bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-Pass Serpentine Cooling Designs for Negating Coriolis Force Effect on Heat Transfer: 45-Degree Angled Rib Turbulated Channels
Authors: Singh Prashant , Ji Yongbin , Ekkad Srinath V.
Published: August 2018

Traditional gas turbine blades are equipped with serpentine passages arranged along the height, wherein the coolant flows radially outward in 1st passage and radially inward in 2nd passage. Prior experimental studies have established that for traditional two-pass rib roughened ducts, under the influence of Coriolis and centrifugal forces, the heat transfer gets enhanced on trailing side for radially outward flow and gets reduced on the leading side for a radially outward flow. A reverse trend in heat transfer is observed for radially inward flow. Rotation induced forces result in non-uniform heat transfer coefficient distribution which results in non-uniform metal temperatures under steady state condition. Present study addresses the problem of non-uniform heat transfer distribution on leading and trailing sides due to rotation effect. Experimental investigation of two configurations has been carried out, where Coriolis effect was negated by aligning the coolant flow vector and rotation vector such that their cross product was effectively a null vector. Novel multi-passage serpentine ducts featuring 45-degree angled rib turbulators with four-passage and six-passage configurations have been studied. Transient liquid crystal thermography experiments were carried out under stationary and rotating conditions. Heat transfer experiments were carried out for Reynolds numbers ranging from 12000 to 80000 under stationary conditions and rotating heat transfer experiments were carried out at two Rotation numbers of 0.05 and 0.11. We found that the heat transfer characteristics of serpentine passages were not influenced by Coriolis force after the 2nd passage. The local heat transfer distribution on leading and trailing sides of serpentine passages were near-similar to each other and comparable with corresponding stationary cases. The contribution of multiple passages connected with 180-degree bends towards overall frictional losses has been evaluated in terms of pumping power and normalized friction factor. The configurations are ranked based on their thermal hydraulic performances over a wide range of Reynolds numbers. The heat transfer enhancement levels of four-passage rib roughened duct was higher than the six-passage configuration and the six-passage configuration had slightly higher thermal hydraulic performance compared to four-passage configuration.
Numerical and Experimental Study of Shrouded Blade Dynamics Considering Variable Operating Points
Authors: Kaptan Ferhat , Panning-von Scheidt Lars , Wallaschek Jörg
Published: August 2018

The optimization of the mechanical design process of turbomachinery has been a subject of research for decades. In this context, many researchers developed efficient numerical methods to calculate the vibration response of bladed disks. In most cases, the studies are restricted to one single operating point of the system, which is sufficient for many applications. For turbomachinery with variable operating points, the conventional computation methods must be extended. Changing the turbine’s rotational speed Ω leads to entirely new load conditions. On the one hand, structural mechanical properties (e.g. stiffening effects) depend on the rotational speed. On the other hand, in case of coupled blades, the pressure distributions in the joints are sensitive to the rotational speed. In this paper, a model of a steam turbine blade is investigated numerically and experimentally. Beside the tip shroud contact, multiple contacts at the root of the blade are considered. The steady-state vibration response is calculated by the well-known harmonic balance method (HBM) and an alternating frequency-time scheme (AFT). In case of variable operating conditions, the stiffness matrix can be described as a matrix polynomial of second order in Ω2. The preload at the joints is based on nonlinear quasistatic finite element analysis and also depends on the rotational speed. For the first time, a computational methodology is presented for the calculation of the forced response of a fully bladed disk with multiple contacts considering rotational speed dependent structural mechanical properties and, in particular, contact pressures. The experimental study is conducted in two steps. Firstly, a single blade model is investigated at non-rotating test conditions. Here, the blade is clamped with two dummies at the shroud. The vibration response is measured for various pressure distributions at the shroud contact. The comparison with simulation results shows a very good agreement. The second step of the experimental study will be the future investigation of a bladed disk assembly on a rotating test rig. An overview of the test rig including operation conditions, excitation methods and measurement techniques is given at the end of the paper.
Micro Gas Turbine Cycle Humidification for Increased Flexibility: Numerical and Experimental Validation of Different Steam Injection Models
Authors: De Paepe Ward , Renzi Massimiliano , Montero Carrerro Marina , Caligiuri Carlo , Contino Francesco
Published: August 2018

With the current shift from centralized to more decentralized power production, new opportunities arise for small-scale Combined Heat and Power (CHP) production units like micro Gas Turbines (mGTs). However, to fully embrace these opportunities, the current mGT technology has to become more flexible in terms of operation — decoupling the heat and power production in CHP mode — and in terms of fuel utilization — showing flexibility in the operation with different Lower Heating Value (LHV) fuels. Cycle humidification e.g. by performing steam injection, is a possible route to handle these problems. Current existing simulation models are able to correctly assess the impact of humidification on the cycle performance, but they fail to provide detailed information on the combustion process. To fully quantify the potential of cycle humidification, more advanced numerical models — preferably validated — are necessary. These models are not only capable of correctly predicting the cycle performance, but they can also handle the complex chemical kinetics in the combustion chamber.

In this paper, we compared and validated such a model with a typical steady-state model of the steam injected mGT cycle based on the Turbec T100. The advanced one is an in-house MATLAB® model, based on the NIST database for the characterization of the properties of the gaseous compounds with the combustion mechanisms embedded according to the Gri-MEch 3.0 library. The validation one was constructed using commercial software (Aspen® Plus), using the more advance RKS-BM property method and assuming complete combustion by using a Gibbs reactor. Both models were compared considering steam injection in the compressor outlet or in the combustion chamber, focussing only on the global cycle performance. Simulation results of the steam injection cycle fuelled with natural gas and syngas showed some differences between the two presented models (e.g. 5.9% on average for the efficiency increase over the simulated steam injection rates at nominal power output for injection in the compressor outlet); however, the general trends that could be observed are consistent. Additionally, the numerical results of the injection in the compressor outlet were also validated with steam-injection experiments in a Turbec T100, indicating that the advanced MATLAB® model overestimates the efficiency improvement by 25 % to 45 %. The results show the potential of simulating the humidified cycle using more advanced models; however, in future work, special attention should be paid to the experimental tuning of the model parameters in general and the recuperator performance in particular to allow correct assessment of the cycle performance.
Film Cooling Characteristics of a High Lift Blade Including Tip and Platform Flow Interactions
Authors: Naik S. , Lerch A.
Published: August 2018

This paper investigates the aerodynamic and film cooling characteristics of a first stage turbine high lift blade. The blade operating conditions are representative of those normally found in a heavy-duty gas turbine. The airfoil incorporates several rows of film cooling holes located at various axial positions along the airfoil chord and the blade tip. Additionally the impact of the platform leading edge rim purge flow has been investigated and its interaction with the airfoil aerodynamic and film cooling characteristics. The film cooling holes are geometrically three-dimensional in shape, and depending on the location on the airfoil, they consist of various fan shapes, which are either compounded or in-line with the external main flow direction.

Numerical studies and experimental investigations in a linear cascade have been conducted for a range of exit Mach and Reynolds numbers. The influence and sensitivity of the coolant ejected from the airfoil, tip and the platform rim purges on the overall airfoil film cooling has been investigated for a range of operating conditions.

The measured film cooling effectiveness on the airfoil, blade tip and platform surfaces compared well with the predictions. The suction side film cooling effectiveness, which consisted of two pre-throat film rows, proved to be very effective up to the suction side trailing edge. The impact of variations in the airfoil cooling flows showed that the film cooling was relatively in-sensitive on the suction side. However, on the blade tip, it was found that the film cooling characteristics are strongly dependent on the clearances and the tip coolant ejection rate. On the platform surface, the impact of variations in the rim purge flows was evident, but proved not to alter the global film cooling characteristics on neither the airfoil nor the platform surfaces significantly.
Comprehensive Geometric Description of Manufacturing Scatter of High Pressure Turbine Nozzle Guide Vanes for Probabilistic CFD Analysis
Authors: Voigt Paul , Högner Lars , Fiedler Barbara , Voigt Matthias , Mailach Ronald , Meyer Marcus , Nasuf Alkin
Published: August 2018

The increasing demands on jet engines require progressive thermodynamic process parameters, which typically lead to higher aerothermal loadings and accordingly to designs with high complexity. State of the art high pressure turbine (HPT) nozzle guide vane (NGV) design involves vane profiles with three-dimensional features including a high amount of film cooling and profiled endwalls (PEW).

Typically, the specific massflow, also called capacity, which governs the engine’s operation, is set by the HPT NGV. Hence, geometric variations due to manufacturing scatter of the HPT NGV’s passage can affect relevant aerodynamic quantities and the entire engine behavior. Within the traditional deterministic design approach, the influences of those geometric variations are covered by conservative assumptions and engineering experience. This paper addresses the consideration of variability due to manufacturing of HPT NGVs through probabilistic CFD investigations.

In order to establish a statistical database, 80 HPT NGVs are digitized with a high precision optical 3D scanning system to record the outer geometry. The vane profiles are parametrized by a section based approach. For this purpose, traditional profile theory is combined with a novel method that enables the description of NGV profile variability taking the particular leading edge (LE) shape into account. Furthermore, the geometric variability of PEWs is incorporated by means of principle component analysis (PCA).

On this basis, a probabilistic system assessment including a sensitivity analysis in terms of capacity and total pressure loss coefficient is realized. Sampling-based methods are applied in order to conduct a variety of 3D CFD simulations for a typical population of profile and endwall geometries. This probabilistic investigation using realistic input parameter distributions and correlations contributes to a robust NGV design in terms of relevant aerodynamic quantities.
Turbocharger-Based Hybrid Systems: Modeling and Validation of a Free Spool Subject to Compressor Surge
Authors: Abrassi Alessio , Traverso Alberto , Ferrari Lorenzo
Published: August 2018

Compressor surge is one of the main problem that may affect fuel cell gas turbine hybrid systems, because of the energy stored in the volume containing the high temperature pressurized fuel cell stack. The problem becomes even more crucial because in such kind of system, the fuel cell is the most sensitive and costly component that has to be preserved by abrupt pressure changes.

In order to determine the behavior of a dynamic compressor in its whole range of operating conditions, a calculation model was implemented in TRANSEO, a software tool for transient and dynamic analysis of microturbine and fuel cell based-cycles (based on Matlab-Simulink environment). The modeling procedure has been derived from the Greitzer’s 1976 nonlinear dynamic approach; the resulting T-RIG1 model predicts the transient response of a compression system and is able to simulate both normal and instable transient conditions. Several investigations have been done in order to characterize the impact of different parameters and configurations on the system response. The validation, in the frequency domain, was performed comparing calculations with experimental data measured from a dedicated test rig, where a small size turbocharger has been operated in stable and unstable conditions. In particular, the present work demonstrates the capability of the T-RIG1 model to simulate a free shaft turbocharger performance and instability, with the future purpose to develop feasible strategies for surge detection and recovery, applicable to turbocharger-based hybrid systems.
On Deposit Sintering and Detachment From Gas Turbines
Authors: Casari Nicola , Pinelli Michele , Suman Alessio , di Mare Luca , Montomoli Francesco
Published: August 2018

Solid particles ingestion can deteriorate performance and stability of gas turbines through the build-up of deposits on the aerofoils. In some cases, the effect is sufficient to require an engine shut-down or to cause a failure. The fouling phenomenon can be characterized by two different phases: particle sticking and deposit evolution. The sticking process of an impinging particle has been deeply studied with several models available in the literature, both deterministic and stochastic. A less investigated phase is the the evolution of the deposit over time. A deposit is subjected to several forces that either tend to make it sticking to the surface or to detach from it. In the hot section of the gas turbine, the forces that act on the build-up tending to make it to adhere to the surface can be traced back to the van der Waals forces and, possibly capillary force if a certain amount of liquid phase is present. On the other hand, the detaching mechanism is related to the component investigated: if the particle is deposited on a vane, the drag and the shearing force are the only forces that tend to detach the particle, if a rotor blade is investigated, the centrifugal forces must be considered as well.

On top of that, the deposit evolves over time in what is called sintering. During this process, the single particles deposited can melt together forming necks. If the temperature is sufficiently high, these necks increase in size until the former pores among particles are completely filled. This process is of paramount importance if the effect of the applied forces on the deposit needs to be investigated. The amount of material detached is indeed strongly dependent on the tension exchanged within various layers that constitute the build-up.

This article focuses on the prediction of the build-up evolution on an HPT nozzle. The sintering process is modeled and related to the resisting strength of the deposit: an increasing sintering time reduces the deposit porosity and thus increase its strength. In order to monitor the stability of the deposit, the balance among detaching and attaching forces is carried out. The evolution of the vane shape is taken into account by using a moving mesh technique.
Influence of Intrarow Interaction on the Aerodynamic Damping of an Axial Turbine Stage
Authors: Müller Tobias R. , Vogt Damian M. , Vogel Klemens , Phillipsen Bent A.
Published: August 2018

The present numerical study aims at examining the influence of intrarow interaction effects in aerodynamic damping predictions of an axial turbine rotor. The investigated operating point corresponds to a resonance crossing associated with the fundamental engine order of the stator blade row. Accordingly, the pressure perturbations induced by the vibration of the rotor at its modal frequency are found to be coincident in frequency and thus superimpose with the pressure perturbations resulting from intrarow interaction phenomena. A methodology for extracting vibration induced pressure perturbations for the subsequent calculation of the vibration induced modal aerodynamic damping is established and applied within the scope of the present study.

Applying this methodology, both the influence of the underlying mean and transient flow field as well as the influence of acoustic wave reflections at the adjacent stator blade row is investigated on the predicted aerodynamic damping. In this context, the underlying mean flow field, which is found to be slightly altered in the presence of intrarow interaction phenomena, was proven to have a significant influence on vibration induced pressure perturbations. Moreover, acoustic wave reflections at the adjacent stator blade row are found to have the capability of influencing the aerodynamic damping depending on their actual phasing when impinging onto the turbine rotor.
Numerical and Experimental Investigation on an Effusion-Cooled Lean Burn Aeronautical Combustor: Aerothermal Field and Metal Temperature
Authors: Bertini D. , Mazzei L. , Puggelli S. , Andreini A. , Facchini B. , Bellocci L. , Santoriello A.
Published: August 2018

Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NOx and soot in particular). Its implementation, however, involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. A reduced coolant mass flow rate in conjunction with higher compressor discharge temperature negatively affect the cooling potential thus requiring the exploitation of efficient schemes such as effusion cooling.

This work describes the experimental and numerical final validation of an aeronautical effusion-cooled lean-burn combustor. Full annular tests were carried out to measure temperature profiles and metal temperature distributions at different operating conditions of the ICAO cycle. Such an outcome was obtained also with an in-house developed CHT methodology (THERM3D). RANS simulations with the Flamelet Generated Manifold combustion model were performed to estimate aerothermal field and heat loads, while the coupling with a thermal conduction solver returns the most updated wall temperature. The heat sink within the perforation is treated with a 0D correlative model that calculates the heat pickup and the temperature rise of coolant. The results highlight an overall good capability of the proposed approach to estimate the metal temperature distribution at different operating conditions. It is also shown how more advanced scale-resolving simulations could significantly improve the prediction of turbulent mixing and heat loads.
Selection of Dynamic Testing Measurement Locations for Integrally Bladed Disks
Authors: Beck Joseph A. , Kaszynski Alex A. , Brown Jeffrey M. , Gillaugh Daniel L. , Scott-Emuakpor Onome E.
Published: August 2018

The selection of sensor locations during dynamic testing of integrally bladed disks (Blisks) is discussed for measuring experimental mode shapes. As-manufactured geometries of the experimental Blisk are obtained in point-cloud form via a structured light optical measurement system. The nominal finite element mesh of the Blisk is then “morphed” to the average sector of as-measured, point-cloud geometry through a mesh metamorphosis algorithm. A ray-tracing algorithm is developed for selecting observable degrees of freedom (DOFs) of the morphed mesh to an overhead laser scanning vibrometer. This set of DOFs is then down-selected since measuring tens-of-thousands of points is in-feasible during experimental testing. This selection is carried out using a Cyclic Effective Independence Method that exploits a Blisk’s cyclic symmetry to greatly reduce computational expenses. Furthermore, the approach allows for selecting points belonging to specific engine order excitations typical in engine operating environments that can be excited during bench top traveling wave testing. Measurement point locations are compared for three cyclic symmetry finite element models: a nominal coarse mesh density, a nominal fine mesh density, and a fine mesh density morphed to average sector geometries.
Active Subspace Development of Integrally Bladed Disk Dynamic Properties due to Manufacturing Variations
Authors: Beck Joseph A. , Brown Jeffrey M. , Kaszynski Alex A. , Carper Emily B.
Published: August 2018

The impact of geometry variations on integrally bladed disk eigenvalues is investigated. A large population of industrial Bladed Disks (Blisks) are scanned via a structured light optical scanner to provide as-measured geometries in the form of point-cloud data. The point cloud data is transformed using Principal Component Analysis that results in a Pareto of Principal Components (PCs). The PCs are used as inputs to predict the variation in a Blisk’s eigenvalues due to geometry variations from nominal when all blades have the same deviations. A large subset of the PCs are retained to represent the geometry variation, which proves challenging in probabilistic analyses because of the curse of dimensionality. To overcome this, the dimensionality of the problem is reduced by computing an active subspace that describes critical directions in the PC input space. Active variables in this subspace are then fit with a surrogate model of a Blisk’s eigenvalues. This surrogate can be sampled efficiently with the large subset of PCs retained in the active subspace formulation to yield a predicted distribution in eigenvalues. The ability of building an active subspace mapping PC coefficients to eigenvalues is demonstrated. Results indicate that exploitation of the active subspace is capable of capturing eigenvalue variation.
Numerical and Experimental Investigations on Optimized 3D Compressor Airfoils
Authors: Mihalyovics Jan , Brück Christian , Peitsch Dieter , Vasilopoulos Ilias , Meyer Marcus
Published: August 2018

The objective of the presented work is to perform numerical and experimental studies on compressor stators. This paper presents the modification of a baseline stator design using numerical optimization resulting in a new 3D stator. The Rolls Royce in-house compressible flow solver HYDRA was employed to predict the 3D flow, solving the steady RANS equations with the Spalart-Allmaras turbulence model, and its corresponding discrete adjoint solver. The performance gradients with respect to the input design parameters were used to optimize the stator blade with respect to the total pressure loss over a prescribed incidence range, while additionally minimizing the flow deviation from the axial direction at the stator exit. Non-uniform profile boundary conditions, being derived from the experimental measurements, have been defined at the inlet of the CFD domain. The presented results show a remarkable decrease in the axial exit flow angle deviation and a minor decrease in the total pressure loss. Experiments were conducted on two compressor blade sets investigating the three-dimensional flow in an annular compressor stator cascade. Comparing the baseline flow of the 42° turning stator shows that the optimized stator design minimizes the secondary flow phenomena. The experimental investigation discusses the impact of steady flow conditions on each stator design while focusing on the comparison of the 3D optimized design to the baseline case. The flow conditions were investigated using five-hole probe pressure measurements in the wake of the blades. Furthermore, oil-flow visualization was applied to characterize flow phenomena. These experimental results are compared with the CFD calculations.
Shrouded CMC Rotor Blades for High Pressure Turbine Applications
Authors: Boyle Robert J. , Agricola Lucas M. , Parikh Ankur H. , Ameri Ali A. , Nagpal Vinod K.
Published: August 2018

The density of Ceramic Matrix Composite (CMC) materials is approximately 1/3 the density of metals currently used for High Pressure Turbine (HPT) blades. A lower density, and consequently lower centrifugal stresses, increases the feasibility of shrouding HPT blades. Shrouding HPT blades improves aerodynamic efficiency, especially for low aspect ratio turbine blades. This paper explores aerodynamic and structural issues associated with shrouding HPT rotor blades. Detailed Navier-Stokes analysis of a rotor blade showed that shrouding improved blade row aerodynamic efficiency by 1.3%, when the clearance was 2% of the blade span. Recessed casings were used. Without a shroud the depth of the recess equaled the clearance. With a shroud the recess depth increased by the shroud thickness, which included a knife seal. There was good agreement between the predicted stage efficiency for the unshrouded blades and the experimentally measured efficiency. Structural analysis showed a strong interaction between stresses in the shroud and peak stresses at the hub of the blade. A thin shroud of uniform thickness only moderately increased maximum blade stress, but there were very high stresses in the shroud itself. Increasing shroud thickness reduced stresses in the shroud, but increased blade stresses near the hub. A single knife seal added to the thin shroud noticeably decreased maximum shroud stress, without increasing maximum blade stress. Maximum stresses due to pressure loads and combined pressure and centrifugal loads were nearly the same as the maximum stresses for individual pressure or centrifugal loads. Stresses due to a 100K temperature difference across the blade walls were much lower than centrifugal or pressure load stresses.
An Experimental Study of Resonance Frequency Detuning Applied to Blade Mistuning
Authors: Lopp Garrett K. , Kauffman Jeffrey L.
Published: August 2018

Turbomachinery blade technology has recently trended towards the use of monolithic bladed disks. Although offering a wealth of benefits, this construction removes the blade attachment interface present in the conventional design, thus unintentionally removing a source of friction-based damping needed to counteract large vibrations during resonance passages. This issue is further exacerbated for blade mistuning, which is well-known to induce vibration localization with correspondingly larger vibration magnitudes. Recently, an alternative method to reduce vibration, termed Resonance Frequency Detuning (RFD), utilizes the variable stiffness properties of piezoelectric materials embedded on-blade to detune the response when approaching a resonance crossing, thus resulting in reduced vibration. For a single-degree-of-freedom (SDOF) system, the vibration reduction performance and the optimal stiffness state switching is well-defined. Previously, RFD has been experimentally validated on a representative blade for a sufficiently well-separated vibration mode, thus satisfying the SDOF assumption. No such experimental validation currently exists for a system with closely-spaced modes or, more specifically, applied to blade mistuning. This work utilizes an academic blisk machined in the form of 8 blades attached to a central hub. Each blade incorporates two collocated piezoelectric patches located near the blade root: one patch provides the stiffness state modulation, while the other patch provides actuation to mimic engine order excitations. For the forcing configuration studied, experimental results show qualitative agreement to numerical results with the vibratory response associated with the optimal stiffness state switch showing reductions across all blades.
Effects of Endwall 3D Contouring on Film Cooling Effectiveness of Cylindrical Hole Injections at Different Locations on Vane Endwall
Authors: Chen Pingting , Gao Hongyu , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2018

With the development of gas turbine, the secondary flow loss in vane passage is getting higher. To reduce the strength of secondary flows within vane passage, endwall 3D contouring is an effective design. Endwall 3D contouring can lead to significant changes in the secondary flow vortices, which lead to changes on jet-to-secondary flow interaction and then changes on the film cooling effectiveness. Meanwhile, the geometry configuration of the contoured endwall, such as the rising and falling on the endwall, can also have an impact on film cooling performance. As a result, the film cooling performance on contoured endwall differs from that on flat endwall. Understanding the difference in film cooling characteristics on the contoured endwall and flat endwall may help to make better endwall contouring design and better endwall film cooling arrangement.

The present experiment compares the film cooling effectiveness of cylindrical hole injections at different locations on 3D contoured endwall versus flat endwall in an NGV (nozzle guide vane) passage. The measurement is performed in a low speed wind tunnel with a F-class annular sector NGV cascade. The cylindrical hole injections are located as 4 different rows at −30% axial chord, 30% axial chord, 50% axial chord and 70% axial chord. Endwall pressure distribution is measured with pressure taps by pressure sensor while film cooling effectiveness is measured using PSP (Pressure Sensitive Paint). Two density ratios with 1.0 and 1.5 and several average blowing ratios are investigated. Effects of endwall contouring, density ratio and blowing ratio on film cooling effectiveness are obtained and the results are presented and explained in this investigation.
Analysis of Rotordynamic and Thermodynamic Performance of a Multistage Centrifugal Compressor Operating in the Minimum Flow Region
Authors: Giachi Marco , Vannini Giuseppe , Di Pillo Pier Luigi
Published: August 2018

In this paper both rotordynamic and thermodynamic analysis of a multistage centrifugal compressor running with one or more stages in post-stall condition are presented. The purpose of this study is to demonstrate the machine can operate stable and safe in such condition (i.e. stable condition means the head vs. flow operating curve shall have negative slope and safe means a vibration free machine). This allows to extend the operating range at lower flow with respect to the current day-by-day design practice. Experimental results from ASME PTC10 Class 2 test carried out on a seven-stage compressor are shown to validate the analysis.
Unsteady Responses of the Impeller of a Centrifugal Compressor Exposed to Pulsating Backpressure
Authors: Shu Mengying , Yang Mingyang , Martinez-Botas Ricardo F. , Deng Kangyao , Shi Lei
Published: August 2018

The flow in intake manifolds of internal combustion engine becomes more unsteady because of engine downsizing which is achieved by reducing cylinder number and increasing the boosting. Turbocharger compressor is thus exposed to the enhanced pulsating backpressure. This paper studies responses of a centrifugal compressor to the pulsating backpressure via experimentally validated numerical method. Firstly, CFD model with the volute and all impeller passages is established and validated by experimental measurements. Then the unsteady three-dimensional simulation is conducted on a single passage imposed by the pulsating backpressure conditions which are obtained by 1-D unsteady simulation. Results show that the performance of the passage evidently deviates from steady performance. Hysteresis loops of the performance appear at pulsating backpressure conditions, which encapsulate the performance at steady conditions. Moreover, the unsteadiness of the impeller performance is enhanced as the mass flow rate reduces. The performance and flow structures of the impeller near stall for the pulsating case are more favorable than that at corresponding constant backpressure. Furthermore, flow structures at points with the same instant mass flow rate are also notably different when they are located at different strokes of the pulse. The flow in the impeller is determined by not only the instant boundary condition but also the evolution history of flow field. The dynamic stall which is analogue to the phenomenon on pitching airfoil happens in the compressor and delays the instability of the device when it is exposed to pulsating backpressure. This study provides useful insights in the influence of pulsating backpressure on compressor performance in actual engine situations, from which better turbo-engine matching might be benefited.
Improving the Flutter Margin of an Unstable Fan Blade
Authors: Stapelfeldt Sina , Vahdati Mehdi
Published: August 2018

The aim of this paper is to introduce design modifications which can be made to improve the flutter stability of a fan blade. A rig fan blade, which suffered from flutter in the part-speed range and for which good quality measured data in terms of steady flow and flutter boundary is available, is used for this purpose. The work is carried out numerically using the aeroelasticity code AU3D. Two different approaches are explored; aerodynamic modifications and aero-acoustic modifications. In the first approach, the blade is stabilized by altering the radial distribution of the stagger angle based on the steady flow on the blade. The re-staggering patterns used in this work are therefore particular to the fan blade under investigation. Moreover, the modifications made to the blade are very simple and crude and more sophisticated methods and/or an optimization approach could be used to achieve the above objectives with a more viable final design. This paper, however, clearly demonstrates how modifying the steady blade aerodynamics can prevent flutter. In the second approach, flutter is removed by drawing bleed air from the casing above the tip of the blade. Only a small amount of bleed (0.2% of the total inlet flow) is extracted such that the effect on the operating point of the fan is small. The purpose of the bleed is merely to attenuate the pressure wave which propagates from the trailing edge to the leading edge of the blade. The results show that extracting bleed over the tip of the fan blade can improve the flutter margin of the fan significantly.
Gas Temperature Measurement in Engine Conditions Using Uniform Crystal Temperature Sensors (UCTS)
Authors: DeVoe Jason , Thomas Anastasia , DeVoe Reagan , Ginzbursky Edward
Published: August 2018

Validation and tuning methods for analytical algorithms used in modeling heat transfer for engine parts, such as turbine blades, require the direct comparison of calculated and experimental metal temperature measurement results. It is important to ensure that the geometric characteristics as well as the boundary condition parameters of the gas flow are held in common for both the physical experiment and the calculation. Unfortunately, the task of obtaining knowledge of the gas parameters such as the radial temperature profile at the turbine inlet is far from trivial. The authors will briefly survey commonly used methods and the uncertainties related to their application based on publicly available data. Among these techniques, a relatively new method of using Uniform Crystal Temperature Sensors (UCTS) for gas temperature measurement, may offer some advantages and will be analyzed in greater detail.

The authors use 3D Finite Element Analysis code to analyze sources of potential systematic error for gas temperature measurement using UCTS. A matrix of varying materials and configurations is evaluated. Recommendations drawn from this analysis will enable analytical designers and instrumentation engineers to optimize the application of this technique specific to their test requirements.
Annular Heat Transfer Enhancement Using Jet Impingement
Authors: Curbelo Andres , Hanhold Alex , Lopez Cesar , Kapat Jayanta S. , Lott Philippe T. , Ruedel Uwe W.
Published: August 2018

Heat transfer in annuli has been widely investigated over the years. Annular channels are found in multiple industry applications, ranging from electronic equipment to nuclear reactor cooling. In order to enhance heat transfer, internal passages are augmented with roughness elements such as dimples, pimples, ribs, fins, and other features. However, the use of impingement cooling mechanism has not been utilized for such annular channels. An experimental study of impingement cooling within an annulus with the outer surface of the annulus being heated uniformly is conducted. Multiple flows as a function of Jet Reynolds number in the range of 16,000 to 46,000 are fundamentally examined. An impingement sleeve with an annular ratio of 0.92 was experimentally tested and compared to RANS numerical simulation results. Temperature Sensitive Paint (TSP) was utilized to experimentally obtain the local Heat Transfer distribution along the annular wall and close channel cap, which is normalized by the baseline annulus heat transfer distribution. Heat transfer results for the annular surface is compared with available correlations. Pressure drop across the facility is characterized at the inlet and exit of the experimental set up.
Advancements in H Class Gas Turbines and Combined Cycle Power Plants
Authors: Vandervort Christian
Published: August 2018

The power generation industry is facing unprecedented challenges. High fuel costs combined with an increased penetration of renewable power has resulted in greater demand for high efficiency and operational flexibility. Imperative for a reduced carbon footprint places an even higher premium on efficiency. Power producers are seeking highly efficient, reliable, and operationally flexible solutions that provide long-term profitability in a volatile environment. New generation must also be cost-effective to ensure affordability for both domestic and industrial consumers.

Gas turbine combined cycle power plants provide reliable, dispatch-able generation with low cost of electricity, reduced environmental impact, and improved flexibility. GE’s air-cooled, H-class gas turbines (7/9HA) are engineered to achieve greater than 63% net, combined cycle efficiency while delivering operational flexibility through deep, emission-compliant turndown and high ramp rates. The largest of these gas turbines, the 9HA.02, exceeds 64% combined cycle efficiency (net, ISO) in a 1 × 1, single-shaft configuration. In parallel, the power plant has been configured for rapid construction and commissioning enabling timely revenue generation for power plant developers and owners.

The HA platform is enabled by 1) use of a simple air-cooling system for the turbine section that does not require external heat exchange and the associated cost and complexity, and 2) use of well-known materials and coatings with substantial operating experience at high firing temperatures. Key technology improvements for the HA’s include advanced cooling and sealing, utilization of unsteady aerodynamic methodologies, axially staged combustion and next generation thermal barrier coating (TBC). Validation of the architecture and technology insertion is performed in a dedicated test facility over the full operating range. As of February 2018, a total of 18 HA power plants have achieved COD (Commercial Operation).

This paper will address three topics relating to the HA platform: 1) gas turbine product technology, 2) gas turbine validation and 3) integrated power plant commissioning and operating experience.
Thermoacoustic Modes of Quasi-1D Combustors in the Region of Marginal Stability
Authors: Silva Camilo F. , Yong Kah Joon , Magri Luca
Published: August 2018

It may be generally believed that the thermoacoustic eigenfrequencies of a combustor with fully acoustically reflecting boundary conditions depend on both flame dynamics and geometry of the system. In this work, we show that there are situations where this understanding does not strictly apply.

The purpose of this study is twofold. In the first part, we show that the resonance frequencies of two premixed combustors with fully acoustically reflecting boundary conditions in the region of marginal stability depend only on the parameters of the flame dynamics, but do not depend on the combustor’s geometry. This is shown by means of a parametric study, where the time delay and the interaction index of the flame response are varied and the resulting complex eigenfrequency locus is shown. Assuming longitudinal acoustics and a low Mach number, a quasi-1D Helmholtz solver is utilized. The time delay and interaction index of the flame response are parametrically varied to calculate the complex eigenfrequency locus. It is found that all the eigenfrequency trajectories cross the real axis at a resonance frequency that depends only on the time delay. Such marginally stable frequencies are independent of the resonant cavity modes of the two combustors, i.e. the passive thermoacoustic modes.

In the second part, we exploit the aforementioned observation to evaluate the critical flame gain required for the systems to become unstable at four eigenfrequencies located in the marginally stable region. A computationally-efficient method is proposed. The key ingredient is to consider both direct and adjoint eigenvectors associated with the four eigenfrequencies. Hence, the sensitivity of the eigenfrequencies to changes in the gain at the region of marginal stability is evaluated with cheap and accurate calculations.

This work contributes to the understanding of thermoacoustic stability of combustors. In the same manner, the understanding of the nature of distinct resonance frequencies in unstable combustors may be enhanced by employing the analysis of the eigenfrequency locus here reported.
Flutter Analysis of a Flexible UHBR Fan at Different Flight Conditions
Authors: Schuff Matthias , Reisberg Jannik
Published: August 2018

A flexible UHBR fan is investigated at different flight conditions with a focus on static deflections and aeroelastic stability. Operating points at varying inlet conditions, which are comparable according to the Mach similarity principle, are investigated. However, not all the aerodynamic characteristics remain identical and aerodynamic damping of mode shape vibrations is changed.

When steady deformations of the fan blades are taken into account, the deviation between different inlet conditions increases further. This is mainly due to torsional deflections, changing the effective angle of attack and causing a general shift of the compressor map.

Even though the subsequent changes in flutter predictions are not severe for most parts of the compressor map, the behavior at the boundaries is sensitive to the real flight condition.

As shown, the Mach similarity principle is not suitable for investigating aeroelastic stability throughout the whole flight envelope, especially when the static blade deformation is not neglectable. The reason for this can be found in the complex interaction between dimension-less numbers (Mach, Reynolds), sized values (pressure difference or aerodynamic loading, natural frequency) and their dependency on each other.
Cross-Talk Compensation for Blade Root Flap- and Edgewise Moments on an Experimental Research Wind Turbine and Comparison to Numerical Results
Authors: Bartholomay Sirko , Marten David , Sánchez Martínez Mariano , Alber Jörg , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver , Klein Annette Claudia , Lutz Thorsten , Krämer Ewald
Published: August 2018

In the current paper a method to correct cross-talk effects for strain-gauge measurements is presented. The method is demonstrated on an experimental horizontal axis wind turbine. The procedure takes cross-moments (flap-wise on edgewise moments and vice versa) as well as axial acceleration into account. The results from the experimental setup are compared to numerical URANS calculations and the medium-fidelity code Qblade for a baseline case and two yawed inflow situations.
Application of Dry-Friction Whip and Whirl Solution Methods to Systems With Support Asymmetry
Authors: Wilkes Jason C.
Published: August 2018

Dry-friction whip and whirl occurs when a rotor contacts a stator across a clearance annulus. In a general sense, the relative motion between the two bodies is described by a circular precessing motion. While this problem is generally well understood, the author is unaware of any papers that discuss the problem for systems having asymmetric rotor or stator supports. The current work will investigate a general model to describe dry-friction whip and whirl for the case of continuous contact between a rotor and stator in the presence of asymmetry. This paper will show that for light asymmetry, the rotor and stator motions are elliptical; however, the relative motion between the two bodies remains circular.
Design, Modeling, and Implementation of an Electrically-Driven Seal Gas Booster
Authors: Garceau Sean W. , Bowen John S.
Published: August 2018

This paper outlines the simulation, evaluation, and implementation of an electrically-driven seal gas booster in a tandem dry seal application. The electric boost compressor makes it feasible to supply seal gas to a process compressor’s seals during indefinite pressurized hold. Extended pressurized hold times reduce gas compressor station hydrocarbon emissions by reducing the number of unplanned compressor depressurization events. Traditional pneumatic seal gas boosters require regular depressurized maintenance intervals. The paper addresses the overall decrease in utility demand of the electric seal gas booster when compared to a pneumatic seal gas booster. The total cost difference between the two systems was determined for both initial investment and operational cost.

A steady-state simulation of a single impeller centrifugal boost compressor, within a package dry seal gas system utilizing differential pressure control to regulate seal gas flow, was conducted to evaluate overall system performance, design requirements, and constraints. The simulation validated a system design. The design was installed in an operational gas transmission compressor’s seal system for performance monitoring. The field testing data was compared to simulation output parameters to validate the simulation and confirm key performance characteristics. Additional process conditions and multi-body process compressor configurations were evaluated through simulation.

The use of differential pressure control, when compared to a flow control for seal gas regulation, has some key differentiating characteristics with regards to implementation of the electric seal gas booster in a package dry seal system [1, 2]. Seal gas source location, supplied internally or externally, is an important consideration for the system’s performance. Continuous operational with the electric seal gas booster requires additional control strategies to manage the process compressor case pressure.