Effects of endwall geometry and stacking on two-stage supersonic turbine performance (original) (raw)
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Turbine blades and vanes of modern aero-engines are commonly manufactured by casting. The casting process often introduces slight geometry variations. In the endwall region this leads to inter-platform steps, gaps and leakage flows. This paper determines the underlying loss mechanisms associated with each of these geometric features and guides designers in minimizing their impact on efficiency. The paper shows that the presence of an inter-platform step causes a pair of vortical structures to be superimposed onto the blade existing secondary flow structure. These are shown to always increase loss. When manufacture variations are considered the optimal design intent blade is shown to be one where the suction side endwall is lower than the pressure side endwall. The paper shows that when leakage mass flow is introduced the presence of a step can either raise or reduce loss. A correlation which gives the optimal step height for a set leakage mass flow is presented. In the final part of the paper measured engine vane geometries are used to determine the impact of endwall geometry variation on turbine stage efficiency.
Volume 7: Turbomachinery, Parts A, B, and C, 2010
The application of non-axisymmetric end walls in turbine stages has gained wide spread acceptance as a means to improve the performance of turbines in both power generation and aero-derivative applications. Non-axisymmetric end walls are aimed at the control of secondary flows and to a large extent have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. Little or no literature is available describing their performance at conditions other than design.
Sensitivity Analysis of Supersonic Turbine Trailing Edges
2018
The use of compact architectures on aircraft turbine engines challenges the design and management of structural and thermal load requirements. Even operating in subsonic conditions, supersonic regimes may develop at the high pressure turbine passages,<br> experiencing complex compression and expansion wave systems that interact with adjacent stages of the turbine. When cooling<br> flow is ejected through the blade trailing edge slots, non-symmetrical con gurations can appear due to the interaction of the injected flow with the surrounding flow eld, leading to undesired loads and eciency loses.<br> In this work, a combination of RANS simulations, global stability and sensitivity analysis is employed to identify and explain the physical mechanisms of this phenomenon. A global mode associated with the geometrical expansion of the trailing edge slot is identified, and linked to the non-symmetrical con gurations. To conclude, the regions where the flow would be more sen...
Computational Analysis of Unsteady Flow in a Partial Admission Supersonic Turbine Stage
Volume 2D: Turbomachinery, 2014
Turbines used in upper stage engine for a rocket are sometimes designed as a supersonic turbine with partial admission. This study deals with numerical investigation of supersonic partial admission turbine in order to understand influences on the unsteady flow pattern, turbine losses and aerodynamic forces on rotor blades due to partial admission configuration. Two-dimensional CFD analysis is conducted using "Numerical Turbine" code. Its governing equation is URANS (Unsteady Reynolds Averaged Navier-Stokes Simulation) and fourth-order MUSCL TVD scheme is used for advection scheme. The unsteady simulation indicates that strongly nonuniform circumferential flow field is created due to the partial admission configuration and it especially becomes complex at 1 st stage because of shock waves. Some very high or low flow velocity regions are created around the blockage sector. Nozzle exit flow is rapidly accelerated at the inlet of blockage sector and strong rotor LE shock waves are created. In contrast, at rotor blade passages and Stator2 blade passages existing behind the blockage sector, working gas almost stagnates. Large flow separations and flow mixings occur because of the partial admission configuration. As a result, additional strong dissipations are caused and the magnitude of entropy at the turbine exit is approximately 1.5 times higher than that of the full admission. Rotor1 blades experience strong unsteady aerodynamic force variations. The aerodynamic forces greatly vary when the Rotor1 blade passes through the blockage inlet region. The unsteady force in frequency domain indicates that many unsteady force components exist in wide frequency region and the blockage passing frequency component becomes pronounced in the circumferential direction force. Unsteady forces on Rotor2 blades are characterized by a low frequency fluctuation due to the blockage passing.
2011
Turbine manufacturers are continually striving to improve turbine performance, and thus reduce emissions, which has been accelerated with the inception of the Kyoto protocol. One of the areas that have received attention is the controlling of secondary flows. The current investigation looks at the use of endwall contouring to reduce the effect of secondary flows. Endwall contouring has been shown to have promise by several researchers. The numerical investigation was based on the experimental geometry which was based on the cascade geometry of Ingram. The same boundary conditions were used, but the numerical investigation was unsteady. The steady state experimental and numerical results were also used as a basis for comparison of the isentropic stage total-to-total efficiency. The experimental time averaged velocity magnitude plots show reasonable correlation, but fail to capture the steep gradients between 25% and 35% span and between 75% and 85% span. Looking at the time dependent...
Sensitivity Analysis of Supersonic Turbine
2018
The use of compact architectures on aircraft turbine engines challenges the design and management of structural and thermal load requirements. Even operating in subsonic conditions, supersonic regimes may develop at the high pressure turbine passages, experiencing complex compression and expansion wave systems that interact with adjacent stages of the turbine. When cooling flow is ejected through the blade trailing edge slots, non-symmetrical configurations can appear due to the interaction of the injected flow with the surrounding flow field, leading to undesired loads and efficiency loses. In this work, a combination of RANS simulations, global stability and sensitivity analysis is employed to identify and explain the physical mechanisms of this phenomenon. A global mode associated with the geometrical expansion of the trailing edge slot is identified, and linked to the non-symmetrical configurations. To conclude, the regions where the flow would be more sensitive to flow modifica...
Mid-Span Losses in Turbine Blades at Subsonic and Supersonic Speeds
HAL (Le Centre pour la Communication Scientifique Directe), 2017
The effects of compressibility are intrinsic to many axial flow turbomachines, is. Both subsonic and supersonic speed ranges are considered in this investigation. Subsonic surface base pressures, and wake energy separation, are a direct result of periodic von Kármán vortex shedding. This is the principal cause of both wake energy separation and the related subsonic base static pressure deficit. At high subsonic speeds a 17 o C temperature difference across the wake was observed. This time-averaged temperature separation was a manifestation of the energy separation (Eckert-Weise) effect. At supersonic speeds the trailing edge base pressure, and the wake energy separation, exhibit different characteristics from the subsonic behavior. Shock waves from the trailing edge may impinge on the adjacent suction surface adversely affecting the downstream boundary layer. Supersonic flows usually cause shock and expansion waves and this may occur in steady flows. Other wake modes may also involve von Kármán vortex shedding from the confluence region of the wake. This is not the only form of shedding and anomalous, or exotic, shedding may also play an important role.
The effects of shape and size on duct-augmented horizontal axis turbine performance
Wind Engineering, 2020
This article seeks to contribute to knowledge on duct-augmented turbines by investigating the influence of the key geometric parameters of the duct on the turbine performance: (i) duct expansion angle and length, (ii) position of the duct relative to the rotor and (iii) added geometric features to the duct. A new analytic model is proposed for the duct-augmented turbine and used for the investigation. The proposed analytic model used in this study was developed with existing momentum and blade element analysis methodologies serving as its basis. Using the proposed analytic model, the duct length is found to be more influential on the duct turbine system performance than the duct expansion angle. In addition, the performance can be enhanced by addition of a flange to the duct trailing edge. The study also highlights that the optimum rotor location within a duct is slightly behind the minimum duct area.
Endwall aerodynamic losses from turbine components within gas turbine engines
Propulsion and Power Research, 2017
A survey of research on aerodynamic loss investigations for turbine components of gas turbine engines is presented. Experimental and numerically predicted results are presented from investigations undertaken over the past 65 plus years. Of particular interest are losses from the development of secondary flows from airfoil/endwall interactions. The most important of the airfoil/endwall secondary flows are passage vortices, counter vortices, and corner vortices. The structure and development of these secondary flows are described as they affect aerodynamic performance within and downstream of turbine passage flows in compressible, high speed flows with either subsonic or transonic Mach number distributions, as well as within low-speed, incompressible flows. Also discussed are methods of endwall contouring, and its consequences in regard to airfoil/endwall secondary flows.