A fully three-dimensional compressible inverse design method for the design of radial and mixed flow turbomachines is described. In this method the distribution of the circumferentially averaged swirl velocity rV-theta-BAR on the meridional geometry of the impeller is prescribed and the corresponding blade shape is computed iteratively. Two approaches are presented for solving the compressible flow problem. In the approximate approach the pitchwise variation in density is neglected and as a result the algorithm is simple and efficient. In the exact approach the velocities and density are computed throughout the three-dimensional flow field by employing a fast fourier transform in the tangential direction. The results of the approximate and exact approach are compared for the case of a high-speed (subsonic) radial-inflow turbine and it is shown that the difference between the blade shapes computed by the two methods is well within the manufacturing tolerances. The method was validated by calculating the flow through a designed high-speed radial-inflow turbine by using a three-dimensional inviscid Euler solver. Very good correlation was obtained between the specified and computed rV-theta-BAR-distributions.

A compressible three‐dimensional design method for radial and mixed flow turbomachinery blades

A limited number of aerodynamic shape design concepts have been surveyed and an attempt has been made to classify them. Characteristics, both positive and negative, of the more prominent methods were outlined. Future research is expected to concentrate on the use of Navier-Stokes equations and applications to threedimensional configurations. Interdisciplinary constrained optimization is expected to play a more prominent role in the immediate future. Adjoint operator/control theory and its variations are the most promising concepts for interdisciplinary aerodynamic shape design which involves a large number of variables. This theory is expected to constitute the major development area in future research.

Aerodynamic shape design and optimization - Status and trends

Aerodynamic shape design and optimization

This paper presents a detailed flow and heat transfer characteristic analysis on gas turbine first-stage turbine under hot streak inlet conditions. Two kinds of inlet total temperature conditions are specified at the turbine stage inlet. The first is uniform inlet total temperature, and the second is hot streak 2D total temperature contour The two kinds of inlet conditions have the same mass-averaged total temperature and the same uniform inlet total pressure. The hot streak total temperature contours are obtained according to the exit shape of an annular-can combustor. The ratio of the highest total temperature in the hot streak to the mass-averaged total temperature is about 1.23, and one hot streak corresponds to two vane passages and four blade passages. Six hot streak circumferential positions relative to the Vane 1 leading edge varied from -2% to 81% pitch are computed and analyzed. The results show that hot streak obviously increases the nonuniform degree of vane heat load in comparison with the uniform total temperature inlet condition. The change in hot streak circumferential position leads to the circumferential parameter variation at stator exit and also leads to different transient periodic fluctuating characteristics of heat load and pressure on the rotor blade surface. The hot streak of relative pitch at 65% obtains a similar heat load for the two vanes corresponding to one hot streak and small fluctuation in the averaged heat load on the rotor blade. [DOI: 10.1115/1.2988172]

Numerical Investigation on Unsteady Effects of Hot Streak on Flow and Heat Transfer in a Turbine Stage

Effects of Hot Streak and Airfoil Clocking on Heat Transfer and Aerodynamic Characteristics in Gas Turbine

The results of recent studies have shown that combustor exit temperature distortion can cause excessive heat load of high-pressure turbine (HPT) rotor blades. The heating of HPT rotor blades can lead to thermal fatigue and degrade turbine performance. In order to explore the influence of hot streak temperature ratio on the temperature distributions of HPT airfoil surface, three-dimensional multiblade row unsteady Navier-Stokes simulations have been performed in a vaneless counter-rotating turbine (VCRT). The hot streak temperature ratios from 1.0 (without hot streak) to 2.4 were used in these numerical simulations, including 1.0, 1.2, 1.6, 2.0, and 2.4 temperature ratios. The hot streak is circular in shape with a diameter equal to 25% of the span. The center of the hot streak is located at 50% of span and 0% of pitch (the leading edge of the HPT stator vane). The predicted results show that the hot streak is relatively unaffected as it migrates through the HPT stator. The hot streak mixes with the vane wake and convects towards the pressure surface (PS) of the HPT rotor when it moves over the vane surface of the HPT stator. The heat load of the HPT rotor increases with the increase of the hot streak temperature ratio. The existence of the inlet temperature distortion induces a thin layer of cooler air in the HPT rotor, which separates the PS of the HPT rotor from the hotter fluid. The numerical results also indicating the migration characteristics of the hot streak in the HPT rotor are predominated by the combined effects of secondary flow and buoyancy. The combined effects that induce the high-temperature fluid migrate towards the hub on the HPT rotor. The effect of the secondary flow on the hotter fluid increases as the hot streak temperature ratio is increased. The influence of buoyancy is directly proportional to the hot streak temperature ratio. The predicted results show that the increase of the hot streak temperature ratio trends to increase the relative Mach number at the HPT rotor outlet, and decrease the relative flow angle from 25% to 75% span at the HPT rotor outlet. In the other region of the HPT outlet, the relative flow angle increases when the hot streak temperature ratio is increased. The predicted results also indicate that the isentropic efficiency of the VCRT decreases with the increase of the hot streak temperature ratio.

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Numerical Investigation on the Influence of Hot Streak Temperature Ratio in a High-Pressure Stage of Vaneless Counter-Rotating Turbine

In this paper, three-dimensional multiblade row unsteady Navier-Stokes simulations at a hot streak temperature ratio of 2.0 have been performed to reveal the effects of rotor tip clearance on the inlet hot streak migration characteristics in high pressure stage of a Vaneless Counter-Rotating Turbine. The hot streak is circular in shape with a diameter equal to 25% of the high pressure turbine stator span. The hot streak center is located at 50% of the span and the leading edge of the high pressure turbine stator. The tip clearance size studied in this paper is 2.0mm (2.594% high pressure turbine rotor height). The numerical results indicate that the hot streak mixes with the high pressure turbine stator wake and convects towards the high pressure turbine rotor blade surface. Most of hotter fluid migrates to the pressure surface of the high pressure turbine rotor. Only a few of hotter fluid rounds the leading edge of the high pressure turbine rotor and migrates to the suction surface. The migration characteristics of the hot streak in the high pressure turbine rotor are dominated by the combined effects of secondary flow, buoyancy and leakage flow in the rotor tip clearance. The leakage flow trends to drive the hotter fluid towards the blade tip on the pressure surface and to the hub on the suction surface. Under the effect of the leakage flow, even partial hotter fluid near the pressure surface is also driven to the rotor suction surface through the tip clearance. Compared with the case without rotor tip clearance, the heat load of the high pressure turbine rotor is intensified due to the effects of the leakage flow. And the results indicate that the leakage flow effects trend to increase the low pressure turbine rotor inlet temperature at the tip region. The air flow with higher temperature at the tip region of the low pressure turbine rotor inlet will affect the flow and heat transfer characteristics in the downstream low pressure turbine.Copyright © 2008 by ASME

Tip Clearance Effects on Inlet Hot Streak Migration Characteristics in High Pressure Stage of a Vaneless Counter-Rotating Turbine

In order to explore the influence of hot streak temperature ratio on the low pressure stage of a vaneless counter-rotating turbine, three-dimensional multiblade row unsteady Navier-Stokes simulations have been performed. The predicted results show that hot streaks are not mixed out by the time they reach the exit of the high pressure turbine rotor The separation of colder and hotter fluids is observed at the inlet of the low pressure turbine rotor After making interactions with the inner-extending and outer-extending shock waves in the high pressure turbine rotor the hotter fluid migrates toward the pressure surface of the low pressure turbine rotor and most of the colder fluid migrates to the suction surface of the low pressure turbine rotor The migrating characteristics of the hot streaks are dominated by the secondary flow in the low pressure turbine rotor The results also indicate that the secondary flow intensifies in the low pressure turbine rotor when the hot streak temperature ratio is increased. The effects of the hot streak temperature ratio on the relative flow angle at the inlet of the low pressure turbine rotor are very remarkable. The isentropic efficiency of the vaneless counter-rotating turbine decreases as the hot streak temperature ratio is increased.

Influence of Hot Streak Temperature Ratio on Low Pressure Stage of a Vaneless Counter-Rotating Turbine

To reveal the unsteady flow characteristics of a vaneless counter-rotating turbine (VCRT), a three-dimensional, viscous, unsteady computational fluid dynamics (CFD) analysis was performed. The results show that unsteady simulation is superior to steady simulation because more flow characteristics can be obtained. The unsteady effects in upstream airfoil rows are weaker than those in downstream airfoil rows in the VCRT. The static pressure distribution along the span in the pressure surface of a high pressure turbine stator is more uniform than that in the suction surface. The static pressure distributions along the span in the pressure surfaces and the suction surfaces of a high pressure turbine rotor and a low pressure turbine rotor are all uneven. The numerical results also indicate that the load of a high pressure turbine rotor will increase with the increase of the span. The deviation is very big between the direction of air flow at the outlet of a high pressure turbine rotor and the axial direction. A similar result can also be obtained in the outlet of a low pressure turbine rotor. This means that the specific work of a high pressure turbine rotor and a low pressure turbine rotor is big enough to reach the design objectives.

Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine

An aerodynamic design method, which based on the Mean Stream Surface Method (MSSM), has been developed in designing the centrifugal compressor impeller blades. As a component of a CAD system for centrifugal compressor, it is convenient to use the presented method for generating impeller blade geometry, taking care of manufacturing as well as aerodynamic aspects.The design procedure starts with an S2m indirect solution. Afterwards from the specified S2m surface, by the use of Taylor series expansion, the blade geometry is generated by straight-line elements to meet the requirement of manufacture. Simultaneously, the fluid dynamic quantities across the blade passage, can be determined directly. In terms of these results, the designer can revise the distribution of angular momentum along the shroud and hub, which are associated with blade loading to get satisfactory velocities along the blade surfaces in order to avoid or delay flow separation.Copyright © 1989 by ASME

Zhao Xiaolu

Papers

Numerical Investigation on the Influence of Hot Streak Temperature Ratio in a High-Pressure Stage of Vaneless Counter-Rotating Turbine

Tip Clearance Effects on Inlet Hot Streak Migration Characteristics in High Pressure Stage of a Vaneless Counter-Rotating Turbine

Influence of Hot Streak Temperature Ratio on Low Pressure Stage of a Vaneless Counter-Rotating Turbine

Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine

An Approximate 3-D Aerodynamic Design Method for Centrifugal Impeller Blades