Shu Fujimoto

Large Eddy Simulation of Film Cooling Flows Using Octree Hexahedral Meshes

Today, high temperatures are needed for the inlet gas of turbines to increase the efficiency of gas turbines. The vanes and blades of a turbine that are exposed to hot gas must be cooled, and film cooling is now being widely applied to gas turbines because of its high cooling effectiveness. Recently, numerous researchers have conducted numerical simulations of film cooling flows using Reynolds-averaged Navier–Stokes (RANS) simulation, detached eddy simulation (DES), and large eddy simulation (LES) turbulence models, along with structured and/or unstructured meshes. In fact, for cooling designers, both the prediction accuracy and turnaround time (TAT) of their mesh generations are important to speedily and repeatedly optimize the locations of film cooling holes and shapes. Several researchers have examined the prediction accuracy and effectiveness of film cooling flows in case of RANS in order to minimize the TAT of mesh generation such as for unstructured meshes. However, few papers have considered LES.In this paper, the open-source computational fluid dynamics (CFD) toolkit OpenFOAM [17] is used as the solver, and LES is used to numerically simulate the film cooling flow into the zero-pressure gradient cross-flow on a flat plate from cylindrical holes, which is one of the most typical and basic test cases. LES is used because of its ability to capture the flow unsteadiness and non-uniformity observed in film cooling flows. In addition, surface-adjusted octree hexahedral meshes, which are relatively easy to generate automatically are used. The mesh generation tool used in this study is snappyHexMesh, which is included in OpenFOAM. The experimental data presented by Sinha et al. [15] are used. Because the film cooling effectiveness strongly depends on certain parameters and conditions, those of the simulated film cooling flow are set to the experimental parameters and conditions as closely as possible. In this study, the density ratio DR is set to 2.0, and the blowing ratio BR is set to 0.5 and 1.0 with the steady cross-flow inlet. In addition, a case is considered where BR = 0.5 (DR = 2.0), with an unsteady turbulent cross-flow inlet.In the case of LES, the results obtained using the octree hexahedral meshes are compared with those of the experiment and my previous film cooling study (Fujimoto [32]), which was conducted using multiblock structured meshes. The results show that the prediction accuracy using the octree hexahedral meshes is equivalent to that using the multiblock structured meshes, even though the mesh generation TAT is significantly smaller.Copyright

Study on Advanced Internal Cooling Technologies for the Development of Next-Generation Small-Class Aircraft Engines

An innovative internal cooling structure named multislot cooling has been invented for high-pressure turbine (HPT) nozzles and blades. This cooling structure has been designed to be simple and inexpensive and to exhibit good cooling performance. In order to confirm the cooling performance of this structure, test pieces of dummy turbine nozzles were manufactured. Three geometric parameters (width of slots, overall height of cooling channel, and height of jet impingement) are associated with these test pieces. The cooling performance tests were conducted by using these test pieces for several Reynolds numbers of the mainstream hot gas [2.2 × 10 5 -3.4 × 10 5 ] and cooling airflow [3 × 10 3 -1 × 10 4 ]. Infrared images of the heated surfaces of the test pieces were captured for every Reynolds number in the tests, and then the distributions of the cooling effectiveness were obtained. Simultaneously the pressure losses were measured, This paper describes the hot gas flow tests performed to confirm the effects of the geometric parameters on the cooling performance and pressure loss, and to obtain data of Nusselt number and pressure loss coefficient for the design of turbine nozzles in the future by applying this new cooling structure to next-generation small-class aircraft engines. Additionally a preliminary analysis of airfoil cooling was performed to evaluate both cooling performance of conventional impingement cooling and multislot cooling when applied to a HPT nozzle. As a result it was found that the multislot cooling is well applicable to cooling of HPT airfoils.

Experimental Study on the Cooling Performance of a Turbine Nozzle With an Innovative Internal Cooling Structure

An innovative cooling structure named multi-slot cooling was invented for high-pressure turbine (HPT) nozzles and blades. This cooling structure has been designed to be simple, inexpensive, and to exhibit good cooling performance. In a previous study (GT2008-50444), the basic design data on the cooling effectiveness and pressure loss coefficients for HPT cooling design were obtained by using simple test pieces. In this study, the cooling performance of the HPT nozzle with a multi-slotted cooling structure in a cascade was reported. First, the HPT nozzle with a multi-slotted cooling structure and its outer profile were selected; its cooling structure was designed by using the data in the previous study and trial-and-error method. Subsequently, ceramic casting cores and casting nozzles were manufactured by way of trial. Furthermore the cooling performance test for the multi-slotted cooling nozzle (TEST #1) in an annular sector cascade test rig was conducted, and the cooling effectiveness fields and pressure loss data were obtained. In addition, the measurement test for determining the heat transfer coefficient on the nozzle (TEST #2) and that for determining the film cooling effectiveness on the nozzle (TEST #3) were conducted. And then, cooling performance of the multi-slotted cooling nozzle was evaluated by using these data. As a result, for the typical configuration, it was confirmed that the basic design data obtained in the previous study are applicable to designing nozzles with multi-slot cooling by introducing a minor modification and the cooling performance of multi-slot cooling is equivalent to that of the conventional cooling under the test condition; consequently, it was confirmed that the multi-slot cooling is well applicable to the cooling of actual HPT airfoils except in the case that its configuration is significantly changed.© 2009 ASME