bluuebunny/crossref_metadata_2025 huggingface dataset:
Corner Separation Dynamics in a Linear Compressor Cascade
Authors: Zambonini Gherardo , Ottavy Xavier , Kriegseis Jochen
Published: September 2016

This paper considers the inherent unsteady behavior of the three dimensional separation in the corner region of a subsonic linear compressor cascade equipped of thirteen NACA 65-009 profile blades. Detailed experimental measurements were carried out at different sections in spanwise direction achieving, simultaneously, unsteady wall pressure signals on the surface of the blade and velocity fields by time-resolved PIV measurements. Two configurations of the cascade were investigated with an incidence of 4° and 7°, both at Re = 3.8 * 105 and Ma = 0.12 at the inlet of the facility. The intermittent switch between the two statistical preferred sizes of separation, large and almost suppressed, is called bimodal behaviour. The existence of such oscillation, reported at first in previous experimental and numerical works on the same test rig, is confirmed for both incidences. Additionally, the present PIV measurements provide, for the first time, time-resolved flow visualizations of the size switch of the separation with an extended field of view covering the entire blade section. The interaction of random large structures of the incoming boundary layer with the blade is found to be a predominant element that destabilizes the separation boundary. The recirculation region enlarges when these high vorticity perturbations blend with larger eddies situated in the aft part of the blade. Such massive separation persists until the blockage in the passage causes the breakdown of the largest structures in the aft part of the blade. The flow starts again to accelerate and the separation is almost suppressed. Finally, POD analysis is carried out to decompose flow modes and to contribute to the clarification of underlying cause-effect-relations, which predominate the dynamics of the present flow scenario.
Variations of Anchoring Pattern of a Bluff-Body Stabilized Laminar Premixed Flame as a Function of the Wall Temperature
Authors: Berger Sandrine , Richard Stéphane , Duchaine Florent , Gicquel Laurent
Published: September 2016

Aircraft engine components are subject to hostile thermal environments. The solid parts in the hot stages encounter very high temperature levels and gradients that are critical for the engine lifespan. Combustion chamber walls in particular exhibit very heterogeneous thermal fields. The prediction of this specific thermal field is a very complex task as it results from complex interactions between fresh gas injections, cooling flow distributions, combustion, flame stabilization and thermal transfers to the solids. All these phenomena are tightly coupled and do not evolve linearly. Today, the design phase of a combustion chamber is strongly enhanced by the use of high fidelity computations such as Large Eddy Simulations (LES). However, thermal boundary conditions are rarely well known and are thus treated either as adiabatic or as approximated isothermal conditions. Such approximations on thermal boundary conditions can lead to several errors and inaccurate predictions of the combustion chamber flow field. With this in mind and to foresee the potential difficulties of LES based Conjugate Heat Transfer (CHT) predictions, the effect of the wall temperature on a laminar premixed flame stabilization is numerically investigated in this paper for an academic configuration. The considered case consists of a squared cylinder flame holder at a low Reynolds number for which several wall-resolved Direct Numerical Simulations (DNS) are performed varying the bluff-body wall thermal condition. In such a set-up, the reactive flow and the flame holder interact in a complex way with an underlying strong impact of the wall temperature. For a baseline configuration where the flame holder wall temperature is fixed at 700K, the flow field is steady with a flame stabilized thanks to the recirculation zone of the flame holder. As the wall temperature is decreased, the position of the stabilized flame moves further downstream. The flame remains steady until a threshold cold temperature is reached below which an instability appears. For solid temperatures above 700 K, the flame is seen to move further and further upstream. For very hot conditions, the flame even stabilizes ahead of the bluff-body. The various flow solution bifurcations as the flame stabilization evolves are detailed in this paper. Heat flux distribution along the bluff-body walls are observed to be dictated by the flame stabilization process illustrating different mechanisms while integration of these fluxes on the whole flame holder surface confirms that various theoretical equilibrium states may exist for this configuration. This suggests that computation of more realistic cases including thermal conduction in the bluff-body solid part could lead to different converged results depending on the initial thermal state.
A Comparison of Actuator Disc Models for Axial Flow Fans in Large Air-Cooled Heat Exchangers
Authors: Wilkinson Michael B. , Louw Francois G. , van der Spuy Sybrand J. , von Backström Theodor W.
Published: September 2016

The performance of large mechanical draft air-cooled heat exchangers is directly related to fan performance which is influenced by atmospheric wind conditions, as well as the plant layout. It is often necessary to numerically model the entire system, including fans, under a variety of operating conditions.

Full three-dimensional, numerical models of axial flow fans are computationally expensive to solve. Simplified models that accurately predict fan performance at a lesser expense are therefore required. One such simplified model is the actuator disk model (ADM). This model approximates the fan as a disk where the forces generated by the blades are calculated and translated into momentum sources. This model has been proven to give good results near and above the design flow rate of a fan, but not at low flow rates. In order to address this problem two modifications were proposed, namely the extended actuator disk model (EADM) and the reverse engineered empirical actuator disk model (REEADM).

The three models are presented and evaluated in this paper using ANSYS FLUENT. The models are simulated at different flow rates representing an axial flow fan test facility. The resulting performance results and velocity fields are compared to each other and to previously simulated three dimensional numerical results, indicating the accuracy of each method. The results show that the REEADM gives the best correlation with experimental performance results at design conditions (ϕ = 0.168) while the EADM gives the best correlation at low flow rates.

A comparison of the velocity profiles shows that none of the three models predict the radial velocity distribution at low flow rates correctly, however the correlation improves at flow rates above ϕ = 0.105. In general the upstream velocity profiles, where reversed flow occurs through the fan, are poorly predicted at low flow rates. At the flow rates above ϕ = 0.137 the correlation between the velocity profiles for the simplified modes and the three dimensional results is good.
Modeling of Compressor Drum Cavities With Radial Inflow
Authors: Amirante D. , Sun Z. , Chew J. W. , Hills N. J. , Atkins N. R.
Published: September 2016

Reynolds-Averaged Navier-Stokes (RANS) computations have been conducted to investigate the flow and heat transfer between two co-rotating discs with an axial throughflow of cooling air and a radial bleed introduced from the shroud. The computational fluid dynamics (CFD) models have been coupled with a thermal model of the test rig, and the predicted metal temperature compared with the thermocouple data.

CFD solutions are shown to vary from a buoyancy driven regime to a forced convection regime, depending on the radial inflow rate prescribed at the shroud. At a high radial inflow rate, the computations show an excellent agreement with the measured temperatures through a transient rig condition. At a low radial inflow rate, the cavity flow is destabilized by the thermal stratification. Good qualitative agreement with the measurements is shown, although a significant over-prediction of disc temperatures is observed. This is associated with under prediction of the penetration of the axial throughflow into the cavity. The mismatch could be the result of strong sensitivity to the prescribed inlet conditions, in addition to possible shortcomings in the turbulence modeling.
Control of Tip Leakage in a High Pressure Turbine Cascade Using Tip Blowing
Authors: Volino Ralph J.
Published: September 2016

Blowing from the tip of a turbine blade was studied experimentally to determine if total pressure loss could be reduced. Experiments were done with a linear cascade in a low speed wind tunnel. Total pressure drop through the blade row and secondary velocity fields in the passage between two blades were measured. Cases were documented with various blowing hole configurations on flat and squealer tipped blades. Blowing normal to the tip was not helpful, and in some cases increased losses. Blowing from the bottom of a squealer cavity provided little benefit. With a flat tip, blowing from holes located near and inclined toward the pressure side generally reduced total pressure drop by reducing the effect of the tip leakage vortex. Holes near the axial location of maximum loading were most helpful, while holes closer to the leading and trailing edges were not as effective. Higher jet velocity resulted in larger total pressure drop reduction. With a tip gap of 1.5% of axial chord, jets with a velocity 1.5 times the cascade inlet velocity had a significant effect. A total pressure drop reduction of the order 20% was possible using a jet mass flow of about 0.4% of the main flow. Jets were most effective with smaller tip gaps, as they were more able to counter the leakage flow.
Aerodynamic Performance of Novel Lightweight Turbine Blade
Authors: Okita Yoji , Nita Kozo , Kubo Seiji
Published: September 2016

The primary contribution of this research is to clarify the aerodynamic performance of a novel lightweight turbine blade with internal cooling passage and external film cooling, which is invented aiming at drastic weight reduction of a cooled blade. With a considerably thinner airfoil, a significant separation region is formed along the pressure side, and therefore aerodynamic performance with such a flow field should be investigated.

First, the lightweight cooled airfoil is designed. In the design process, a conventional thick airfoil is first defined as a baseline. With the baseline airfoil, only the mid and rear part of pressure side profile is redesigned to thin the airfoil without any change in the suction side geometry. The airfoil geometry is optimized so as not to bring significant aerodynamic loss increase. In this numerical optimization, the airfoil shape is gradually changed and evaluated step by step. In every step, an adjoint variable method is used to seek better airfoil shape, and then the generated new shape is evaluated with full RANS calculation. This iteration is repeated until any further recognizable weight reduction cannot be obtained without sensitive pressure loss increase and/or the airfoil shape reaches some geometrical constraints. The resultant optimized airfoil is approximately 20% lighter than the baseline hollow airfoil without any noticeable change in aerodynamic loss in the numerical solution.

Next, the optimized airfoil is tested in a high speed linear cascade rig to verify its aerodynamic performance. The baseline airfoil is also tested for comparison. The rig is composed of six airfoil passages. The compressed air is supplied to the cascade and discharges to the atmospheric exhaust chamber. The air is also heated up to about 540 K upstream of the cascade. The cascade exit Mach number at the design point is 1.25, while in the experiment other several off-design conditions are also tested to check if there is any Mach number sensitivity. At the design point, the optimized lightweight airfoil shows less total pressure loss compared to the baseline airfoil. Also, at any other off-design Mach number conditions tested, the magnitude of the pressure loss is less with the lightweight airfoil. These results verify that the proposed airfoil does not only bring a considerable weight advantage but also compares favorably with the conventional airfoil in aerodynamic performance.
Numerical Investigation of Entropy Generation Distributions in a Transonic Compressor
Authors: Nan Xi , Liu Le , Ma Ning , Lu Qian , Lin Feng
Published: September 2016

Highly irreversible flows can arise from the rotor tip region which cause compressor performance degradation. The understanding of the flow irreversibility and the spatial distribution in the rotor passage may provide hints to retrofit rotor geometries as well as design efficiency-friendly casing treatments. This paper presents a numerical investigation on the spatial distributions of entropy generation through a control volume analysis on a transonic compressor. The typical loss sources can be classified as the viscous shear on solid boundaries, the shockwaves at the leading edge and within the passage, the tip leakage vortex and the turbulence mixing in the rotor wake in the tip region, however, it is hard to distinguish their individual contributions because they always interact with each other. To avoid this difficulty, this paper targets at the spatial distribution of entropy generation since it can tell the local losses quantitatively as the results of local flow structures and their interactions. Tip clearance is used as a controlled parameter for the investigation. By varying the tip clearance over the blade chord, the tip leakage flow is energized and thus examined first, followed by the other changes of inflow structures reacting to the tip clearance variation. The changes in entropy generation distributions are then carefully compared. Based on the results, the dominative contributor on entropy generation and its impact on total loss are identified. Finally, new casing designs with stepped tip gaps that may ameliorate the entropy generation of the tip region are discussed and numerically validated.
Application of Latest Gas Turbine Technologies and Verification Results
Authors: Nishimura Yoshiaki , Sugawara Tomoyuki , Tada Kazuyuki , Masada Junichiro , Ai Toshishige , Iwasaki Tatsuya
Published: September 2016

Utility companies and gas turbine manufacturer alike are working diligently to improve Gas Turbine Combined Cycle (GTCC) efficiency in order to reduce fossil fuel consumption as well as CO2 emissions.

Tohoku Electric Power Co., Inc. started operating large size GTCC in 1984 with Mitsubishi D series gas turbines. Since then, the company has lead the application of first of class Mitsubishi gas turbines. The company applied the first M701G gas turbine in 1999 and this successful experience was followed in 2010 with the single-shaft Sendai GTCC featuring the first M701F4.

The M701F5 was introduced in 2011 by Mitsubishi Hitachi Power Systems, LTD. (MHPS) and Tohoku Electric pioneered one more time its application at the No.3 Shin-Sendai Power Plant in 2015.

The M701F5 features the combination of technologies verified in other gas turbine frames. This paper introduces the feature of the M701F5 gas turbine including its technologies and verification results.
Improving the Efficiency of Heavy-Fuelled Gas Turbines: The Successful Experience Achieved at the Yugadanavi 300 MW CCGT in Sri Lanka
Authors: Marikkar Nuhuman , Vierling Matthieu , Aboujaib Maher , Sokolov Dmitry , Monetti Bruno , Russell Robert , Meskers Donald , Verdy Christophe , Moliere Michel
Published: September 2016

An important asset of heavy duty gas turbines (“GT”) is their ability to burn a large variety of hydrocarbons, including low grade ones such as ash-forming fuels, in a well-controlled manner while achieving fairly high energy conversion efficiency.

In fact, there is still a considerable margin for improving the efficiency of gas turbines burning ash forming fuels if one succeeds in reducing the deposition of the ash in the turbine section which represents however a challenging technology lock.

The main difficulty for achieving this ambitious objective lies in the additional fouling entailed by the “inhibition process”. Indeed a magnesium-based corrosion inhibitor is injected into the GT combustors in order to suppress the corrosion threat placed by the highly fusible vanadium species coming from the fuel. This additive represents a substantial increase in the amount of ash crossing the machine whereby substantially accentuating the fouling of the hot gas path parts.

Within a joint initiative, LTL Holdings Ltd, GE Power & Water and the UTBM University have successfully tested a novel family of vanadium inhibitors called “bimetallic inhibitors” that combines magnesium and iron and lead to a considerable reduction in ash deposition while keeping intact the anti-corrosion protection. This new inhibitor family brings a decisive improvement in GT efficiency as well as a significant increase in plant availability. Indeed it enables reducing the frequency of the machine shutdowns that are periodically required to remove the ash deposits through water wash. In addition, iron procures an interesting soot suppression effect.

The paper outlines the development carried out in this project and sets out the successful field test performed in 2015 at the Yugadanavi 300 MW power plant in Sri Lanka.
Flow Analysis of a High Flowrate Centrifugal Compressor Stage and Comparison With Test Rig Data
Authors: Weber Anton , Morsbach Christian , Kügeler Edmund , Rube Christoph , Wedeking Matthias
Published: September 2016

The flow field inside a single-stage centrifugal compressor characterized by a high flowrate of Φ = 0.15 and a design total pressure ratio of approximately 1.4 is analysed numerically. The stage geometry consists of a radially oriented inlet duct with uniform inflow without swirl, a 90 deg inlet bend in front of the impeller, the shrouded impeller itself followed by a large radial vaneless diffuser, a 180 deg U-turn, a radially oriented turning vane, a subsequent 90 deg bend, and as the last item a long axial exit duct. The impeller blades have large fillets at hub and tip and thick blunt trailing edges. Due to the rotating shroud, a labyrinth seal is placed above the impeller with 5 seal tips. The complete leakage region is also included in the CFD analysis. The blade numbers for the impeller and vane are 15 and 14, respectively. The test rig has recently been built at the Institute of Propulsion and Turbomachinery at RWTH Aachen University (Germany).

The first part of the CFD work presented was carried out before the first experimental data were available. Using the k-ω turbulence model of Wilcox (1988), a number of principal steady RANS calculations were performed to investigate the following: Impact of near wall grid resolution and turbulence model wall boundary condition treatment, impact of impeller fillets, and the influence of leakage flow. This part is completed by a comparison of steady RANS simulations with the time-mean results of unsteady RANS analyses of one blade passage. For the calculations presented in the second part, experimental data are available at the inflow and outflow planes. At these planes overall mean values were deduced. Additionally, 3- and 5-hole probe data are available at spanwise traverse planes located at the zenith of the U-turn and in the exit plane. For part two a finer grid with y+ values of approximately unity for all solid walls was used. In addition to the Wilcox k-ω model and the Menter SST k-ω model, two higher level turbulence models — the explicit algebraic Reynolds stress model Hellsten EARSM k-ω and the differential Reynolds stress model SSG/LRR-ω — have been tested and compared with the experiments. The agreement in terms of overall performance (total pressure ratio, isentropic efficiency) is satisfactory for all turbulence models used, but there are some differences: the k-ω model is shown to be the most stable one towards stall. On the other hand, it is shown that details of the flow field in terms of the two spanwise traverses can be better represented by the more advanced turbulence models. All CFD simulations have been performed at 100% shaft speed.
Multi-Objective Optimization of the Impingement-Film Cooling Structure of a HPT Endwall Using Conjugate Heat Transfer CFD
Authors: Chi Zhongran , Liu Haiqing , Zang Shusheng
Published: September 2016

This paper discusses the approach of cooling design optimization of a HPT endwall with 3D Conjugate Heat Transfer (CHT) CFD applied. This study involved the optimization of the spacing of impingement jet array and the exit width of shaped holes, which were different for each cooling cavity. The optimization objectives were to reduce the wall temperature level and also to increase the aerodynamic performance of the gas turbine.

The optimization methodology consisted of an in-house parametric design & CFD mesh generation tool, a CHT CFD solver, a database of wall temperature distributions, a metamodel, and a genetic algorithm (GA) for evolutionary multi-objective optimization. The CFD tool was validated against experimental data of an endwall at CHT conditions. The metamodel, which could efficiently predict the aerodynamic loss and the wall temperature distribution of a new individual based on the database, was developed and coupled with Non-dominated Sorting Genetic Algorithm II (NSGA-II) to accelerate the optimization process.

Through optimization search, the Pareto front of the problem was found costing only tens of CFD runs. By comparing with additional CFD results, it was demonstrated that the design variables in the Pareto front successfully reached the optimal values. The optimal spacing of each impingement array was decided accommodating the local thermal load while avoiding jet lift-off of film coolant. It was also suggested that using cylindrical film holes near throat could benefit both aerodynamics and cooling.
A Single Formulation for Uncertainty Propagation in Turbomachinery: SAMBA PC
Authors: Ahlfeld Richard , Montomoli Francesco
Published: September 2016

This work newly proposes an uncertainty quantification method named SAMBA PC (Sparse Approximation of Moment-Based Arbitrary Polynomial Chaos) that offers a single solution to many current problems in turbomachinery applications. At the moment every specific case is characterized by a variety of different input types such as histograms (from experimental data), normal PDFs (design rules) or fat tailed PDFs (for rare events). Thus, the application of UQ requires the adaptation of ad hoc methods for each individual case. A second problem is that parametric PDFs have to be determined for all inputs. This is difficult if only few samples are available. In gas turbines, however, the collection of statistical information is difficult, expensive and having scarce information is the norm. A third critical limitation is that if using Non-Intrusive Polynomial Chaos methods the number of required simulations grows exponentially with increasing numbers of input uncertainties: the so-called ‘curse of dimensionality’.

In this work it is shown that the fitting of parametric PDFs to small data sets can lead to large bias and the direct use of the available data is more accurate. This is done by propagating uncertainty through several test functions and the CFD simulation of a diffuser, highlighting the impact of different PDF fittings on the output. From the results it is concluded that the direct propagation of the experimental data set is preferable to the fit of parametric distributions if data is scarce. Thus, the suggested method offers an alternative to the maximum entropy theorem to handle scarce data.

SAMBA simplifies the mathematical procedure for many different input types by basing the polynomial expansion on moments. Its moment-based expansion automatically takes care of arbitrary combinations of different input data.

SAMBA is also numerically efficient compared to other UQ implementations. The relationship between the number of random variables and number of simulation is linear (only 21 simulations for 10 input random variables are required). It is shown that SAMBA’s algorithm can propagate a high number of input distributions through a set of nonlinear analytic test functions. Doing this the code needs a very small number of simulations and preserves a 5% error margin. SAMBA’s flexibility to handle different forms of input distributions and a high number of input variables is shown on a low pressure turbine blade based on H2 profile. The relative importance of manufacturing errors in different location of the blade is analyzed.
Uncertainty Quantification of Heat Transfer for a Highly Loaded Gas Turbine Blade Endwall Using Polynomial Chaos
Authors: Zhu Peiyuan , Yan Yong , Song Liming , Li Jun , Feng Zhenping
Published: September 2016

The durability of highly loaded gas turbine blade is significantly impacted by high heat transfer. The heat transfer performance of the gas turbine endwall can be varied significantly due to the impacts of uncertainties in the manufacturing process and operation conditions. In this work, an uncertainty quantification (UQ) method is proposed by integrating generalized polynomial chaos expansions, non-intrusive spectral projection and Smolyak sparse grids. Then coupled with three dimensional (3D) Reynolds-Averaged Navier-Stokes (RANS) solutions, an uncertainty quantification procedure is carried out for heat transfer performance of highly loaded blade endwall. Wherein, the effects of the variation of geometric parameters and operation conditions are taken into account.

Specifically, the endwall heat transfer performance of a typical highly loaded turbine blade named Pack-B is numerically investigated. The turbulence intensity Tuinlet and Reynolds number Reinlet of inlet flow are considered as flow condition uncertainty parameters. As geometrical uncertainty parameters, the radius r and minimum angle α of blade root fillet are considered. These uncertainty factors have important influence on the secondary flow structure, resulting in significant variation of heat transfer performance of the endwall. Non-intrusive Polynomial Chaos (NIPC) is used to build a surrogate to reduce the quantity of the time consuming CFD simulation. A total of 137 sparse-grid-based design-of-experiment computations were carried out to build the high-fidelity surrogate. Using above method, the probability density function of the Nusselt number ( Nu ) of the endwall is obtained. The overall variation of Nu can be more than 10% due to the effect of the uncertainty factors. Finally, the sensitivity analysis shows that Reinlet has the most important influence on heat transfer performance of the whole endwall and other uncertainty factors also have significant effect on heat transfer performance at some local regions of the endwall such as wake region and middle part of blade passage.
Experimental and Numerical Flow Analysis of Low-Speed Fans at Highly Loaded Windmilling Conditions
Authors: Ortolan Aurélie , Courty-Audren Suk-Kee , Binder Nicolas , Carbonneau Xavier , Challas Florent
Published: September 2016

This paper aims for the analysis of experimental and numerical results of windmilling flow topologies far from freewheeling condition. Two fans were investigated: a baseline design and an innovative one meant to reach good performance in both compressor and turbine modes. Experiments are conducted with global and local characterizations to determine energy recovery potential and local loss mechanisms. The numerical study is carried out with mixing plane steady simulations, the results of which are in fair agreement with experimental data. The difference of local topology between freewheeling and highly loaded windmill demonstrates that classical deviation rules such as Carter’s are not well-suited to highly loaded windmilling flows. Finally, under certain conditions, the minor influence of the stator on the rotor topology indicates that non rotating elements can be considered as loss generators.
Investigation of Hot Film Jet Vortex Effects on Droplets Characteristics Over Aero-Engine Inlet Strut
Authors: Zhang Yun , Ke Peng , Yang Chunxin , Yu Guangfeng
Published: September 2016

The jetted hot film could affect the trajectories of the water droplets near the aero-engine inlet strut surface, which equipped with the ice protection system combined the internal impingement heat transfer and the external hot air film heating. To evaluate the droplets impingement characteristics of four ice-protection structures designed with different film-slot jet angles, a droplets impingement computation method based on Eulerian framework was developed and validated. The influences of film-slot angle and blowing ratio on the impingement characteristics for droplet diameter of 20μm were investigated and the jet vortex was found to be an important factor. The results indicated that the local collection efficiency and the impingement limitation could decrease significantly due to the blowing from the external hot-film, and the influence would be more significant in case that the film-slot was closer to the leading edge. For example, the average local collection efficiencies of four typical configurations with different slot angles and positions decreased 82%, 8%, 1% and 0.5% respectively comparing to those without air film. Besides that, the maximum local collection efficiency and the impingement limitation decreased with the increasing blowing ratios, and the film-slot nearest to the leading edge was most sensitive to the blowing ratio. It was also found that no droplets impinged on the rear surface after the jet slots at some higher blowing ratios.
Unsteady CFD Investigation of Effusion Cooling Process in a Lean Burn Aero-Engine Combustor
Authors: Mazzei L. , Picchi A. , Andreini A. , Facchini B. , Vitale I.
Published: September 2016

The use of lean burning flames stabilized by highly swirling flows represents the most effective technology to limit NOx emissions in modern aeroengine combustors. In these devices up to 70% of compressed air is admitted in the combustor through the injection system, which is usually designed to give strong swirling components to air flow. Complex fluidynamics is observed with large flow recirculations due to vortex breakdown and precessing vortex core, that may result in a not trivial interaction with liner cooling flows close to combustor walls. This interaction and its effects on the local cooling performance make the design of the cooling systems very challenging and time-consuming, considering design and commission of new test rigs for detailed analysis. Keeping in mind costs and complexities related to the investigation of swirl flow/wall cooling interaction by experimental approach, CFD can be considered an accurate and reliable alternative to understand the associated phenomena. The widely known overcomes of RANS formulation (e.g. underestimation of mixing and inability to properly describe swirling flows) and the more and more impressive increase in computational resources, pushed hybrid RANS-LES models as valuable and affordable approaches to accurately solve the main turbulent flow structures.

This work describes the main findings of a CFD analysis intended to accurately investigate the flow field and wall heat transfer as a result of the mutual interaction between a highly swirling flow generated by a lean burn nozzle and a slot-effusion liner cooling system. In order to overcome some limitations of RANS approach, the simulations were performed with SST-SAS, a hybrid RANS-LES model. Moreover, the significant computational effort due to the presence of more than 600 effusion holes was limited exploiting two different modelling strategies: a homogeneous model based on the application of uniform boundary conditions on both aspiration and injection sides, and another solution that provides a coolant injection through point mass sources within a single cell. CFD findings were compared to experimental results coming from an investigation carried out on a three sector linear rig. The comparison pointed out that advanced modelling strategies, i.e. based on discrete mass sources, are able to reproduce the effects of mainstream-coolant interactions on convective heat loads. Validated the approach through a benchmark against time-averaged quantities, the transient data acquired were examined in order to better understand the unsteady behaviour of the thermal load through a statistical analysis, providing useful information with a design perspective.
Optimization of a Centrifugal Pump Impeller by Controlling Blade Profile Parameters
Authors: Siddique Md. Hamid , Mrinal K. R. , Samad Abdus
Published: September 2016

A multi-surrogate based optimization is a technique for the optimization of a turbomachinery impeller shape, which reduces the total design time. Computational analysis and surrogate-based optimization methodology have been implemented for the shape optimization of a centrifugal impeller blade in this problem. Geometric parameters such as impeller inlet and two-point control Bezier curve blade profile were selected as design variables. The objective was to maximize the total head as well as the efficiency of the pump using surrogate based optimization methods. A sample space was created for the design variables based on the sensitivity of the variable to the objective function and literature survey give a range of sample space. A three-dimensional Reynolds-averaged Navier-Stokes equations were solved to analyze the performance of the pump and the results were validated with experimental results. The simulations were done at different design points within the sample space to train the surrogate and to find the design optimum point using genetic algorithm. The shape of the impeller was optimized, to decrease the input power and improve the total head by varying the inlet and exit angles of the impeller.
Multi-Point Optimization of Recirculation Flow Type Casing Treatment in Centrifugal Compressors
Authors: Tun Min Thaw , Sakaguchi Daisaku , Numakura Ryusuke , Wang Baotong
Published: September 2016

In this paper, an optimization design approach to recirculation flow type casing treatment for centrifugal compressors of turbochargers has been performed. The optimization code is a global exploring system based on a metamodel assisted evolutionary algorithm. In this study, the objective functions of the optimization are adiabatic efficiency at design flow rate and near surge flow rate condition. Several optimized shapes on a “Pareto front” are selected in order to discuss the effect of casing treatment at the point of view of suppression of flow separation and a reduction of leading edge flow separation. The influence of optimized recirculation flow rate on the optimization output is also discussed. Increase in adiabatic efficiency of optimized casing treatment at near surge flow rate is discussed by the streamwise relative velocity distribution, reversed flow zone, static entropy distribution and flow incidence at impeller inlet. Detailed sensitivity of design variables on the adiabatic efficiency at design and off-design conditions was carried out.
Direct Coupling of a Two-Dimensional Fan Model in a Turbofan Engine Performance Simulation
Authors: Templalexis Ioannis , Alexiou Alexios , Pachidis Vassilios , Roumeliotis Ioannis , Aretakis Nikolaos
Published: September 2016

Coupling of high fidelity component calculations with overall engine performance simulations (zooming) can provide more accurate physics and geometry based estimates of component performance. Such a simulation strategy offers the ability to study complex phenomena and their effects on engine performance and enables component design changes to be studied at engine system level. Additionally, component interaction effects can be better captured. Overall, this approach can reduce the need for testing and the engine development time and cost.

Different coupling methods and tools have been proposed and developed over the years ranging from integrating the results of the high fidelity code through conventional performance component maps to fully-integrated three-dimensional CFD models.

The present paper deals with the direct integration of an in-house two-dimensional (through flow) streamline curvature code (SOCRATES) in a commercial engine performance simulation environment (PROOSIS) with the aim to establish the necessary coupling methodology that will allow future advanced studies to be performed (e.g. engine condition diagnosis, design optimization, mission analysis, distorted flow).

A notional two-shaft turbofan model typical for light business jets and trainer aircraft is initially created using components with conventional map-defined performance. Next, a derivative model is produced where the fan component is replaced with one that integrates the high fidelity code. For both cases, an operating line is simulated at sea-level static take-off conditions and their performances are compared.

Finally, the versatility of the approach is further demonstrated through a parametric study of various fan design parameters for a better thermodynamic matching with the driving turbine at design point operation.
The Effect of Chevrons on the Primary and Secondary Swirlers on the Dynamic Behavior of the Flow Generated by a Counter-Rotating Radial-Radial Swirler
Authors: Lin Sheng-Chieh , Estefanos Wessam , Brennan James , Tambe Samir , Jeng San-Mou
Published: September 2016

An experimental investigation was conducted to study the effect of chevrons on the dynamic behavior of the swirling flow generated by a counter-rotating radial-radial swirler. 3X models of a low swirl number swirler (SN ≈ 0.6) were used to achieve lower velocities for the same Reynolds number (Re) and enhanced visibility of the flow characteristics by enabling high spatial and temporal resolutions. Three swirler configurations were used, including the baseline with no chevrons. Configuration 2 features chevrons on the trailing edge of the primary swirler, and configuration 3 has chevrons on the trailing edge of both primary and secondary swirlers. The swirlers were tested in water flow at Reynolds number (Re) = 51,500 which corresponds to the typical operational pressure drop of 4% of atmospheric pressure for the corresponding 1X model of the swirler at ambient conditions. Water testing was used since it allows additional slowing down of the flow dynamic features so that they can be captured and analyzed. Measurements were conducted in a vertical plane passing through the swirler centerline, and two horizontal (cross-sectional) planes using a High-Speed, Two Dimensional, Particle Image Velocimetry (2D PIV) system to obtain the mean, turbulent and dynamic behavior of the flow. Results of this study introduce the concept of chevrons on swirlers as a promising approach to change the flow dynamic behavior and thus, affect combustion dynamics. The results show that the presence of chevrons break down the region of high modal energy into several smaller regions. However, configuration 2 has few regions of the highest modal energy among the configurations, whereas the modal energy values for configurations 3 has the lowest magnitudes. Thus, the secondary chevrons in configuration 3 play an important role to eliminate these high-energy local spots as well as meet the requirement to break down the large scale structures.
Use of Rib Turbulators to Enhance Post-Impingement Heat Transfer for Curved Surface
Authors: Hossain Jahed , Garrett Christian , Curbelo Andres , Harrington John , Wang Wenping , Kapat Jay , Thorpe Steven , Maurer Michael
Published: September 2016

The present study aims to investigate the heat transfer and pressure loss characteristics for multiple rows of jets impinging on a curved surface in the presence of rib turbulators. The target plate contains a straight section downstream of the impingement section. The rib turbulators are added only over the straight section, in an attempt to enhance the heat transfer while minimizing the pressure loss. The jet plate configuration in this study has fixed jet hole diameters and hole spacing. For the curved plate, the radius of the target plate is 32 times the diameter of the impingement holes. Impingement array configuration was chosen such that validation and comparison can be made with the open literature. For all configurations, crossflow air is drawn out in the streamwise direction. Average jet Reynolds numbers ranging from 55,000 to 125,000 were tested. Heat transfer characteristics are measured using steady state temperature sensitive paint (TSP) to obtain local heat transfer distribution. The experimental results are compared with CFD simulations. CFD results show that CFD simulations predict the heat transfer distribution well in the post-impingement area with turbulators.
Optimized Aerodynamic Design of Aggressive Intermediate Turbine Duct With Strut Fairings Using Genetic Algorithms
Authors: Yang Chen , Wu Hu
Published: September 2016

Three different optimization methods using genetic algorithms have been developed, aiming to achieve better aggressive intermediate turbine duct (ITD) performance. To overcome defects of simple genetic algorithms, a niche genetic algorithm is used, for its better adaptability to multi-peak function. These three methods are two-dimensional optimization for pursuing the highest static pressure coefficient; two-dimensional optimization via controlling static pressure coefficient; and a further three-dimensional optimization. The second method introduces a restrainer to make sure the maximum value of static pressure coefficient gradient less than a limitation. A simulation case, an ITD with eight struts, was implemented to demonstrate the capabilities of the presented optimization methods. Compared to the baseline ITD, the results show as follow. The first method obtains a best static pressure coefficient but a severe separation. The second optimization method with static pressure coefficient gradient control can definitely suppress separation in the ITD, the second method also obtains better static pressure coefficient and the lowest total pressure loss coefficient. The third method, a further three-dimensional optimization can obtain better ITD overall performance because of a more realistic simulation. Nevertheless, the second two-dimensional optimization method can get good enough results while it is apparently much more time-saving compared to three-dimensional one, which make it more suitable for engineering applications.
Theoretical Analysis of the Static Characteristics of the Carbon Segmented Seal
Authors: Arghir Mihai , Mariot Antoine
Published: September 2016

The segmented carbon seal is regularly used for sealing bearing chambers of aeronautical turboengines or as part of a buffer seal in space turbopumps. The seal operates with contaminated air or with an inert gas and is made of many identic carbon segments (generally three or six) with reciprocally overlapping ends. The segments are serrated against the rotor by the pressure difference between the upstream and the downstream chambers and by a circumferential (garter) spring. The pressure difference and an axial spring press the segments also against the stator. The inner cylindrical surface of each segment is provided with pads that create an aerodynamic lift proportional to the rotor speed. Following this lift force, the segments of the seal are pushed away from the rotor and the seal opens. The contact between the rotor and the segments is lost and an axial leakage path is thus created. Although it was developed since long, a model for calculating the characteristics of the segmented seal is completely absent from the scientific literature. The goal of the present work is to fill this gap at least for the static characteristics (leakage and torque). The analysis is carried out for a single segment of the seal by supposing that all the segments have the same characteristics. Each segment has a planar motion (i.e. three degrees of freedom) and therefore the film thickness under each pad is not uniform. Given the stationary operating conditions (pressure difference and rotation speed), the present model calculates the equilibrium position of each segment on the bases of the lift and of the friction force acting on the pads, of the friction forces acting on the nose of the seal and of the radial and axial springs. Once found the static equilibrium position, the leakage and the torque of the seal are calculated. A parametric study enlightens the importance of the pad waviness, of the pocket depth and of the spring forces on the characteristics of the segmented seal.
Predictive LES for Jet Aeroacoustics: Current Approach and Industrial Application
Authors: Tyacke James , Naqavi Iftekhar , Wang Zhong-Nan , Tucker Paul , Boehning Peer
Published: September 2016

The major techniques for measuring jet noise have significant drawbacks, especially when including engine installation effects such as jet-flap interaction noise. Numerical methods including low order correlations and Reynolds-Averaged Navier-Stokes (RANS) are known to be deficient for complex configurations and even simple jet flows. Using high fidelity numerical methods such as Large Eddy Simulation (LES) allow conditions to be carefully controlled and quantified. LES methods are more practical and affordable than experimental campaigns. The potential to use LES methods to predict noise, identify noise risks and thus modify designs before an engine or aircraft is built is a possibility in the near future. This is particularly true for applications at lower Reynolds numbers such as jet noise of business jets and jet-flap interaction noise for under-wing engine installations. Hence, we introduce our current approaches to predicting jet noise reliably and contrast the cost of RANS-Numerical-LES (RANS-NLES) with traditional methods. Our own predictions and existing literature are used to provide a current guide, encompassing numerical aspects, meshing and acoustics processing. Other approaches are also briefly considered. We also tackle the crucial issues of how codes can be validated and verified for acoustics and how LES based methods can be introduced into industry. We consider that hybrid RANS-(N)LES is now of use to industry and contrast costs, indicating the clear advantages of eddy resolving methods.