A simplified configuration of variable stator vanes, which has a uniform hub clearance and a stationary hub surface, is applied to a high-loaded multistage compressor. Comparisons of endwall flow structures are made between the ideal and the simplified configurations. After validating numerical results of the ideal stator configuration with experiment data, the third stator and all stators are modified with the simplified configuration in two separate cases. Flow structures and loss characteristics in the endwall region are investigated numerically in detail at design point. Limited corner separation near the suction side and comparatively strong secondary flow near the pressure side make similar contributions to endwall loss at design point for the baseline configuration, while the shear flow of the blade tip and the endwall boundary layer are regarded as important sources of loss for the modified configuration.

Cooling technologies have been widely applied to protect the turbine blades at high inlet temperature, which also makes the aero-thermal coupled phenomenon more remarkable. Nevertheless, the aero-thermal phenomenon had not been considered in traditional throughflow methods and led to challenges of cooled turbine design. This paper proposes a new cooling model for the aero-thermal coupled throughflow method which was first proposed by the same author. The cooling model considers the variation of the temperature caused by air cooling both along the stream and span direction to improve the heat flux calculation accuracy. The impacts of heat transfer on mainstream enthalpy and entropy are further studied in this paper. The equivalent blade thickness and the estimation method of the heat exchange area were also introduced into the cooling model. The cooling model is validated with experimental data of the Mark II profile. This paper applies the method in the design of a high-pressure axial turbine, of which the first stator is cooled with convective cooling. With the prescribed blade temperature limitation, the flow field properties and the coolant requirement are predicted. The three dimensional CHT analysis is performed to validate the aerothermal coupled throughflow method, and the aerodynamic parameter predicted by the throughflow method is in accordance with the 3-D CHT analysis.

As the increase of the energy consumption and the deterioration of environment, a carbon tax will be imposed in China to reduce carbon emissions strictly and the industrial waste heat recovery has been getting more attention. The Organic Rankine Cycle (ORC) system has been proven to be a promising solution for the utilization of the low-grade heat sources. There are five waste heat sources from a 1.2 million ton reforming and extraction unit in Shijiazhuang Refining & Chemical Company of China. The temperatures of the waste heat sources are 98∼80°C, 104∼80°C, 147∼80°C, 205∼80°C and 205∼80°C, and the heat loads are 6.5MW, 11.5MW, 8.6MW, 3.8MW and 2.2MW, respectively. This paper studies the thermal design and performance optimization of a comprehensive utilization system for these waste heat sources, using ORC technology. The selection of suitable organic fluid is studied and the working parameters are designed and optimized with the application of the first law and the second law of thermodynamics. When the ORC systems are designed separately for the recovery of five waste heat sources, and the total power output is 3338.89kW with different organic working fluids. However this kind of designs leads to a very complex recovery system which needs large investment and space occupation. To reduce the overall system complexity, a single ORC system is proposed to recover all five heat sources, and the total amount of output power will only be 2813.02kW, due to the large exergy loss. With the above results shown, and for the purpose of simple system with large power output, this paper further studies the dual ORC systems heat recovery plan, with R245fa as the top cycle working fluid and R141b as the bottom cycle working fluid. The total amount of power output to 3353.27kW. The dual systems with single working fluid heat recovery plan is also studied, and with R141b as the working fluid for both the top cycle and the bottom cycle, the total amount of power output is 3325.03kW, and the heat recovery system is simple and compact, with good economical benefit.

Two applications of the non-linear eddy-viscosity model EARSM are presented in the simulations of transonic turbulent flow involving shock waves and other related complex features. The simulations are implemented applying an in-house CFD program based on the unstructured discontinuous Galerkin method, an alternative discretization method of the classical finite volume one to precisely capture the flow features. A series of turbulence feature variables in boundary layers are comparatively observed and analyzed. For the first case of transonic flow over a bump, the redistribution effect of Reynolds stress components rooted in the non-linear constitution relation promotes streamwise turbulence fluctuation and suppresses the normal one in boundary layer, comparing with the traditional linear constitution relation, especially when passing the shocks. The production magnitudes of the turbulence shear stress and kinetic energy for the non-linear model show slightly more sensitive to perturbations, such as the occurrence of shock front or compression corner, than the linear one. For the second case of a transonic turbine vane, similar redistribution effect of the non-linear model is also verified on suction surface around the strong shock. The straightforward redistribution effect is absent on pressure surface around middle part of the vane with favorable pressure gradients. There the non-linear model evaluates higher magnitudes of streamwise, normal and shear Reynolds stress components than the linear one, thus resulting locally stronger heat convection and higher surface temperature.

Conjugate heat transfer is a key feature of modern gas turbine, as cooling technology is widely applied to improve the turbine inlet temperature for high efficiency. Impact of conjugate heat transfer on heat loads and thermodynamic efficiency is a key issue in gas turbine design. This paper presented a through flow calculation method to predict the impact of heat transfer on the design process of a convective cooled turbine. A cooling model was applied in the through flow calculations to predict the coolant requirements, as well as a one-dimensional mixing model to evaluate some key parameters such as pressure losses, deviation angles and velocity triangles because of the injection cooling air. Numerical simulations were performed for verification of the method and investigation on conjugate heat transfer within the blades. By comparing these two calculations, it is shown that the through flow calculation method is a useful tool for the blade design of convective cooled turbines because of its simplicity and flexibility.

Curvature discontinuity may exist in the surface, especially at the leading edge, of a compressor blade. The importance of curvature continuity or discontinuity has been realized, but its definite influences and mechanisms still need research. In this paper, an optimization method is proposed to design continuous-curvature blade profiles from datum blades, and a Reynolds-Averaged Navier-Stokes (RANS) solver with a transition model is used to examine the flowfields and performances of different blade profiles. Large eddy simulations of several cases are also presented to validate the RANS results. The effects of leading-edge-blend-point curvature continuity and the main-surface curvature continuity are studied separately. The results show that the curvature continuity at the leading-edge blend point helps to eliminate the separation bubble, and thus improves the blade performance. The main-surface curvature continuity is also found beneficial, although its effects are much smaller than those of the blend-point curvature continuity. Boundary-layer equations of the blade profiles are analyzed in terms of order of magnitude to further study the different curvature-continuity effects of the blend point and main surface theoretically. The analysis reveals the physical facts that produce the pressure spike around a leading-edge blend point with a discontinuous curvature, and thus explains how the optimized continuous-curvature leading edge removes the pressure spike and the related separation. The analysis also finds that the high spike appearing near the nose of a continuous-curvature leading edge at larger incidences is controlled by the large nose curvature rather than curvature discontinuity. The dual separation mechanisms also help to solve the so-called sharp leading edge paradox.

Performance prediction method of the modern gas turbine is an important tool for the engine design and performance analysis. This paper integrates a hybrid cooling model to the previous research of gas turbine performance prediction method which is applied to predict the multi-shaft gas turbine performance. The cooling model, combined with the semi-empirical model and analytical model, had been originally proposed for the investigation of turbine convective cooling or film cooling performance. The aim of the work is to apply the hybrid model to effectively estimate the coolant requirement in the gas turbine performance prediction, therefore to improve the reliability of the analysis in the innovative gas turbine cycle. The analysis involved a three-shaft gas turbine. Experiments were carried out on the engine, and the effectiveness of the prediction method is validated by the experiment. Consequently detailed performance characteristic of the engine is investigated under different stagger angles of the variable-angle nozzle, revealing how the stagger angle of the variable-angle nozzle and the turbine inlet temperature affect the gas turbine performance. The analysis is considered valuable for the engine operation and components optimization.

A framework for the simulations of conjugate heat transfer (CHT) problems using discontinuous Galerkin (DG) methods on unstructured grids is presented. The compressible fluid dynamic equations and solid heat conduction equations are discretized into the explicit DG formulations simultaneously. The Bassi-Rebay method is used in the gradients computation inside both fluid and solid domains. Fully coupled strategy based on the data exchange process via the numerical flux of interface quadrature points is devised. Various turbulence models and the local-variable-based transition model γ -Re θ are assimilated into the unified algorithm framework. The feasibility of the methodology is validated by some test cases. The work can be viewed as a primary attempt towards further investigations of DG and other high-accuracy methods applications in the engineering CHT problems.

Analytical and experimental researches on the characteristics of a three-shaft gas turbine are presented in the paper. The concerned gas turbine engine includes a twin-shaft gas generator and a third shaft — the free turbine for power generation. The free turbine uses a variable-angle nozzle (VAN) for fuel saving and load-adjusting flexible. The engine performance is calculated by using the multi-dimensional Newton-Raphson method, which is based on a set of matching constraints described by the error matrix and the performance maps of the related components. It has a better accuracy and stability than those of some other methods (e.g. parameter cycle method) and is well suitable for solving the off-design problem. The suggested prediction method, presented as a computer program written in Fortran 95, is extremely flexible and can be employed to various engine configurations. Experiments are carried out on the concerned engine by controlling the stagger angle of the VAN, then adjusting the fuel consumption for different outputs. The accuracy of the prediction method is validated by the experiment. Detailed performance characteristic of the engine is investigated under five different stagger angles of the VAN when the T 3 value was controlled from 85% to 105% of its design value, revealing how the T 3 and the stagger angle of the VAN affect the gas turbine performance. The results are useful for the engine operation and components optimization.

The tip clearance flow has a significant influence on the compressor performance and stability. CFD, which is a current tool, has been widely used to investigate the flow by many researchers. In this paper, an unstructured-grid code based on a RKDG method was developed with an improved vertex-based slope limiter to ensure the nonlinear stability. The limiter tests show that the improved limiter has less numerical dissipation and it can keep the high-order accuracy. The performance for NASA Rotor 37 was simulated to validate the RKDG code. The results are compared with the experimental data and the ones computed by NUMECA FINE ™ /Turbo. It is shown that the results computed by the RKDG code are in better agreement with the experimental data, which implies that the high-order accuracy method is very important for improving the CFD reliability. Finally, the tip clearance flow of the compressor was investigated using the RKDG code. It is found that the tip leakage jet flow could be separated into two parts and they go downstream separately without mixing.

In this paper Discontinuous Galerkin Method (DGM) is applied to solve the Reynolds-averaged Navier-Stokes equations and S-A turbulence model equation in curvilinear coordinate system. Different schemes, including Lax-Friedrichs (LF) flux, Harten, Lax and van Leer (HLL) flux and Roe flux are adopted as numerical flux of inviscid terms at the element interface. The gradients of conservative variables in viscous terms are constructed by mixed formulation, which solves the gradients as auxiliary unknowns to the same order of accuracy as conservative variables. The methodology is validated by simulations of double Mach reflection problem and three-dimensional turbulent flowfield within compressor cascade NACA64. The numerical results agree well with the experimental data.

Spalart-Allmaras (S-A) model based Delayed Detached Eddy Simulation (DDES) is performed to investigate the flow field in a compressor cascade (NACA64A-905) with experimental data for calibration. The value of the modeling coefficient C DES in DDES is open for revision and depends heavily on the numerical schemes. The effects of C DES on the DDES results are studied and an optimal C DES value is estimated for the specific case, with MUSCL reconstructed Roe scheme incorporated in in-house CFD codes. C DES value of 0.2 is turned out reliable concerning both accuracy and convergence. S-A model is also performed for comparison. Results from different methods indicate that the time-averaged results by DDES with C DES of 0.2 are more consistent with the experimental results than those by S-A model. The instantaneous flow field predictions show that DDES is well capable of capturing the unsteady features of the cascade flow, especially the wake mixing process.

An attempt is made in the present paper to apply DES (Detached Eddy Simulation), which is based on S-A model of RANS, for investigating the flow field around a subsonic compressor rotor with a tip clearance of 2% blade height. Comparison of the results by DES and S-A model shows that DES model can capture more intensive vortex flow, such as tip leakage flow, double leakage flow, as well as interaction between the leakage flow and wake flow downstream of the rotor passage. DES model predicts more complicated flow at the separation region near the hub. DES simulation for different operation conditions also reveals interesting details. The shedding angle and strength of the tip leakage flow changes with the blade loading. The starting point of the leakage vortex moves towards the leading edge when the blade loading increases. Double leakage is observed only at the design and higher loading conditions, and is not at a lower loading condition. The tip leakage vortex splits into two branches downstream of the rotor blade due to interaction with the wake flow. Instantaneous results show unsteadiness of the tip leakage vortex. Alternating regions of higher and lower loss is found along the time-averaged leakage vortex trajectory. Obvious is also the unsteadiness in the separation region near the hub.