Laser Doppler anemometry experiment

Figure 9.10(a) compares velocity profiles obtained in a dynamic NMR microscopy experiment performed at 30°C using 1.6 x 10 Da poly (ethylene oxide) (PEO) dissolved in water at a range of concentrations between 0.5% and 4.5% (w/v) where the solution is forced through a Teflon capillary with internal diameter 700 jum [17, 18]. A transition from Newtonian to non-Newtonian behaviour is observed as the concentration increases, an effect that is consistent with a measured value of (p of around 0.5%. Pressure heads of up to 21 atm were used to drive the polymer solution from the header tank reservoir through the capillary. A power law fit to the high concentration velocity profiles yields an exponent of 0.4, similar to that found in laser Doppler anemometry experiments using polyethylene melts [127]. 

Since 1995 the experimental work has been concentrated on preparation of the second phase of investigations in water (WAMIX II) and providing a comparable testing arrangement in sodium (NAMIX experiment). For measurements of local velocity (see Fig. 1) and temperature as well as their fluctuations in the WAMIX test-section, laser Doppler anemometry and resistance thermometry are applied in a modified test-section. To make these measuring techniques applicable, some modifications on the water loop were also made. 

Recent experiments on pipe turbulence or with planar mixing layers (Ambari and Guyon, 1982 Scharf, 1985), using stroph-ometry or laser Doppler anemometry, do suggest that polymer additives can suppress certain small scales. But detailed proposals, such as equation (25), for the truncation, remain to be checked. 

Figure 18.18 (left) exhibits the calculated gas flow field from an individual gas jet at atomization pressure po = 0.5 MPa (polPa = 5). The diameter at the nozzle exit is 3 mm. The simulation is conducted based on the 2D axisymmetric geometry (see Fig. 18.15). Five cells with shocks can be found after the nozzle exit. Figure 18.18 (right) exhibits the velocity distribution at the centre line of the jet. The experimental data were obtained by laser Doppler anemometry (LDA) [26]. A good agreement is achieved between experimental data and numerical simulation results, for example in the location and number of shock cells, the calculated length of the supersonic core of the jet and the decay rate of the gas velocity in the subsonic region. Only the amplitudes of the velocity fluctuation differ between experiment and simulation the peak in velocity values behind the shock is more intense than those measured in the experiment. The experimental deviation may be caused by the behaviour of the tracer particles used for LDA measurements. These small but still inertial tracer particles cannot follow the steep velocity gradients across a shock exactly. The k-co SST model indicates a better performance than the standard k-e model.

Figure 4.5 shows results of both experiment and CFD in a swirl tube with a cylindrical body (Peng et ah, 2002). In the left-hand figure a series of measurements are shown where the boundary between the up- and downwardly directed flow has been determined using laser-Doppler anemometry (LDA, we... 

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