The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed which accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter which accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.
For future efficient and light aero-engines it is essential to develop optimized lubrication systems. These systems require increased temperature and pressure levels in combination with high rotational speeds without compromising the high level of safety and reliability. This applies especially to the bearing chamber as one of the most challenging components of the oil system. Due to the mixing of the sealing airflow and the lubrication oil a complex air- / oilflow is formed inside the chamber. In order to gain a deeper insight into the physical phenomena of the flow inside the bearing chamber a multiyear fundamental study has been initiated. This study focuses for the first time on detailed measurements of the local air- / oilflow field. In the first phase of the project experiments have been carried out to determine the rotating and swirling pure airflow. Hence a specially adapted three dimensional Laser Doppler Anemometry (LDA) system was used to resolve the complex flow. The results revealed that different flow patterns occurred depending on the ratio between the shaft speed and the airflow rate. In the near future it is aimed to resolve the droplet flow also to provide a complete knowledge of the air- / oilflow in bearing chambers.
Increasing the efficiency of modern jet engines does not only imply to the mainstream but also to the secondary air and oil system. Within the oil system the bearing chamber is one of the most challenging components. Oil films on the chamber walls are generated from oil droplets, ligaments, or film fragments, which emerge from bearings, seal plates and shafts, and enter the bearing chamber with an angular momentum. Furthermore, shear forces at its surface, gravity forces, and the design of scavenge and vent ports strongly impact the behavior of the liquid film. The present paper focuses on the experimental determination of the film thickness in various geometries of bearing chambers for a wide range of engine relevant conditions. Therefore, each configuration was equipped with five capacitive probes positioned at different circumferential locations. Two analytical approaches are used for a comprehensive discussion of the complex film flow.
The pharmacokinetics and applicability of aerosol amphotericin B administrations were studied in 40 neutropenic patients and 4 healthy volunteers. Particle size was measured and pulmonary deposition was demonstrated by radioisotope studies. Inhalations were easy to administer and were well tolerated, with minimal systemic absorption of the drug.Invasive pulmonary aspergillosis (IPA) is a serious fungal infection in immunocompromised or neutropenic patients (3). The incidence of and mortality from IPA vary depending on the degree and duration of immunosuppression or neutropenia. After bone marrow transplantation (BMT), mortality can be as high as 95% (3, 12). Various strategies for systemic or topical prophylaxis of IPA have been developed (4,6,8,13,14,16,17), but they are still unsatisfactory (1,5,18). The use of aerosol amphotericin B (aeroAmB) is a promising approach. In a rat model, aeroAmB was effective as prophylaxis for IPA (15), and high concentrations of amphotericin B (AmB) were achieved in the lung tissues of these animals (10). Prophylactic aeroAinB has been used successfully in neutropenic patients, but little is known about the distribution and pharmacokinetics of aeroAmB in humans (2, 9). The goals of the present study were to determine the particle size, organ distribution, and pharmacokinetics of aeroAmB and to evaluate its clinical applicability. At first, the particle size of aeroAmB was determined by using a Phase-Doppler-Particle-Analyser (Aerometrics, Mountain View, Calif.), which allowed noninterfering optical measurements of individual particles at a size range of 0.53 to 18.5 ,um. For the measurements 10 mg of the AmB preparation for intravenous administration (Squibb, Munich, Federal Republic of Germany) were diluted with sterile water to a total volume of 5 ml and were placed into a RespirGard II nebulizer (Marquest, Englewood, Colo.). An air pressure of 1.8 x 105 Pa was used to drive the nebulizer, and particle sizes were measured at the mouthpiece of the device. A narrow particle size distribution was demonstrated, with a mean diameter of 2.6 ,um; 10% of the particles had a diameter of less than 0.9 ,um and 90% had a diameter of less than 4.2 ,um. The mass median diameter was 4.8 pum (Fig. 1)
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