bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Numerical Investigation of the Flow Inside the Return Channel of a Centrifugal Process Compressor
Authors: Rube C. , Rossbach T. , Wedeking M. , Grates D. R. , Jeschke P. 
Published: August 2015

This paper presents the first detailed experimental performance data for a new centrifugal process compressor test rig. Additional numerical simulations supported by extensive pressure measurements at various positions allow an analysis of the operational and loss behavior of the entire stage and its components.
The stage investigated is a high flow rate stage of a single-shaft, multistage compressor for industrial applications and consists of a shrouded impeller, a vaneless diffuser, a U-bend and an adjoining vaned return channel. Large channel heights due to high flow rates induce the formation of highly three-dimensional flow phenomena and thus enlarge the losses due to secondary flows. An accurate prediction of this loss behavior by means of numerical investigations is challenging. The published experimental data offer the opportunity to validate the used numerical methods at discrete measurement planes, which strengthens confidence in the numerical predictions.
CFD simulations of the stage are initially validated with global performance data and extensive static pressure measurements in the vaneless diffuser. The comparison of the pressure rise and an estimation of the loss behavior inside the vaneless diffuser provide the basis for a numerical investigation of the flow phenomena in the U-bend and the vaned return channel. The flow acceleration in the U-bend is further assessed via the measured two-dimensional pressure field on the hub wall. The upstream potential field of the return channel vanes allows an evaluation of the resulting flow angle. Measurements within the return channel provide information about the deceleration and turning of the flow. In combination with the numerical simulations, loss mechanisms can be identified and are presented in detail in this paper.
Design and Performance Measurements of a 6 kW High-Speed Micro Gas Turbine Prototype
Authors: Grönman Aki , Honkatukia Juha , Sallinen Petri , Backman Jari , Uusitalo Antti , Turunen-Saaresti Teemu , Jaatinen-Värri Ahti 
Published: August 2015

Small portable electricity generating systems are suitable in remote locations where the access by vehicles is restricted or not even possible. These kind of places include for example catastrophic areas after earthquakes or tropical cyclones. Such machines can also be used as auxiliary power units in motor or sail boats. Gas turbine based electricity generation systems offer a good alternative for typical engine-generator units which are characterized by lower specific powers. It is suggested that the power to weight ratio of a 6 kW micro gas turbine can be more than eight times higher than that of the corresponding engine-generator unit. The biggest drawback is the higher specific fuel consumption; however, by introducing a recuperator, the specific fuel consumption can be improved.
In this article, the design process and experiments of a 6 kW micro gas turbine prototype are described and discussed in detail. The built non-recuperated prototype is based on a commercial, small jet engine originally designed to give thrust to radio controlled model airplanes. The jet nozzle of the jet engine was replaced by an axial power turbine which was directly connected to a small, high speed permanent magnet generator. The experiments showed the potential of the prototype.
Dynamics and Turbulence Characteristics of Wake-Boundary Layer Interaction in a Low Pressure Turbine Blade
Authors: Berrino M. , Lengani D. , Simoni D. , Ubaldi M. , Zunino P. , Bertini F. 
Published: August 2015

The paper analyzes the unsteady interaction between an impinging wake and the suction side boundary layer of a low pressure turbine cascade operating under unsteady inflow conditions. The instantaneous flow fields are obtained with Particle Image Velocimetry (PIV) for two different free-stream turbulence intensities (FSTI) and two orthogonal measurement planes (a blade-to-blade and a wall-parallel plane, respectively). The large data set has been post-processed by means of Proper Orthogonal Decomposition (POD) to provide a solid statistical interpretation of the physics of this complex unsteady interaction.
For the analysis of the blade-to-blade plane measurements, the paper takes advantage of the POD properties, which consist in splitting spatial (POD modes) and temporal (POD eigenvector) information. The phase identification of each PIV image within the wake passing period is then extracted from the eigenvectors of properly selected POD modes in order to reconstruct a phase-averaged velocity field. This post-processing allow us to separately account for the contribution to deterministic and stochastic unsteadiness as well as to have a look at the most significative scales of turbulence generating during the different phase of the wake-boundary layer interaction process.
The detailed analysis is completed by the measurements in a wall-parallel plane (aligned with the blade span). Instantaneous images and POD modes in this plane allow recognizing the presence of three-dimensional disturbances, induced by low and high speed travelling streaks (Klebanoff mode). These coherent structures have been shown to play a significant role in the unsteady transition process of the boundary layer at both low and elevated FSTI, and results reported in the paper further characterize their role in the transition process.
Damping Behavior of Blades From Small Radial Turbines
Authors: Hemberger David , Filsinger Dietmar , Bauer Hans-Jörg 
Published: August 2015

Next to excitation forces and the dynamic properties of mistuned structures the damping behavior is a key feature to evaluate the dynamic turbine blade response and thus the HCF life of a bladed disk (blisk). Just as the determination of the mistuning properties and the assessment of the vibration excitation, the evaluation of damping is also subject to uncertainty especially considering the wide operating range of a small radial turbine of a turbocharger. Since the total damping is composed of material damping, structural damping and aerodynamic damping, which are affected by parameters, like the eigenform of the vibration, the magnitude of the vibration amplitude and aerodynamic properties, the total damping can be strongly dependent on the operating conditions.
The study at hand provides results from investigations that allow estimating the contribution of aerodynamic damping on the total damping. Experimental and numerical analysis of radial turbines from turbochargers for vehicular engines with variable turbine inlet vanes were performed. Measurements under different environmental conditions such as at rest and during operation, as well as unsteady CFD calculations and, coupled flow and structural calculations were carried out.
A change in total damping could be found depending on the density of the surrounding gas by vibration measurements in operation on the hot gas test bench. But it was also shown that the total damping is decisively influenced by the mistuning of the structure. On one side the structural damping is varied by the variation in mistuned blade vibration amplitudes and otherwise the aerodynamic damping is influenced by the different inter blade phase angles (IBPA ) due to the mistuning, which is a symptom of geometric differences and material inhomogeneity in the wheels.
Finally, the estimated total damping values were utilized in forced response calculations using a mistuned FE-model of a real turbine and excitation forces from unsteady CFD calculation. The magnitudes of the measured vibration amplitudes were compared with results from numerical analysis to validate the numerical model with focus on the investigation about the total damping. The deviation between the results was ±10% for different eigenforms and excitation orders.
Uncertainty Quantification of Hot Gas Ingestion for a Gas Turbine Nozzle Using Polynomial Chaos
Authors: Panizza Andrea , Bonini Alessio , Innocenti Luca 
Published: August 2015

One of the most critical parameters in the design process of cooled hot gas components, is the Back Flow Margin (BFM). This dimensionless parameter quantifies the margin to hot gas ingestion through a cooled component wall. A correct evaluation of this parameter is crucial in order to avoid component failure. In presence of combustion chambers that exhibit low pressure losses, BFM becomes one of the most restrictive requirements in the thermal design of cooled components.
In this work, a conceptual BFM assessment of the first nozzle of an HP gas turbine is described. The component is subject to the highest thermal load; complex cooling systems are required to ensure an acceptable metal temperature and to match life time requirement. Due to manufacturing tolerances and fluid dynamic uncertainties, hot gas ingestion events are possible also for a nozzle that exhibits BFM higher than zero in nominal conditions, even if with a low probability. Here, the cooling scheme of the nozzle is modeled using an in-house fluid network tool that allows a quick and accurate computation of the equivalent cooling scheme and thus the occurrence of hot gas ingestion, corresponding to a negative flow rate in one of the cooling sub-models.
However, as the probability of hot gas ingestion is rather small, an accurate estimation of this event based on the standard Monte Carlo method requires a huge number of runs. A more efficient estimation of this probability can be obtained using stochastic expansion methods, such as the Polynomial Chaos Expansion. Pseudospectral approximations based on either a tensor-product expansion or the Sparse Pseudospectral Approximation Method (SPAM) are used, in order to estimate the probability of hot gas ingestion and the sensitivity to random parameters. The results are compared with those coming from Monte Carlo method, showing the superior accuracy of the stochastic expansion methods.
A Shape Memory Alloy-Based Morphing Axial Fan Blade: Part II — Blade Shape and CFD Analyses
Authors: Suman Alessio , Fortini Annalisa , Aldi Nicola , Merlin Mattia , Pinelli Michele 
Published: August 2015

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper experimental and CFD numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed.
Starting from the experimental results proposed in the first part of this work, a morphing blade, made of Shape Memory Alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques.
After the analyses in the wind tunnel CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with non-activated blades and with activated blades.
The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan.
This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life thanks to a strong relationship between the engine thermal request and the cooling fan performance.
A Detailed Uncertainty Analysis of Adiabatic Film Cooling Effectiveness Measurements Using Pressure Sensitive Paint
Authors: Natsui Greg , Little Zachary , Kapat Jayanta S. , Dees Jason E. , Laskowski Gregory 
Published: August 2015

Pressure sensitive paint (PSP) can be a powerful tool in measuring the adiabatic film cooling effectiveness. There are two distinct sources of error for this measurement technique; the ability to experimentally obtain the data and the validity of the heat and mass transfer analogy for the problem being studied. This paper will assess the experimental aspect of this PSP measurement specifically for film cooling applications.
Experiments are conducted in an effort to quantifiably bound expected errors associated with temperature non-uniformities in testing and photo-degradation effects. Results show that if careful experimental procedures are put in place, both of these effects can be maintained to have less than 0.022 impact on effectiveness.
Through accurate semi-in-situ calibration down to 4% atmospheric pressure, the near-hole distribution of effectiveness is measured with high accuracy. PSP calibrations are performed for multiple coupons, over multiple days. In addition, to reach a partial pressure of 0 the calibration vessel was purged of all air by flowing CO2.
The primary contribution of this paper lies in the uncertainty analysis performed on the PSP measurement technique. A thorough uncertainty analysis is conducted and described, in order to completely understand the presented measurements and any shortcomings of the PSP technique. This quantification results in larger, albeit more realistic, values of uncertainty, and helps provide a better understanding of film cooling effectiveness measurements taken using the PSP technique. The presented uncertainty analysis takes into account all random error sources associated with sampling and calibration, from intensities to effectiveness.
Adiabatic film cooling effectiveness measurements are obtained for a single row of film cooling holes inclined at 20 degrees, with CO2 used as coolant. Data is obtained for six blowing ratios. Maps of uncertainty corresponding to each effectiveness profile are available for each test case. These maps show that the uncertainty varies spatially over the test surface, high effectiveness corresponds to low uncertainty. The noise floors can be as high as 0.04 at effectiveness levels of 0. Day-to-day repeatability is presented for each blowing ratio and shows that laterally averaged effectiveness data is repeatable within 0.02 effectiveness.
Interval Analysis on Aero-Engine Rotor System With Misalignment
Authors: Wang Cun , Ma Yanhong , Zhang Dayi , Hong Jie 
Published: August 2015

Misalignment is a usual phenomenon in rotating machines. The rotor centerlines are not collinear at the couplings and the rotors operate in incorrect axial positions in a multi-span rotor. The effects of misalignment of flexible rotor system are summarized as the variation of joint stiffness and additional misalignment excitation force based on the dynamic model established.
The variation of joints stiffness is difficult to describe, meanwhile the misalignment excitation and rotor unbalance changes with different assembly and operating conditions. The distributions of these parameters which have significant effect on rotor dynamics are unknown, but the intervals of uncertain parameters are usually easier to get. An interval analysis method based on Taylor expansion and direct integration, which solves the dynamic response of rotor system under complex excitations including misalignment and multi unbalance with different frequencies and excitation points is presented. The differential equation of rotor system is formulated by combination of the matrixes of an actual rotor system finite element model and interval excitation vectors. The responses of a single spool and two spools with misalignment and unbalance are calculated by the interval analysis method. The results indicate that the method is effective and reflects some dynamic influence of misalignment and unbalance on rotor system. Second harmonic frequency appears, and rotor orbit is irregular. The response reflects the uncertain interval distribution characteristics, and the frequency components on different locations of the rotor have different characteristics.
Bird Strike Analysis of a Composite Aircraft Wing
Authors: Jammi Srinivasa R. , Shivakumar P. 
Published: August 2015

Bird strikes have been a concern to aviation safety in both civil and military aircrafts. The external surfaces of an aircraft which include wing leading edges are susceptible to bird-strikes. Recently topology optimization is used to realize an aircraft wing concept design using Aluminum in (2009) [1] and optimize its weight. To make it lighter further, a composite wing was derived in (2010) [2]. Here, Fibre Metal Laminates (FMLs) with layers of aluminium alloy and high strength glass fibre have been used. The impact analysis is performed using a SPH model for the bird. Based on the modal analysis, the impact time is determined to capture the modes with high participation factor. The response obtained in time domain is converted to frequency domain and it is shown that the response has predominantly these modal components.
For the given FMLs wing configuration the stress levels obtained are well within the orthotropic yield limits of the structure. All the layers of the composite structure are found to be intact.
Development of a New Universal Inverse Through-Flow Program and Method for Fully Coupled Split-Flow Turbomachinery Systems
Authors: Acarer Sercan , Özkol Ünver 
Published: August 2015

Streamline curvature technique for inverse through-flow modeling of turbomachinery is still one of the most prevalent alternatives in design. Even though the subject has been studied in numerous aspects over many years, open literature on fully coupled split-flow turbomachinery system design which is encountered in turbofan engines, is still limited. The principal method, viable for analysis mode, may easily give rise to undesired streamline distortion near the splitter leading edge whilst operating in design mode. Besides, spanwise discontinuity of flow properties along the stagnation streamline prior to final solution convergence may be another outcome.
The present study is geared towards eliminating these potential drawbacks by developing an alternative generally-applicable split-flow scheme incorporated in a recently developed streamline curvature software. This new scheme disposes the need to define a stagnation streamline, while preserving full coupling between the main and split ducts. This is achieved through removal of by-pass ratio restriction, which makes local velocity vector always perfectly aligned with the splitter leading edge without any limit on fan-splitter axial distance. A two-step validation strategy is followed: Firstly, 2D split-flow solutions of the developed method for representative duct geometries having design by-pass ratios ranging between 0.25 and 6.5, but without turbomachinery, are compared with a commercial CFD software; Secondly, the method is compared with 3D viscous CFD solution of NASA Rotor 37 geometry, whose flowpath is modified to include a downstream flowpath splitter.
It is shown that the proposed scheme can be used as a practical alternative to the conventional treatment that promises minimal effort to implement to an existing compressor streamline curvature methodology.
A Curvature Based Algorithm for Treatment of Cooling Holes in Polygon Meshes of Turbine Blades
Authors: Högner Lars , Voigt Matthias , Vogeler Konrad , Meyer Marcus , Berridge Christopher 
Published: August 2015

Reliable parametrisation methods are required within the scope of probabilistic analysis to predict the influence of geometric variations. But in case of turbine blades, the external surface is potentially disturbed by cooling holes in such a way that methods for aerofoil parametrisation could fail.
This paper shows an automated pre-process for turbine blade parametrisation. The presented algorithm locates cooling holes and generates a smooth surface to ensure the functionality of parametrisation methods.
The cooling holes are located based on the approximated curvature of the polygon mesh. Afterwards, the identified areas of high local curvature are removed. Finally, a combined hole filling and smoothing algorithm is applied.
Experimental Investigation of Swirl and Flow Structure Inside a Rotor-Stator Cavity
Authors: Facchini Bruno , Massini Daniele , Picchi Alessio , Micio Mirko , Bavassano Francesco , Mantero Marco 
Published: August 2015

In order to ensure safety, predictable and acceptable life of gas turbine engines an important task is the design of the secondary air system (SAS).
To avoid hot gas path ingestion, one of the most critical concerns in a well-performing SAS is the understanding of the air motion within of the stator-rotor cavity systems. The state of the art of the fluid solver tools used to predict the flow behaviour inside cavities is generally based on codes with correlative approaches, in order to reduce calculation times and computational resources.
In order to improve the precision of correlations, by means of data with reduced associated uncertainty, experimentalists performed an experimental campaign selecting a simple test case composed by a rotating disc facing a flat stator. Imposing several working conditions, the rotational speed was varied in order to gain a rotational Reynolds number up to 1.2 × 106 which is one order of magnitude less than real seals working conditions. The analysis of the swirl rate as well as the frictional moment exerted by the rotor on the fluid was carried out based on different sealing mass flows. Pressure probes were used to obtain radial distribution of static and total pressure on the stator side. In order to deepen the analysis on the flow behaviour inside cavity, flow field measurements using a 2D PIV system was performed on two different planes: velocity contours were used to help the detection of the core region.
Finally, the wide database of the experimental results were used to improve a simple model able to predict the behaviour of rotor-stator cavities including the effect of the inlet geometry of the cavity.