Gang Lin

Heat Transfer Enhancement for Gas Turbine Internal Cooling by Application of Double Swirl Cooling Chambers

Improvement of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount in internal cooling channels with enhanced convective cooling. Nowadays the state of the art internal cooling technology for thermally high-loaded gas turbine blades consists of multiple serpentine-shaped cooling channels with angled ribs. Besides, huge effort is put on the development of more advanced internal cooling configurations with further internal heat transfer enhancements. Swirl chamber flow configurations, in which air is flowing through a pipe with a swirling motion generated by tangential jet inlet, have a potential for application as such advanced technology. This paper presents the validation of numerical results for a standard swirl chamber, which has been investigated experimentally in a reference publication. The numerical results obtained with application of the SST k-ω model show the best agreement with the experiment data in compare with other turbulence models. It has been found at the inlet region that the augmentation of the heat transfer is nearly seven times larger than the fully developed non-swirl flow. Within the further numerical study, another cooling configuration named Double Swirl Chambers (DSC) has been obtained and investigated. The numerical results are compared to the reference case. With the same boundary conditions and Reynolds number, the heat transfer coefficients are higher for the DSC configuration than for the reference configuration. In particular at the inlet region, the DSC configuration has even higher circumferentially averaged heat transfer enhancement in one section by approximately 41%. The globally-averaged heat transfer enhancement in DSC configuration is 34.5% higher than the value in the reference SC configuration. This paper presents the configuration of the DSC as an alternative internal cooling technology and explains its major physical phenomena, which are the reasons for the improvement of internal heat transfer.Copyright

Leading Edge Cooling of a Gas Turbine Blade With Double Swirl Chambers

The gas turbine blade leading edge area has locally extremely high thermal loads, which restrict the further increase of turbine inlet temperature or the decrease of the amount of coolant mass flow to improve the thermal efficiency. Jet impingement heat transfer is the state of the art cooling configuration, which has long been used in this area. In the present study, a modified double swirl chambers cooling configuration has been developed for the gas turbine blade leading edge. The double swirl chambers cooling (DSC) technology is introduced by the authors and comprises a significant enhancement of heat transfer due to the generation of two anti-rotating swirls. In DSC cooling the reattachment of the swirl flows with the maximum velocity at the middle of the chamber leads to a linear impingement effect, which is most suitable for the leading edge cooling for a gas turbine blade. In addition, because of the two swirls both suction side and pressure side of the blade near the leading edge can be very well cooled. In this work, a comparison among three different internal cooling configurations for the leading edge (impingement cooling, swirl chamber and double swirl chambers) has been investigated numerically. With the same inlet slots and the same Reynolds number based on hydraulic diameter of channel the DSC cooling shows overall higher Nusselt number ratio than that in the other two cooling configurations. Downstream of the impingement point, due to the linear impingement effect, the DSC cooling has twice the heat flux in the leading edge area than the standard impingement cooling channel.Copyright

Novel Gas Turbine Blade Leading Edge Cooling Configuration Using Advanced Double Swirl Chambers

The Double Swirl Chambers (DSC) cooling technology, which has been introduced and developed by the authors, has the potential to be a promising cooling technology for further increase of gas turbine inlet temperature and thus improvement of the thermal efficiency. The DSC cooling technology establishes a significant enhancement of the local internal heat transfer due to the generation of two anti-rotating swirls. The reattachment of the swirl flows with the maximum velocity at the center of the chamber leads to a linear impingement effect on the internal surface of the blade leading edge nearby the stagnation line of gas turbine blade. Due to the existence of two swirls both the suction side and the pressure side of the blade near the leading edge can be very well cooled. In this work, several advanced DSC cooling configurations with a row of cooling air inlet holes have been investigated. Compared with the standard DSC cooling configuration the advanced ones have more suitable cross section profiles, which enables better accordance with the real blade leading edge profile. At the same time these configurations are also easier to be manufactured in a real blade. These new cooling configurations have been numerically compared with the state of the art leading edge impingement cooling configuration. With the same configuration of cooling air supply and boundary conditions the advanced DSC cooling presents 22–26% improvement of overall heat transfer and 3–4% lower total pressure drop. Along the stagnation line the new cooling configuration can generate twice the heat flux than the standard impingement cooling channel. The influence of spent flow in the impinging position and impingement heat transfer value is in the new cooling configurations much smaller, which leads to a much more uniform heat transfer distribution along the chamber axial direction.Copyright

High efficient steam turbine design based on automated design space exploration and optimization techniques

Due to the world-wide increasing demand for energy and the simultaneous need in reduction of CO2 emissions in order to meet global climate goals, the development of clean and low emission energy conversion systems becomes an essential and challenging task within the future clean energy map. In this paper the design process of a highly efficient large scale USC steam turbine is presented. Thereby, automated design space exploration based on an optimization algorithm is applied to support the identification of optimal flow path parameters within the preliminary and the detailed design phases. The optimization algorithm is first integrated with a 1D-mean line design code to automatically identify the optimal major turbine layout in terms of number of stages, reaction degrees, flow path geometry and basic airfoil parameters. Based on a progressive multi-section optimization coupled with a parametric airfoil generator and a CFD code, the profile shapes of each airfoil row are adapted to local flow conditions and systematically optimized to minimize aerodynamic losses in each turbine stage. A final 3D flow simulation of one representative optimized stage confirms the achievement of a highly efficient steam turbine design that fulfills both climatic and economic requirements.

Heat Transfer Enhancement Using Wedge-Shaped Detached Ribs With Grooves in Internal Cooling Channel

As the state of the art internal cooling configuration the serpentine passage with angled ribs has been developed for many decades and is now widely used in almost all the blade internal cooling applications. To further increase the thermal efficiency of gas turbine, the development of new internal cooling configurations is necessary. In the present study, a new internal cooling configuration, which is characterized by placing modified wedge-shaped detached ribs above the grooves, has been obtained and investigated. Under this new cooling configuration, the main effect for enhancement of heat transfer in standard ribbed channel, the separation and reattachment of the main flow, has been retained. Additional improvements can be found in several areas as follows: (1) flow near rib corner is not stagnant anymore and both corner vortexes near the rib have been eliminated, (2) the increased velocity in groove leads to locally high heat flux. With the same channel dimension, ribs pitch-height ratio, boundary conditions and the Reynolds number based on hydraulic diameter the new cooling configuration shows higher Nusselt number ratio at the ribbed wall by approximately 25–32%. The globally-averaged thermal performance parameter shows a 19–25% better heat performance by this kind of cooling configuration.Copyright

Vibration Analysis of Shrouded Turbine Blades for a 30 MW Gas Turbine

Turbine blades are subjected to high static and dynamic loads. In order to reduce the vibration amplitude means of friction damping devices have been developed, e.g. damping wires, interblade friction dampers and shrouds. This paper presents both numerical and experimental results for investigating the dynamical behavior of shrouded turbine blades. The studies are focused on the lowest family of the bladed disk.The aspect of experimental studies, the effect of the shroud contact force on the resonance frequency of the blade was examined by using the simplified blade test stand. Based on the result of the simplified blade studies, the shroud contact force of the real blade was determined in order to stabilize the resonance frequencies of the bladed disk system. The resonance frequencies and mode shapes of the real bladed disk assembly were measured in no rotation and room temperature condition. Finally, the dynamic strains were measured in the actual engine operations by using a telemetry system.The aspect of analytical studies, a non-linear vibration analysis code named DATES was applied to predict vibration behavior of a shrouded blade model which includes contact friction surfaces. The DATES code is a forced response analysis code that employs a 3-dimensional friction contact model. The Harmonic Balance Method (HBM) is applied to solve resulting nonlinear equations of motion in frequency domain. The simulated results show a good agreement with the experimental results.Copyright

Helium Brayton Cycles With Solar Central Receivers: Thermodynamic and Design Considerations

Concentrated Solar Power (CSP) technologies are considered to provide a major contribution for the electric power production in the future. Several technologies for such kind of power plants are already in operation. Parabolic troughs, parabolic dishes, Fresnel multi-facet reflectors or heliostats in combination with a central receiver are applied for concentration of the solar irradiation. The energy conversion cycles usually are water/steam cycles (Rankine cycles), but also open gas turbine cycles (Brayton cycle) or combined cycles are possible. One option is to apply closed Brayton cycles using fluids like carbon dioxide or helium.With respect to commercial considerations, the main parameter driving the decision on which cycle to apply for energy conversion is the thermal efficiency of the process. This is due to the fact, that in case of a power plant without additional fuel supply, no fuel costs have to be considered to determine the levelized electricity costs (LEC). Thus, in the first place the capital costs determine the LEC. In CSP plants one main driver for the capital costs are the heliostats and the mirror size, which are necessary to generate the desired amount of electric power. The necessary solar aperture area directly depends on the thermal efficiency of the energy conversion cycle.In this paper different closed Helium Brayton Cycles for application with solar central receivers are analyzed thermodynamically. The thermodynamic calculations are performed by application of a self-developed thermodynamic calculation software, which considers the real gas properties of the fluid. The software calculates the cycle’s thermodynamic diagrams (e.g. T-s-, h-s-diagrams) and determines its efficiency.The results show that thermal efficiencies of approximately 46.6% (and higher) can be reached with a Helium Brayton Cycle. One important parameter is the turbine inlet gas temperature, which is not less than 900 °C. This means that the pressurized receiver for this technology has to bear even higher temperatures.Furthermore, the paper deals with design considerations for compressor and turbine within the closed Helium Brayton Cycle. Based on dimensionless parameters, the major parameters like stage types, number of stages, rotational speed etc. are determined and discussed.Copyright