Multiple smoke wires are used to investigate the secondary flow near the endwall of a plane cascade with blade shapes used in high-performance turbine stages. The wires are positioned parallel to the endwall and ahead of the cascade, within and outside the endwall boundary layer. The traces of the smoke generated by the wires are visualized with a laser light sheet illuminating various cross sections around the cascade. During the experiment, a periodically fluctuating horseshoe vortex system of varying number of vortices is observed near the leading edge of the cascade. A series of photographs and video tapes was taken in the cascade to trace these vortices. The development and evolution of the horseshoe vortex and the passage vortex are clearly resolved in the photographs. The interation between the suction side leg of the horseshoe vortex and the passage vortex is also observed in the experiment. A vortex induced by the passage vortex, starting about one-fourth of the curvilinear distance along the blade on the suction surface, is also found. This vortex stays close to the suction surface and above the passage vortex in the laminar flow region on the blade. From this flow visualization, a model describing the secondary flows in a cascade is proposed and compared with previous published models. Some naphthalene mass transfer results from a blade near an endwall are cited and compared with the current model. The flows inferred from the two techniques are in good agreement.

Flow Visualization in a Linear Turbine Cascade of High Performance Turbine Blades

An important problem that arises in the design and the performance of axial flow turbines is the understanding, analysis, prediction and control of secondary flows. Sieverding1 has given a review of secondary flow literature, covering up to 1985. In this paper a brief review of pre-1985 work is given, and then a survey of open literature secondary flow investigations since the Sieverding review is presented. Most of the studies reviewed deal with plane or annular cascade flows. Tip clearance effects are not covered. The basic secondary flow picture for a turbine cascade, as measured and verified by a number of investigators is described. Recent work that shows refined secondary flow vortex structures is examined. A flow parameter based on inlet boundary layer properties used to predict horseshoe vortex swirl is presented. Work on secondary flow loss reduction, involving airfoil geometry, endwall fences and endwall contouring is briefly reviewed. A new leading edge bulb geometry that has demonstrated impressive loss reduction is considered. It is concluded that accurate routine prediction of secondary flow losses has not yet been achieved, and must await either a better turbulence model or more experiments to reveal new endwall loss production mechanisms. Lastly, loss is examined from the standpoint of entropy generation.

Secondary Flows in Axial Turbines—A Review

The porting of twoand three-dimensional Euler solvers from a conventional CPU implementation to the novel target platform of the Graphics Processing Unit (GPU) is described. The motivation for such an effort is the impressive performance that GPUs offer: typically 10 times more floating point operations per second than a modern CPU, with over 100 processing cores and all at a very modest financial cost. Both codes were found to generate the same results on the GPU as the FORTRAN versions did on the CPU. The 2D solver ran up to 29 times quicker on the GPU than on the CPU; the 3D solver 16 times faster. Nomenclature cv Specific heat capacity at constant volume e Specific total energy = cvT + 1 2 V 2 h0 Specific stagnation enthalpy p Pressure t Time u,v Cartesian components of velocity V Velocity (magnitude) T Temperature Yp Stagnation pressure loss coefficient = p01−p0 p01−p2 tb302@cam.ac.uk gp10006@cam.ac.uk

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Acceleration of a 3D Euler solver using commodity graphics hardware

The Durham Linear Cascade has been redesigned with the nonaxisymmetric profiled end wall described in the first part of this paper, with the aim of reducing the effects of secondary flow. The design intent was to reduce the passage vortex strength and to produce a more uniform exit flow angle profile in the radial direction with less overturning at the wall. The new end wall has been tested in the linear cascade and a comprehensive set of measurements taken. These include traverses of the flow field at a number of axial planes and surface static pressure distributions on the end wall. Detailed comparisons have been made with the CFD design predictions, and also for the results with a planar end wall. In this way an improved understanding of the effects of end wall profiling has been obtained. The experimental results generally agree with the design predictions, showing a reduction in the strength of the secondary flow at the exit and a more uniform flow angle profile. In a turbine stage these effects would be expected to improve the performance of any downstream blade row. There is also a reduction in the overall loss, which was not given by the CFD design predictions. Areas where there are discrepancies between the CFD calculations and measurement are likely to be due to the turbulence model used. Conclusions for how the three-dimensional linear design system should be used to define end wall geometries for improved turbine performance are presented.

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Nonaxisymmetric Turbine End Wall Design: Part II—Experimental Validation

The distribution of adiabatic film-cooling effectiveness on the endwall of a large-scale low-speed linear turbine cascade has been measured using a new technique. This technique is based on an established surface-flow visualization technique, and makes use of the reaction between ammonia gas and a diazo surface coating. A new method of calibration has been developed to relate the result of the reaction to surface concentration of coolant. Using the analogy that exists between heat and mass transfer, the distribution of film-cooling effectiveness can then be determined. The complete representation of the film-cooling effectiveness distribution provided by the technique reveals the interaction between the coolant ejected from the endwall and the secondary flow in the turbine blade passage. Over- and undercooled regions on the endwall are identified, illustrating the need to take these interactions into account in the design process. Modifications to the cooling configuration examined in this paper are proposed as a result of the application of the ammonia and diazo technique.

Heat Transfer Committee Best Paper of 1995 Award: Distribution of Film-Cooling Effectiveness on a Turbine Endwall Measured Using the Ammonia and Diazo Technique

Resume des resultats de recherches experimentales effectuees sur les ecoulements secondaires au cours de la derniere decade, dans le but de donner une image de nos connaissances actuelles sur les aspects fondamentaux des ecoulements secondaires. Description detaillee des structures tourbillonnaires de l'ecoulement secondaire et de leur influence sur les caracteristiques de couche limite a la paroi d'extremite, ainsi que de l'origine, de la croissance, et de la distribution spatiale des pertes dans des passages d'aubes de turbine

Recent Progress in the Understanding of Basic Aspects of Secondary Flows in Turbine Blade Passages

Reliable cascade data are esssential to the development of high-speed turbomachinery, but it has long been suspected that the tunnel environment influences the test results. This has now been investigated by testing one plane gas turbine rotor blade section in four European wind tunnels of different test sections and instrumentation. The Reynolds number of the transonic flow tests was Re2 = 8 × 105 based on exit flow conditions. The turbulence was not increased artificially. A comparison of results from blade pressure distributions and wake traverse measurements reveals the order of magnitude of tunnel effects.

The Transonic Flow Through a Plane Turbine Cascade as Measured in Four European Wind Tunnels

The paper describes the experimental investigation of the three-dimensional flow through a low-speed, low aspect ratio, high turning annular turbine nozzel guide vane. The flow is explored by means of double-head, four-hole pressure probes in twelve axial planes from upstream to far downstream of the blade row. The results are presented under the form of contour plots and spanwise pitch-averaged distributions of losses, flow angles, and static pressure distributions. The concept of presenting the evolution of the endwall boundary layer under the form of streamwise and crossflow velocity components is discussed in detail.

Experimental Study of the Three-Dimensional Flow Field in an Annular Turbine Nozzle Guidevane

Reliable cascade data are essential to the development of highspeed turbomachinery, but it has long been suspected that the tunnel environment influences the test results. This has now been investigated by testing one plane gas turbine rotor blade section in four European wind tunnels of different test sections and instrumentation. The Reynolds number of the transonic flow tests was Re2 = 8 · 105 based on exit flow conditions. The turbulence was not increased artificially. A comparison of results from blade pressure distributions and wake traverse measurements reveals the order of magnitude of tunnel effects.Copyright © 1985 by ASME

: This paper presents results of an experimental investigation on the effect of a skewed inlet boundary layer on the flow field in a low speed, low aspect ratio, high turning annular turbine nozzle guide vane. Three test series, differing by their degree of inlet skew, were performed. The flow was explored by means of double head four hole pressure probes in five axial planes from upstream to far downstream of the blade row. Results are presented in the form of contour plots and spanwise pitch-averaged distributions. The axial evolution of the measured pitch-averaged spanwise flow angle distribution is compared with a three dimensional, inviscid, rotational flow calculation.

C. H. Sieverding

Papers

Recent Progress in the Understanding of Basic Aspects of Secondary Flows in Turbine Blade Passages

The Transonic Flow Through a Plane Turbine Cascade as Measured in Four European Wind Tunnels

Experimental Study of the Three-Dimensional Flow Field in an Annular Turbine Nozzle Guidevane

The Transonic Flow Through a Plane Turbine Cascade as Measured in Four European Wind Tunnels

Effects of a Skewed Inlet End Wall Boundary Layer on the 3-D Flow Field in an Annular Turbine Cascade,