This paper presents a comprehensive study on the stagnation properties namely the total pressure and total temperature for supercritical CO2 flows including the methodology, applications and detailed analysis. Due to the high nonlinear real gas effect, it is practically impossible to have explicit expressions between static and its corresponding stagnation properties. The equations of obtaining the real gas stagnation properties as well as their physical meanings related to fluid dynamics need to be reconsidered. In this paper, the stagnation pressure and temperature for sCO2 flows are accurately calculated in a way that implicitly iterated from stagnation enthalpy and entropy without any addendum assumptions. Accordingly, this approach is applied to typical applications that essentially exert stagnation properties. The total pressure and total temperature of typical sCO2 flows in which contain significant real gas characteristics are numerically studied by using our in-house CFD code coupled with real gas models. It is found that the real gas tends to preserve more internal energy than the ideal gas during irreversible flow process especially with the presence of shockwaves. Finally, as a regular indicator of viscous flow loss, the total pressure loss for a sCO2 compressor cascade is evaluated.

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Pneumatic probes are commonly used to determine the flow vector as well as the thermodynamic state of the fluid in turbomachinery applications. The conventional method to measure a flow passage velocity or pressure field is to move the probe to discrete positions and to hold a certain settling time before valid data can be recorded. This study presents a measurement methodology leading to a reduction in the required measurement duration of up to 70-90%, depending on the level of flow field resolution. The approach is based on the concept of continuously traversing probes as introduced by Gomes et al. [1]. However, the system model is changed by reducing the transfer function to a single PT1-behavior. While the experiments conducted by Gomes et al. [1] were limited to only linear cascade measurements, the method used here is extended to turbomachinery applications with highly complex flow structures. The continuous traverse measurements are validated through a comparison with conventional discrete measurements that include characteristic settling time. For this purpose, tests have been performed in an axial diffuser test rig operated with air and a low pressure steam turbine. The results obtained with the new approach show a good match, thus proving the viability of the proposed method for turbomachinery applications. For future tests, a significant reduction in measurement time and cost can be achieved.

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The work characteristics and loss-generation mechanism of a single-stage axial flow compressor in windmilling operation were investigated via experiments and computational fluid dynamics analyses. The windmilling state occurs when air flowing through an unlit engine drives the compressor rotor blades, similar to a turbine. This phenomenon applies mostly to aircraft engines, where it is caused by ram pressure. When the inlet flow coefficient is gradually increased in the design, the rotor blades gradually enters the windmilling operation from the tip toward the hub. This research has focused on two windmilling operations: free windmilling (FW) and highly loaded (HL) windmilling. In the case of FW, the net work performed by the rotor blades to the fluid is canceled out (zero), and the rotor is in an idle state. In the HL windmilling condition, the work performed to the rotor blades by the fluid increases, the compressor acts as a turbine, and power is generated. According to the detailed numerical results, the total-pressure loss under the free and HL windmilling conditions was mainly caused by three flow structures: (1) tip leakage flow from the suction surface (SS) to the pressure surface (PS) near the leading edge and that from the PS to the SS near the trailing edge; (2) the interaction of leading-edge separation vortices due to the highly negative incidence and the rotor leading-edge vortex; and (3) the boundary- layer separation near the hub wall. Surface-pressure measurement on a rotating rotor blade revealed that the distribution of the rotor operating mode existed not only in the spanwise direction but also in the chordwise direction under the windmilling operations. The turbine mode region was observed near the leading edge, while the compressor mode region was observed near the trailing edge, even in the HL windmilling condition. Therefore, the driving force of the windmilling was dominated not by the area of the turbine mode on the rotor surface but by the strength of the operating mode, i.e., the static-pressure difference between the SS and PS on the rotor. Finally, the unsteady flow field within blade-to-blades passages was investigated via an unsteady detached eddy simulation, and the differences in the loss-generation mechanism between the FW and HL windmilling conditions were examined.

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Within the last three years, Kawasaki Heavy Industries Ltd. and B&B-AGEMA have worked on a technology to support experimental tests for development of the Micromix combustor of pure hydrogen, allowing a very close online visual (Visible and Infrared light) access to the burner. The invented borescope has been designed by means of Conjugate Heat Transfer (CHT) and Finite Element (FE) simulations. Different design variations have been tested numerically. Within this course, the internal cooling pathways have been improved and the structure enhanced to ensure an acceptable life time of the highly loaded borescope head located directly downstream of the flame. Here, the local temperature reaches values around 1600 K. After digital development and manufacturing, the first borescope prototype could have been successfully operated in two low pressure and two high pressure tests (two times with a visible light (VIS) and two times with an Infrared (IR) camera). In the paper, the development process as well as the operational experience and the experimental test results are presented. The information on the Micromix combustor behavior revealed by the borescope technology help to better understand the behavior of the combustor, improve the design and plan the operation strategy within the real gas turbine.

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Centrifugal compressor applied to turbochargers is required to operate stably in wide range from choking to surging. In our past research, it was suggested that impellers which induced tip leakage vortex breakdown at relatively high flow rate might stabilize internal flow by generating circumferential uniform blockage region near blade tip at low flow rate. In this study, authors investigated whether modifying a given impeller to induce the tip leakage vortex breakdown could reduce the surging flow rate or not. Pressure measurement of the conventional impeller showed that unstable pressure fluctuation occurred at smaller flow rate side than the peak pressure point. Furthermore, it was clarified by unsteady numerical calculation that the rotating stall occurred with circumferentially non-uniform reverse flow. On the other hand, in the new impeller increasing its inducer loading, unsteady numerical calculation showed that the blade tip leakage flow was strengthened and generated a circumferentially uniform blockage region, which could stabilize its internal flow. As a result of performance test of the new impeller, considering that the surging flow rate at the same shaft speed was reduced by 3% and the pressure ratio at the surging point had been improved from 2.8 to 2.9, the surging flow rate at the pressure ratio of 2.8 could be reduced by 8%. In this way, it was found that the tip leakage flow was dominant with the stall phenomenon of the centrifugal compressor, and it was also confirmed that the tip leakage vortex control was one of the effective means for the operation range enhancement.

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This paper presents detailed measurements and post-test simulations of the penny cavity leakage flow and its interaction with the mainstream flow in an annular cascade wind tunnel. The annular cascade wind tunnel consists of a single row of 30 variable stator vanes, derived from a high-pressure compressor stator with inner and outer vane disks, called pennies, which - when assembled in the hub and casing walls - leave cylindrical-shaped ring gaps called penny cavities. The wind tunnel runs at a Mach number of 0.34 at the stator inlet and a Reynolds number of 3.82 x 105 based on axial chord length at 50% span. Two different penny gap sizes on the hub are compared to a reference case without a penny gap. Detailed 2D-traverses were performed with multi-hole pressure and hot-wire-probes covering 2.5 passages in the inflow and outflow of the stator row. Pressure taps were embedded in the airfoil surface and inside the penny cavity. Surface oil flow measurements were conducted with different colors for the vane suction side, pressure side, hub and the penny cavity to detect the secondary flow phenomena. Reynolds- averaged Navier-Stokes (RANS) simulations, using the measured boundary conditions, were compared to experimental data. As a result, a relative increase in the total pressure loss coefficient of 1.9% for the nominal and 6.8% for the double penny gap was measured compared to no-penny cavity. The additional penny losses are limited to the lower 40% span. The post-test simulations are in good agreement with the measurements, showing that the outflow from the penny cavity on the suction side generates vortices, which cause additional losses. The penny vortices are detected in the outlet plane by an increase in turbulence intensity and streamwise vorticity. However, the additional penny losses are overestimated in the simulation by up to 7.3%. A change in the pressure fields with an increasing penny gap size, both around the airfoil and inside the penny cavity, can be seen in the numerical and experimental results. The outflow regions of the penny cavity, estimated by simulations, are confirmed by the results of the surface oil flow measurements. In summary, this paper consolidates previous numerical analyses carried out by the authors [13-16] on penny cavity leakage flow effects with experimental data for different penny gap sizes.

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The multi-parameter comprehensive evaluation method of gas turbine can accurately grasp the state of engine health. Eight evaluation indicators were chosen from the condition of engine gas path degradation, the combustion system and the whole machine vibration. Aimed at the uncertainty of data information, the objective attribute weights were gotten based on the method of the combination of fuzzy clustering and information entropy by calculating the mutual information. In view of the equilibrium of data, another objective weights were gotten using the entropy weight method. Then the linear weighted sum method of the two was used to get the final objective weights of indicators. Subjective weights were obtained by analytic hierarchy process. Integrating the subjective and objective weights, multiplication combination method was used to determine the final weights. The multi-attribute comprehensive evaluation of gas turbine health status was carried out combined with a 2,000 hours test. Results show that the method can integrate the advantages of objective and subjective weighting methods, evaluation results are in line with the practical experience, which means it is a feasible way to the gas turbine condition assessment and maintenance decision.

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