Erlendur Steinthorsson

Effect of Squealer Tip on Rotor Heat Transfer and Efficiency

Calculations were performed to simulate the tip flow and heat transfer on the GE-E 3 first-stage turbine, which represents a modern gas turbine blade geometry. Cases considered were a smooth tip, 2 percent recess, and 3 percent recess. In addition, a two-dimensional cavity problem was calculated. Good agreement with experimental results was obtained for the cavity calculations, demonstrating that the k-ω turbulence model used is capable of representing flows of the present type. In the rotor calculations, two dominant flow structures were shown to exist within the recess. Also areas of large heat transfer rate were identified on the blade tip and the mechanisms of heat transfer enhancement were discussed. No significant difference in adiabatic efficiency was observed for the three tip treatments investigated.

Conjugate Heat Transfer Effects on a Realistic Film-Cooled Turbine Vane

A conjugate heat transfer solver has been developed and applied to a realistic film-cooled turbine vane for a variety of blade materials. The solver used for the fluid convection part of the problem is the Glenn-HT general multiblock heat transfer code. The solid conduction module is based on the Boundary Element Method (BEM), and is coupled directly to the flow solver. A chief advantage of the BEM method is that no volumetric grid is required inside the solid – only the surface grid is needed. Since a surface grid is readily available from the fluid side of the problem, no additional gridding is required. This eliminates one of the most time consuming elements of the computation for complex geometries. Two conjugate solution examples are presented - a high thermal conductivity Inconel nickel-based alloy vane case and a low thermal conductivity silicon nitride ceramic vane case. The solutions from the conjugate analyses are compared with an adiabatic wall convection solution. It is found that the conjugate heat transfer cases generally have a lower outer wall temperature due to thermal conduction from the outer wall to the plenum. However, some locations of increased temperature are seen in the higher thermal conductivity Inconel vane case. This is a result of the fact that film cooling is a two-temperature problem, which causes the direction of heat flux at the wall to change over the outer surface. Three-dimensional heat conduction in the solid allows for conduction heat transfer along the vane wall in addition to conduction from outer to inner wall. These effects indicate that the conjugate heat transfer in a complicated geometry such as a film-cooled vane is not governed by simple one-dimensional conduction from the vane surface to the plenum surface, especially when the effects of coolant injection are included.

Numerical Prediction of Heat Transfer in a Channel With Ribs and Bleed

In the present work numerical simulations for flow in a straight channel with square cross section is presented. While three of the walls of the channel are smooth the remaining wall was simulated to possess a combination of ribs and bleed holes. To allow for a comparative evaluation of the said heat transfer promoters that same wall was also simulated with holes only; ribs only; or simply smooth. Reynolds numbers from 10,000 to 38,000 based on the hydraulic diameter were considered. Very general multi-block structured grids were used to allow good grid quality around ribs and into the holes, and also to minimize the number of cells required. Turbulence was accounted for by a k-ω turbulence model which does not require reference to distance to a wall. Good agreement with experimental results demonstrate that the structured multi-block approach with the k-ω turbulence model is efficient and viable even for very complicated geometries.Copyright

Internal Passage Heat Transfer Prediction Using Multiblock Grids and a k-ω Turbulence Model

Numerical simulations of the three-dimensional flow and heat transfer in a rectangular duct with a 180° bend were performed. Results are presented for Reynolds numbers of 17,000 and 37,000 and for aspect ratios of 0.5 and 1.0. A k-ω turbulence model with no reference to distance to a wall is used. Direct comparison between single block and multiblock grid calculations are made. Heat transfer and velocity distributions are compared to available literature with good agreement. The multi-block grid system is seen to produce more accurate results compared to a single-block grid with the same number of cells.Copyright

Unsteady Analysis of Blade and Tip Heat Transfer as Influenced by the Upstream Momentum and Thermal Wakes

The effect of the upstream wake on the blade heat transfer has been numerically examined. The geometry and the flow conditions of the first stage turbine blade of GE s E3 engine with a tip clearance equal to 2 percent of the span was utilized. Based on numerical calculations of the vane, a set of wake boundary conditions were approximated, which were subsequently imposed upon the downstream blade. This set consisted of the momentum and thermal wakes as well as the variation in modeled turbulence quantities of turbulence intensity and the length scale. Using a one-blade periodic domain, the distributions of unsteady heat transfer rate on the turbine blade and its tip, as affected by the wake, were determined. Such heat transfer coefficient distribution was computed using the wall heat flux and the adiabatic wall temperature to desensitize the heat transfer coefficient to the wall temperature. For the determination of the wall heat flux and the adiabatic wall temperatures, two sets of computations were required. The results were used in a phase-locked manner to compute the unsteady or steady heat transfer coefficients. It has been found that the unsteady wake has some effect on the distribution of the time averaged heat transfer coefficient on the blade and that this distribution is different from the distribution that is obtainable from a steady computation. This difference was found to be as large as 20 percent of the average heat transfer on the blade surface. On the tip surface, this difference is comparatively smaller and can be as large as four percent of the average.

Automatic block merging methodology using the method of weakest descent

A methodology for automatic block merging is developed to the point where a complicated multi-block grid system is supplied and a merged system with connectivity information is returned. The objective of the method is to produce the minimum number of blocks. The recently developed Method of Weakest Descent (MWD) is described and its application to representative test cases is presented. The MWD is based on the premise that the more internal faces of a multi-block grid that can be removed, the lower the final number of blocks. With each internal face that is removed, other faces are disqualified from being removed as a result of the merging of two blocks. The MWD chooses which internal face to remove so as to minimize the number of disqualified faces, thus diminishing the set of available faces at the slowest rate (i.e. weakest descent). Reducing the available faces at the slowest rate allows more blocks to be merged before all valid internal faces are removed. When more than one candidate disqualify the same number of other faces, the choice among those candidates is made randomly. Because of this randomness, each application of the MWD can produce different results. Many tests have been done, with the number of initial blocks ranging from 12 to 7936. The tests have shown that, for most cases, every application of the MWD produces a result near the expected minimum. Repeated application increases the likelihood of realizing the actual minimum.

TRAF3D.MM - A multi-block flow solver for turbomachinery flows

An overview of a methodology for simulating steady flow and heat transfer in turbomachinery is presented. The methodology is the basis for a computer code called TRAF3D.MB. The objective behind the development of the methodology and the computer code is to improve the capability to predict heat transfer in turbomachinery flows. The computer code is used to study turbomachinery flows and to test turbulence models in the prediction of turbomachinery flows. Key aspects of the methodology are (a) multi block grid systems for complicated geometries, (b) finite volume discretization and (c) multigrid convergence acceleration. A target has also been to make the computer code modular, for example to allow flexibility in implementing and testing turbulence models. Currently two turbulence model have been implemented, an algebraic turbulence model and a two equation (k-co) turbulence model. Sample results are presented.

Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E 3 first stage turbine, which represents a modem gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow undertuming at smaller tip clearances. NOMENCLATURE

Computations of Viscous Flows in Complex Geometries Using Multiblock Grid Systems

Generating high quality, structured, continuous, body-fitted grid systems (multiblock grid systems) for complicated geometries has long been a most laborintensive and frustrating part of simulating flows in complicated geometries. Recently, new methodologies and software have emerged that greatly reduce the human effort required to generate high quality multiblock grid systems for complicated geometries. These methods and software require minimal input from the user-typically, only information about the topology of the block structure and number of grid points. This paper demonstrates the use of the new breed of multiblock grid systems in simulations of internal flows in Complicated geometries. The geometry used in this study is a duct with a sudden expansion, a partition and an array of cylindrical pins. This geometry has many of the features typical of internal coolant passages in turbine blades. The grid system used in this study was generated using a commercially available grid generator. The simulations were done using a recently developed flow solver, TRAF3D,MB, that was specially designed to use multibl0ck grid systems.

Unsteady Turbine Blade and Tip Heat Transfer Due to Wake Passing

The geometry and the flow conditions of the first stage turbine blade of GE’s E3 engine have been used to obtain the unsteady three-dimensional blade and tip heat transfer. The isothermal wall boundary condition was used. The effect of the upstream wake of the first stage vane was of interest and was simulated by provision of a “gust” type boundary condition upstream of the blades. A one blade periodic domain was used. The consequence of this choice was explored in a preliminary study which showed little difference in the time mean heat transfer between a 1:1 and 2:3 vane/blade domains. The full three-dimensional computations are of the blade having a clearance gap of 2% the span. Comparison between the time averaged unsteady and steady heat transfer is provided. It is shown that there is a significant difference between the steady and time mean of unsteady blade heat transfer in localized regions. The differences on the suction side of the blade in the near hub and near tip regions were found to be rather significant. Steady analysis underestimated the blade heat transfer by as much as 20% as compared to the time average obtained from the unsteady analysis. As for the blade tip, the steady analysis and the unsteady analysis gave results to within two percent.