bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Numerical Investigation of Tip Leakage Flow in a 1 1/2 Stage Turbine Rig Comparing Flat and Cavity-Squealer Tip Geometries
Authors: Kegalj Martin , Schmid Gregor , Wartzek Fabian , Schiffer Heinz-Peter , Willer Lars 
Published: July 2013

Tip leakage loss is one of the main loss mechanisms in shroudless high-pressure turbines. Efficiency reducing phenomena are the reduction of mass turned by the blade, and the mixing of the tip leakage and passage flow. Applying a cavity squealer tip is a promising technique to reduce the tip leakage loss. The study investigates the influence of a cavity squealer on the flow field of a 3D high-pressure turbine.
The 1 1/2 stage turbine test rig is equipped with steady and unsteady measurement techniques, like five-hole probe, 2-component hot wire, oil & dye visualization, unsteady wall pressure probes and particle-image-velocimetry measurements. To improve the flow phenomena interpretation, unsteady numerical simulations were carried out using a commercial solver.
Experimental and Analytical Surge Cycle Analysis of a High Pressure Aero Engine Compressor
Authors: Waniczek Phillip , Schoenenborn Harald , Jeschke Peter 
Published: July 2013

The unsteady flow field during surge of the front rotor of an eight-stage axial aero engine compressor has been investigated experimentally and analytically. For that purpose, two newly designed multi-sensor probes are installed up- and downstream of the first rotor. Surge experiments are conducted at four different speed lines (75–93% speed) covering a wide range of the compressor map and measurements have been taken at two different channel heights (50% and 70% span). The results show that the flow field varies extremely during surge up- and downstream of the rotor. In contrast to the flow at the rotor leading edge, which is nearly independent of the rotor speed, the flow at the rotor trailing edge is highly dependent of the rotor speed. Therefore, the performance of the rotor during surge is dependent on the reverse through-flow of the stators. At low speeds the flow passes the stators without any changes in the flow direction. If speed is increased the reverse flow is guided more and more by the stators. These different flow conditions have a direct impact on the process of energy conversion of the rotor during the surge event. The incoming reverse flow at the rotor trailing edge impinges on the blade from the suction surface side at lower speeds and turns to the pressure surface side when speed is increased. Hence, the deviation and specific work grow.
In addition to the surge experiments simulations of the surge events are conducted with a 1D code called SYSQ3D. The simulations and experiments match well and underline the capability of the new multi-sensor probes to accurately measure the flow patterns during surge.
Multidisciplinary Multipoint Optimization of a Transonic Turbocharger Compressor
Authors: Van den Braembussche R. A. , Alsalihi Z. , Verstraete T. , Matsuo A. , Ibaraki S. , Sugimoto K. , Tomita I. 
Published: July 2013

A transonic centrifugal compressor for turbocharger applications has been redesigned by means of a multidisciplinary multipoint optimization system composed of: a 3D Navier-Stokes solver, a Finite Element stress Analyzer, a Genetic Algorithm and an Artificial Neural Network. The latter makes use of a database, containing the geometry and corresponding performance of previously analyzed impellers and allows a considerable reduction in computational effort. The performance of every new geometry is verified by a 3D Navier-Stokes solver. A Finite Element Analysis verifies the mechanical integrity of the impeller.
The geometrical description of the impeller has been extended to better adapt the inducer part of the impeller to transonic flows. The splitters are no longer copies of the full blades but specially designed for minimum losses and equal mass flow on both sides. The blade thickness and number of blades are unchanged because defined by robustness and inertia considerations.
The operating range is guaranteed by a two-step optimization procedure. The first one provides information allowing a modification of the inlet section to guarantee the required choking mass flow and a more accurate prediction of the boundary conditions for the Navier-Stokes analysis of the modified impeller. The second one predicts the performance curve of the new geometry for which the choking mass flow is known.
It is shown how these extensions of the optimization method have led to a considerable improvement of the efficiency and corresponding pressure ratio, while respecting the surge and choking limits without increase of the stress level.
Gradient Enhanced Surrogate Models Based on Adjoint CFD Methods for the Design of a Counter Rotating Turbofan
Authors: Backhaus Jan , Aulich Marcel , Frey Christian , Lengyel Timea , Voß Christian 
Published: July 2013

This paper studies the use of adjoint CFD solvers in combination with surrogate modelling in order to reduce the computational cost of the optimization of complex 3D turbomachinery components. The method is applied to a previously optimized counter rotating turbofan, with a shape parameterized by 104 CAD parameters.
Through random changes on the reference design, a small number of design variations are created to serve as training samples for the surrogate models. A steady RANS solver and its discrete adjoint are then used to calculate objective function values and their corresponding sensitivities. Kriging and neural networks are used to build surrogate models from the training data. To study the impact of the additional information provided by the adjoint solver, each model is trained with and without the sensitivity information. The accuracy of the different surrogate model predictions is assessed by comparison against CFD calculations.
The results show a considerable improvement of the fitness function approximation when the sensitivity information is taken into account. Through a gradient based optimization on one of the surrogate models, a design with higher isentropic efficiency at the aerodynamic design point is created. This application demonstrates that the improved surrogate models can be used for design and optimization.
Hub Injection Flow Control in a Turbine Exhaust Diffuser
Authors: Volkmer Silke , Kuschel Benjamin , Hirschmann Andreas , Schatz Markus , Casey Michael , Montgomery Matthew 
Published: July 2013

Downstream of a modern combined cycle gas turbine there is generally an abrupt end of the turbine inner hub wall leading to a backward facing step with separation and flow recirculation on the hub axis. This can lead to a strong hub wake with high losses in the center of the diffuser. The interaction between the end of the hub and the downstream axial diffuser can have a significant influence on diffuser flow field and hence on overall gas turbine performance. To minimize the hub wake the flow can be guided to the axis by reducing the diameter of the hub. But this can still lead to separation on the extended hub and to a strong hub wake. This paper describes experimental and numerical investigations of the use of flow injection to control the flow separation on the hub and to guide the main flow towards the axis of the diffuser to reduce the hub wake.
A new test rig has been built at the Institute of Thermal Turbomachinery and Machinery Laboratory of the University of Stuttgart, Germany (ITSM). This rig features an active flow control device based on hub flow injection with a Coanda-effect to influence the hub wake flow. In addition to experimental studies, steady CFD (computational fluid dynamics) simulations have been performed for this configuration and validated using the experimental data.
Test results and flow field computations confirm that the flow control device tested can have a beneficial influence on diffuser performance at specific conditions. If it is the casing flow which separates then hub injection has little effect. If the casing flow is attached, and a hub separation limits the performance, then hub jet flow injection can be highly beneficial. The results also indicate that the mass flow injected in the hub jet control device has to be carefully balanced.
General Capability of Parametric 3D Blade Design Tool for Turbomachinery
Authors: Siddappaji Kiran , Turner Mark G. , Merchant Ali 
Published: July 2013

A design tool for generating 3D blades for various turbomachinery applications using a parametric approach has been developed. The tool can create a variety of 3D blade geometries based on only a few basic parameters and limited interaction with a CAD system. A general approach for creating the blade geometries is implemented which makes it robust and easy to create different 3D blade shapes for various turbomachinery components. The geometric and aerodynamic parameters are used to create 2D airfoils and these airfoils are stacked on the desired stacking axis. The tool generates a specified number of 2D blade sections in a 3D Cartesian coordinate system. These sections can be lofted in a CAD package to obtain a solid 3D blade model, which has been demonstrated using Unigraphics-NX and Solidworks.
The geometry modeler can also be used for generating 3D blades with special features like bent tip, split tip and other concepts, which can be explored with minimum changes to the blade geometry. The use of control points for the definition of splines makes it easy to modify the blade shapes quickly and smoothly to obtain the desired blade model. Blade shapes for axial turbomachines, radial turbomachines and wind turbines are generated to show the general capability of the tool. Other novel blade shapes are also shown which shows the full utility of this tool when integrated with CAD. The executable of the code that generates sections is freely available on the web.
Optimization of Turbomachinery Flow Surfaces Applying a CFD-Based Throughflow Method
Authors: Pasquale David , Persico Giacomo , Rebay Stefano 
Published: July 2013

This work proposes an optimization strategy for the preliminary stage of turbomachinery design, based on the application of a throughflow code in the context of a fully automated optimization strategy. The code solves for the circumferentially-averaged flow equations, including the effects of aerodynamic and friction forces and of blade thickness; the outcome of the code is the flow distribution on the meridional surface. In this research the definition of an ‘optimal’ mean flow surface is the final aim of a multi-objective optimization procedure, in which non-concurrent goals are simultaneously considered. Evolutionary algorithms are used in the global optimization process, based on the coupling of a Genetic Algorithm with a metamodel.
The optimization method is applied to a low speed axial compressor, for which the optimization goals are the minimization of aerodynamic loss and discharge kinetic energy at the exit of the stage, as well as the uniformity of work exchange along the blade span. The method proves to match all the objectives, providing a clear improvement with respect to classical and well-established design methods.
Flow Control in an Aggressive Inter-Turbine Duct Using Low Profile Vortex Generators
Authors: Zhang Yanfeng , Hu Shuzhen , Zhang Xue Feng , Benner Michael , Vlasic Edward 
Published: July 2013

This paper presents the experimental investigation of the flow in an aggressive inter-turbine duct (AITD). The goal is to improve the understanding of the flow mechanisms within the AITD and of the underlying physics of low-profile vortex generators (LPVGs).
The flow structures in the AITD are dominated by counter-rotating vortices and boundary layer separations in both the casing and hub regions. At the first bend of the AITD, the casing boundary layer separates in a 3D mode because of the upstream wakes; this is followed by a massive 2D boundary layer separation. Due to the effect of the radial pressure gradient at the first bend, the streamwise vorticity generated by the casing 3D separation stays close to the casing endwall, and later mixes with the casing counter-rotating vortices formed at the second bend.
By using LPVGs with different configurations installed on the casing, the casing boundary layer separation is significantly reduced. The streamwise vortices generated by the LPVGs have the potential to generate another pair of counter-rotating vortices at the AITD second bend, which help to delay/prevent the boundary layer separation. Therefore, the total pressure loss in the AITD was significantly reduced.
Simulation of Radial Compressor Aeroacoustics Using CFD
Authors: Mendonça Fred , Baris Onur , Capon Geoff 
Published: July 2013

This paper focuses on the application of CFD to the prediction of radial compressor aeroacoustics. It concentrates mainly on automotive turbocharger operations in the low mass-flow range where blade leading-edge and tip separation reduce the compressor performance and induce transient flow behaviour. Whereas the blade-passing is tonal and at high frequency, usually beyond the human hearing range, transience in the flow are turbulence-dominated, broad-band in nature, and in magnitude a significant source of aeroacoustics which appears well within the range of peak human hearing (1–5kHz). Other noise sources occur due to distortions in the flow upstream of the compressor face, and rotating stall.
The simulation methodology enumerated here pays attention to all the above flow-induced aeroacoustics. Due consideration is given to turbulence modelling, to ensure that both the narrow-band and broad-band sources are directly resolved in the CFD. Appropriate discretisation practices are adopted, so as to capture both turbulent-convection and sound-propagation mechanisms. Pressure-wave non-reflective boundary conditions are applied to the computational boundaries to remove any artificial resonances in the domain.
STAR-CCM+, the commercial CFD code used here, was previously benchmarked against experimental data for the same compressor under ideal installation conditions, then the compressor performance assessed under real installation conditions [1]. The main foci of the studies reported here are to exploit possible improvements in modelling of the device performance and efficiency curves using more detailed wall modelling, comparing low-y+ versus high-y+ wall resolution, and to explore the viability for transient CFD calculations to capture the noise sources in the compressor at the challenging low mass flow end of the performance characteristic.
Advanced Thermal Management for Modern Diesel Engines: Optimized Synergy Between Engine Hardware and Software Intelligence
Authors: Körfer Thomas , Busch Hartwig , Kolbeck Andreas , Severin Christopher , Schnorbus Thorsten , Honardar Sharareh 
Published: July 2013

Both, the continuous tightening of the exhaust emission standards and the global efforts for a significant lowering of CO2 output in public traffic display significant developments for future diesel engines. These engines will utilize not only the mandatory Diesel oxidation catalyst (DOC) and particulate trap (DPF), but also a DeNOx aftertreatment system as well — at least for heavier vehicles. The DOC as well as actually available sophisticated DeNOx aftertreatment technologies, i.e. LNT and SCR, depends on proper exhaust gas temperatures to achieve a high conversion rates. This aspect becomes continuously critical due to intensified measures for CO2 reduction, which will conclude in a drop of exhaust gas temperatures. Furthermore, this trend has to be taken into account regarding future electrification and hybridization scenarios. In order to ensure the high NOx conversion rates in the EAS intelligent temperature management strategies will be required, not only based on conventional calibration measures, but also a further upgrade of the engine hardware.
Advanced split-cooling and similar thermal management technologies offer the merit to lower CO2 emissions on one hand and increase exhaust gas temperature at cold start and warm-up simultaneously on the other hand. Besides this, also variable valve train functionalities deliver a substantial potential of active thermal management. In the context of this paper various concepts for exhaust gas temperature management are investigated and compared. The final judgment will focus on the effectiveness concerning real exhaust temperature increase vs. corresponding fuel economy penalty. Further factors, like operational robustness, consequences on operational strategies and related software algorithms as well as cost are assessed. The utilized reference engine in this advanced program is represented by a refined I-4 research engine to achieve best combustion efficiency at minimal engine-out emissions. The detailed studies were performed with an injection strategy, featuring one pilot injection and one main injection event, and an active, advanced closed-loop combustion control. The engine used in this study allows fulfillment of Euro 6 and Tier 2 Bin 5 emissions standards, while offering high power densities above 80 kW/ltr.
As a résumé, it can be stated, that with all accomplished variations a significant increase in temperature downstream low pressure turbine can be achieved. The PI and PoI quantities define dominant parameters for emission formation under cold and warm conditions. By using an exhaust cam-phaser CO-, HC- and NOx emissions can be significantly lowered, separating VVT functions from the other investigated strategies.
Investigating Trends in Simulated Ignition Timing Across a Wide Range of Conditions Including Fuel Reactivity
Authors: Johnson Michael V. , Goldsborough S. Scott , Smith Timothy A. , McConnell Steven S. 
Published: July 2013

Continued interest in kinetically-modulated combustion regimes, such as HCCI and PCCI, poses a significant challenge in controlling the ignition timing due to the lack of direct control of combustion phasing hardware available in traditional SI and CI engines. Chemical kinetic mechanisms, validated based on fundamental data from experiments like rapid compression machines and shock tubes, offer reasonably accurate predictions of ignition timing; however utilizing these requires high computational cost making them impractical for use in engine control schemes. Empirically-derived correlations offer faster control, but are generally not valid beyond the narrow range of conditions over which they were derived.
This study discusses initial work in the development of an ignition correlation based on a detailed chemical kinetic mechanism for three component gasoline surrogate, composed of n-heptane, iso-octane and toluene, or toluene reference fuel (TRF). Simulations are conducted over a wide range of conditions including temperature, pressure, equivalence ratio and dilution for a range of tri-component blends in order to produce ignition delay time and investigate trends in ignition as pressure, equivalence ratio, temperature and fuel reactivity are varied. A modified, Arrhenius-based power law formulation will be used in a future study to fit the computed ignition delay times.
Numerical Comparative Analysis of In-Cylinder Tumble Flow Structures in Small PFI Engines Equipped by Heads Having Different Shapes and Squish Areas
Authors: Falfari Stefania , Bianchi Gian Marco , Nuti Luca 
Published: July 2013

For increasing the thermal engine efficiency, faster combustion and low cycle-to-cycle variation are required. In PFI engines the organization of in-cylinder flow structure is thus mandatory for achieving increased efficiency. In particular the formation of a coherent tumble vortex with dimensions comparable to engine stroke largely promotes proper turbulence production extending the engine tolerance to dilute/lean mixture. For motorbike and scooter applications, tumble has been considered as an effective way to further improve combustion system efficiency and to achieve emission reduction since layout and weight constraints limit the adoption of more advanced concepts. In literature chamber geometry was found to have a significant influence on bulk motion and turbulence levels at ignition time, while intake system influences mainly the formation of tumble vortices during suction phase. The most common engine parameters believed to affect in-cylinder flow structure are:
1. Intake duct angle;
2. Inlet valve shape and lift;
3. Piston shape;
4. Pent-roof angle.
The present paper deals with the computational analysis of three different head shapes equipping a scooter/motorcycle engine and their influence on the tumble flow formation and breakdown, up to the final turbulent kinetic energy distribution at spark plug. The engine in analysis is a 3-valves pent-roof motorcycle engine. The three dimensional CFD simulations were run at 6500 rpm with AVL FIRE code on the three engines characterised by the same piston, valve lift, pent-roof angle and compression ratio. They differ only in head shape and squish areas. The aim of the present paper is to demonstrate the influence of different head shapes on in-cylinder flow motion, with particular care to tumble motion and turbulence level at ignition time. Moreover, an analysis of the mutual influence between tumble motion and squish motion was carried out in order to assess the role of both these motions in promoting a proper level of turbulence at ignition time close to spark plug in small 3-valves engines.
A Numerical Investigation of Combustion Chamber Geometry Effects on Natural Gas Direct Injection Properties in a SI Engine With Centrally Mounted Multi-Hole Injector
Authors: Yadollahi Bijan , Boroomand Masoud 
Published: July 2013

Due to the vast resources of natural gas (NG), it has emerged as an alternative fuel for SI internal combustion engines in recent years. The need to have better fuel economy and less emission especially that of greenhouse gases has resulted in development of NG fueled engines. Direct injection of natural gas into the cylinder of SI internal combustion engines has shown great potential for improvement of performance and reduction of engine emissions especially CO2 and PM. Direct injection of NG into the cylinder of SI engines is rather new thus the flow field phenomena and suitable configuration of injector and combustion chamber geometry has not been investigated completely.
In this study a numerical model has been developed in AVL FIRE software to perform investigation of direct natural gas injection into the cylinder of spark ignition internal combustion engines. In this regard, two main parts have been taken into consideration aiming to convert an MPFI gasoline engine to direct injection NG engine. In the first part of study multidimensional numerical simulation of transient injection process, mixing and flow field have been performed via different validation cases in order to assure the numerical model validity of results. Adaption of such a modeling was found to be a challenging task because of required computational effort and numerical instabilities. In all cases present results were found to have excellent agreement with experimental and numerical results from literature.
In the second part, using the moving mesh capability, the validated model has been applied to methane injection into the cylinder of a direct injection engine. Five different piston head shapes have been taken into consideration in investigations. An inwardly opening multi-hole injector has been adapted to all cases. The injector location has been set to be centrally mounted. The effects of combustion chamber geometry have been studied on mixing of air-fuel inside cylinder via quantitative and qualitative representation of results. Based on the results, suitable geometrical configuration for a NG DI engine has been discussed.