bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Mode Characteristics of Rotating Instability With Different Tip Clearances
Authors: Yang Zeyuan , Ming Lele , Wu Si , Wu Yadong , Tian Jie , Ouyang Hua
Published: October 2022

Rotating Instability (RI) is an unsteady aerodynamic phenomenon occurring at off-design conditions in axial compressors, featuring side-by-side peaks below the blade passing frequency (BPF) in pressure spectra. Especially when the mode orders of RI are close to the blade number the interaction effect could generate intense tip clearance noise, which could not be cut-off by the duct. Moreover, RI is regarded as a potential indicator for stall and surge. According to previous studies the mechanism of RI could be classified as the unsteady vortex system theory and the shear layer instability theory. This paper presents an experiment in a low-pressure single-rotor compressor, comparing the RI characteristics with two different tip clearances at different operating conditions. A total of 28 Kulite transducers were circumferentially mounted on the casing wall to measure the pressure fluctuation in the two configurations. Utilizing the compressive sensing (CS) method based on the double-uniform sampling point (DUSP) technique the mode orders of RI could be accurately determined. Through throttling the RI phenomenon was observed in different range of flow rates under both tip clearance configurations. The evolution pattern of RI is profoundly affected by the tip clearance size, i.e., the RI phenomenon only presents a two-stage “strengthen-weaken” pattern with the nominal gap, while shows a three-stage “strengthen-weaken-strengthen” pattern with the larger gap. Moreover, the mode characteristics of RI in the frequency domain are analyzed. Based on the experimental results several discussions on the mechanism of RI are proposed. These findings do not conform with the unsteady vortex system theory, but provides evidence for the shear layer instability theory.
Calibrated Rotation-Helicity-Quadratic Constitutive Relation Spalart-Allmaras (R-H-QCR SA) Model for the Prediction of Multi-Stage Compressor Characteristics
Authors: Matsui Kotaro , Tani Naoki , Perez Ethan , Kelly Ryan T. , Jemcov Aleksandar
Published: October 2022

Compressor performance prediction is still one of the significant interests in the turbomachinery research field. The two critical parameters for compressor design are adiabatic efficiency and stability margin. The Spalart-Allmaras (SA) turbulence model and modified SA models are widely used in that design process. However, the prediction accuracy is not always satisfactory. In most cases, the SA model predicts larger stall mass flow, and the RC-QCR SA model underestimates efficiency. This study proposes a new combination of the modified SA model (R-H-QCR model). R-H-QCR stands for Rotation-Helicity-Quadratic constitutive relation. The model increases or decreases turbulent viscosity based on flow rotation, energy backscatter, and anisotropy of turbulence flow field. The Bayesian inference framework calibrates the model parameters to predict accurately both efficiency and stability in the 3.5 stage compressor. The R-H-QCR, RC-QCR, and default SA models are evaluated in the multi-stage compressor. For the performance prediction, the R-H-QCR model predicts a better stability margin than the SA model and better efficiency than the RC-QCR model. In addition, the spanwise distribution of normalized total pressure is well captured by the R-H-QCR model, indicating that the R-H-QCR model improves flow field prediction.
Experimental and Numerical Advancement of the MGT Combustor Towards Higher Hydrogen Capabilities
Authors: Ćosić Bernhard , Wassmer Dominik , Kluß David , Jaeschke Alexander , Reichel Thoralf , Paschereit Christian Oliver
Published: October 2022

Blending of natural gas with hydrogen is a viable pathway for the decarbonization of industrial gas turbines for combined heat and power applications. Very high blending ratios of hydrogen are needed to achieve significant CO2 emission reductions. However, burning high hydrogen contents in the gas turbine is challenging in terms of NOx emissions and the mitigation of flashback risks as well as suppressing thermoacoustic instabilities. This paper illustrates a design modification to improve the hydrogen capabilities of the Advanced Can Combustion (ACC) system and its ultra-low emission industrial swirl burner for the MGT6000 gas turbine that was originally designed for pure natural gas combustion. A flow conditioner is installed upstream of the swirler aiming to decrease the fuel amount close to the combustor walls and thereby increase the flashback resistance of the burner. High pressure (≈14bar) full power (≈4MWth) single can combustion tests and atmospheric burner tests are used for the assessment of the hydrogen capabilities for the original and the retrofitted burner. Different levels of hydrogen blending of up to 45 vol-% at high pressure and 93 vol-% at atmospheric conditions as well as different gas turbine relevant flame temperatures are assessed in terms of emissions, flame flashback and thermoacoustic stability. Low speed thermocouple measurements at the burner walls are identified as a good precursor for hydrogen induced flame flashback at the walls. The amplitude of the thermocouple fluctuation is observed to be similar for atmospheric and elevated pressure. Moreover, it is shown that the increase in NOx emissions associated to hydrogen blending can be transferred from atmospheric conditions to elevated pressure. The experimental dataset is used for the calibration of Computational Fluid Dynamics (CFD) calculations to allow for the assessment at different operating conditions and future modifications. The CFD is focused on the prediction of flashback resistance for different blends of hydrogen and natural gas at high pressure conditions.
Multi Operating Point Aerodynamic Optimization of a Radial Compressor Impeller for an Application in High Temperature Heat Pump
Authors: Schaffrath Robert , Kriese Maximilian , Kajasa Bojan , Köhler Martino , Nicke Eberhard , Voß Christian
Published: October 2022

The decarbonization of production processes plays an important role on the way to environmentally friendly economy. Especially, the implementation of high temperature heat pumps (HTHP) offers a great potential to replace fossil fuel-based energy infrastructure. A major issue for the introduction of HTHP is the initial cost and regarding the payback period. However, there is still potential in increasing the coeffcient of performance (COP) of HTHP for the economic integration in existing industrial processes. One important possibility is the dedicated development and design of turbocompressors for this application and the planned heat transfer medium including the aerodynamic optimization of compressor geometry. Against this background an automated aerodynamic optimization method for radial compressor blade geometry for superheated steam is presented. The optimization refers to two different operating points of the HTHP and focuses on maximizing the isentropic efficiency of the impeller geometry as well as the pressure ratio. The algorithm is accelerated by data-driven metamodels and is implemented in a high-performance cluster environment. The boundary condition of the inherent computational fluid dynamics (CFD) calculation comes from the thermodynamic cycle calculation of the whole HTHP system. A two-stage compression with intercooling between the compressor stages are foreseen. Our approach shows an increment of both objective functions in both operating points and the satisfaction of further side conditions for the low pressure compressor (LPC). Furthermore, it results in an increment of 5 percent points of isentropic efficiency and 13 percent points of static to total pressure ratio in comparison to our initial geometry. These impeller optimizations result in a COP increment of 5 percent. The resulting geometry will be interpreted in the context of aerodynamic behavior. Based on that results additionally, a flow-cut optimization for the high pressure compressor (HPC) is given and evaluated. The results are comparable to aerodynamic optimization in different research fields like aircraft engines or stationary gas turbines and contribute to optimized multistage compressor design for HTHP.
Aerodynamic Noise Characteristics of Axial Flow Fan in Narrow Space and Noise Reduction Based on Flow Control
Authors: Sun Zonghan , Chai Pengfei , Tian Jie , Du Zhaohui , Ouyang Hua
Published: October 2022

The aeroacoustic characteristics of a power module in the electric vehicle charging pile is studied by experimental and numerical methods. In the free field, a single cooling fan mainly emits tonal noise, while the far-field noise of fans in parallel satisfied the superposition of incoherent sound sources. However, when two fans in parallel delivered air into the power module, the noise increased significantly, especially broadband noise. Referring to the power module, a narrow space model with cooling fan supplying air inward is constructed. The computational fluid dynamics (CFD) results show that the mass flow rate of the fan is reduced due to the obstacles downstream, which weakens the heat dissipation performance. Part of the fluid forms reflux, interacts with the fan and strengthens the corner vortex. By setting guide holes on the casing near the flow blockage to arrange flow, the flow resistance is reduced and the total mass flow rate of the fan is increased by 2.5%. The reflux and corner vortex are dispersed, and the vortices develop downstream, thus reducing the interaction with the fan. The predicted tonal sound pressure level (SPL) decreases by 3.2 dBA based on acoustic analogy method. The broadband noise caused by shedding vortex is also predicted and discussed by a semi-empirical model. In the noise reduction experiment of the real power module, combining inlet bellmouth on the fan and guide holes on the casing, the total SPL was significantly reduced by 2.9 dBA. Especially, based on bellmouth, guide holes brought an additional 1.9 dBA tonal noise reduction and 1.0 dBA total SPL reduction. The study indicates that appropriate flow control is important to improve the heat dissipation and reduce noise of the power module. These results are helpful to develop higher power charging system.
Numerical Investigation of Near-Tip Modifications for a Highly-Loaded Low-Speed Rotor Under the Influence of Double Leakage
Authors: Eckel Jannik , von Jeinsen Philipp , Gümmer Volker
Published: October 2022

This paper numerically investigates the flow field in the tip region of a highly-loaded axial low-speed compressor rotor. The rotor in focus is of a hybrid blade configuration, featuring a tandem profile in the mid-span region and single blade profiles near the endwalls. The simulated 1.5-stage configuration also consists of a single row IGV and a tandem stator. Due to high loading coefficients (ψ = 0.58) in combination with moderate flow coefficients (φ = 0.58), double leakage of the tip leakage vortex plays a major role at all operating conditions. As already shown in the past, double leakage is a stability influencing dominant flow phenomenon in compressor rotors and influencing that can be the key to an efficient working range enhancement on compressor stages. This work introduces a simple and powerful method of enhancing the working range for low-speed rotors under the influence of double leakage. It is shown, that modifications to the pressure side shape of rotor tip profiles can influence the interaction of the tip leakage vortex with the adjacent blade, comparable to the effects of casing treatments. These unconventional blade shapes result from the transformations from tandem blade configurations to hybrid blades near the endwalls, as Eckel et al. have shown [1]. The resulting single blade profile close to the tip features a convex profile element (an increase in local thickness, called the -“belly”), which significantly influences the local static pressure gradients. This unusual pressure-side profiling can change mass flow over the tip and, by correct positioning, may reduce the amount of double leakage and, consequently, increase the rotors efficient working range. This work presents the geometry definitions for the hybrid blade single-segments, a detailed analysis of the impact on design and off-design operating conditions together with their underlying flow phenomena, and finally proposes design guidelines for the blade-tip geometries of highly-loaded rotors under the influence of double leakage.
Investigating the Mixture Quality in Multi-Injector Burner Systems, Part I: Experimental Setup
Authors: Marquez Macias Fabian , Hirsch Christoph , Sattelmayer Thomas , Huth Michael , Meisl Jürgen
Published: October 2022

A new approach to calculate the mixture statistics in multi-injector burner systems from a single injector data base is presented in the paper. In such systems, the mixture quality is highly sensitive to the flow rate and the skewness of the inflow velocity profile. To determine the mixture fraction statistics from these two parameters for a particular injector in a multi-injector configuration, O-POD is suggested using results from RANS-CFD as the observable. The O-POD mixing database is determined experimentally from two setups: First the mixture quality in a single injector at ideal inflow conditions is studied. Then the same injector type is investigated in a generic multi-injector burner system (MIB). To characterise the mixture quality, the mixing probability mass function (PMF) at the injector exit is measured by means of LIF and high speed imaging. The data obtained for both the single injector under ideal inflow and the MIB are presented. These studies of the mixture behaviour reveal that an asymmetric inflow velocity profile leads to a significant increase of unmixedness, which is seen as a negative skewness of the mixing PMFs. This effect becomes stronger at higher momentum flux density ratios due to the higher penetration depth of the fuel jets. The application of the O-POD to the database shows that the PMF can be accurately modeled with only 3 modes.
An Euler-Based Throughflow Approach for Centrifugal Compressors – Part A: Extension and Modifications of Models
Authors: Jenzen Rebecca , Woiczinski Christian , Schuster Sebastian , Brillert Dieter
Published: October 2022

This paper presents the extension and validation of an Euler-based throughflow solver for the analysis of centrifugal compressors. The conservation equations are augmented with aerodynamic models suitable for describing a centrifugal compressor. The paper analyzes the impact of the varying meridional pitch angle on the blade force model and proposes two different approaches to consider this variation in the calculation. Further, the paper includes the development and implementation of additional loss models based on enthalpy loss coefficients, which take into account the different loss mechanisms in centrifugal compressors. In this contribution, the modifications are introduced and discussed. To validate the modifications, they are implemented in an existing Euler-based throughflow solver called tFlow. First, the extended solver is compared with the results of computational fluid dynamics (CFD) and calibrated with respect to the total efficiency at the design point. The resulting performance values predicted by the extended solver at off-design conditions are in good agreement with the CFD results. Subsequently, in Part B of the paper, experimental data is used to validate the predicted performance values of the extended solver. The experiments are carried out on a centrifugal compressor test rig described and explained in detail in Part B of this paper. The performance values predicted by the extended solver are in good agreement with the experimental data with respect to the pressure ratio.
Blisk With Small Geometry Mistuning and Blend Repair: As-Measured FE Model and Experimental Verification
Authors: Zhou Biao , Zhao Jingchao , Ye Nan , Berruti Teresa M.
Published: October 2022

This paper presents an ‘As-Measured Model’ of a blended blisk, built upon the measurement of the true geometry of the blisk by the 3D optical scanning technology. This high-fidelity model aims to account for the variances of blade frequencies and mode shapes within the real blisk in the presence of both the blend repair and inherent geometry mistuning due to manufacturing, etc. An improved mesh updating strategy is proposed to adapt a seed blisk finite element model to the measured geometry. The resultant ‘as-measured model’ is therefore able to accurately represent the measured blade-to-blade geometry variances. The classical blade detuning test in combination with a novel ‘correction’ procedure is employed to experimentally evaluate the ‘blade-alone’ frequency mistuning pattern in the real blisk. Experimental verification of the ‘as-measured model’ demonstrates that it is able to not only capture the ‘blade-alone’ frequency and mode shape variations due to both the blend and intrinsic blade geometry variances, but also to reproduce the global dynamics of the blended blisk with acceptable accuracy.
Effects of Sideslip Direction on a Rear Fuselage Boundary Layer Ingesting Fan
Authors: Castillo Pardo Alejandro , Hall Cesare A.
Published: October 2022

Boundary layer ingestion (BLI) offers potential reductions in fuel burn and emissions. The propulsive fuselage concept features an aft fan that ingests the 360° fuselage boundary layer. A critical condition for this configuration occurs when a sideslip angle arises between the aircraft longitudinal axis and the free-stream velocity. The sideslip flow in combination with the air-frame generates inlet distortion that depends on the sideslip direction. In particular, the sideslip increases flow into the windward side of the intake and reduces the flow on the opposite side, leading to either co-swirl or counter-swirl at the fan face.

This paper investigates the effect of sideslip direction on the aerodynamics of an aft BLI fan. Experimental measurements have been taken in a low-speed fan rig with representative total pressure and swirl distortion. These tests have been complemented by full-annulus URANS simulations to understand the impact of sideslip on the rotor and OGV flow fields.

The results show that positive sideslip (sideslip that produces counter-swirl) increases the fan work and incidence, but the additional losses are relatively small. However, negative sideslip results in lower loading, negative incidence and greater losses. The stage loading was 28% higher and the stage efficiency was 1.65% higher for positive versus negative sideslip. The positive sideslip case was also found to lose some operating range, equivalent to 2% of nozzle area. Overall, the fan design tolerates the sideslip distortion well and demonstrates the importance of the coupling of both swirl and total pressure distortion with the fan aerodynamics.
Experimental Investigation of Effusion Film Cooling on a Cylindrical Leading Edge Model
Authors: Huang I-Cheng , Lin Kuan-Hsueh , Huang Chih-Yung , Liu Yao-Hsien
Published: October 2022

Effusion film cooling is effective for cooling high temperature turbine blades because it requires less coolant and produces a more uniform temperature distribution than conventional film cooling. Effusion cooling for a cylindrical model representing the leading edge of a gas turbine blade was investigated. The experiment was performed in a low-speed wind tunnel at a Reynolds number of 100,000. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness. Additive manufacturing was used to fabricate a porous structure on the test cylinder for effusion cooling. Both simple and compound angles were used for cooling injection. The effects of streamwise and spanwise hole spacings, turbulence intensities (1%, 8.7%), and blowing ratios (0.075, 0.15, 0.3, and 0.6) were studied. The effusion hole diameter was 0.1 cm, and the spanwise hole pitch-to-diameter ratios were either 2 or 4. Compared with conventional film cooing, effusion cooling achieved higher cooling effectiveness and produced better coolant coverage. Increasing the streamwise spacing noticeably reduced the cooling effectiveness for the simple-angle design due to film liftoff; the compound-angle designs thus achieved higher effectiveness. The simple-angle holes were more sensitive to changes in the mainstream turbulence intensity; increases in the turbulence intensity promoted the mixing of the coolant with the mainstream. Moreover, effusion cooling was more resistant to coolant lift-off at high blowing ratios.
Experimental Investigation Into Oil Shedding From a Rotating Cup Geometry
Authors: Cageao Paloma Paleo , Johnson Kathy , Ambrose Stephen , Omar Rajab
Published: October 2022

Oil shedding from rotating components and static elements within rotating systems has a number of applications within the design and understanding of transmission systems as well as wider industrial applications. There is a reasonable body of prior research on liquid ejection from rotating cups and discs where the cup/disc element is on the end of the rotative. This study reports results from an experimental investigation where a cup element was mounted onto a relatively large diameter shaft with the shaft extending through the cup. The primary aim of the study was to investigate and characterise the shedding behaviour over a range of shaft speeds and oil supply rates.

High speed images were acquired of shedding from the cup at 90° and 270° from top dead centre (clockwise rotation). Three disintegration modes are observed: droplet, ligament and sheet with transition dependent on operating condition. Transition boundaries on non-dimensional regime maps are compared to published literature showing a good match to data for a spinning disc.

In some industrial configurations of interest oil sheds from a rotating component/element onto a static surface prior to subsequent ejection into a chamber or housing. In such cases the tangential component of velocity of the shedding oil is significantly reduced. This current work explores the effect on oil disintegration and shedding when a static element is introduced into the system. The flow behaviour of the air-oil interface at the edge of the static and on the front face of the static element was recorded as part of the investigation and showed a range of flow patterns including stratified smooth film, stratified wavy film with some droplet shedding and turbulent film with significant droplet shedding.
Application of Intentional Mistuning to Reduce the Vibration Susceptibility of a Steam Turbine Wheel
Authors: Beirow Bernd , Golze Mark , Popig Frederik
Published: October 2022

Intentional mistuning is employed for a last stage turbine wheel featuring 51 blades to alleviate both the flutter susceptibility and maximum forced response. Primarily, operations at nominal speed under part-load conditions may cause unfavorable flow conditions facilitating flow separation. As a consequence, the original design intention with identical blades features negative aerodynamic damping ratios with respect to the first bending mode family. In order to prevent any self-excited vibration phenomena, intentional alternate mistuning is utilized to increase the least aerodynamic damping ratio as far as it takes a positive value and hence, to contribute to a stabilization of the rotor. For the purpose of numerically analyzing the vibration behavior, reduced order models are built up, which are based on modal reduction techniques, namely the subset of nominal system modes and the fundamental mistuning model. These types of models conveniently allow for considering both different mistuning distributions in terms of probabilistic analyses and the aeroelastic interaction by means of prescribing aerodynamic damping ratios and aeroelastic natural frequencies of the tuned counterpart or aerodynamic influence coefficients, respectively. A detailed study is presented regarding the correction of frequency mistuning magnitudes in terms of considering the impact of centrifugal stiffening, which plays a significant role in case of long low pressure turbine blades featuring high aspect ratios.

Since alternate intentional mistuning cannot be implemented perfectly, every bladed wheel as manufactured will exhibit small but unavoidable structural deviations from the design intention, which are known as random mistuning. To ensure the robustness of the intentional mistuning solution in terms of positive aerodynamic damping ratios at any time, comprehensive probabilistic analyses are conducted with respect to superimposing random structural mistuning at first. Secondly, the impact of varying mistuning magnitude is analyzed. Thirdly, the robustness towards aerodynamic mistuning is investigated by means of small variations of aeroelastic influence coefficients and consequently, the inter blade phase angle dependent aerodynamic damping curves. Moreover, it becomes apparent that alternate intentional mistuning superimposed with both, random structural and aerodynamic mistuning also mitigates the maximum forced response at part-speed conditions.
CFD Flow Field Assessment and Performance Map Generation of A Turbocharger Radial Turbine Attempted to Be Matched With a Downsized Diesel Engine
Authors: El Hameur Mohamed Amine , Cerdoun Mahfoudh , Tarabet Lyes , Ferrara Giovanni
Published: October 2022

The present paper aims to propose an efficient methodology to match aerodynamically a 1.5 l, three cylinders downsized Diesel engine, with a selected turbocharger to boost its performance based on 1D codes and CFD simulation. In this aspect, a radial turbine’s stage was sized and designed applying 1D preliminary design in-house codes. Then, a CFD simulation was established to investigate the flow field through its components and to predict its performance. Based on the simulation data, a turbine’s map was generated via gas-dynamic simulation software. On the other hand, a turbocharger compressor was selected from a database. Therefore, the performance maps of the designed turbine and the selected compressor were matched with the engine simulation model. From the findings, the new turbocharged engine developed an operating area far from the compressor limits at the entire engine speed range, with a surge margin of 23.37% at the engine rated power. The engine thermal efficiency, brake specific fuel consumption, compressor and turbine isentropic efficiencies measured on the new turbocharged engine expressed an enhancement at the engine rated speed of about 6.79%, 6.36%, 19.91% and 3.86%, respectively, compared with the original engine. Furthermore, maximum deviations of 7.43% and 0.47% were measured between the new and the original turbocharged engines in terms of in-cylinder pressure and temperature, respectively, which guarantee the engine’s thermodynamic strength. Finally, the developed methodology reported satisfactory results in terms of the engine’s secure functioning and predicted performances, which can be considered as an important basis before initiating any detailed conception.
Comparing Gradient-Free and Gradient-Based Multi-Objective Optimization Methodologies on the VKI-LS89 Turbine Vane Test Case
Authors: Hottois Romain , Châtel Arnaud , Coussement Grégory , Verstraete Tom , De Bruyn Tom
Published: October 2022

The present paper addresses the multi-objective aerodynamic shape optimization of the two-dimensional LS-89 turbine cascade. The objective is to minimize the entropy generation at subsonic and transonic flow conditions while maintaining the same flow turning. Nineteen design variables are used to parametrize the geometry. The optimization problem is used to compare two major classes of optimization algorithms and at the same time deduce if this problem has multiple local solutions or one global optimum. A first optimization strategy uses a gradient-based Sequential Quadratic Programming algorithm. This SQP algorithm allows to directly handle the non-linear constraints during the optimization process. An adjoint solver is used for computing the sensitivities of the flow quantities with respect to the design variables, such that the additional gradient computational cost is nearly independent of the number of design variables. In addition, the same optimization problem is performed with a gradient-free - metamodel assisted - evolutionary algorithm. A comparison of the two Pareto-fronts obtained with both methods shows that the gradient-based approach allows to find the same optimum at a reduced computational cost. Moreover, the results suggest that the considered optimization problem is uni-modal. In other terms, it is characterized by a single optimal solution.
New Method for Cycle Performance Prediction Based on Detailed Compressor and Gas Turbine Flow Calculations
Authors: Petrovic Milan V. , Wiedermann Alexander , Banjac Milan B. , Milic Srdjan , Petkovic Djordje , Madzar Teodora
Published: October 2022

Gas turbines have made significant progress in recent years. The efficiencies of the compressor and turbine were improved based on achievements in aerodynamics, i.e., on the introduction of numerical flow simulation. The introduction of massive cooling and thermal barrier coating permitted a considerable increase in the turbine inlet temperature. These developments led to a significant increase in the thermal efficiency of gas turbines. However, most of the existing tools for predicting cycle performance are based on 0D compressor and turbine maps for the efficiency and pressure ratio as a function of the mass flow. Such tools cannot simulate all new trends in gas turbines in the most efficient way. The new method proposed here is a 2D method based on detailed flow calculations in the compressor and the gas turbine. Previously developed through-flow tools for compressor/turbine flow simulation and performance prediction were applied for this purpose. The processes in the compressor and the turbine are connected by calculation of the processes in the combustion chamber and the secondary and cooling air system. The turbine inlet temperature is determined by an iterative procedure. The method allows the accurate prediction of performance at every operating point. Air cooling bleeds in the compressor and its injections in the turbine blades can be simulated precisely. Also, adjustments of the inlet guide and stator vanes and their influence on compressor behavior can be accurately taken into account at every operating point. Finally, calculation of the combustion and the flow in the compressor and the turbine allows a simulation with correct gas composition and humidity of the air. The method is demonstrated on a case of an industrial gas turbine. The numerical results were compared with experimental data and showed very good agreement. The procedure is rapid and robust and permits optimization of the different solutions during the design phase.
Investigation of the Transient Closing Behavior of a Radially Adaptive Seal
Authors: Lofts James , Schwitzke Corina , Bauer Hans-Jörg , Peltier Vincent , Zhou Kunyuan
Published: October 2022

New radial adaptive sealing concepts in the secondary air system have the potential to increase the partial load efficiency of turbomachinery and accelerate load ramps. These seals are pressure activated, adjusting to engine conditions in order to maintain a minimum gap width during the entire load cycle, defined as the seal’s operating gap width. In this context a hydrostatic advanced low-leakage (HALO) seal was experimentally investigated in the adaptive seals test rig at the Institute for Thermal Turbomachinery (ITS), with a focus on the transient behavior of the seal closing to its’ operating gap width. For this measurement campaign, the pressure ratio, pressure difference, pressure ramp speed and swirl were varied over a series of closing-hold-opening pressure cycle test runs. All measurements were performed without rotation of the test rig rotor.

In this paper, the results of these experimental investigations are presented and analysed. From these results, the relative influence of the pressure difference and the pressure ratio across the seal on the transient seal behavior is compared. Of particular interest is the effect of changing the pressure ramp gradient on the operating gap width. Additionally, the results are compared against previous published HALO-seal investigations. The results presented in this study give detailed insight into the transient movement of a HALO seal under various engine-similar influencing parameters. This is crucial to understanding how the seal behavior and performance will be affected when operating under different conditions and in different applications.
A Predictive Method for Helicopters Engine Installation Losses Determination
Authors: Di-Marco Alexandre , Lecauchois Claire , Fayard Benoit , Sagaut Pierre
Published: October 2022

Helicopter performance is key element for the competitiveness of the aircraft and is usually define during flight test. Due to the increasingly complicated design of air intake, estimating the installation effect prior to flight test can be useful to minimize effort and cost. This paper proposed a methodology to predict helicopters engine installation effect that can be used prior to any flight test. For that purpose a two step methodology has been developed using first CFD simulation to determine the aerodynamic and aerothermal disturbances generated by the helicopter air intake and then a thermodynamic engine model to estimate the installation losses. These two steps were validated against in flight measurements and it has been shown that combining all individual effects in the model improve the quality of the installation losses prediction. The global accuracy in terms of installation losses absolute value and shape show that the proposed method provide sufficient accuracy in an industrial context.
Effect of Solidity and Aspect Ratio on the Aerodynamic Performance of Axial-Flow Fans With 0.2 Hub-to-Tip Ratio
Authors: Masi Massimo , Danieli Piero , Lazzaretto Andrea
Published: October 2022

Aspect ratio and solidity play complementary roles in the aerodynamic design of axial fan rotor blades. Few studies have experimented the effect of the aspect ratio of rotor blades on the performance of low-speed axial fans or on its interaction with blade solidity in terms of fan aerodynamic performance. This study examined the selection of the solidity and blade aspect ratio in the preliminary design of low-pressure industrial fans with minimized hub-to-tip ratios. The aim of this study was to make available to the fan community experimental data that allow determination of the optimal aspect ratio as a function of the blade solidity.

Various aspects of the performance of 16 prototypes of a 315-mm-diameter propeller fan were compared. The industrial fan prototypes all had a hub-to-tip ratio of 0.2 and were derived from four baseline designs conceived to ideally achieve the same best efficiency operation with different values of the aspect ratio. In addition, the prototypes’ assemblies were conceived to allow operation with different blade counts, i.e., with different rotor solidities at a fixed blade aspect ratio. The aerodynamic performance of the fans, measured in accordance with the ISO-5801 standard, was evaluated to assess the sensitivity and trends of the fan pressure and efficiency with respect to the blade aspect ratio and solidity. The measured effects of the aspect ratio and solidity are discussed on the basis of data available in the literature. The results of the experimental analysis were used to formulate general guidelines for the preliminary design of propeller fans with minimized hub-to-tip ratios.
Simulation of the Overall Transient Operation of Gas Turbines
Authors: Petkovic Djordje , Banjac Milan B. , Milic Srdjan , Madzar Teodora , Petrovic Milan V. , Wiedermann Alexander
Published: October 2022

Reduction of the start-up time and flexible operation require comprehensive testing and modification of a gas turbine. The cost of this testing can be significantly reduced by using reliable dynamic models to simulate critical regimes without the possibility of damage. This paper describes a dynamic model, called GTDyn, for simulation of the complete transient operation of gas turbines, from start-up to shutdown. In addition to basic transient phenomena, volume packing, and heat soakage, the effects of the tip clearance change on the performance are also included. The performance of the compressor and the turbine are described using steady-state characteristics, while component dynamics are modeled with the conversation laws in the form of ordinary differential equations. The applied component characteristics are calculated using through-flow solvers. A large number of compressor maps are implemented to include adjustments of stator blades and changes in tip clearances. The model is paired with a control system for the regulation of speed/load and turbine exit temperature. For the start-up sequence, a mode with starter assistance is implemented. The developed model was applied for simulating multiple start-ups to analyze the influence of thermal states on machine performance. The numerical results are compared with experimental data for an industrial single-shaft, air-cooled gas turbine. The comparison includes temperatures and pressures at inlet and outlet stations of each component, inlet mass flow, IGV adjustment, fuel mass flow, gas turbine speed, and power. The numerical results for starter power and compressor tip clearance are also presented.
Effects of the Surge Motion on the Performance of Floating Wind Turbine Considering Blade Structural Flexibility
Authors: Zhou Le , Shen Xin , Chen Jiajia , Yin Fanfu , Du Zhaohui
Published: October 2022

The flexible deformation of the slender blade has non-negligible effects on the performance of modern megawatt wind turbines, especially under marine environments where additional six degrees of motion is introduced by floating platform. In this research, an aeroelastic coupling model is established based on the lifting surface free vortex wake (LS-FVW) method and geometrically exact beam theory (GEBT) method. By adopting the model developed, the effects of the surge motion on the unsteady aeroelastic performance of floating offshore wind turbines (FOWTs) are investigated with the NREL 5 MW wind turbine. The results show that, the surge motion will increase the average power and thrust of FOWT, while the blade deformation has the opposite effect. The increase of the amplitude and frequency of the surge motion will increase the fluctuation amplitude and frequency of the power, thrust and structural deformation of the wind turbine. Besides, the smaller the amplitude or frequency of the surge, the stronger the ability of the wind turbine-floating platform system to restore stability.
Impact of Post-Stall Extrapolation and Rotational-Augmentation Models on the Performance of Stall-Controlled Wind Turbines
Authors: Papi Francesco , Nocentini Alberto , Melani Pier Francesco , Bianchini Alessandro
Published: October 2022

While most wind energy comes today from utility-scale machines, small wind turbines SWTs can still play a role in off-grid installations or in the context of distributed production and smart energy systems. Due to cost reasons, SWTs (especially up to 100kW) are usually controlled via progressive stall of the blades. Accurate airfoils polars are therefore key in engineering simulation models, not only to ensure predictive blade performance, but are also pivotal for proper controller tuning and an effective evaluation of loads. This study presents an analysis on the impact of post-stall extrapolation methods for airfoil polars, combined with the rotational-augmentation correction, on the aero-servo-elastic simulation of a stall-controlled wind turbine. The selected test case is the UNIFI 50kW RWT, a 50kW reference turbine recently developed by Università degli Studi di Firenze. Aero-servo-elastic simulations are carried out with the open-source code OpenFAST by NREL considering typical turbine Design Situations. Several post-stall extrapolation methods are tested on the same set of polars, also including the 3D correction. Results prove that the performance of turbines like the one studied here is strongly dependent on these methods, especially after the needed correction for rotational-augmentation is applied. In this view, dedicated studies and experimental validations in the next future could help increase the predictivity of low-order numerical models, establish new engineering best-practices, and finally increase the economic feasibility of small wind turbines.
Application of an Automatic Mesh Convergence Procedure for the Large Eddy Simulation of a Multipoint Injection System
Authors: Puggelli Stefano , Leparoux Julien , Brunet Clément , Mercier Renaud , Liberatori Luce , Zurbach Stephan , Cabot Gilles , Grisch Frédéric
Published: October 2022

Lean combustion is an attractive alternative to limit pollutants levels in order to meet the imposed limitations for the next generation of civil aero-engines. However, its implementation involves important technological questions related to the augmentation of the air dedicated to the combustion process. An effort on the injection system design is required and Large Eddy Simulation (LES) can be a useful tool in order to explore the design of novel concepts. At the state of the art, the validation of LES in high-pressure reactive conditions and in presence of the liquid phase is still limited. This shrinks the understanding and optimization of lean devices. The industrial project PERCEVAL, between Safran Tech and the CORIA laboratory, aims at extending the actual knowhow on lean combustion. Novel optical experimental techniques have been developed at CORIA to gain detailed information on industrial injection systems at high-pressure conditions. Within PERCEVAL, Safran Tech is in charge of the assessment of LES by using the experimental data-set collected at CORIA. In this framework, a novel Automatic Mesh Convergence (AMC) procedure, based on adaptive mesh refinement, has been developed in the YALES2 platform to speedup the calculation process. In the present paper, the AMC framework is described and then applied on the lean injection system designed at Safran Tech and tested during PERCEVAL. An analysis is carried out to evaluate the interest and gains offered by the AMC framework.
A Stepped Shaft Labyrinth Seal vs. a Pocket Damper Seal: Leakage and Dynamic Force Coefficients Under Wet Gas Operation
Authors: Torres José , San Andrés Luis , Yang Jing
Published: October 2022

Centrifugal compressors use annular gap seals, typically labyrinth type, to restrict process gas leakage from high-pressure regions to low-pressure regions. Modern machinery favors pocket damper seals (PDS) which produce significantly more effective damping than labyrinth seals (LS) do. Presently, liquid tolerant compressors enable efficient deep sea oil and gas (O&G) production facilities; and seals supplied with a two-phase flow mixture, liquid in gas, can have a large impact on the dynamic stability and leakage performance of O&G turbomachinery. The paper details experimental results for the leakage and force coefficients procured in a wet gas test rig hosting both a stepped shaft PDS and LS. The two seals have similar geometry and operate with shaft speeds up to 5,250 rpm (surface speed = 35 m/s) and pressure ratios (inlet/exit) = 2.5 to 4.2. The seals are supplied a light oil in air mixture whose liquid volume fraction (LVF) reaches up to 10% (liquid mass fraction > 90%). Both seals feature the same shaft diameter D = 127 mm, axial length L = 0.38D, four blades (and eight 45° pockets). The LS has a 15% larger clearance than the PDS, hence it leaks more. For a pure gas condition (LVF = 0), the PDS is 25% more effective to restrict leakage than is the LS. Supplied with a wet gas, the mass flow through the seals grows since the mixture density increases. The effective clearance (Cr.e) of the PDS tends to decrease as LVF increases whereas that for the LS increases. The direct stiffness (K) for both seals is small and becomes negative as the liquid content increases. The cross-coupled stiffnesses are too small for accurate identification. The PDS produces a greater direct damping (C) than the LS when operating with a wet gas of identical LVF. The PDS C significantly grows as the LVF increases from 0% to 0.7%. Derived from a computational fluid dynamics model, predictions of leakage agree well with the measurements, whereas force coefficients are roughly ½ of the experimental ones. Changes in the LVF produced broadband subsynchronous vibrations (SSV) in the PDS, not so in the LS. The experimental results are a reference for the engineered design of LSs and PDSs operating with two-phase flow.
Field Testing and Operation of a 300 kW Active Magnetic Bearing Supported Turboexpander-Generator for Natural Gas Pressure Letdown
Authors: Khatri Rasish , Hawkins Larry , Liu Jeremy , Ortiz Neri Massimiliano , Cangioli Francesco , Biliotti Davide
Published: October 2022

A 300 kW turboexpander-generator was developed by Baker Hughes, in conjunction with Calnetix Technologies, for use in a natural gas pressure letdown application. A prior technical publication [1] describes the synchronous permanent magnet generator design and presented some preliminary test data from the prototype unit. In this paper, the machine design, including rotordynamics and active magnetic bearing (AMB) system design, are reviewed. Unbalance response measurements made during a standard mechanical running test at the manufacturer’s facility are shown, including comparisons to predictions made using API 617 guidelines. Turboexpander and generator operating data collected from the initial field installation in Bologna, Italy are then covered in detail. Field data presented includes aerodynamic performance data, closed-loop AMB transfer functions, and plant transfer functions at various power levels, vibration data from spin testing, backup bearing clearance measurements made using the magnetic bearings, thrust load vs. power curves, and generator efficiency at various power levels. The measurements made in the field confirm that the turboexpander-generator meets all customer requirements. Additionally, important case studies are presented, which demonstrate the magnetic bearings diagnosing real field problems. As of 2020, the machine is operating in parallel with a legacy Joule-Thomson valve. A future technical paper will discuss comparisons of predictions and measurements related to a series of shutdown tests performed on the machine under various shutdown scenarios.