bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Inlet Swirl on Endwall Film Cooling in Neighboring Vane Passages
Authors: Zhang Yang , Li Yifei , Bian Xiutao , Yuan Xin
Published: August 2017

The distribution of film cooling effectiveness of endwall film-cooling holes is considered to be periodic between neighboring high pressure turbine passages in most cascade experiments. In reality, because of the difference in the number of combustors and vanes, the flow fields of neighboring passages are completely different. The secondary flow, especially the passage vortex, is dominated by the upstream inlet rotating flow whose relative flow direction is the reverse between the neighboring vane passages. Specifying the direction of rotation to simulate inlet swirl introduces new challenges in film-cooling design. The present experiment compares five groups of endwall film-cooling with anticlockwise rotating flows at inlet at different clocking positions, and the film-cooling effect is analyzed to investigate the effects of inlet rotating flow. The inlet flow condition of neighboring passages is simulated by switching the position of a swirler fan. Hence, different rotating inlet flow conditions in different positions are achieved.

The GE-E3 airfoil was used in the cascade rig, with a scaled-up factor of 1.95. The inlet Reynolds number is 1.48 × 105 and the Mach number is 0.07. The effects of the blowing ratio and relative positions of the swirler are investigated in the experiment. Adiabatic film-cooling effectiveness is probed by using pressure-sensitive paint (PSP). The coolant is simulated by nitrogen with which a density ratio of around 1.0 can be achieved. Fan-shaped film-cooling holes are introduced into the endwall surface as well as trailing edge discharge holes. The cooling performance of the combustor-turbine gap leakage flow is not considered. Fan-shaped film-cooling holes are introduced into the endwall surface as well as upstream slot. The cooling performance of the combustor-turbine gap leakage flow is considered in this case.

A Pair of nozzle guide vane (NGV) passages are investigated simultaneously by which the film cooling effectiveness can be compared for the same case at the endwall surface. The inlet rotating flow is simulated by an upstream swirler, with five relative positions along the pitchwise direction. According to the experimental results, the inlet rotating flow dominates the film cooling effectiveness distribution at the endwall. The averaged film cooling effectiveness changes substantially with the change in swirler position. The rotating flow at the endwall region mainly interacts with the main flow to modify incidence angle. The influence of the inlet rotating flow is more obvious at the upstream portion. Meanwhile the downstream portion is not as sensitive to rotating flow as the upstream portion.
A High-Loaded Axial Compressor Bifurcate Stator Blade Aerodynamic Design and Vorticity Dynamics Diagnosis for Flow Structure
Authors: Chen Huanlong , Yu Menghan , Li Linxi , Liu Huaping
Published: August 2017

On the flow instability caused by large scale boundary-layer flow separation in highly loaded compressor/fan blade passage, a novel bifurcate compressor blade is designed based on pressure gradient control idea for blade passage flow, and a distinctive variable solidity bifurcate blade concept and three-dimensional blade design technology are integrated to achieve this design idea in this paper.

The quantitative flow information for the bifurcate blade passage is obtained by numerical simulation method to investigate the separation flow structure and dynamic mechanism near the wall and in the wake flow area. Besides, the complex influence of vortex structure evolution and the dynamic mechanism of low energy fluid redistribution being controlled in boundary-layer flow area would be revealed by applying the vorticity dynamics theory. The variable law of design parameters is explored in order to decrease aerodynamic loss, to delay flow separation near the wall and corner for the blade surface, to restructure blade aerodynamic loading, to form gentle pressure gradient and to diminish wake flow loss.

The results indicate that although extra aerodynamic loss is generated by the geometric mutation of bifurcate segment, the bifurcate blade effectively restrains the migration of high-entropy secondary flow fluid in the shroud corner area, thus substantially decreasing the loss near endwall/corner, which remarkably promotes the aerodynamic performance, particularly under the condition of positive incidence angle. Moreover, the bifurcate blade skillfully remolds the pressure gradient on the blade surface, and promotes total pressure as well as velocity for the wake area that would be beneficial for the downstream rotor blade. With the introduction of key physical concepts and flow parameters of vortex/vorticity dynamics, such as boundary vorticity flux, vorticity vector, skin-friction vector and tangential pressure gradient, the physical root source and mechanism of gentle pressure gradient formation, wake flow structure being weakened, and flow separation reduction for the endwall and corner are further revealed.
Effects of Hydrogen Fueling on NOx Emissions: A Reactor Model Approach for an Industrial Gas Turbine Combustor
Authors: Kroniger D. , Lipperheide M. , Wirsum M.
Published: August 2017

Addition of hydrogen (H2) to gas turbine fuel has recently become a topic of interest facing the global challenges of CO2 free combustion. As a drawback, Nitrogen oxide (NOx) emissions are likely to increase in hydrogen-rich fuel combustion which in return limits the use of the technology. In the course of this development, a model-based quantification of NOx emission increase by fuel flexibility may identify possible operation ranges of this technology. This paper evaluates the effect of an increased hydrogen fraction in the fuel on the NOx emissions of a non-premixed 10 MWth gas turbine combustor. A simple reactor network model has been set up using a perfectly stirred reactor (PSR) to simulate the flame zone and a plug flow reactor (PFR) to simulate the post flame zone. The change of residence time in the flame zone is accounted for by an empirical expression. The model is validated against data from high-pressure test rig experiments of an industrial non-premixed gas turbine combustor. The model results are in good agreement with the experimental data. Based on the model results, a fundamental correlation of the effect of hydrogen on the NOx emissions is formulated.
Aeroacoustic Analysis of Low-Speed Axial Fans With Different Rotational Speeds in the Design Point
Authors: Buchwald Patrick , Vogt Damian M. , Grilliat Julien , Laufer Wolfgang , Schmitz Michael B. , Lucius Andreas , Schneider Marc
Published: August 2017

One of the main design decisions in the development of low-speed axial fans is the right choice of the blade loading versus rotational speed, since a target pressure rise could either be achieved with a slow spinning fan and high blade loading or a fast spinning fan with less flow turning in the blade passages. Both the blade loading and the fan speed have an influence on the fan performance and the fan acoustics and there is a need to find the optimum choice in order to maximize efficiency while minimizing noise emissions. The present paper addresses this problem by investigating five different fans with the same pressure rise but different rotational speeds in the design point. In the first part of the numerical study, the fan design is described and steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are conducted in order to identify the performance of the fans in the design point and in off-design conditions. The investigations show the existence of an optimum in rotational speed regarding fan efficiency and identify a flow separation on the hub causing a deflection of the outflow in radial direction as the main loss source for slow spinning fans with high blade loadings. Subsequently, Large Eddy Simulations (LES) along with the acoustic analogy of Ffowcs Williams and Hawkings (FW-H) are performed in the design point to identify the main noise sources and to determine the far-field acoustics. The identification of the noise sources within the fans in the near-field is performed with the help of the power spectral density of the pressure. In the far-field, the sound power level is computed using different parts of the fan surface as FW-H sources. Both methods show the same trends regarding noise emissions and allow for a localization of the noise sources. The flow separation on the hub is one of the main noise sources along with the tip vortex with an increase in its strength towards lower rotational speeds and higher loading. Furthermore, a horseshoe vortex detaching from the rotor leading edge and impinging on the pressure side as well as the turbulent boundary layer on the suction side represent significant noise sources. In the present investigation, the maximum in efficiency coincides with the minimum in noise emissions.
Design and Analysis of a Novel Split Sliding Variable Nozzle for Turbocharger Turbine
Authors: Hu Leon , Sun Harold , Yi James , Curtis Eric , Zhang Jizhong
Published: August 2017

Variable geometry turbine (VGT) has been widely applied in internal combustion engines to improve the engine transient response and torque at low speed. One of the most popular variable geometry turbine is the variable nozzle turbine (VNT), in which the nozzle vanes can be rotated along the pivoting axis and thus the flow passage through the nozzle can be adjusted to match with different engine operating conditions. One disadvantage of the VNT is the turbine efficiency degradation due to the leakage flow in the nozzle endwall clearance, which is needed to allow the nozzle vanes to rotate without sticking. Especially at small nozzle open condition, there is large loading on the nozzle and high pressure gradient between the nozzle pressure and suction side. Strong leakage flow exists inside the nozzle endwall clearance from pressure side to suction side, leading to large flow loss and turbine stage efficiency degradation.

In the present paper, a novel split sliding variable nozzle turbine (SSVNT) has been proposed to reduce the nozzle leakage flow and to improve turbine stage efficiency. The idea is to divide the nozzle into two parts: one part is fixed and the other part can slide along the partition surface. The mechanism of nozzle flow passage variation in SSVNT is different from that of the traditional pivoting VNT. The sliding vane and the fixed vane together form an integrated vane. The flow of the turbine is determined by the passage of the integrated vanes. When moving the sliding vane to large radius position, the nozzle flow passage opens up and the turbine has high flow capacity. When moving the sliding vane towards small radius position, the nozzle flow passage closes down and the turbine has low flow capacity. As the fixed vane doesn’t need endwall clearance, there is no leakage flow inside the fixed vane and the total leakage flow through the integrated vane can be reduced. Based on calibrated numerical modeling, the analysis results showed that there is up to 12% turbine stage efficiency improvement with the SSVNT design at small nozzle open condition while maintaining the same flow capacity and efficiency at large nozzle open condition, compared to the conventional VNT. The mechanism of efficiency improvement in the SSVNT design has also been discussed.
Experimental and Numerical Analysis of the Secondary Flow Across the Interphase Balance Drum of a High Pressure Back-to-Back Centrifugal Compressor
Authors: Carmicino Carmine , Maiuolo Francesco , Rizzo Emanuele
Published: August 2017

With the major aim of gathering information on the machine lateral stability in high pressure-high density conditions, and of assessing the prediction capabilities of the in-house design tools and overall process, a back-to-back centrifugal compressor has been instrumented and tested in several operating conditions. The present paper focuses on the secondary flows across the interphase balance drum of the back-to-back compressor, where the sealing is accomplished with a honeycomb seal. The compressor interphase section has been instrumented with dedicated special probes for the clearance measurement associated to pressure and flow angle probes in order to characterize pressure distributions and swirl variations depending on the specific operating range. The experimental data acquired over the machine operation have been compared with a three-dimensional steady-state numerical analysis results obtained from the simulation, carried out with a Reynolds averaged Navier-Stokes (RANS) approach, of the flowfield in the complex interphase secondary system composed by the impeller cavities and the honeycomb seal. This paper addresses the comparison between numerical results and experimental data, which allowed the matching of models with experiments in terms of pressure distribution and the complex flowfield. Finally, all the data have been used to validate an in-house one-dimensional flow network solver for pressure distribution and leakage flow calculations along cavities and seals. Results have shown a general good agreement between measured data and calculation output. In particular, computational fluid dynamic analysis provided detailed pressure and velocity distributions that allowed gaining insight in the physics of such a complex region. The one-dimensional model has been demonstrated to be a fast and reliable tool to well predict local pressure variations inside cavities and seals and, consequently, the residual axial thrust.
Investigation of Strip Seal Leakage With Special Focus on Seal Groove Design and Relative Displacement of Sealing Surfaces
Authors: Huber Thomas , Bricaud Cyrille , Zierer Thomas
Published: August 2017

Tight sealing lines are vital in large gas turbines (GT) to achieve high performance and efficiency. Leakage including rim purge air can sum up to 30% of the total cooling and leakage air consumption of a gas turbine. Leakage through static strip seals contributes about 1/3 to all leakage air. Considering the seal design as on drawings, sealing quality is generally influenced by the seal type, sealing groove curvature and the sealing groove roughness. In addition the sealing quality depends strongly on the geometric deviation of the groove compared to ideal design. This is caused by manufacturing deviations or relative movements of the grooves during operation of the parts containing the sealing.

In the article at hand, different seal designs and pertinent sealing quality is discussed. More in detail, it is discussed the geometric relation of seal, groove and misalignment to predict the seal position relative to its groove confinements. The risk of seal clamping can be judged and adaptation of seal or groove geometry can be derived. The effect of leakage increase due to misalignment is investigated by a test matrix varying seal length and curvature radius of groove as well as radial misalignment.
Small Jet Engine Centrifugal Compressor Stability Margin Assessment
Authors: Pečinka Jiři , Jílek Adolf , Kmoch Petr
Published: August 2017

Centrifugal compressors with low and moderate pressure ratio usually have characteristic with a wider stable operating region. Flat speed lines allow substantial reduction of the air mass flow rate with almost constant pressure ratio and without sudden surge occurrence. The surge is typically preceded by a stall or mild surge causing significant and thus quite easily detectable pressure oscillations. The preceding unstable operation is oscillatory yet still quite safe compared to deep surge. Research described in this paper deals with changes in both the engine slow pressures and fast parameters (pressures, noise, vibrations). Parameters were measured along constant speed lines from the operating line point down near to the compressor surge line. The goal was to describe typical changes in engine parameters and to define a stipulated limit of engine safe operation. Newly defined criteria of centrifugal compressor stable run will allow evaluation of engine operability, without the need to drive the engine into the compressor surge repeatedly.
Multidisciplinary Design of a Three Stage High Speed Booster
Authors: Lejon Marcus , Grönstedt Tomas , Glodic Nenad , Petrie-Repar Paul , Genrup Magnus , Mann Alexander
Published: August 2017

The paper describes a multidisciplinary conceptual design of an axial compressor, targeting a three stage, high speed, high efficiency booster with a design pressure ratio of 2.8. The paper is outlined in a step wise manner starting from basic aircraft and engine thrust requirements, establishing the definition of the high speed booster interface points and its location in the engine. Thereafter, the aerodynamic 1D/2D design is carried out using the commercial throughflow tool SC90C. A number of design aspects are described, and the steps necessary to arrive at the final design are outlined. The SC90C based design is then carried over to a CFD based conceptual design tool AxCent, in which a first profiling is carried out based on a multiple circular arc blade definition. The design obtained at this point is referred to as the VINK compressor. The first stage of the compressor is then optimized using an in-house optimization tool, where the objective functions are evaluated from detailed CFD calculations. The design is improved in terms of efficiency and in terms of meeting the design criteria put on the stage in the earlier design phases. Finally, some aeromechanical design aspects of the first stage are considered. The geometry and inlet boundary conditions of the compressor are shared with the turbomachinery community on a public server. This is intended to be used as a test case for further optimization and analysis.
Aerodynamic Excitation Analysis of Radial Turbine Blades due to Unsteady Flow From Vaneless Turbine Housings
Authors: Netzhammer Stephan , Vogt Damian M. , Kraetschmer Stephan , Leweux Johannes , Koengeter Andreas
Published: August 2017

Turbocharger turbine blades are subjected to resonant excitation that can lead to High Cycle Fatigue (HCF). In vaneless turbines the excitation primarily stems from asymmetries in the turbine housing such as the volute and the tongue. Given the nature of such asymmetries, the excitation is of a Low Engine Order (LEO) type.

The present study deals with the effect of radial turbine housing design on LEO resonant excitation of turbine blades. The study focuses on two geometrical key design parameters of a twin-scroll turbine housing for a radial turbine which is the rotor-tongue distance and the circumferential angle between both tongues. The generalized force approach is used to identify the critical blade surface regions in order to understand the excitation mechanism of each specific design and to assess the differences of design variants with respect to the baseline design. The presented approach is highly practicable, because it is less expensive than full FSI-simulations.

This approach is validated on tip timing test data from full-scale experiments. Correlation to test data shows that the presented approach is capable of capturing the relative trends reliably and hence can efficiently be employed in an industrial design process such as to minimize blade vibration amplitudes. It is shown that a reduction of blade vibration amplitudes by a factor of 10 could be achieved.
Detailed Examination of a Modified Two-Staged Micro Gas Turbine Combustor
Authors: Schwärzle A. , Monz T. O. , Huber A. , Aigner M.
Published: August 2017

Jet-stabilized combustion is a promising technology for fuel flexible, reliable, highly efficient combustion systems. The aim of this work is a reduction of NOx emissions of a previously published two-staged MGT combustor [1, 2], where the pilot stage of the combustor was identified as the main contributor to NOx emissions. The geometry optimization was carried out regarding the shape of the pilot dome and the interface between pilot and main stage in order to prevent the formation of high temperature recirculation zones. Both stages have been run separately to allow a detailed understanding of the flame stabilization within the combustor, its range of stable combustion, the interaction between both stages and the influence of the modified geometry. All experiments were conducted at atmospheric pressure and an air preheat temperature of 650 °C. The flame was analyzed in terms of shape, length and lift-off height, using OH* chemiluminescence images. Emission measurements for NOx, CO and UHC emissions were carried out. At a global air number of λ = 2, a fuel split variation was carried out from 0 (only pilot-stage) to 1 (only main stage). The modification of the geometry lead to a decrease in NOx and CO emissions throughout the fuel split variation in comparison with the previous design. Regarding CO emissions, the pilot stage operations is beneficial for a fuel split above 0.8. The local maximum in NOx emissions observed for the previous combustor design at a fuel split of 0.78 was not apparent for the modified design. NOx emissions were increasing, when the local air number of the pilot stage was below the global air number. In order to evaluate the influence of the modified design on the flow field and identify the origin of the emission reduction compared to the previous design, unsteady RANS simulations were carried out for both geometries at fuel splits of 0.93 and 0.78, respectively, using the DLR in-house code THETA with the k-w SST turbulence model and the DRM22 [3] detailed reaction mechanism. The numerical results showed a strong influence of the recirculation zones on the pilot stage reaction zone.
Experimental and Numerical Investigation of Sweeping Jet Film Cooling
Authors: Hossain Mohammad A. , Prenter Robin , Lundgreen Ryan K. , Ameri Ali , Gregory James W. , Bons Jeffrey P.
Published: August 2017

A companion experimental and numerical study was conducted of the performance of a row of 5 sweeping jet (SJ) film cooling holes consisting of conventional curved fluidic oscillators with an aspect ratio (AR) of unity and a hole spacing of P/D = 8.5. Adiabatic film effectiveness (η), thermal field (θ), convective heat transfer coefficient (h) and discharge coefficient (CD) were measured at two different freestream turbulence levels (Tu = 0.4% and 10.1%) and four blowing ratios (M = 0.98, 1.97, 2.94 and 3.96) at a density ratio (DR) of 1.04 and hole Reynolds number of ReD = 2800. Adiabatic film effectiveness and thermal field data were also acquired for a baseline 777-shaped hole. The sweeping jet film cooling hole showed significant improvement in cooling effectiveness in the lateral direction due to the sweeping action of the fluidic oscillator. An unsteady RANS simulation was performed to evaluate the flow field at the exit of the hole. Time resolved flow fields revealed two alternating streamwise vortices at all blowing ratios. The sense of rotation of these alternating vortices is opposite to the traditional counter rotating vortex pair (CRVP) found in a ‘jet in crossflow’ and serves to spread the film coolant laterally.
Two-Phase Flow Large Eddy Simulations of a Staged Multipoint Swirling Burner: Comparison Between Euler-Euler and Euler-Lagrange Descriptions
Authors: Cunha Caldeira Mesquita Léo , Vié Aymeric , Ducruix Sébastien
Published: August 2017

A two-staged swirling burner is numerically simulated through large eddy simulations. The impact of the liquid phase modeling approach is evaluated comparing the Eulerian and Lagrangian frameworks for two different operation points, full pilot injection and full multipoint injection. For the full multipoint injection, since the operation point is closer to a Lean Premixed Prevaporized (LPP) regime, both liquid phase models present similar flame structure (an M flame). For the full pilot injection, Eulerian and Lagrangian approaches result in different flames for equivalent boundary conditions: the Eulerian simulation produces a ‘tulip’ flame, while the Lagrangian spray forms a lifted flame. To assess the model sensitivity to boundary conditions parameters, complementary Lagrangian simulations are made varying injected droplets’ diameter and spray angle, this time resulting in a ‘tulip’ flame very similar to the Eulerian one. Finally, a last Eulerian simulation is made, where the injected droplets’ diameter is increased, still leading to a ‘tulip’ flame, showing that the strong interaction between liquid phase and flame highly impact the results.
Experimental Investigation of an Inverted Brayton Cycle Micro Gas Turbine for CHP Application
Authors: Agelidou Eleni , Monz Thomas , Huber Andreas , Aigner Manfred
Published: August 2017

Decentralized heat and power (CHP) production constitutes a promising solution to reduce the primary energy consumption and greenhouse gas emissions. Here, micro gas turbine (MGT) based CHP systems are particularly suitable due to their low pollutant emissions without exhaust gas treatment.

Typically, the electrical power demand for single houses ranges from 1 to several kWel. However, downsizing turbocharger components of a conventional MGT CHP system can reduce electrical efficiencies since losses like seal and tip leakages, generally do not scale proportionally with size. By introducing an inverted Brayton Cycle (IBC) based MGT this potential can be exploited. The IBC keeps the volumetric flows constant while mass flow and thermodynamic work are scaled by the ratio of pressure level. Since the performance of turbocharger components is mainly driven by the volumetric flow they should be applicable for both cycles. Hence, smaller power outputs can be achieved.

The overall aim of this work, is the development of a recuperated inverted MGT CHP unit for a single family house with 1 kWel. This paper presents an experimental study of the applicability and feasibility of a conventional MGT operated in IBC mode. The demonstrator was based on a single shaft, single stage conventional MGT. Reliable start up and stable operation within the entire operating range from 180 000 rpm to 240 000 rpm are demonstrated. The turbine outlet pressure varied between 0,5 bar (part load) and 0,3 bar absolute (full load). All relevant parameters such as pressure losses and efficiencies of the main components are investigated.

Moreover, the power output and the mechanical and thermal losses were analyzed in detail. Although the results indicated that the mechanical and heat losses have a high influence on the performance and economic efficiency of the system, the prototype shows great potential for further development.
The History of Integrated Gasification Combined-Cycle Power Plants
Authors: Phillips Jeffrey N. , Booras George S. , Marasigan Jose
Published: August 2017

Integrated gasification combined-cycle (IGCC) power plants offer a way to use solid or heavy liquid hydrocarbons, such as asphalt, in high-efficiency combined-cycle power plants. This paper reviews the history of IGCC power plants from the first unit, which was built in Germany in the 1970s, to the current wave of IGCCs being deployed in the 2010s. It draws heavily from the Electric Power Research Institute (EPRI) archive of information about IGCCs, which chronicles 40 years of nurturing the development of a number of coal gasification technologies. Insights from the operating experiences of earlier IGCCs will be examined, a comprehensive table listing all IGCCs built to date is provided and photos from many of the plants are included. The paper concludes with some recommendations for research and development which could set the direction for future applications of IGCC technologies.
Heat Transfer in a Rotating Rib-Roughened Wedge-Shaped U-Duct
Authors: Ding Liang , Tian Shuqing , Deng Hongwu
Published: August 2017

Heat transfer in a rotating two-pass trapezium-shaped channel, with staggered 90-deg ribs on both leading and trailing surfaces is experimentally investigated. The hydraulic diameter of the first and second pass is 24.5 mm and 16.9 mm, respectively. The inlet Reynolds number and rotational speed range from 10000 to 50000 and zero to 1000 rpm, respectively, which results in the inlet rotation number varying from zero to 1.0. The heated copper plate technique is employed to measure the regional averaged heater transfer coefficients. Pressure drops are measured by newly designed rotating pressure measurements module. Both ribbed cases and smooth cases are compared to present rib enhancement effect.

For non-rotating result, the results show that the trailing surface presents much higher heat transfer than other cases due to the special wedge-shaped geometry. The ribbed wedge-shaped achieves enhanced regional heat transfer performances than the smooth case at all locations. Compared with the non-rotating results in the first pass, heat transfer on both trailing and leading surfaces is enhanced except for the position near the turn region, but weakened on outer surface in stream-wise direction. And at high rotation numbers, the highest maximum heat transfer on railing surface happens at a location of approximately X/D = 10. In the first pass, rotation always enhances heat transfer on the trailing surface as rotation number increases and the rotation-to-stationary Nusselt number ratio reaches to 2.0 at the rotation number of 0.5. The leading and outer surfaces both have a critical rotation number located at Roc = 0.05.
Design and Analysis of a Sliding Mode Parameter Limit Regulating System for Turbo Fan Engine
Authors: Yuan-suo Zhang , Jin-wei Tao , Xin-chen Mai
Published: August 2017

In this paper, a sliding mode (SM) parameter limit regulating system is designed to regulate the fuel flow rate to the turbofan engine. Firstly, a linear engine model is identified using a general engine dynamic nonlinear model. Then based on the one Lyapunov function, one SM parameter limit regulating system is designed mainly including regulators design, selector design and integrator design. After that the feedback gains and coefficient sets (switching gain and boundary thickness for every regulator) of the SM regulators are optimized and chosen. Finally, the global asymptotical stability of the regulating system is demonstrated. The simulation results also show that SM parameter limit regulator functions all the time during engine transient state control process, and the design SM parameter limit regulating system ensures that the target steady speed state or limit steady state can be attained in finite time interval without exceeding critical parameter limits.
Gas Thermometry Using Two-Thermocouple Radiation Correction
Authors: Martin Christopher , LePera Stephen , Vandsburger Uri
Published: August 2017

The current work is the first in a series of investigations to develop a method for high-temperature thermometry of gaseous flows using thermocouple pairs with disparate convective properties to infer the contribution of radiation. Two thermocouples of deliberately dissimilar bead geometry are placed side-by-side in a flow while the two beads are heated by surface radiation. Their dissimilar responses to radiation cause a predictable divergence between the two temperature measurements.

The current approach improves upon others found in literature owing to its in-situ measurement for convection coefficients rather than dependence on empirical estimation. Each bead is deliberately overheated, and the time constant of the thermal decay back to equilibrium indicates the intensity of convection. Here, we perform this measurement in air while varying velocity, duration of overheat, and intensity of overheat. We compare the calculated temperature correction against the known air temperature.

Heat transfer through the probe wires to the ceramic probe support was found to have a strong effect on the correction, although corrected values were always closer to the actual gas temperature than the original uncorrected value. In conditions of mild radiation loading, the effect was sufficiently symmetric between the two beads to allow effective correction. All measurements indicated that if additional information about the probe body temperature was collected in addition to the thermocouple measurements, the correction could be improved significantly.
EBFOG: Deposition, Erosion and Detachment on High Pressure Turbine Vanes
Authors: Casari Nicola , Pinelli Michele , Suman Alessio , Montomoli Francesco , di Mare Luca
Published: August 2017

Fouling and erosion are two pressing problems that severely affect gas turbine performance and life. When aircraft fly through a volcanic ash cloud the two phenomena occur simultaneously in the cold as well as in the hot section of the engine. In the high pressure turbine, in particular, the particles soften or melt due to the high gas temperatures and stick to the wet surfaces. The throat area, and hence the capacity, of the HP turbine is modified by these phenomena, affecting the engine stability and possibly forcing engine shutdown.

This work presents a model for deposition and erosion in gas turbines and its implementation in a three dimensional Navier-Stokes solver. Both deposition and erosion are kept into account, together with deposit detachment due to changed flow conditions. The model is based on a statistical description of the behaviour of softened particles. The particles can stick to the surface or can bounce away, eroding the material. The sticking prediction relies on the authors’ EBFOG model. The impinging particles which do not stick to the surface are responsible for the removal of material.

The model is demonstrated on a high pressure turbine vane. The performance deterioration and the throat area reduction rate are carefully monitored. The safe-to-fly time through a cloud can be inferred from the outcome of this work as important piece of on-board information for the flight crew.
On Improving the Surge Margin of a Tip-Critical Axial Compressor Rotor
Authors: Lejon Marcus , Grönstedt Tomas , Andersson Niklas , Ellbrant Lars , Mårtensson Hans
Published: August 2017

Delaying breakdown of the flow in the tip region of a tip-critical compressor rotor as long as possible, i.e. improving the surge margin, is of great interest to the turbomachinery community and is the focus of this study. The surge margin of ten compressor rotors is evaluated numerically, each with different blade loading and geometry at the tip. Previous work in the field has shown the dependence of an interface in the tip region of a compressor rotor between the incoming flow and the tip clearance flow with the passage flow coefficient ϕ. Previous work in the field has also shown that a higher incoming meridional momentum in the tip region can be beneficial to the surge margin of a tip-critical rotor. The present study generalizes these findings by taking into account the local blade loading of the rotor tip section and the level of loss in the tip region. The surge margin is found to improve if the blade loading of the rotor tip section is increased, which acts to increase the incoming mass flow rate and improve the surge margin provided that an increase in loss, mainly related to the strength and direction of the tip clearance flow, does not negate the effect as the compressor is throttled. Two quantities are proposed as objective functions to be used for optimization to achieve a compressor rotor with high surge margin based on the flow field at the design point. Finally, an optimization and analysis of the results is made to demonstrate the proposed objective functions in practise.
Effect of Foil Geometry on the Static Performance of Thrust Foil Bearings
Authors: Fu Gen , Untaroiu Alexandrina , Swanson Erik
Published: August 2017

Gas foil bearings use ambient air as working fluid, which forms the hydrodynamic wedge between the rotor surface and the compliant foil structure, therefore they are oil-free and environmental friendly. Compared to traditional bearings, gas foil bearing can operate in extreme conditions such as high temperature and high rotating speed. They also provide better damping and stability characteristics and have larger tolerance to debris and rotor misalignment. Gas foil bearings have been successfully applied to micro and small sized turbomachinery, such as micro gas turbine and cryogenic turbo expander. In the previous decades, a lot of theoretical and experimental work have been conducted to investigate the properties of gas foil bearings. However, very little work has been done to study the influence of the foil bearing pad geometry configuration using computational fluid dynamics (CFD). This study proposes a robust approach to analyze the effect of the foil geometry on the performance of a six pads thrust foil bearing.

In this study, a 3D CFD model for a parallel six pads thrust foil bearing is built using ANSYS-CFX software. The full Navier-Stokes equations are solved in the fluid domain. Taking into account the rotational periodicity, the computational model is simplified and only one pad of the thrust foil bearing is analyzed. In order to predict the thermal property, the total energy with viscous dissipation is used. Practical boundary conditions are used in the baseline CFD model. The results of the baseline modes is further compared with a modified Reynolds equation solution. Based on this model, the geometry of the thrust foil bearing is parameterized and analyzed using the design of experiments (DOE) methodology. In this paper, the selected geometry parameters of the foil structure include: minimum film thickness, inlet film thickness, the ramp extent on the inner circle, the ramp extent on the outer circle, the arc extent of the pad, and the orientation of the leading edge. A factorial design technique is employed to sample the design space in DOE. The objectives in the sensitivity study are selected as load force and friction torque. An optimal foil geometry is derived based on the results of the DOE process by using a goal driven optimization technique to maximize the load force and minimize the friction torque. The results show that the geometry of foil structure is a key factor for foil bearing performance. The numerical approach proposed in this study is expected to be useful from the thrust foil bearing design perspective.
Characterization of a Three-Dimensional Leading-Edge Separation Bubble on Swept, Low Aspect-Ratio Propeller Blades
Authors: Koyama Maldonado Ye-Bonne , Delattre Gregory , Illoul Cedric , Dejeu Clement , Jacquin Laurent
Published: August 2017

Leading-edge vortex flows are often present on propeller blades at take-off, however, their characteristics and aerodynamic impact are still not fully understood. An experimental investigation using Time Resolved Particle Image Velocimetry (TR-PIV) has been performed on a model blade in order to classify this flow with respect to both delta wing leading-edge vortices and the low Reynolds number studies regarding leading-edge vortices on rotating blades. A numerical calculation of the experimental setup has been performed in order to assess usual numerical methods for propeller performance prediction against TR-PIV results. Similar characteristics were found with non slender delta wing vortices at low incidence, which hints that the leading-edge vortex flow may generate vortex lift. The influence of rotation on the characteristics of the leading-edge vortex is compared to that of the pressure gradient caused by the circulation distribution. A discussion on the quality of the PIV reconstruction for close-wall structures is provided.
Printed Circuit Heat Exchanger Flow Distribution Measurements
Authors: Lance Blake W. , Carlson Matthew D.
Published: August 2017

Printed circuit heat exchangers (PCHEs) have an important role in supercritical CO2 (sCO2) Brayton cycles because of their small footprint and the high level of recuperation required for this power cycle. Compact heat exchangers like PCHEs are a rapidly evolving technology, with many companies developing various designs. One technical unknown that is common to all compact heat exchangers is the flow distribution inside the headers that affects channel flow uniformity. For compact heat exchangers, the core frontal area is often large compared with the inlet pipe area, increasing the possibility of flow maldistribution. With the large area difference, there is potential for higher flow near the center and lower flow around the edges of the core. Flow maldistribution increases pressure drop and decreases effectiveness. In some header geometries, flow separation inside the header adds to the pressure drop without increasing heat transfer.

This is the first known experiment to test for flow maldistribution by direct velocity measurements in the headers. A PCHE visualization prototype was constructed out of transparent acrylic for optical flow measurements with Particle Image Velocimetry (PIV). The channels were machined out of sheets to form many semi-circular cross sections typical of chemically-etched plates used in PCHE fabrication. These plates were stacked and bolted together to resemble the core geometry. Two header geometries were tested, round and square, both with a normally-oriented jet.

PIV allows for velocities to be measured in an entire plane instantly without disturbing the flow. Small particles of approximately 10 micrometers in diameter were added to unheated water. The particles were illuminated by two laser flashes that were carefully timed, and two images were acquired with a specialized digital camera. The movement of particle groups was detected by a cross-correlation algorithm with a result of about 50k velocity measurements in a plane. The velocity distribution inside the header volume was mapped using this method over many planes by traversing the PCHE relative to the optical equipment. The level of flow maldistribution was measured by the spatially-changing velocity coming out of the channels. This effect was quantified by the coefficient of variation proposed by Baek et al. The relative levels of flow maldistribution in the different header geometries in this study were assessed. With highly-resolved velocity measurements, improvements to header geometry to reduce flow maldistribution can be developed.
Effects of Hole Pitch to Diameter Ratio P/D of Impingement and Film Hole on Laminated Cooling Effectiveness
Authors: Zhou Weilun , Deng Qinghua , He Wei , Feng Zhenping
Published: August 2017

The laminated cooling, also known as impingement-effusion cooling, is believed to be a promising gas turbine blade cooling technique. In this paper, conjugate heat transfer analysis was employed to investigate the overall cooling effectiveness and total pressure loss of the laminated cooling configuration. The pitch to film hole diameter ratio P/Df of 3, 4, 5, 6, combined with pitch to impingement hole diameter ratio P/Di of 4, 6, 8, 10, are studied at the coolant mass flux G of 0.5, 1.0, 1.5, 2.0 kg/(sm2bar) respectively. The results show that overall cooling effectiveness of laminated cooling configuration increases with the decreasing of P/Df and the increasing of the coolant mass flux in general. However P/Df smaller than 3 may leads to a serious blocking in first few film holes at low coolant mass flux. The large P/Di that makes the Mach number of impingement flow greater than 0.16 may cause unacceptable pressure loss. The increment of overall cooling effectiveness depends on the difference between the deterioration of external cooling and the enhancement of internal cooling. Pressure loss increases exponentially with P/Di and G, and it increases more slowly with P/Df that compared to P/Di and G. The mixing loss takes up the most pressure loss at low coolant mass flux. With the increasing of the whole pressure loss, the proportion of throttling loss and laminated loss becomes larger and finally takes up the most of the whole pressure loss. When the sum of throttling loss and laminated loss is greater than mixing loss, the increment of system pressure ratio is unreasonable that compared to the increment of overall cooling effectiveness.
Numerical Simulation of Dynamic Flow Characteristics in a Centrifugal Water Pump Considering Shaft Torsional Vibration
Authors: Lv Shen , Zhang Xiang-Yuan , Jiang Chen-Xing , Li Wan-You , Shuai Zhi-Jun , Yan An
Published: August 2017

The complex three-dimensional turbulent flow field in a centrifugal water pump is numerically simulated considering torsional vibration of the shaft. The characteristic frequency and the frequency modulation phenomenon is investigated when the fluctuated-rotation-speed is considered. The results show that the amplitude of pressure fluctuation is bigger when the rotating-speed of shaft is unsteady, indicating that the speed fluctuations of impellers intensify the nonuniformity and instability of the whole flow field inside the pump. Besides, the Blade Passing Frequency (BPF) has obvious sidelobe frequency peaks when different frequency rate of speed appears. It can be concluded that sidelobes maybe come from the torsional vibration of the shaft. The main findings of this work can provide prediction of the pump performance and information for further optimal design of centrifugal pumps as well.
Modelling Strategies for Large-Eddy Simulation of Lean Burn Spray Flames
Authors: Puggelli S. , Bertini D. , Mazzei L. , Andreini A.
Published: August 2017

During the last years aero-engines are progressively evolving toward design concepts that permit improvements in terms of engine safety, fuel economy and pollutant emissions. With the aim of satisfying the strict NOx reduction targets imposed by ICAO-CAEP, lean burn technology is one of the most promising solutions even if it must face safety concerns and technical issues. Hence a depth insight on lean burn combustion is required and Computational Fluid Dynamics (CFD) can be a useful tool for this purpose. In this work a comparison in Large-Eddy Simulation (LES) framework of two widely employed combustion approaches like the Artificially Thickened Flame (ATF) and the Flamelet Generated Manifold (FGM) is performed using ANSYS® Fluent v16.2. Two literature test cases with increasing complexity in terms of geometry, flow field and operating conditions are considered. Firstly, capabilities of FGM are evaluated on a single swirler burner operating at ambient pressure with a standard pressure atomizer for spray injection. Then a second test case, operated at 4 bar, is simulated. Here kerosene fuel is burned after an injection through a prefilming airblast atomizer within a co-rotating double swirler. Obtained comparisons with experimental results show the different capabilities of ATF and FGM in modelling the partially-premixed behaviour of the flame and provides an overview of the main strengths and limitations of the modelling strategies under investigation.
Numerical Study on Heat Transfer Performance of a New-Proposed Pin-Fin in an Internal Channel
Authors: Ye Lv , Liu Zhao , Gao Chun , Yang Xing , Feng Zhenping
Published: August 2017

This paper numerically investigated the flow and heat transfer characteristics in a rectangular channel with pin-fin arrays. The channel simulates a wide aspect ratio (W/E = 3) internal cooling passage of gas turbine blade. The pin-fin applied in the simulation is a new-proposed geometry which consists of a cylinder body with a fixed ratio of diameter to channel height, D0/E = 1/4, and a rounded tip. Each case corresponds to a specific pin-fin array geometry of detachment spacing C between the pin-tip and endwall. In the rig studied, 18 rows of pin-fins are in staggered arrangement along the streamwise direction. The investigation on pin-fin performance has been made mainly into two aspects. One is the effect of diameter of the rounded tip Dh on heat transfer performance and pressure loss in the system, while the other is the effect of detachment C. All the cases have been performed with the range of the Reynolds numbers from 15,000 to 25,000. The SST k–w turbulence model is employed for all the computational analysis. Results reveal that the presence of rounded-tip pin-fin with a detachment effectively promotes the wall-flow interactions and enhances heat transfer on endwalls. The rounded tip diameter has a slight effect on heat transfer and pressure drop in the channel. In the study range, relatively higher detachment promotes higher heat transfer coefficient. In general, the new-proposed pin-fin geometry induces greater heat transfer enhancement and yields relatively lower pressure drop.