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The erosion caused by sand particles significantly influences the safety of radial inflow turbine in Compressed Air Energy Storage (CAES) system which operated in desert area. In present study, effects of tip leakage flow on erosion of a CAES radial inflow turbine are investigated at different tip clearances and total pressure ratios. A CFD model coupling Tabakoff and Grant erosion model is utilized for the analysis. Results illustrate that the trailing edge of stator, the leading edge of rotor blades, the shroud and hub surfaces near inlet of rotor cause more severe erosion at each tip clearance. Therefore, wear-resistant coating should be adopted. The severe erosion can also be found at blade tip of rotor. However, it is gradually suppressed with the increase of tip clearance. With the increase of total pressure ratio, the region with higher erosion rate on the shroud of rotor gradually extends to downstream. However, the erosion rate at leading edge of rotor blades is decreased obviously. In conclusion, the erosion effect can be alleviated remarkably when the tip clearance size is of 2% and total pressure ratio is more than 1.84, while the isentropic efficiency is almost kept the same.

In this paper a novel casing treatment structure i.e. leading edge suspended groove shroud end wall structure is proposed in order to reduce the tip clearance losses in highly loaded helium compressor. The highly loaded design method of helium compressor can effectively resolve the problem of helium compression in high temperature gas cooled reactor (HTGR) plants. However, smaller blade height and increase in blade loading cause higher tip clearance leakage losses. The result shows that the leading edge suspended groove shroud structure in highly loaded helium compressor rotor effectively controls the formation of the tip clearance leakage flow and reduces the tip clearance leakage loss. 30° groove slope minimizes the total clearance losses close to blade tip. Moreover, It increases the efficiency of the highly loaded helium compressor by 0.4% at 1 mm tip clearance gap.

A shrouded oscillating-foil turbine is proposed to augment the energy extraction performance. The oscillating foil undergoes combined plunging and pitching motion to convert the flow energy. A diffuser is introduced into the oscillating-foil-based turbine as the shroud. The speed-up and energy extraction performance of the turbine were assessed numerically. The effects of three cost-independent geometrical factors, namely shroud entrance width, shroud angle and streamwise distance between shroud and foil, and shroud sectional shape on energy extraction performance were investigated in detail. The optimal motion parameters for the shrouded oscillating-foil turbine were re-explored due to the altered flow field in the shroud. The results demonstrated that the maximum energy extraction efficiency of bare oscillating foil (0.336) can be augmented by 35.8% to 0.456 by appropriate arrangement of the shroud with a relative chord length of 0.8. The optimal motion parameters for the shrouded foil are slightly different from those of bare foil. The re-tuned motion parameters can further improve the efficiency to 0.47. Considering both the manufacturing cost of the shaped sections and their performance, it is more advantageous and attractive to use a flat plate as the shroud in engineering practices.

This paper concentrates on the application of blade-end treatment to axial compressors by means of the optimization algorithm. The blade-end treatment reduces the end wall losses and extends the stable margin by modifying blade shape near the end wall region. It contains three types of passive flow control measures, i.e., the end-bend, end-dihedral and end-sweep treatment. Firstly, the effects of blade-end treatment were reviewed based on the open literature published over the past 30 years. All of these effects essentially influence the compressor performance by changing the blading loading distributions in the streamwise or spanwise directions. There is a trade-off between the improved end wall flows and the deteriorated mid-span flows. It’s difficult to quantitatively apply these measures to achieve an optimal balance according to the traditional engineering experience. Optimization algorithm provides an efficient access to resolve this issue by automatically obtaining the utmost benefit. Secondly, an optimization example of NASA Stage 35 was conducted to validate against the summarized flow mechanisms. The optimal geometry parameters of cantilever stator vane near the end wall region were obtained by employing a surrogate model in conjunction with a genetic algorithm for optimization. Finally, optimization results indicated that the optimal vane blade featured an obvious combination of forward end-sweep, positive end-dihedral and end-bend. The stator total pressure losses were reduced with the blade-end treatment based on optimization method. A significant reduction of loss occurred near the shroud region, from the 80% span to the casing, while the performance was degraded within the mid-span region, approximately 50%–80% span. The resulting mechanisms are consistent with the knowledge obtained from the literature review and this will provide meaningful guidance on the further compressor design process.

Thermal stress is one of major causes of cracking in high-temperature components of gas turbines. This paper presents a thermo-structural analysis of cracks on the vane of a gas turbine for power generation. The vane components include three airfoils with hub and shroud sections. The airfoils have serpentine-type internal passages and film cooling holes on the pressure-side surfaces for cooling. The conjugate heat transfer problem was solved to accurately evaluate heat transfer on the vane using computational fluid dynamics software, CFX. Based on the conjugate heat transfer result, thermal expansion and thermal stress were evaluated using structural analysis software, ANSYS. The results showed that an irregular temperature distribution induced anisotropic thermal expansion in the vane segments, including the shroud and hub sections, and that the anisotropic thermal expansion caused serious stress concentrations. Among the three airfoils, the middle one was the most stressed because the thermal expansion was constrained by deformed hub and shroud sections. The predicted locations of stress concentration coincided with the locations of cracks on the actual vane after an operating period. The prediction provides general information on the initiation of cracks on a vane segment having multiple airfoils.

A one stage horizontal axis wind turbine with a shroud and lobed ejector was designed for the efficient utilization of low-grade wind energy by taking into consideration the effect of the shroud and lobed ejector. The performance of the proposed wind turbine was evaluated using the commercial software CFX. Simulation results indicated that the wind energy utilization efficiency of the proposed wind turbine increased to 66–73% at a low wind speeds ranging from 2 to 6 m/s. It was found that the complex vortices in the flow field outside the wind turbine included stream-wise vortices, normal vortices behind the lobes, and three large scale vortex rings. The shroud and lobed ejector structure in the back of the proposed wind turbine produced such an effect that the pressure at the wind turbine exit was reduced so that the turbine power output was increased by 240%. It is therefore concluded that the proposed wind turbine can be used for efficient utilization of low-grade wind energy.

This paper discusses the details of unsteady experimentation and analysis of a twin-entry variable geometry turbine for an automotive turbocharger. The turbine in this study is the product of design progression from a commercial nozzleless unit to a single-entry variable geometry and consequently to a twin-entry unit. The main features of the turbine were kept similar across all configurations for equivalent comparison basis. The unsteady curves of the twin-entry turbine exhibited the conventional looping characteristics representing filling and emptying effects, which was also the case for the nozzleless and single-entry nozzled turbine. The swallowing capacity of the twin-entry turbine, during full admission testing, was recorded to be inconsistent between the two entries, in particular they were at different pressure ratio levels – the shroud end entry was in most cases more pressurized compared to the hub end entry, as much as 13%. Contrarily, during out-of-phase testing the swallowing capacity of both the turbine entries was found to be similar. The cycle-averaged efficiency of the nozzled turbine either twin or single-entry was found to depart significantly from the equivalent quasi-steady, in comparison to the nozzleless single-entry turbine, this was as much as 32%.