A conjugate heat transfer analysis methodology has been defined and applied to an Air Force film cooled turbine vane consisting of 648 cooling holes. An unstructured computational mesh was used to model both the fluid and metal sides of the turbine vane. A summary of the numerical methods employed by Code Leo is provided along with a description of the coupling procedure employed between the fluid and heat conduction computations. Numerical simulations were conducted at multiple mesh resolutions to assess accuracy and repeatability. A detailed review is presented for the numerical solution obtained from a fine mesh consisting of 24 million elements (8 million solid, 16 million fluid) covering all 648 film holes. Results showed that cooled air from the film holes formed a protective layer around the airfoil surfaces and endwalls as intended. Low metal temperatures were present not only on the external surfaces exposed to hot gas, but also around the entrances to the film cooling holes. Cooled air was also observed to pile up along the pressure surface at mid-span. Solution convergence was achieved in approximately 15,000 iterations and 100 hours elapsed time on a dual-socket Intel E5504 workstation. The combination of fast turnaround time with accurate metal temperature prediction will enable conjugate heat transfer analysis to be easily incorporated into routine design processes to better address durability goals.

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A low pressure turbine blade was designed to produce a 17% increase in blade loading over an industry-standard airfoil using integrated flow control to prevent separation. The design was accomplished using two-dimensional CFD predictions of blade performance coupled with insight gleaned from recently published work in transition modeling and from previous experiments with flow control using vortex generator jets (VGJs). In order to mitigate the Reynolds number lapse in efficiency associated with LPT airfoils, a mid-loaded blade was selected. Also, separation predictions from the computations were used to guide the placement of control actuators on the blade suction surface. Three blades were fabricated using the new design and installed in a two-passage linear cascade facility. Flow velocity and surface pressure measurements taken without activating the VGJs indicate a large separation bubble centered at 68% axial chord on the suction surface. The size of the separation and its growth with decreasing Reynolds number agree well with CFD predictions. The separation bubble reattaches to the blade over a wide range of inlet Reynolds numbers from 150,000 down to below 20,000. This represents a marked improvement in separation resistance compared to the original blade profile which separates without reattachment below a Reynolds number of 40,000. This enhanced performance is achieved by increasing the blade spacing while simultaneously adjusting the blade shape to make it less aft-loaded but with a higher peak cp. This reduces the severity of the adverse pressure gradient in the uncovered portion of the modified blade passage. With the use of pulsed VGJs, the design blade loading was achieved while providing attached flow over the entire range of Re. Detailed phase-locked flow measurements using three-component PIV show the trajectory of the jet and its interaction with the unsteady separation bubble. Results illustrate the importance of integrating flow control into the turbine blade design process and the potential for enhanced turbine performance.

SynopsisPoly(ethy1ene terephthalate) containing hexabromobenzene, tricresyl phosphate, or a combination of triphenyl phosphate and hexabromobenzene, pentabromotoluene, or octabromobiphenyl was extruded or spun at 280°C into monofilaments or lowdenier yarn, respectively. Only combinations of the phosphorus-and halogen-containing compounds resulted in flame-retardant poly(ethy1ene terephthalate) systems, without depreciating their degree of luster and color quality. The melting temperature, the reduced Viscosity, and the thermal stability above 400°C of these flame-retardant systems were in most cases comparable to those of poly(ethy1ene terephthalate) itself. Phosphorus-bromine synergism was proposed with flame inhibition occurring mostly in the gas phase.

An experimental procedure is outlined to examine the potential of thermoplastic sheets in draw forming. Experiments carried out on a variety of materials indicate that the following requirements must be fulfilled for a thermoplastic sheet to be cold formable: (1) The glass transition of polymer should be above ambient temperature and above the temperature of forming, (2) tensile elongation at break should equal or exceed 30%, (3) ratio of tensile to compressive yield stress should equal or exceed 1.6 and (4) sheet must not yield locally (neck) when strained in tension. An experimental method has been developed to determine the compressive, friction and bending forces which oppose the drawing force exerted by the punch. It is shown that the compressive force is, in most cases, largest. A stress analysis is carried out leading to an expression correlating the maximum depth of draw as a function of basic properties of sheets such as tensile strength (St*) and compressive yield stress (Sc). The effect of rolling on drawability is examined and interpreted in terms of the ratio St*/Sc. The cold formed items have a lower heat distortion temperature than their thermoformed counterparts.