High-loaded Turbine Research Articles

Numerical studies on shock wave and boundary layer interaction in the high-load turbine rotor cascades

Design of transonic high-load turbine is the essential approach to improve thrust-to-weight ratio of gas turbine engines. The shock wave and boundary layer interaction (SWBLI) in high-load turbine is one of the important unsteady sources and the main source of loss in turbine stages. In order to study mechanism of SWBLI in high-load turbine, rotor blades with loading coefficients range from 1.6 to 2 were designed and Delayed Detached Eddy Simulations (DDES) were carried out. The influences of loading coefficient, exit isentropic Mach number and incidence angle on characteristics of shock wave, SWBLI as well as flow details in the blade passages were compared. Results indicated the shock wave was generated and enhanced as exit isentropic Mach numbers increased leading to the increase of 2.8% in the total pressure loss coefficient. There was not significant difference in the total pressure loss coefficient as loading coefficient increased, however the shock wave was stronger and the separation bubble was longer at the loading coefficient of 1.6. Meanwhile, the influence of strong separation near the leading edge of suction surface induced by variation of incidence angles on the characteristics of the shock wave and the loss was also obvious.

Experimental and Numerical Investigations for Dual−Cavity Tip Aerodynamic Performance in the Linear Turbine Cascade

Experimental and numerical studies of a linear high-loaded turbine cascade with a dual−cavity tip structure are presented in this paper. The experimental conditions contained an increase in the outlet Mach number from 0.42 to 0.92, a change in the incidence angle from −15° to 15° and an increase in the relative clearance size from 0.36% to 1.4%. The ability of the dual−cavity tip to control leakage losses and vortices is assessed using the total pressure coefficient and the Q-criterion. This research indicates that the leakage vortex interacts strongly with the passage vortex, and the change in working conditions affects the balance between the two vortices and thus the flow field structure. The experimental and numerical results prove that the dual−cavity tip can reduce losses in all operating conditions, with the best control effect reduced by 0.025 in a large clearance size condition. In addition, the leakage control effect of the blade tip structure is more influenced by the incoming flow angle and clearance size than the Mach number.

Effect of Slot Jet Flow on Non-Axisymmetric Endwall Cooling Performance of High-Load Turbines

As vane inlet temperatures and turbine loadings are increasing, the aerodynamic and thermal management for the endwalls of gas turbines have received increased attention. Non-axisymmetric endwalls are becoming popular due to their proficient capabilities to modify the secondary flow fields and to change the film cooling performance on the endwalls. In this study, by considering the interaction between mainstream and purge flow based on non-axisymmetric endwall contouring, the numerical research model used in the present research was established. Based on the validated numerical method, the influence of the non-axisymmetric endwall contouring on the film-cooling effectiveness and aerodynamic characteristics was studied. Furthermore, the effect of different inclination angles on the film-cooling performance of the contoured endwalls was also investigated. The results indicate that for the high-load turbine vane used in this research, various types of non-axisymmetric endwall contouring can alter the aero-dynamic characteristics and cooling performance simultaneously. By inhibiting the secondary flows, non-axisymmetric endwall contouring can reduce the total cascade pressure loss coefficient by 0.305%. In addition, non-axisymmetric endwall contouring can significantly enhance the effective coverage area of purge flow up to 28.29%, and the endwall near the suction side can achieve better cooling performance. Finally, non-axisymmetric endwall contouring can improve the protective effect of large-angle purge flow.

Experimental and Numerical Investigation of High Load Turbine Blade Tip Cavity Structures

Abstract Leakage flow loss is an important factor affecting the aerodynamic efficiency of turbines. In this paper, experimental and numerical computational studies were used to investigate three different tips of a highly loaded turbine rotor. The single-cavity tip formed by squealers was considered as the original structure. Based on this, two improved structures were developed, namely, cavity winglet tip (CWT) and double-cavity combined winglet tip (DCWT). Five-hole probe and oil flow visualization were used for experimental studies, and numerical calculations were used to analyze vortex system structure and loss development. It was found that the double-cavity combined winglet tip structure can effectively change the vortex structure inside the cavity and reduce the leakage flowrate. At the same time, the aerodynamic performance was optimized by 4%.

4 패드 저널 베어링 2상 유동 2-FSI 해석

A four-pad journal bearing is used to support high-speed, high-load turbine generators. The direct lubrication type has the merits of low power loss, low pad temperature, and high load capacity. Direct lubrication offers the additional advantages of good vibration and anti-shock characteristics. The simulation of bearings of this type requires two-phase fluid analysis because the fluid consists of a mixture of oil and air. Apart from this, because of the movement of the rotor and tilting pad, two-phase two-fluid structure interaction (2-FSI) simulation is required to determine the final locations of the rotor and pads. Finally, based on these locations, a static simulation is conducted to determine the temperature, pressure, and the oil and air distribution. The rotor moves 0.5 mm in the direction of negative gravity and the tilting pad rotates 0.09, 0.035 degrees with a minimum gap of 78 mm and maximum pressure of 10 MPa.

Numerical Investigations of the Influence of Unsteady Vane Trailing Edge Shock Wave on Film Cooling Effectiveness of Rotor Blade Leading Edge

Unsteady numerical simulations of a high-load transonic turbine stage have been carried out to study the influences of vane trailing edge outer-extending shockwave on rotor blade leading edge film cooling performance. The turbine stage used in this paper is composed of a vane section and a rotor one which are both near the root section of a transonic high-load turbine stage. The Mach number is 0.94 at vane outlet, and the relative Mach number is above 1.10 at rotor outlet. Various positions and oblique angles of film cooling holes were investigated in this research. Results show that the cooling efficiency on the blade surface of rotor near leading edge is significantly affected by vane trailing edge outer-extending shockwave in some cases. In the cases that film holes are close to leading edge, cooling performance suffers more from the sweeping vane trailing edge outer-extending shockwave. In addition, coolant flow ejected from oblique film holes is harder to separate from the blade surface of rotor, and can cover more blade area even under the effects of sweeping vane trailing edge shockwave. As a result, oblique film holes can provide better film cooling performance than vertical film holes do near the leading edge on turbine blade which is swept by shockwaves.

929 高負荷タービン翼列の二次流れ損失低減に関する研究(GS-5 流体機械(3))

929 高負荷タービン翼列の二次流れ損失低減に関する研究(GS-5 流体機械(3))

Computational study of the effects of shroud geometric variation on turbine performance in a 1.5-stage high-loaded turbine

Generally speaking, main flow path of gas turbine is assumed to be perfect for standard 3D computation. But in real engine, the turbine annulus geometry is not completely smooth for the presence of the shroud and associated cavity near the end wall. Besides, shroud leakage flow is one of the dominant sources of secondary flow in turbomachinery, which not only causes a deterioration of useful work but also a penalty on turbine efficiency. It has been found that neglect shroud leakage flow makes the computed velocity profiles and loss distribution significantly different to those measured. Even so, the influence of shroud leakage flow is seldom taken into consideration during the routine of turbine design due to insufficient understanding of its impact on end wall flows and turbine performance. In order to evaluate the impact of tip shroud geometry on turbine performance, a 3D computational investigation for 1.5-stage turbine with shrouded blades was performed in this paper. The following geometry parameters were varied respectively: The aim of this paper is to isolate the influence of shroud and cavity geometry modifications on turbine aerodynamicnamic performance and to obtain clear trends of efficiency changes caused by different tip shroud geometry. Moreover, interaction between leakage flow and mainstream for different shroud configuration is also highlighted in order to penetrate into the physical mechanisms producing them. Due to the limitations of the model selected in this paper, the aim of research is not to put forward the design rules of turbine shroud. However, the results obtained from this work will be useful to the integrated design and optimization of turbine with shrouded blades.

Control of secondary flow loss in turbine cascade by streamwise vortex

An experimental and numerical study of flow control in a high-loaded turbine cascade was performed in order to reduce the secondary flow losses by means of streamwise vortices. The interaction mechanisms between the streamwise vortex and the secondary vortex and the impact of the streamwise vortex position on the performance of the turbine cascade are discussed in detail. The results indicate that streamwise vortex can effectively reduce the stagnation pressure loss and the flow deviation. The control effect is significantly dependent on the relative location of the streamwise vortex with respect to the cascade. It can suppress the development of the pressure side leg of the horseshoe vortex better if the streamwise vortex is close to the suction side of blade leading edge. The experimental and computational results in this configuration show a decrease in stagnation pressure loss at the cascade exit by 6.5 ± 1.0% and 5.4%, respectively.

Preconditioning method and engineering application of large eddy simulation

On applying large eddy simulation (LES) to engineering interest, one of the keys is to obtain two-order low-dissipation shock-capturing schemes adapted to LES. Therefore, the preconditioning method for all speed flows is adopted. However, the accuracy of preconditioned schemes is not satisfactory because of the poor performance of stability of preconditioning techniques especially in viscous flows. The reason of unstability is attributed to the unstability structure in the preconditioned eigenvalue matrix. Based on Roe scheme and two assumptions for low-Mach-Number flows, the new scheme named Low-Speed-Roe scheme is deduced for removing the unstability structure. Numerical experiments show that this scheme has the reasonable computational stability. For general-precision problems, Low-Speed-Roe scheme has similar behavior as the classical preconditioned Roe scheme. For simulations of high-accuracy requirement such as LES, Low-Speed-Roe scheme can obtain better results of complex flows, such as the laminar separation bubble on the suction surface of the high-loaded turbine blade T106.

A Study of Advanced High-Loaded Transonic Turbine Airfoils

The development of high-performance turbine airfoils has been investigated under the condition of a supersonic exit Mach number. In order to obtain a new aerodynamic design concept for a high-loaded turbine rotor blade, we employed an evolutionary algorithm for numerical optimization. The target of the optimization method, which is called evolutionary strategy (ES), was the minimization of the total pressure loss and the deviation angle. The optimization process includes the representation of the airfoil geometry, the generation of the grid for a blade-to-blade computational fluid dynamics analysis, and a two-dimensional Navier-Stokes solver with a low-Re k-ε turbulence model in order to evaluate the performance. Some interesting aspects, for example, a double shock system, an early transition, and a redistribution of aerodynamic loading on blade surface, observed in the optimized airfoil, are discussed. The increased performance of the optimized blade has been confirmed by detailed experimental investigation, using conventional probes, hotfilms, and L2F system.

Aerodynamic Design and Investigation of a High-Loaded Turbine

Aerodynamic Design and Investigation of a High-Loaded Turbine