of structure for Cs2NaInF6 (a = 8.905 Å) has been confirmed and xF determined to be xF = 0.229; in consequence: In–F = 2.039 Å [430 (hkl) with h + k = 2n and h = 0 to 7; R = 11.1%; Mo? Kα.]. The Madelung Part of Lattice Energy is calculated and discussed in detail. 相似文献