Band 28, Heft 2

Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

This paper presents the effectiveness of perforated arc tabs to enhance the mixing of axi-symmetric subsonic and sonic jets. Measurements of centerline velocity decay and velocity distribution in the directions along and normal to the tabs were carried out in the controlled jet, from a convergent nozzle with two arc-tabs placed at diametrically opposite locations at the nozzle exit, were carried out. Similar measurements were done for the uncontrolled jets, for comparison. Mach 0.6, 0.7, 0.9 and sonic jet at nozzle pressure ratios 2 and 3 were tested. It is found that the perforated arc-tabs greatly enhance the jet mixing of both subsonic and sonic jets. The core length comes down by 65%, 66%, 62% and 75%, for Mach 0.6, 0.7, 0.9 and correctly expanded Mach 1 jets, respectively.

In the last decades the main efforts of aero engine designers have been focused on the possibility to increase maximum attainable thrust while reducing specific fuel consumption. As consequence, very high bypass ratio turbofan engines have been developed, ensuring the specific fuel consumption reduction by means of the increased propulsion efficiency. However this way to operate cannot be followed indefinitely, and some new techniques need to be thought. In this work it has been considered the possibility to increase the efficiency of the engine modifying the working thermal cycle. In fact, by means of the development of a numeric thermodynamic code, it has been simulated the thermal behavior of a turbofan engine in which the practices of intercooling and regeneration are introduced.

Both jet impingement and forced convection are attractive cooling mechanisms widely used in cooling gas turbine blades. Convective heat transfer from impinging jets is known to yield high local and area averaged heat transfer coefficients. Impingement jets are of particular interest in the cooling of gas turbine components where advancement relies on the ability to dissipate extremely large heat loads. Current research is concerned with the measurement and comparison of both jet impingement and forced convection heat transfer in the Reynolds number range of 10,000 to 30,000. This study is aimed at experimentally testing two different setups with forced convection and jet impingement in rotating turbine blades up to 700 RPM. This research also observes Coriolis force and impingement cooling inside the passage during rotating conditions within a cooling passage. Local heat transfer coefficients are obtained for each test section using thermocouple technique with slip rings. The cross section of the passage is 10 mm × 10 mm without ribs and the surface heating condition has enforced uniform heat flux. The forced convection cooling effects were studied using serpentine passages with three corner turns under different rotating speeds and different inlet Reynolds numbers. The impingement cooling study uses a straight passage with a single jet hole under different Reynolds numbers of the impingement flow and the cross flow. In summary, the main purpose is to study the rotation effects on both the jet impingement and the serpentine convection cooling types. Our study shows that rotation effects increase serpentine cooling and reduce jet impingement cooling.

Dental air turbine handpieces have been widely used in clinical dentistry for over 30 years, however, little work has been reported on their performance. In dental air turbine handpieces, the types of flow channel and turbine blade shape can have very different designs. These different designs can have major influence on the torque, rotating speed, and power performance. This research is focused on the turbine blade and the flow channel designs. Using numerical simulation and experiments, the key design parameters which influence the performance of dental hand pieces can be studied. Three types of dental air turbine designs with different turbine blades, nozzle angles, nozzle flow channels, and shroud clearances were tested and analyzed. Very good agreement was demonstrated between the numerical simulation analyses and the experiments. Using the analytical model, parametric studies were performed to identify key design parameters.