bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance Uncertainty Quantification for Centrifugal Compressors: Part 1—Stage Performance Variation
Authors: Panizza Andrea , Iurisci Giuseppe , Sassanelli Giuseppe , Sivasubramaniyan Sankaran 
Published: July 2013

In modern industrial practice, the quality of a new product is achieved by identifying characteristics critical to quality (CTQs) and minimizing deviation from targets, rather than merely optimizing CTQs in the absence of variation. Estimating the variation of CTQs is thus critical to understand and correctly manage risk caused by different interacting sources of uncertainty.
We have developed a method to estimate performance variability for centrifugal compressor stages. In this paper, we quantify the performance variation due to impeller manufacturing variability of two stage families. The stages studied are 2D stages designed for multi-purpose applications and 2D stages for high head applications. In a related paper, the stage performance variability here determined is considered together with other sources of variation to compute the variation in flange-to-flange performance for a full compressor.
The proposed approach propagates the uncertainty of the design parameters to the stage aerodynamic performance through a Monte Carlo method. In order to keep a low computational budget, calibrated 1D/2D aerodynamic models have been run in parallel to compute the performance of the stages with randomly modified geometry. The results allow the quantification of the stage performance variability and the identification of the main sources of variation.
As a step towards the corresponding analysis for a complete centrifugal compressor, results from this study have been used as input for a method where all factors affecting the flange-to-flange performance are considered. The method and the results are discussed in a companion paper.
Cavity Flow Modeling in an Industrial Centrifugal Compressor Stage at Design and Off-Design Conditions
Authors: Guidotti Emanuele , Naldi Giovanni , Tapinassi Libero , Chockalingam Valliappan 
Published: July 2013

Numerical tools and test equipments used in the design and validation of modern centrifugal compressor stages need to be at the state-of-the-art. In particular, a big effort is currently made to correctly model secondary flows that play a relevant role in the accuracy of the performance prediction.
This paper presents the flow analysis of a high efficiency centrifugal compressor stage using high accurate computational fluid dynamics with a particular attention to the cavity flows modeling. Experimental data were also available and used to validate the numerical results. The key experimental data coming from an advanced FRAPP (Fast Response Aerodynamic Pressure Probe) and traditional probes are presented in the study as overall performance and flow features details. Test data are in fact necessary to validate and continuously improve the numerical techniques.
The geometry of the stage including full modeling of the secondary flows cavities were faithfully reproduced in the computational model. The availability of new in-house automated tools for cavity meshing allow compressor aero-designers to accurately resolve leakage flows with a reasonable increase in computational and user time.
The results of the computational model were in excellent agreement with the experimental data both in terms of overall performance and main flow field structures. Also details of the flow features inside the cavities matched the test data very well. Only using high accurate geometry modeling including leakage flows was possible to capture important flow features that instead were not correctly simulated with simplified computational models.
Multidisciplinary Optimization of a Turbocharger Radial Turbine
Authors: Mueller Lasse , Alsalihi Zuheyr , Verstraete Tom 
Published: July 2013

This paper presents a multidisciplinary design optimization of a turbocharger radial turbine for automotive applications with the aim to improve two major manufacturer requirements: the total-to-static efficiency and the moment of inertia of the radial turbine impeller. The search for the best design is constrained by mechanical stress limitations, by the mass flow and power, and by aerodynamic constraints related to the isentropic Mach number distribution on the rotor blade.
The optimization of the radial turbine is performed with a two-level optimization algorithm developed at the von Karman Institute for Fluid Dynamics (VKI). The system makes use of a Differential Evolution algorithm, an Artificial Neural Network (ANN), and a database as a compromise between accuracy and computational cost. The ANN performance predictions are periodically validated by means of accurate steady state 3D Navier-Stokes and centrifugal stress computations.
The results show that it is possible to improve the efficiency and the moment of inertia only in a few numbers of iterations while limiting the stresses to a maximum value. Based on the large number of evaluated designs during the optimization, this paper provides design recommendations of a turbocharger radial turbine at least for a good preliminary design.
The Effect of Two Different Endwall-Penny Concepts for Variable Stator Vanes in a Compressor Cascade
Authors: Gottschall Marcel , Vogeler Konrad , Mailach Ronald 
Published: July 2013

The article describes investigations on the influence of two possible endwall-penny concepts for variable stator vanes to secondary flow field development and the performance of high pressure compressors. Concept I uses a penny covering the whole vane chord with no radial clearances, whilst the concept II applies a piecewise flattened polygonal hub or casing to achieve constant radial gaps. Both approaches were converted to a linear cascade of modern stator profiles. Measurements were conducted with a 5-hole-probe in planes up- and downstream the cascade as well as with pressure tappings on the airfoil and the endwall. Additional 3D numerical calculations were carried out to gain information about the flow field inside the cascade. These analyses were performed at three stagger angles and two characteristic Reynolds numbers with a constant cascade turning to model the adjusting range of aircraft engines.
Compared to a reference case without endwall contour and no clearance the results indicate slightly increased efficiency due to smaller total pressure losses for both concepts. The penny edges as well as the polygonal endwall at the cascade inlet are responsible for a higher turbulence in the inlet boundary layer, which results in a smaller endwall separation that is detected with outlet loss distributions. Considering the cascade loading in terms of flow turning, a small overall benefit was achieved with both configurations caused by much higher overturning near the wall. These tendencies increase with the stagger angle at part-load conditions of the compressor. Furthermore, the results were compared with a part gap configuration of a variable vane with benefits concerning pressure losses and flow turning. For lower cascade loadings the concept I still reaches the highest overall flow turning. This benefit compared to the part gap configuration nearly disappears at the high stagger angle. Additionally, both concepts feature a much higher flow angle deviation along the blade height and significant increased losses.
Generation of Gas Turbine Component Maps on Basis of Operational Data
Authors: Zwingenberg M. , Dobrzynski B. , Klumpp S. , Werner K. , Benra F.-K. 
Published: July 2013

This paper describes how operational data from heavy duty gas turbines can be used for component map generation. The main aspects described are the data evaluation and validation process, the applied degradation correction methodology and the component map generation using calibrated streamline curvature methods for compressor and turbine.
The operational data storage system of heavy duty gas turbines can be used, in case the customer agreed to provide the data, for fleet statistics, degradation behavior investigation or component map generation. The update of existing component maps using operational data is mainly necessary for older gas turbines types since the available numerical gas turbine models do not always represent the current state of knowledge.
The process of generating component maps based on operational data requires several steps which are explained in detail in this paper. The first step is the data evaluation and validation part. This step is based on a full thermodynamic evaluation including an evaluation of systematic and random uncertainties for all required performance parameters. This generated dataset is then validated using a combination of a Kalman Filter based single fault isolator and a fuzzy logic based multiple fault isolator. A short performance evaluation of this data validation system is given as well.
After the validation part the operational dataset is corrected for aging effects regarding compressor and turbine performance in order to get the new and clean component characteristic. Subsequently, a validated and aging corrected high quality database for the component map generation is available. The applied steps as well as a direct comparison for the compressor efficiency prior and post aging correction are displayed.
In the following steps, already existing streamline curvature methods (SCM) for compressor and turbine are adapted to the generated dataset using a probabilistic based calibration process. The applied optimization technique is identical for compressor and turbine, but two different approaches for the calibration of the loss modeling have been implemented. The compressor SCM is calibrated with a minimum set of modified loss parameters which are modeled as a function of load. For the turbine, the modifications of the loss coefficients are constant over load. This requires an increased set of loss parameters for calibration compared to the compressor. The calibration results for both components are presented and discussed in detail. The calibrated SCMs can now be used for the component map generation in order to yield high quality component maps in accordance with current fleet experience even for older gas turbine frames.
Boundary Layer Control on a Low Pressure Turbine Blade by Means of Pulsed Blowing
Authors: Mack Marion , Niehuis Reinhard , Fiala Andreas , Guendogdu Yavuz 
Published: July 2013

The current work investigates the performance benefits of pulsed blowing with frequencies up to 10 kHz on a highly loaded LPT blade. The influence of blowing position and frequency on the boundary layer and losses are investigated.
Pressure profile distribution measurements and midspan wake traverses are used to assess the effects on the boundary layer under a wide range of Reynolds numbers from 50000 to 200000 at a cascade exit Mach number of 0.6 under steady as well as periodically unsteady inflow conditions.
High frequency blowing at sufficient amplitudes is achieved with the use of fluidic oscillators. The integral loss coefficient calculated from wake traverses is used to assess the optimum pressure ratio driving the fluidic oscillators. The results show that pulsed blowing with fluidic oscillators can significantly reduce the profile losses of the highly loaded LPT blade T161 with a moderate amount of air used in a wide range of Reynolds numbers under both steady and unsteady inflow conditions.
Performance Prediction of Axial Flow Two-Stage Turbine Based on Different Losses Models
Authors: Jouybari H. Javaniyan , Eftari M. , Shahhosseini M. , Rad M. 
Published: July 2013

The flow field in axial turbines is complex and three-dimensional. Therefore, experimental flow field is essential to determine the performance characteristics. However, such testing is always expensive and complex. Simulation of gas turbines is a simple way to reduce testing costs and complexity.
The main objective of this paper is to make a detailed systematic analysis of two-stage, axial flow turbine by using of different loss models and a new suggested algorithm based on one-dimensional simulation. In one-dimensional modeling, the loss models have to be used to determine the entropy increase across each section of axial turbines stage at both the design and off-design conditions.
The calculation used in this modeling is based on common thermodynamics and aerodynamics principles in a mean stream line analysis.
Finally, in order to have a better understanding of the loss models behavior and verify the suggested algorithm accuracy, the analytical results from modeling were compared with experimental results and the comparison shows that good adaptation is obtained.
Aerodynamic Investigation of a High Pressure Ratio Turbo-Expander for Organic Rankine Cycle Applications
Authors: Marconcini Michele , Rubechini Filippo , Arnone Andrea , Del Greco Alberto Scotti , Biagi Roberto 
Published: July 2013

The design of radial-inflow turbines usually relies on one-dimensional or mean-line methods. While these approaches have so far proven to be quite effective, they can not assist the designer in coping with some important issues, such as mechanical integrity and complex flow features. Turbo-expanders are in general characterized by fully three-dimensional flow fields, strongly influenced by viscous effects and passage curvature. In particular, for high pressure ratio applications, such as in organic Rankine cycles, supersonic flow conditions are likely to be reached, thus involving the formation of a shock pattern which governs the interaction between nozzle and wheel components. The nozzle shock waves are periodically chopped by the impeller leading edge, and the resulting unsteady interaction is of primary concern for both mechanical integrity and aerodynamic performance.
This work is focused on the aerodynamic issues and addresses some key aspects of the CFD modelling in the numerical analysis of turbo-expanders. Calculations were carried out by adopting models with increasing level of complexity, from the classical steady-state approach to the full-stage, time-accurate one. Results are compared in details and the impact of the computational model on the aerodynamic performance estimation is discussed.
Investigation on Effect of Centrifugal Compressor Volute Cross-Section Shape on Performance and Flow Field
Authors: Mojaddam Mohammad , Benisi Ali Hajilouy , Movahhedi Mohammad Reza 
Published: July 2013

In this article, the effects of volute cross section shape and centroid profile of a centrifugal compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by measuring rotor speed and flow parameters at the inlet and outlet of the centrifugal compressor. The three dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with SST turbulence model. The compressor characteristic curves were plotted. For model verification, the results were compared with experimental data, showing good agreement.
Modification of a volute was performed by introducing a shape factor for volute cross section geometry. By varying this parameter, new volutes were generated and modeled. The effect of volute cross section shape on compressor pressure ratio and efficiency at design rotational speed were investigated. Also pressure non-uniformity around compressor impeller for new cases was calculated and reported.
The results showed how the cross section shape of the volute can influence the compressor characteristics and the non-uniformity of circumferential static pressure as well.
Probabilistic Analysis of Radial Gear Compressors
Authors: van Lil Thorsten , Voigt Matthias , Vogeler Konrad , Wacker Christian , Rockstroh Uwe 
Published: July 2013

Integrally geared compressors offer a wide range of applications for probabilistic analysis. The combination of a multi shaft compressor with an integral gear under changing operating conditions creates a lot of design challenges.
The gear design needs to meet the requirements of the compression process, like the rotating speed of the pinions or the pinion power. These requirements lead to a specific gear with its specific properties. The examination and verification of the internal correlations between thermodynamics and gear design is one significant objective of the project as a high efficiency of the compression process may be connected with high gear losses, or the other way around.
These design challenges ought to be investigated with probabilistic methods, such as the Monte-Carlo-Simulation. With such methods, it is possible to explore a wide design space automatically in order to learn about correlations between probabilistic input and output parameters as well as in order to choose a better design.
In a first step of this project, all process steps relevant for designing an integrally geared compressor have been combined to form one single automated algorithm. This algorithm is used for Monte-Carlo-Simulations (MCS) with optimal Latin-Hypercube as the sampling method. On the basis of the MCS results, response surfaces can be created to describe the scatter and the behaviour of the result parameters. Furthermore, response surfaces can be used as meta models for optimization and prediction.
This paper seeks to address the use and the performance of response surfaces.
Unsteady Simulation of a 1.5 Stage Turbine Using an Implicitly Coupled Nonlinear Harmonic Balance Method
Authors: Custer Chad H. , Weiss Jonathan M. , Subramanian Venkataramanan , Clark William S. , Hall Kenneth C. 
Published: July 2013

The harmonic balance method implemented within STAR-CCM+ is a mixed frequency/time domain computational fluid dynamic technique, which enables the efficient calculation of time-periodic flows. The unsteady solution is stored at a small number of fixed time levels over one temporal period of the unsteady flow in a single blade passage in each blade row; thus the solution is periodic by construction. The individual time levels are coupled to one another through a spectral operator representing the time derivative term in the Navier-Stokes equation, and at the boundaries of the computational domain through the application of periodic and nonreflecting boundary conditions. The blade rows are connected to one another via a small number of fluid dynamic spinning modes characterized by nodal diameter and frequency. This periodic solution is driven to the correct solution using conventional (steady) CFD acceleration techniques, and thus is computationally efficient. Upon convergence, the time level solutions are Fourier transformed to obtain spatially varying Fourier coefficients of the flow variables. We find that a small number of time levels (or, equivalently, Fourier coefficients) are adequate to model even strongly nonlinear flows. Consequently, the method provides an unsteady solution at a computational cost significantly lower than traditional unsteady time marching methods.
The implementation of this nonlinear harmonic balance method within STAR-CCM+ allows for the simulation of multiple blade rows. This capability is demonstrated and validated using a 1.5 stage cold flow axial turbine developed by the University of Aachen. Results produced using the harmonic balance method are compared to conventional time domain simulations using STAR-CCM+, and are also compared to published experimental data. It is shown that the harmonic balance method is able to accurately model the unsteady flow structures at a computational cost significantly lower than unsteady time domain simulation.
Reformulation of a Three-Dimensional Inverse Design Method for Application in a High-Fidelity CFD Environment
Authors: van Rooij Michel , Medd Adam 
Published: July 2013

Three-dimensional inverse design has been shown to be a reliable and powerful tool for facilitating the refinement of blading design and improving stage matching, thereby providing increased aero-design quality and productivity in difficult design situations. However, inverse design has not been incorporated widely into design systems. Reasons for this may be that many inverse techniques are limited to two dimensional problems, or are highly integrated with a specific flow solver and therefore difficult to integrate with proprietary or commercial CFD methods.
A reformulation of a three-dimensional inverse design method is presented here that overcomes these limitations. The new method is fully consistent with viscous flow modeling. Camber modification is performed using a blade velocity derived from the difference between prescribed and actual pressure loading. The new inverse method completely eliminates differences between analysis and inverse calculations.
Moreover, the reformulation effectively decouples the inverse method from the flow solver. This makes it possible to supplement any CFD-code with the developed inverse design module, provided an interface can be created between the solver and the inverse module through which to pass information on flow and mesh. This makes inverse design available to most design offices.
Angle-of-Attack Effects on Counter-Rotating Propellers at Take-Off
Authors: Brandvik Tobias , Hall Cesare , Parry Anthony B. 
Published: July 2013

Due to their potential for significant fuel consumption savings, Counter-Rotating Open Rotors (CRORs) are currently being considered as an alternative to high-bypass turbofans. When CRORs are mounted on an aircraft, several ‘installation effects’ arise which are not present when the engine is operated in isolation. This paper investigates how flow features arising from one such effect — the angle-of-attack of the engine centre-line relative to the oncoming flow — can influence the design of CROR engines. Three-dimensional full-annulus unsteady CFD simulations are used to predict the time-varying flow field experienced by each rotor and emphasis is put on the interaction of the front-rotor wake and tip vortex with the rear-rotor.
A parametric study is presented that quantifies the rotor-rotor interaction as a function of the angle-of-attack. It is shown that angle-of-attack operation significantly changes the flow field and the unsteady lift on both rotors. In particular, a frequency analysis shows that the unsteady lift exhibits sidebands around the rotor-rotor interaction frequencies. Further, a non-linear increase in the total rear-rotor tip unsteadiness is observed for moderate and high angles-of-attack.
The results presented in this paper demonstrate that common techniques used to mitigate CROR noise, such as modifying the rotor-rotor axial spacing and rear-rotor crop, can not be applied correctly unless angle-of-attack effects are taken into account.
Experimental Study of Injection and Combustion in a Diesel Engine for Heavy Quadricycle Use
Authors: Mancaruso Ezio , Vaglieco Bianca M. , Allocca Luigi , Montanaro Alessandro , Arnone Luigi 
Published: July 2013

An experimental investigation has been carried out on a diesel 1000 cc, two-valve, three-cylinder, engine for heavy quadricycle and off-road applications. The engine was equipped with a unit-pump common rail injection system, automotive derived, with maximum pressure 140 MPa and ECU able to manage multinjection strategies in Euro 4 target for the foreseen applications.
Experimental investigations on the fuel spray have been carried out in an optically accessible vessel at engine gas density. Spatial and temporal spray behavior has been studied by image processing of the evolving jet pictures. Spray tip penetrations, cone angles and fuel spatial density analysis have been extracted and correlated to the injection and engine parameters. On the other side, visible flame propagation and soot formation process have been evaluated by digital imaging at high spatial and temporal resolution using a quartz window of the third cylinder obtained modifying the engine head. Strategies consisting of two injections per cycle, pilot and main, and typical of real engine working conditions have been investigated in the pressure range 43–116 MPa both in terms of injection rates and injected fuel dispersion. The effects of different injection strategies on soot formation and exhaust emissions have been evaluated.