In gas turbine combustors, ignition is achieved by using sparks from igniters to start a flame. The process of sparks interacting with fuel/air mixture and creating self-sustained flames is termed forced ignition. Physical and chemical properties of a liquid fuel can influence forced ignition. The physical effects manifest through processes such as droplet atomization, spray distribution, and vaporization rate. The chemical effects impact reaction rates and heat release. This study focuses on the effect of fuel composition on forced ignition of fuel sprays in a well-controlled flow with a commercial style igniter. A facility previously used to examine prevaporized, premixed liquid fuel-air mixtures is modified and employed to study forced ignition of liquid fuel sprays. In our experiments, a wall-mounted, high energy, recessed cavity discharge igniter operating at 15 Hz with average spark energy of 1.25 J is used to ignite liquid fuel spray produced by a pressure atomizer located in a uniform air coflow. The successful outcome of each ignition events is characterized by the (continued) presence of chemiluminescence 2 ms after spark discharge, as detected by a high-speed camera. The ignition probability is defined as the fraction of successful sparks at a fixed condition, with the number of events evaluated for each fuel typically in the range 600–1200. Ten fuels were tested, including standard distillate jet fuels (e.g., JP-8 and Jet-A), as well as many distillate and alternative fuel blends, technical grade n-dodecane, and surrogates composed of a small number of components. During the experiments, the air temperature is controlled at 27 C and the fuel temperature is controlled at 21 C. Experiments are conducted at a global equivalence ratio of 0.55. Results show that ignition probabilities correlate strongly to liquid fuel viscosity (presumably through droplet atomization) and vapor pressure (or recovery temperature), as smaller droplets of a more volatile fuel would lead to increased vaporization rates. This allows the kernel to transition to a self-sustained flame before entrainment reduces its temperature to a point where chemical rates are too slow. Chemical properties of the fuel showed little influence, except when the fuels had similar physical properties. This result demonstrates that physical properties of liquid fuels have dominating effects on forced ignition of liquid fuel spray in coflow air.

This paper presents a numerical investigation on the rationality and reliability of film cooling experiments, in which the realistic temperature ratio (TR) of mainstream to cooling air are substituted by the density ratio (DR) of ambient air to a foreign gas with high density. Today, advanced gas turbines operate at much higher temperatures than the allowable temperature of turbine component materials, which makes it very difficult to achieve real TR in the most of laboratory environments, because the real TRs are usually larger than 2.0. Therefore, the foreign gas (for example CO 2 ) with high density was widely used to obtain a proper density ratio for simulating the mixing process of cooling air with high temperature mainstream thereby. However, the TR effect on film cooling is not completely replaced by DR, because the influence factors of film cooling performances are not only DR, but also the thermal properties of cooling gas and mainstream, such as specific heat capacity, viscosity and conductivity. In this work, a film-cooled endwall is used as specimen, and DRs are controlled by two ways, i.e. changing mainstream temperatures, and using a foreign gas, respectively. The numerical results of film cooling performances at the same DR obtained by the two ways are analyzed and compared. The analysis reveals the difference of film cooling performances between TR and DR on the film-cooled endwall, and the comparison indicated that the errors caused by the substitution of foreign gas are acceptable, only when BR, DR, Re ∞ and T ∞ are all small, but when BR, DR or Re ∞ increases, the relative error cannot be neglected, and it may reach 30% in real running conditions.

The need to study flow and heat transfer in turbine blade cooling design calls to develop appropriate modelling approaches able to return accurate predictions at a reduced computational costs. Here we propose and scrutinize a quadratic version of the well-known k-ε-ζ-f RANS turbulence models, aiming at sensitizing the model to the effect of rotation in configurations mimicking the flow in turbine internal cooling. Starting from the evidence that rotation modified turbulent flow through a turbulence suppression (enhancement) on the stabilized (destabilized) surface, we modified the Cμ coefficient present in the formulation of turbulent viscosity introducing a dependence on the strain and vorticity tensors, the latter explicitly including solid body rotation. The proposed model was tested on plane channel and square-sectioned duct flows, and then used for simulating a rib-duct rotating channel. Results are assessed against DNS literature data and properly developed LES computations, by examining flow variables, heat transfer and turbulence budgets. We demonstrate that, as for the channel flows, the proposed quadratic model is able to accurately reproduce velocity, temperature and turbulent variables at various angular velocity regimes. In the duct flow the flow is subjected to the mutual influence vorticity induced by rotation and turbulence anisotropy developing close the walls. In particular, the non-linear rotation-sensitized model is able to reproduce the near-wall turbulent kinetic energy distribution close to the suction side, returning a zero value in the mid-span and a small peak close to the wall on the suction side. Turbulent kinetic energy and temperature budgets analysis demonstrates the capabilities of the model in describing all the terms in the equations. Also if some tuning of the model is required, these analysis showed very encouraging results. In fact if the basic mechanisms of turbulence and heat transfer are properly predicted, then it can be expected that the model can be successfully applied to a set of different cases. For such reason, the model was applied to the analysis of flow and heat transfer in a rotating ribduct with reasonably results.

A range of popular hybrid Reynolds averaged Navier-Stokes - large eddy simulation (RANS-LES) methods are tested for cavity and labyrinth seal flows using an in-house high-order computational fluid dynamics (CFD) code and a commercial CFD code. The models include the Spalart-Allmaras (SA) and Menter SST variants of delayed detached eddy simulation (DDES), the Menter scale adaptive simulation (SAS) model, and a new enhanced variant of SA-DDES recently presented in the literature. The latter modifies the original definition of the subgrid length-scale used in DDES based on local vorticity and strain. For both geometries, the meshes are hybrid RANS-LES adequate. Very low levels of resolved turbulent content are observed for both the cavity and labyrinth seal flows for all models apart from the enhanced version of DDES. Similar findings are observed for both the commercial and in-house CFD codes. For both cases most models essentially produce a quasi-two-dimensional flow field with minimal resolved content. For the cavity simulations there is a significant under prediction of turbulent statistics. The enhanced version of SA-DDES shows a significant improvement and resolves turbulent content over a wide range of scales. Improved agreement with experimental measurements is also observed. It is recommended that extreme care should be taken where hybrid RANS-LES simulations are essentially steady but have lower than RANS levels of eddy viscosity.

The present study aims at analysing the Boussinesq constitutive relation validity in a corner separation flow of a compressor cascade. The Boussinesq constitutive relation is commonly used in Reynolds-averaged Navier-Stokes (RANS) simulations for turbomachinery design. It assumes an alignment between the Reynolds stress tensor and the zero-trace mean strain-rate tensor. An indicator that measures the alignment between these tensors is used to test the validity of this assumption in a high fidelity large-eddy simulation. Eddy-viscosities are also computed using the LES database and compared. A large-eddy simulation (LES) of a LMFA-NACA65 compressor cascade, in which a corner separation is present, is considered as reference. With LES, both the Reynolds stress tensor and the mean strain-rate tensor are known, which allows the construction of the indicator and the eddy-viscosities. Two constitutive relations are evaluated. The first one is the Boussinesq constitutive relation, while the second one is the quadratic constitutive relation (QCR), expected to render more anisotropy, thus to present a better alignment between the tensors. The Boussinesq constitutive relation is rarely valid, but the QCR tends to improve the alignment. The improvement is mainly present at the inlet, upstream of the corner separation. At the outlet, the correction is milder. The eddy-viscosity built with the LES results are of the same order of magnitude as those built as the ratio of the turbulent kinetic energy k and the turbulence specific dissipation rate ω. They also show that the main impact of the QCR is to rotate the mean strain-rate tensor in order to realign it with the Reynolds stress tensor, without dilating it.

Supercritical CO 2 (S-CO 2 ) has the potential to be used as the working fluid in a power cycle since S-CO 2 shows a density value high as its liquid phase while the viscosity value remains closer to its gaseous phase. Thus, it requires much less work to compress due to its low compressibility as well as relatively small flow resistance. However, the S-CO 2 leakage flow from turbo-machinery via seal becomes one of the important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions. In the previous turbo expo paper, the effect of the tooth length on the critical flow and comparing the results to the existing two phase system analysis code calculation were presented. In this paper, the gap effect, which is simulated by changing the diameter of a orifice and the number of tooth effect in a labyrinth seal geometry nozzle are presented by using the same experimental facility described in the previous paper. In addition, this paper includes the experimental results under various conditions including not only single phase flow such as supercritical, and gaseous state only but also two phase flow condition.

Badak LNG Plant Bontang have succeeded in mixing different brands of turbomachinery lube oil ISO VG32 which intended to increase flexibility of lube oil usage and eliminate to one brand dependency during operational. The methodology referred to ASTM D7155 Standard Practice for Evaluating Compatibility of Mixtures of Turbine Lubricating Oils and ASTM D4378 Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam, Gas and Combined Cycle Turbines. The study was started from lube oil compatibility test at laboratory. After that, a ratio 70:30 of ISO VG32 existing lube oil (DTE Light) and new lube oil (Turbolube XT32) were mixed and trialed to Fuel Gas Compressor and its Turbine Driver. Lube oil and equipment operating parameter such as viscosity, color, water content, total acid number, foaming tendency, oxidation, metal content, flash point, bearing temperature, filter differential pressure, and vibration were collected and compared to baseline data to analyze deterioration indication of lube oil. As long as eight month trial test, there was no deterioration indication of lube oil mixture and no significant influence to the equipment operating performance. Badak LNG have decided to continue lube oil mixing.

Pressure ratios of modern high pressure radial compressors tend to increase along with pressure fluctuations and the excitation potential on the impellers. The vibrational interactions between side cavities, filled with high pressure fluid, and the impeller structure play an important role in designing a machine for reliable operation. However, they are not yet fully understood. Vibrations at frequencies that have been uncritical at lower pressure levels could become critical at a higher pressure level. Additionally, coupling effects between fluid and structure are becoming stronger at higher fluid densities. For a safe and reliable design, the excitation and the damping mechanism of coupled modes has to be better understood. To understand the interaction, especially regarding the damping behavior, of coupled structure and acoustic modes, a comprehension of the behavior of the uncoupled or weakly coupled modes is required. The structural damping ratio is very small and it has been analyzed in existing literature extensively. The damping behavior of uncoupled acoustic modes, however, is not yet well investigated. This paper focuses on the damping behavior of acoustic modes that are weakly coupled to structure modes. Measurement results gathered at the aeroacoustic test rig at the University of Duisburg-Essen are presented. The results show the influence of fluid pressure variations on the damping behavior of acoustic modes. Therefore, the response functions of some selected acoustic modes are evaluated with the Peak-to-Peak method. In general, the damping decreases with increasing fluid pressure. Furthermore, a relationship of the damping ratio, the kinematic viscosity, and the natural frequency of the acoustic modes has been detected.

Tip leakage loss characterization and modeling plays an important role in small size radial turbine research. The momentum of the flow passing through the tip gap is highly related with the tip leakage losses. The ratio of fluid momentum driven by the pressure gradient between suction side and pressure side and the fluid momentum caused by the shroud friction has been widely used to analyze and to compare different sized tip clearances. However, the commonly used number for building this momentum ratio lacks some variables, as the blade tip geometry data and the viscosity of the used fluid. To allow the comparison between different sized turbocharger turbine tip gaps, work has been put into finding a consistent characterization of radial tip clearance flow. Therefore, a non-dimensional number has been derived from the Navier Stokes Equation. This number can be calculated like the original ratio over the chord length. Using the results of wide range CFD data, the novel tip leakage number has been compared with the traditional and widely used ratio. Furthermore, the novel tip leakage number can be separated into three different non-dimensional factors. First, a factor dependent on the radial dimensions of the tip gap has been found. Second, a factor defined by the viscosity, the blade loading, and the tip width has been identified. Finally, a factor that defines the coupling between both flow phenomena. These factors can further be used to filter the tip gap flow, obtained by CFD, with the influence of friction driven and pressure driven momentum flow.

Over recent decades, the variability and high costs of the traditional gas turbine fuels (e.g. natural gas), have pushed operators to consider low-grade fuels for running heavy-duty frames. Synfuels, obtained from coal, petroleum or biomass gasification, could represent valid alternatives in this sense. Although these alternatives match the reduction of costs and, in the case of biomass sources, would potentially provide a CO 2 emission benefit (reduction of the CO 2 capture and sequestration costs), these low-grade fuels have a higher content of contaminants. Synfuels are filtered before the combustor stage, but the contaminants are not removed completely. This fact leads to a considerable amount of deposition on the nozzle vanes due to the high temperature value. In addition to this, the continuous demand for increasing gas turbine efficiency, determines a higher combustor outlet temperature. Current advanced gas turbine engines operate at a turbine inlet temperature of (1400–1500) °C which is high enough to melt a high proportion of the contaminants introduced by low-grade fuels. Particle deposition can increase surface roughness, modify the airfoil shape and clog the coolant passages. At the same time, land based power units experience compressor fouling, due to the air contaminants able to pass through the filtration barriers. Hot sections and compressor fouling work together to determine performance degradation. This paper proposes an analysis of the contaminant deposition on hot gas turbine sections based on machine nameplate data. Hot section and compressor fouling are estimated using a fouling susceptibility criterion. The combination of gas turbine net power, efficiency and turbine inlet temperature (TIT) with different types of synfuel contaminants highlights how each gas turbine is subjected to particle deposition. The simulation of particle deposition on one hundred (100) gas turbines ranging from 1.2 MW to 420 MW was conducted following the fouling susceptibility criterion. Using a simplified particle deposition calculation based on TIT and contaminant viscosity estimation, the analysis shows how the correlation between type of contaminant and gas turbine performance plays a key role. The results allow the choice of the best heavy-duty frame as a function of the fuel. Low-efficiency frames (characterized by lower values of TIT) show the best compromise in order to reduce the effects of particle deposition in the presence of high-temperature melting contaminants. A high-efficiency frame is suitable when the contaminants are characterized by a low-melting point thanks to their lower fuel consumption.

The reduction of fluid-dynamic losses in high speed gearing systems is nowadays increasing importance in the design of innovative aircraft propulsion systems, which are particularly focused on improving the propulsive efficiency. Main sources of fluid-dynamic losses in high speed gearing systems are windage losses, inertial losses resulting by impinging oil jets used for jet lubrication and the losses related to the compression and the subsequent expansion of the fluid trapped between gears teeth. The numerical study of the latter is particularly challenging since it faces high speed multiphase flows interacting with moving surfaces, but it paramount for improving knowledge of the fluid behavior in such regions. The current work aims to analyze trapping losses in a gear pair by means of three-dimensional CFD simulations. In order to reduce the numerical effort, an approach for restricting computational domain was defined, thus only a portion of the gear pair geometry was discretized. Transient calculations of a gear pair rotating in an oil-free environment were performed, in the context of conventional eddy viscosity models. Results were compared with experimental data from the open literature in terms of transient pressure within a tooth space, achieving a good agreement. Finally, a strategy for meshing losses calculation was developed and results as a function of rotational speed were discussed.

The research work of the present study is focused on the numerical simulation of primary breakup of high-viscosity non-Newtonian fluids. For the experimental investigation of fluid properties such as viscosity, surface tension and flow behaviour on the jet breakup an external mixing twin-fluid nozzle is used, as investigated in a previous study [Müller et al., ASME Turbo Expo 2016, GT2016-56371]. To describe the disintegration process of the fluids, characteristic features like liquid jet morphology, breakup length, breakup frequency and spray angle are evaluated. Furthermore, the primary breakup of slurries is simulated without discretizing the particles as a third phase, which heavily reduced the computational effort. Instead, the physical properties (density, viscosity) of the liquid phase take the influence of the particles into account. The primary breakup was investigated using the open source CFD software OpenFOAM. To gather the morphology of the primary breakup and the flow field characteristics compressible large eddy simulations (LES) were performed and the movement of the gas-liquid interface was captured by means of the Volume of Fluid-Method (VOF). The conducted simulations showed good agreement with experimental results with respect to the characteristic features (e.g. breakup length) and the significant influence of viscosity and surface tension on the primary breakup. It is reasonably justified that the used OpenFOAM code and VOF is sufficient to simulate the primary breakup of particle laden liquids without discretizing particles as a third phase. Moreover, those findings contribute to a better understanding of the physics responsible of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.

Tip leakage flow (TLF) has a large impact on compressor performance and should be accurately predicted by CFD methods. New approaches to turbulence modelling, such as Delayed Detached Eddy Simulation (DDES) have been proposed which allow for greater accuracy of the numerical predictions while the mesh size as well as the central processing unit (CPU) time can be tremendously reduced. In this paper, the numerical simulation of the rotor in a low-speed large-scale axial compressor based on DDES and unsteady Reynolds-Averaged Navier-Stokes (URANS) turbulence models is performed subject to different working conditions of different tip gap sizes, to improve our understanding about the tip leakage vortex (TLV) dynamic mechanisms and discrepancy of these two methods. The rotor simulations are carried out on the same mesh based on the DDES requirements, and compared to experimental stereoscopic particle image velocimetry (SPIV) data before flow physics investigation. The simulation results capture the location of TLV and show qualitatively good agreement with experiments. DDES method brings improvements in time-averaged results over the Reynolds-Averaged Navier-Stokes (RANS) method. Firstly, the time-averaged and instantaneous results are compared to divide the TLV into three parts. Then the anisotropy of the Reynold stress of these two methods are analyzed in the tip leakage flow through Lumley triangle, to see the difference between the way to get the Reynold stress, using Boussinesq-type approximation in URANS and unsteady velocity fluctuation in DDES. The turbulent anisotropy can be derived from the nondimensional form of the anisotropy tensor. In the rotor simulation, the anisotropy varies along the TLV. The anisotropy of RANS method is weak because the eddy viscosity model is isotropic. Last, the velocity fluctuation data along the TLV core at different chord length are transformed to velocity spectra using fast Fourier transformation (FFT) method to discuss the TLV unsteadiness. The high frequency amplitude becomes obvious downstream the TLV because of losing stability. The result of URANS also has a conspicuous frequency but lower than DDES. The amplitude of URANS is much smaller. From this investigation it is determined that URANS can only predict the large-scale low-frequency dominant unsteady features. While the scale of dissipation and unsteadiness of TLV is small, the Reynolds averaging of URANS may neglect this unsteady phenomenon.

Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. Particle sticking implies the change in shape in terms of roughness of the impinged surface. The consequences of these deposits could be dramatic: these effects can shut an aircraft engine down or derate a land-based power unit. This occurrence may happen due to the reduction of the compressor flow rate and the turbine capacity, caused by a variation in the HPT nozzle throat area (geometric blockage due to the thickness of the deposited layer and the aerodynamic blockage due to the increased roughness, and in turn boundary layer). Several methods to quantify particle sticking have been proposed in literature so far, and the experimental data used for their validation vary in a wide range of materials and conditions. The experimental analyses have been supported by (and have given inspiration to) increasingly realistic mathematical models. Experimental tests have been carried out on (i) a full scale gas turbine unit, (ii) wind tunnel testing or hot gas facilities using stationary cascades, able to reproduce the same conditions of gas turbine nozzle operation and finally, (iii) wind tunnel testing or hot gas facilities using a coupon as the target. In this review, the whole variety of experimental tests performed is gathered and classified according to composition, size, temperature and particle impact velocity. Using particle viscosity and sticking prediction models, over seventy (70) tests are compared with each other and with the model previsions providing a useful starting point for a comprehensive critical analysis. Due to the variety of test conditions, the related results are difficult to be pieced together due to differences in particle material and properties. The historical data of particle deposition obtained over thirty (30) years are classified using particle kinetic energy and the ratio between particle temperature and its softening temperature. Qualitative thresholds for the distinction between particle deposition, surface erosion and particle break-up, based on particle properties and impact conditions, are identified. The outcome of this paper can be used for further development of sticking models or as a starting point for new insight into the problem.

Detail investigations on the primary breakup of high-viscosity liquids using external-mixing twin-fluid nozzles at increased system pressure are scarce. Therefore, the research work of the present study is focused on the investigation of pressure influence (1 - 11 bar (abs)) on the primary breakup by numerical simulation based on a previously studied nozzle [Müller et al., ASME Turbo Expo 2016, GT2016-56371]. The pressure influence was investigated for two liquids applying a wide range of viscosities (100 mPa s; 400 mPa s) and two atomizing air velocities (58 m/s; 74 m/s). To describe the disintegration process of the fluids, characteristic features like liquid jet morphology, breakup length and breakup frequency were evaluated. The primary breakup was investigated using the open source CFD software OpenFOAM. To gather the morphology of the primary breakup and the flow field characteristics compressible large eddy simulations (LES) were performed and the movement of the gas-liquid interface was captured by means of the Volume of Fluid-Method (VOF). The conducted simulations showed good agreement with experimental results with respect to the characteristic features (e.g. morphology and breakup length) and revealed a decrease of the breakup length with increasing ambient pressure for a constant liquid mass flow and atomizing air velocity. Moreover, those findings will contribute to a better understanding of the physics of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.

A simulation of the flow through a four-stage low pressure turbine (LPT) of an aero-engine is performed using an eddy-viscosity based RANS model. An analysis of secondary flow details in the vicinity of endwalls and strut surface is performed. An interaction of wakes generated by the swirler vanes and end-wall boundary layers is also studied. The CFD results are compared with own test rig data of LPT obtained in Polonia Aero Lab in Zielonka (Poland). Global flow parameters were reproduced in good agreement with experiment (difference less than 1.5%). Satisfactory agreement between measured and predicted pressure distribution on the surface of inlet strut has been obtained.

A numerical simulation was performed to determine the factors that affect particle deposition on the leading edge in a nozzle guide vane passage. In this study, a new computational particle sticking model in the high temperature environment combining the critical viscosity model with the critical velocity model was developed, which both particle viscosity and elasticity properties were considered in the process of deposition. New numerical implementations were used to simulate the deposition layer thickness evolution. For validating the new sticking model, some low temperature experiments of wax deposition on a vertical plate were performed, which numerical results in the same conditions were compared with. Afterwards, the new particle sticking model was used to predict the deposition on a simplified leading edge with 3 rows of shower cooling holes of nozzle guide vane in aeroengine. A structural mesh of the nozzle guide vane containing a dynamic mesh region around the leading edge for the deposition layer thickness evolution calculation was developed. To match the real condition in high pressure turbine of aero-engine during the airplane’s flight, this study focus on the particles with a diameter less than 100nm. The simulation results showed that the capture rate of the nano-particles in the leading edge was less than 2%. The evolution of the deposition layer thickness changing with the aero-engine operational duration were quantified and analysed. Results showed that shower cooling air could reduce the deposition rate in the leading edge, and features such as particle size, blowing ratio and inlet turbulent dispersion have a strong correlation with the deposition rate and deposition distribution.

In modern gas turbines, film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). Within the past decade, the technology has been improved step by step at B&B-AGEMA and Kawasaki Heavy Industries Ltd.; mainly by means of numerical simulations. The laterally averaged film cooling effectiveness is typically captured with acceptable accuracy, but the experimental measurements still show a deviation from the numerically obtained results with respect to the local film cooling effectiveness distribution behind the film cooling hole. Nevertheless, the film cooling air spread out in the lateral direction is one of the keys for enhancement of the film cooling performance. Thus, more precise simulations are consequently necessary for improvement of the hole shape configuration. The present study involves simulations of a baseline fan shaped hole configuration (“777 hole” investigated by Schroeder and Thole [1][2]) using different turbulence models available in STAR-CCM+ with isotropic and anisotropic turbulence consideration (constitutive relations). Distinct differences with respect to flow phenomena (detachments and vortex creation) can be observed depending on the applied turbulence model. In total, the results show that anisotropic viscosity strongly influences the film cooling performance prediction by CFD for prediction of the film cooling effectiveness, but none of the models provides acceptable accuracy in this regard.

Time spectral method (TSM), as a very effective frequency domain method for analyzing temporal periodic flow field, is more popular than other frequency domain methods such as the nonlinear harmonic method (NLHM), the linear harmonic method (LHM) and the classic harmonic balance method. This is due to the fact that it is much easier to be implemented in an existing steady flow solver. But the aliasing errors caused by the nonlinear terms in the Euler/Navier-Stokes equations can have an adverse effect on the convergence rate. On the worse side, it can even lead to solution instability. This paper will present investigation of the application of the time spectral vanishing viscosity (SVV) method to stabilizing the solution of time spectral method. The spectral vanishing viscosity method has long been investigated for stabilizing spectral solution of conservation laws in space. Its application to time spectral solution of unsteady flow equations is very limited. In this investigation, the accuracy and time cost of the time spectral method with the SVV will be compared with that without the SVV and the traditional time domain dual time stepping method (DT). The stiffness of the SVV and the time spectral source terms is relieved by implicitly integrating the source terms in time using the block Jacobi method (BJ). To accelerate the convergence rate, the Lower Upper Symmetric Gauss Seidel (LU-SGS) method is used as the residual smoother for a multi-stage Runge-Kutta time integration. The following points can be drawn from this investigation: 1. Time spectral vanishing viscosity method can accelerate convergence rate and reduce time cost. 2. Time spectral vanishing viscosity method can improve the solution accuracy and fewer harmonics can be used to analyze the flow field with the SVV than without the SVV.

In modern gas turbine engines, many sophisticated cooling schemes are used to maintain the turbine blade temperature in acceptable levels. These schemes, such as convective cooling, film cooling, impingement cooling and the use of pin fins, can be combined to increase the cooling effectiveness. Jet impingement cooling, pin fins and convective cooling are internal cooling techniques, in which the cooling is achieved based on coolant flow through internal blade channels decreasing the blade metal temperature. Film cooling is an external cooling technique, in which the cold fluid (air) is injected into the hot gas flow through discrete holes providing a coolant film at blade surface, protecting the blade metal. In this way, the present work refers to the numerical investigation of internal and external cooling strategies applied in gas turbines. The methodology developed to analyze such strategies is based on the flat-plate approach with laboratory length scales and Computational Fluid Dynamics (CFD) techniques, being the flow, in the study domain, considered viscous, turbulent and compressible. A commercial CFD program is used to solve the general equations of fluid mechanics with Reynolds Average Navier-Stokes (RANS) technique for steady state regime and Shear Stress Transport (SST) turbulence model to determine the flow eddy viscosity. The combined effects of internal and external cooling is studied through a highly sophisticated scheme, called louver, which combines the effects of impingement and film cooling. Pin fins and ribs turbulator geometries applied in the channel between the impingement and the film cooling have the purpose of evaluating the impact of these geometries on the film cooling effectiveness over the flat surface in comparison to the louver scheme without turbulator. This study concluded that, pin fins proved to be the most promise solution because they increased in 7% the film cooling effectiveness. Ribs also have a good potential to increase the effectiveness, because an increase of 4% in film cooling effectiveness was observed. In addition, the effects of the turbulator are dependent on their location, since the turbulator positioned near the film cooling hole exit showed improvements in the film cooling effectiveness in relation to the turbulator near of the impingement cooling jet.