Turbomachinery of Gas Turbines in CFD

Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 2008

2010

Journal of Science and Arts, 2023

Energy consumption continues to rise due to the increase in the quality of human life. On the other hand, production of these energies must be done with the smaller impact on the environment as possible. All these facts are challenging engineers and researchers from this domain to develop new equipments or to improve the efficiency of the energy production equipments. It was proved that in the case of turbine, if a shroud is applied, the efficiency is raised. Given that in this paper is presented a study performed on different geometry of shrouds with different fixing elements. Computational fluid dynamics (CFD) simulations were performed using ANSYS Fluent software. The numerical domain rigorously reproduces an experimental setup from the laboratory. The rectangular fixing element do not deliver the expected result, instead it decreases the velocity in interest zone. The most important finding is that the velocity of the fluid increases by more than 50% in the most constrained section with convergent-divergent shroud.

A computational study is presented which investigates the predictive performance of two non-linear turbulence closures in simulating the physics pertinent to decelerating turbomachinery flows. The compared approaches are a cubic non-linear k-ε model and an algebraic Reynolds stress model. They have been considered as promising closures for improving the industry CFD state-of-the-art accounting for non-equilibrium effects. The authors adopt a parallel multi-grid algorithm, which is developed with a finite element formulation based on a highly accurate stabilized Petrov-Galerkin method. The finite element formulation is here applied on equal-order Q1-Q1 as well as mixed Q2-Q1 element pairs, and the accuracy of the latter approximation is assessed on near-wall flows simulation. The parallel solution algorithm for Reynolds Averaged Navier-Stokes modeling exploits an overlapping domain decomposition technique based on an "inexact explicit non linear Schwarz method". The compressor flow considered for model benchmarking is highly challenging because of the transitional nature of the flow and the existence of significant leading-and trailing-edge separations. The potential of non-isotropic closures has been investigated. The algebraic stress model is shown to provide a better base-line for non-equilibrium effects simulation with respect to the cubic k-ε model. As it is shown for the studied compressor cascade, the cubic eddy-viscosity model exhibits some predictive weaknesses, among them an excessive turbulence attenuation that results in un-realistically delayed transition to turbulence.

Journal of Turbomachinery, 1997

Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multistage, axial-flow compressors and LP turbines. The tests were run over a broad range of Reynolds numbers and loading levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modern engine components. Measurements of boundary layer characteristics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady flow codes and an unsteady flow code. This is the first time that time-resolved boundary layer measurements and detailed comparisons of measured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part 1 of this paper summarizes all of our experimental findings by using sketches to show how boundary laye...

2014

The effect of endwall contouring on the unsteady flow through a turbine rotor D.I. Dunn Department of Mechanical and Mechatronics Engineering, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Dissertation: PhDEng (Mech) December 2014 With increasing environmental concerns and the drive for a greener economy comes an increased desire to improve turbine engine fuel efficiency and reduce emissions. Unfortunately weight reduction techniques used increase the blade loading, which in turn increases the losses. Non-axisymmetric endwall contouring is one of several techniques being investigated to reduce loss in a turbine. An investigation at Durham University produced a non-axisymmetric endwall design for a linear cascade. An adaption of the most promising endwall was investigated in an annular rotating test rig at the CSIR using steady state instrumentation. The current investigation extends those investigations into the unsteady time domain. Previous investigatio...

Volume 5A: Heat Transfer, 2015

Endwall contouring is a technique used to reduce the strength and development of three-dimensional secondary flows in a turbine vane or blade passage in a gas turbine. The secondary flows locally affect the external heat transfer, particularly on the endwall surface. The combination of external and internal convective heat transfer along with solid conduction determines component temperatures, which affect the service life of turbine components. A conjugate heat transfer model is used to measure the non-dimensional external surface temperature, known as overall effectiveness, of an endwall with non-axisymmetric contouring. The endwall cooling methods include internal impingement cooling and external film cooling. Measured values of overall effectiveness show that endwall contouring reduces the impingement effectiveness alone, but increases the effectiveness of film cooling alone. Given the combined case of both impingement and film cooling, the laterally averaged overall effectivene...

AIP Advances

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...

Mathematical and Computer Modelling, 2013

Nowadays, turbocharged internal combustion engines (ICEs) are very common in automotive powerplants, monopolizing the Diesel sector and having a steadily increasing percentage in the gasoline one. In this frame, the interest in modeling the behavior of the turbomachinery components involved, with the ultimate goal of characterizing the performance of the turbocharged ICE, seems clear. A turbomachine can be simulated using 3D-CFD software, but its computational cost does not allow to reproduce the whole turbocharger test rig. Moreover, the existence of long ducts requires a considerable computational time until the pressure reflections at the boundaries dissipate in order to reach a periodic solution. The use of non-reflecting boundary conditions reduces the needed length of ducts without introducing spurious wave reflections. An anechoic boundary condition (BC) based on the Method of Characteristics has been previously developed, considering the case of an inviscid and adiabatic 1D flow of a perfect gas. However, real flows do not behave in such ideal manner. In this paper, the extension of the scope of the previous BC is sought. In this way, a methodology to evaluate the performance of the anechoic BC under these real flow situations is shown. The consideration of ideal gas instead of perfect gas, the flow viscosity and the non-homentropic flow makes it necessary to modify the Method of Characteristics, since the Riemann Invariants are not constant any more. In this frame they are referred to as Riemann Variables. An additional issue that has been considered is the effect of swirl flow, as the one in the turbine outlet, on the anechoic BC. Some improvements to be implemented in the BC are proposed in order to have a better performance in these real flow situations.

2018

The accuracy of predicting the engine bay flow field with computational fluid dynamics (CFD) is crucial for designing efficient cooling systems for heat sensitive components. The engine cooling fan is the main driving component in cases of high thermal load, such as uphill driving with a trailer, or high speed driving on a highway, when the ram air itself is no longer sufficient for cooling purposes. The most widely used fan modelling method is the Moving Reference Frame (MRF). This method can be used in steady and unsteady simulations, but has the drawback of using a fan geometry that is fixed in the global reference frame and, therefore, causing non-physical low velocity regions in the wake of the blades. The Rigid Body Motion (RBM or "sliding mesh") approach is a more accurate, but also more expensive approach, since it uses an unsteady solver. This study looks closely at the prediction of the flow field in the wake of an axial fan for different freestream velocities and fan speeds using the traditional MRF and RBM approach. In addition, a method that uses the average of flow field data for multiple MRF simulations with different fan positions is presented. Thereby the shadow of the fan blades is removed from the wake and the flow field becomes more uniform without the need of performing unsteady simulations. As a reference, measurements are performed on a vehicle fan with a 2 D Laser Doppler Anemometry setup in a small scale wind tunnel. The results show good agreement between the measurements and the RBM simulations. As expected, the MRF simulations show a distinct blade pattern in the wake flow field. This was successfully removed by the proposed averaged MRF method. Even though there are still some differences between this method and the experimental results, the average MRF method has shown to be applicable as it improves the flow field results at a relatively low computational cost.

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2001

A design method for profiling the end wall to reduce secondary flow has been reported previously. A profile has been tested in the Durham Linear Cascade and the results confirmed the design method. This paper describes the design and testing of a second-generation end wall, where the profiling is more suited to a real turbine. The new end wall has been tested in the linear cascade and a comprehensive set of measurements have been taken. These include traverses of the flow field upstream and downstream of the blade row, surface static pressure distributions on the end wall and flow visualization. Comparisons have been made with the results with a planar end wall and the earlier profiled end wall. Observed reductions in exit angle deviations are even greater than for the first design, although the loss reduction is not as great. The results verify the design, confirming profiled end walls as a means of reducing secondary flow, kinetic energy and loss. Overall an improved understanding...

The increase of efficiency in turbine blading systems is a field of continuous improvement in gas turbine industries. Currently the main efforts are directed towards re-blading by readapting the geometries to thermodynamic conditions. A CFD code can help reveal performance trends in the application of threedimensional blade stacking with competitive costs as compared to experimental testing. Due to the high computing costs involved, the routinely computation of turbulent flow in turbine stages as a trial and error design tool, or coupled to optimization algorithms, is still only feasible under a steady flow assumption and by using wall functions for the near wall solution. In the present work we have applied the k-∈ and the Spalart-Allmaras turbulence models to compute the turbulent flow around 3D turbine blades. For the T106 geometry the computations, using wall functions for the two models, are compared with the Spalart-Allmaras results without wall functions and also with experimental results. The results obtained for the Graz transonic turbine stage are compared with experiments. The accuracy inherent to performance assessment using wall functions is analyzed. This will permit that the following work, related to optimization of blade geometries, can be judged on the base of the accuracy attainable using wall functions.

International Journal of Rotating Machinery

Journal of Thermal Science

This present paper describes three dimensional computational analysis of complex internal flow in a cross flow fan. A commercial computational fluid dynamics (CFD) software code CFX was used for the computation. RNG k-e two equation turbulence model was used to simulate the model with unstructured mesh. Sliding mesh interface was used at the interface between the rotating and stationary domains to capture the unsteady interactions. An accurate assessment of the present investigation is made by comparing various parameters with the available experimental data. Three impeller geometries with different blade angles and radius ratio are used in the present study. Maximum energy transfer through the impeller takes place in the region where the flow follows the blade curvature. Radial velocity is not uniform through blade channels. Some blades work in turbine mode at very low flow coefficients. Static pressure is always negative in and around the impeller region.