bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Axial Stretch on Lumen Collapse of Arteries
Authors: Fatemifar Fatemeh , Han Hai-Chao
Published: September 2016

The stability of the arteries under in vivo pressure and axial tension loads is essential to normal arterial function, and lumen collapse due to buckling can hinder the blood flow. The objective of this study was to develop the lumen buckling equation for nonlinear anisotropic thick-walled arteries to determine the effect of axial tension. The theoretical equation was developed using exponential Fung strain function, and the effects of axial tension and residual stress on the critical buckling pressure were illustrated for porcine coronary arteries. The buckling behavior was also simulated using finite-element analysis. Our results demonstrated that lumen collapse of arteries could occur when the transmural pressure is negative and exceeded a critical value. This value depends upon the axial stretch ratio and material properties of the arterial wall. Axial tensions show a biphasic effect on the critical buckling pressure. The lumen aspect ratio of arteries increases nonlinearly with increasing external pressure beyond the critical value as the lumen collapses. These results enhance our understanding of artery lumen collapse behavior.
Extending the Power-Law Hemolysis Model to Complex Flows
Authors: Faghih Mohammad M. , Keith Sharp M.
Published: September 2016

Hemolysis (damage to red blood cells) is a long-standing problem in blood contacting devices, and its prediction has been the goal of considerable research. The most popular model relating hemolysis to fluid stresses is the power-law model, which was developed from experiments in pure shear only. In the absence of better data, this model has been extended to more complex flows by replacing the shear stress in the power-law equation with a von Mises-like scalar stress. While the validity of the scalar stress also remains to be confirmed, inconsistencies exist in its application, in particular, two forms that vary by a factor of 2 have been used. This article will clarify the proper extension of the power law to complex flows in a way that maintains correct results in the limit of pure shear.
Enhanced Photon Tunneling by Surface Plasmon–Phonon Polaritons in Graphene/hBN Heterostructures
Authors: Zhao B. , Zhang Z. M.
Published: September 2016

Enhancing photon tunneling probability is the key to increasing the near-field radiative heat transfer between two objects. It has been shown that hexagonal boron nitride (hBN) and graphene heterostructures can enable plentiful phononic and plasmonic resonance modes. This work demonstrates that heterostructures consisting of a monolayer graphene on an hBN film can support surface plasmon–phonon polaritons that greatly enhance the photon tunneling and outperform individual structures made of either graphene or hBN. Both the thickness of the hBN films and the chemical potential of graphene can affect the tunneling probability, offering potential routes toward passive or active control of near-field heat transfer. The results presented here may facilitate the system design for near-field energy harvesting, thermal imaging, and radiative cooling applications based on two-dimensional materials.
Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders
Authors: Fornarelli Francesco , Lippolis Antonio , Oresta Paolo
Published: September 2016

In this paper, we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are isothermal and they are aligned with the earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center-to-center spacing (s = 3.6d–4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found, and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=−1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact, the transition occurs due to rearrangement of the near-field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.
Numerical Investigation of Three-Dimensional Separation in an Axial Flow Compressor: The Influence of Freestream Turbulence Intensity and Endwall Boundary Layer State
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo
Published: September 2016

Regions of three-dimensional separations are an inherent flow feature of the suction surface-endwall corner in axial compressors. These corner separations can cause a significant total pressure loss and reduce the compressor's efficiency. This paper uses wall-resolved LES to investigate the loss sources in a corner separation, and examines the influence of the inflow turbulence on these sources. Different subgrid scale (SGS) models are tested and the choice of model is found to be important. The σ SGS model, which performed well, is then used to perform LES of a compressor endwall flow. The time-averaged data are in good agreement with measurements. The viscous and turbulent dissipation are used to highlight the sources of loss, with the latter being dominant. The key loss sources are seen to be the 2D laminar separation bubble and trailing edge wake, and the 3D flow region near the endwall. Increasing the freestream turbulence (FST) intensity changes the suction surface boundary layer transition mode from separation induced to bypass. However, it does not significantly alter the transition location and therefore the corner separation size. Additionally, the FST does not noticeably interact with the corner separation itself, meaning that in this case the corner separation is relatively insensitive to the FST. The endwall boundary layer state is found to be significant. A laminar endwall boundary layer separates much earlier leading to a larger passage vortex. This significantly alters the endwall flow and loss. Hence, the need for accurate boundary measurements is clear.
Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Numerical Investigation
Authors: Burberi E. , Massini D. , Cocchi L. , Mazzei L. , Andreini A. , Facchini B.
Published: September 2016

Increasing turbine inlet temperature is one of the main strategies used to accomplish the demand for increased performance of modern gas turbines. Thus, optimization of the cooling system is becoming of paramount importance in gas turbine development. Leading edge (LE) represents a critical part of cooled nozzles and blades, given the presence of the hot gases stagnation point, and the unfavorable geometrical characteristics for cooling purposes. This paper reports the results of a numerical investigation, carried out to support a parallel experimental campaign, aimed at assessing the rotation effects on the internal heat transfer coefficient (HTC) distribution in a realistic LE cooling system of a high pressure blade. Experiments were performed in static and rotating conditions replicating a typical range of jet Reynolds number (10,000–40,000) and Rotation number (0–0.05). The experimental results consist of flowfield measurements on several internal planes and HTC distributions on the LE internal surface. Hybrid RANS–large eddy simulation (LES) models were exploited for the simulations, such as scale adaptive simulation and detached eddy simulation, given their ability to resolve the complex flowfield associated with jet impingement. Numerical flowfield results are reported in terms of both jet velocity profiles and 2D vector plots on two internal planes, while the HTC distributions are presented as detailed 2D maps together with averaged Nusselt number profiles. A fairly good agreement with experiments is observed, which represents a validation of the adopted modeling strategy, allowing an in-depth interpretation of the experimental results.
Real-Time Estimation of Lithium-Ion Concentration in Both Electrodes of a Lithium-Ion Battery Cell Utilizing Electrochemical–Thermal Coupling
Authors: Dey Satadru , Ayalew Beshah
Published: September 2016

This paper proposes and demonstrates an estimation scheme for Li-ion concentrations in both electrodes of a Li-ion battery cell. The well-known observability deficiencies in the two-electrode electrochemical models of Li-ion battery cells are first overcome by extending them with a thermal evolution model. Essentially, coupling of electrochemical–thermal dynamics emerging from the fact that the lithium concentrations contribute to the entropic heat generation is utilized to overcome the observability issue. Then, an estimation scheme comprised of a cascade of a sliding-mode observer and an unscented Kalman filter (UKF) is constructed that exploits the resulting structure of the coupled model. The approach gives new real-time estimation capabilities for two often-sought pieces of information about a battery cell: (1) estimation of cell-capacity and (2) tracking the capacity loss due to degradation mechanisms such as lithium plating. These capabilities are possible since the two-electrode model needs not be reduced further to a single-electrode model by adding Li conservation assumptions, which do not hold with long-term operation. Simulation studies are included for the validation of the proposed scheme. Effect of measurement noise and parametric uncertainties is also included in the simulation results to evaluate the performance of the proposed scheme.
Application of Artificial Neural Networks for Misfiring Detection in an Annular Pulsed Detonation Combustor Mockup
Authors: Wolff Sascha , Schäpel Jan-Simon , King Rudibert
Published: September 2016

An annular pulsed detonation combustor basically consists of a number of detonation tubes which are firing in a predetermined sequence into a common downstream annular plenum. Fluctuating initial conditions and fluctuating environmental parameters strongly affect the detonation. Operating such a set-up without misfiring is delicate. Misfiring of individual combustion tubes will significantly lower performance or even stop the engine. Hence, an operation of such an engine requires a misfiring detection.

Here, a supervised data driven machine learning approach is used for the misfiring detection. The features used as inputs for the classifier are extracted from measurements incorporating physical knowledge about the given set-up. To this end, a neural network is trained based on labeled data which is then used for classification purposes, i.e., misfiring detection. A surrogate, non-reacting experimental set-up is considered in order to develop and test these methods.
Gradient-Based Adjoint and Design of Experiment CFD Methodologies to Improve the Manufacturability of High Pressure Turbine Blades
Authors: Zamboni Giulio , Banks Gabriel , Bather Simon
Published: September 2016

The tolerance of a turbine blade aerofoil is determined by the requirements to achieve an aerodynamic performance in operation. In fact, the manufacturing tolerance applied to the profile is driven by the effects of geometrical non-conformances on the efficiency and flow capacity of the aerofoil. However, this tolerance also has an impact on the ease with which the aerofoil can be manufactured, with tighter tolerance leading to lower manufacturing conformity.

This paper details the application of an adjoint RANS solver and the according series of Design of Experiments (DoE) CFD calculations for a high pressure turbine blade to the above problem. There are two aims of this work; the first is to show that simpler linear CFD perturbation can be used to evaluate the effect of the geometric non-conformance. The second is to validate the spatial geometric correlation factor of the control points used in the manufacturing process on the performance evaluation with DoE techniques. This also verified the applicability of the adjoint CFD techniques; in fact the adjoint CFD calculation is an order of magnitude less computationally expensive than a large series of DoE RANS CFD calculations.

The results confirm that the peak suction area is the most critical control region for the effect on the efficiency and flow capacity. Moreover, the CFD investigations show that a significant level of correlation exists between the influence factors at different control points. This suggests that not only the amount of geometric deviation but also the stream surface variation of profile tolerance significantly influence the final aerodynamic performance. The results from this calculation allow the creation of a 3D sensitivity map which will be used during the manufacturing of the aerofoil to optimise the control of the spatial distribution of the geometric non-conformance and to directly assess the expected performance effect during the manufacturing quality inspection.

The methodology detailed in this paper shows how the CFD adjoint methods could be used for improved manufacturability of turbine blades ensuring that the critical characteristic features are controlled on the surface, relaxing the profile tolerance on those surface areas where the impact on the aerodynamic performance is predicted to be lower.
Detecting Transition in Flat Plate Flow With Laser Interferometric Vibrometry (LIV)
Authors: Bader Pascal , Sanz Wolfgang , Peterleithner Johannes , Woisetschläger Jakob , Heitmeir Franz , Meile Walter , Brenn Günter
Published: September 2016

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. Relaminarization from turbulent to laminar flow may also occur. The state of the boundary layer is important since it strongly influences transport processes like skin friction and heat transfer.

It is therefore vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position of transition onset and the length of the transitional region. In order to better understand transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper the flow along a flat plate is experimentally studied to investigate laminar-to-turbulent transition.

Measurements were performed for the different free-stream velocities of 5 m/s and 10 m/s. Several measurement techniques were used in order to reliably detect the transitional zone: the Preston tube, hot wire anemometry, thermography and Laser Interferometric Vibrometry (LIV). The first two measurement techniques are extensively in use at the institute ITTM and by other research groups. They are therefore used as a reference for validating the LIV measurement results.

An advantage of the LIV technique is that it does not need any seeding of the fluid and that it is non-intrusive. Therefore this measurement technique does not influence the flow, and it can be used in narrow flow passages since there is no blockage, in contrast to probe-based measurement techniques.

Further to the measurements, computational simulations were performed with the Fluent® and CFX® codes from ANSYS®, as well as with the in-house code Linars. The Menter SST k-ω turbulence model with the γ-ReΘ transition model was used in order to test its capability to predict the laminar-to-turbulent transition.
A 3D Approximate Riemann Solver for the Euler Equations Using Flux Splitting Schemes With a Robust Multigrid
Authors: Im Hong-Sik
Published: September 2016

An explicit 3D approximate Riemann solver for the Euler equations is proposed using the famous shock capturing schemes with a simple cell vertex based multigrid method. A multistage Runge-Kutta time marching scheme with a local time stepping is used to achieve fast convergence to steady state. A Roe’s flux difference splitting, AUSM+, Van Leer and Steger-Warming’s flux vector splitting are implemented as base Riemann solvers with a third order flux reconstruction. It is shown that the proposed Riemann solvers accurately capture the shocks as well as reduce CPU time significantly with new multigrid.
Mixing Enhancement With Rotating Ramps in a Scramjet Engine
Authors: Jin Liang , Huang Wei , Liu Zhen , Liu Jun
Published: September 2016

A concept of mixing enhancement forced by rotating ramps has been presented, which based on the design of stationary ramps and Rim-Rotor Rotary Ramjet Engine. The commercial software Fluent has been conducted to study the nonreacting flowfields in a transverse hydrogen fuel injection channel. The results indicate a slowly increased mixing efficiency when the ramps speed increase. As the ramps rotate at a speed of 6000rpm, the mixing efficency is almost the same as the stationary ramps case. As the ramps rotate at a speed of 54295rpm, a 10%∼20% higher mixing efficiency is obtained.
Numerical Simulations on the Leading Edge Film Cooling With Counter-Inclined Film-Hole Row
Authors: Zhao Dan , Liu Cun-liang , Zhu Hui-ren , Zhai Ying-ni
Published: September 2016

Numerical simulations have been performed on the film cooling characteristics of counter-inclined film-hole rows, which have advantage in manufacturing relative to the usually used parallel-inclined film-hole row structure, on a turbine vane leading edge model. Two types of counter-inclined film-hole row were studied, including collinear counter-inclined film-hole row and non-collinear counter-inclined film-hole row. The distributions of film cooling effectiveness and heat transfer coefficient were obtained for the blowing ratios of 0.5, 1.0, 1.5 and 2.0. The effect of hole pitch on the film cooling effectiveness and heat transfer coefficient was also studied. The results show that the film cooling performances of counter-inclined film-hole rows are not weakened compared to the traditional parallel-inclined film-hole row structure. Film cooling effectiveness of the non-collinear counter-inclined film-hole row is even a little better than the film cooling effectiveness of the traditional film-hole row and collinear counter-inclined film-hole row in the downstream region near the film-hole row. The film cooling effectiveness of the two counter-inclined film-hole row structures decreases with the increase of blowing ratio, while the heat transfer coefficient increases. The change of inclination structure of film-hole row has very little effect on the heat transfer coefficient in the downstream region, while the increase of hole pitch could influence the values of heat transfer coefficient as well as film cooling effectiveness in a relatively notable way.
The Investigations of the Balance Hole Area and Radial Seal Clearance’s Influences on Turbine Efficiency in the Wheel Chamber
Authors: Deng Guoliang , Sun Qi , Wang Shan , Tian Chaoyang , Wu Qi , Zhang Xiaodan , Du Xiaoqin
Published: September 2016

First of all, this paper presents the overall efficiency correlation to the balance hole diameter of the 3-stages air turbine test results. All 3 wheels have the same balance hole geometry, with total 5 holes in the wheel, and the variation of diameter is 0 mm, 16 mm, 25 mm, 30 mm, 40 mm, 50 mm, and 60 mm, respectively. The test results show that the lowest efficiency condition is the one without balance hole, and increases with the hole diameter until 25–30 mm, but decreases after it. Then, a single stage CFD model, including the first stage stator, moving blade, stator hub leakage, and wheel chamber, is built to simulate the stage efficiency trend under steady flow condition. The relative efficiency correlation of the simplified single stage CFD model matches very well with the test results. The CFD results show that, the maximum efficiency happens when there is minor gas suction from the main gas path, about 0.1%–0.2% compared with the main mass flow, but when the gas suction is above 0.2% of the main mass flow, the efficiency decreases, as less flow is passing through the moving blade to convert energy.

Finally, the radial seal clearance’s influences in the wheel chamber between the diaphragm and the wheel is checked by CFD using the same geometry pattern. Five different radial seal clearances model, including 0 mm (ideal condition), 0.6 mm, 1.2 mm, 1.8 mm and 6 mm (without radial seal) are built, under two different balance hole diameter (14 mm and 25 mm), and three different hub seal clearances (0 mm, 0.6 mm and 1.2 mm) conditions. The CFD results show that the throttling effect is very small when the radial clearance is above or equal to 0.6 mm, with almost constant efficiency variation with the clearance up to 6 mm, under specified stator hub clearance and balance hole diameter. Very small deficiency (0.2%) is detected under small balance hole diameter (14 mm) and large stator hub clearance (1.2 mm) condition, as the hub leakage mass flow is much beyond the balance hole flow capability.
Preliminary Design of the ORCHID: A Facility for Studying Non-Ideal Compressible Fluid Dynamics and Testing ORC Expanders
Authors: Head Adam Joseph , De Servi Carlo , Casati Emiliano , Pini Matteo , Colonna Piero
Published: September 2016

Organic Rankine Cycle (ORC) power systems are receiving increased recognition for the conversion of thermal energy when the source potential and/or its temperature are comparatively low. Mini-ORC units in the power output range of 3–50 kWe are actively studied for applications involving heat recovery from automotive engines and the exploitation of solar energy. Efficient expanders are the enabling components of such systems, and all the related developments are at the early research stage. Notably, no experimental gasdynamic data are available in the open literature concerning the fluids and flow conditions of interest for mini-ORC expanders. Therefore, all the performance estimation and the fluid dynamic design methodologies adopted in the field rely on non-validated tools. In order to bridge this gap, a new experimental facility capable of continuous operation is being designed and built at Delft University of Technology, the Netherlands. The Organic Rankine Cycle Hybrid Integrated Device (ORCHID) is a research facility resembling a state-of-the-art high-temperature ORC system. It is flexible enough to treat different working fluids and operating conditions with the added benefit of two interchangeable Test Sections (TS’s). The first TS is a supersonic nozzle with optical access whose purpose is to perform gas dynamic experiments on dense organic flows in order to validate numerical codes. The second TS is a test-bench for mini-ORC expanders of any configuration up to a power output of 100 kWe. This paper presents the preliminary design of the ORCHID setup, discussing how the required operational flexibility was attained. The envisaged experiments of the two TS’s are also described.
Investigating the Effect of Changing the Working Fluid on the Three-Dimensional Flow Within Organic Rankine Cycle Turbines
Authors: White M. , Sayma A. I.
Published: September 2016

For small and micro scale (< 50 kWe) organic Rankine cycle (ORC) systems to be commercially viable, systems are required that can operate efficiently over a range of operating conditions. This will lead to the high volume, low cost production that is critical to improve the current economy of scale, and reduce system costs. This requirement will inevitably mean utilising the same system within a range of different applications and may also require the same turbine to operate in different systems where the working fluid may change. Under these circumstances it is therefore important to develop suitable models that can determine the off design performance of these turbines. This will help to understand how the performance of existing ORC turbines responds to such changes. This topic is also of interest when considering retrofitting existing systems with more modern working fluids, which meet current environmental regulations. Recent work by the authors has developed a turbine design model and produced a candidate radial turbine design. Furthermore a modified similitude theory has been developed and validated, which can be used to predict turbine performance following a change in working fluid. This paper extends this analysis to a wider array of working fluids, and in addition to comparing the important performance parameters such as mass flow rate and turbine efficiency, a detailed comparison of the resulting flow field, blade loading distributions and velocity triangles is also presented. Predictions made using the modified similitude theory are compared to steady and unsteady 3D RANS CFD simulations completed using the commercial solver ANSYS CFX. Real fluid properties are accounted for by generating property tables using REFPROP. By comparing these important flow features the validity of the modified similitude model can be examined to a much greater extent.
Broadband Combustion Noise Simulation of the PRECCINSTA Burner Based on Stochastic Sound Sources
Authors: Grimm Felix , Ohno Duncan , Ewert Roland , Dierke Jürgen , Noll Berthold , Aigner Manfred
Published: September 2016

Combustion noise in the laboratory scale PRECCINSTA burner is simulated with a new, robust and highly efficient approach for combustion noise prediction. The applied hybrid method FRPM-CN (Fast Random Particle Method for Combustion Noise prediction) relies on a stochastic, particle based sound source reconstruction approach. Turbulence statistics from reacting CFD-RANS simulations are used as input for the stochastic method, where turbulence is synthesized based on a first order Langevin ansatz. Sound propagation is modeled in the time domain with a modified set of linearized Euler equations and monopole sound sources are incorporated as right hand side forcing of the pressure equation at every timestep of the acoustics simulations. First, reacting steady state CFD simulations are compared to experimental data, showing very good agreement. Subsequently, the computational combustion acoustics setup is introduced, followed by comparisons of numerical with experimental pressure spectra. It is shown that FRPM-CN accurately captures absolute combustion noise levels without any artificial correction. Benchmark runs show that the computational costs of FRPM-CN are much lower than that of direct simulation approaches. The robustness and reliability of the method is demonstrated with parametric studies regarding source grid refinement, the choice of either RANS or URANS statistics and the employment of different global reaction mechanisms.
Investigation on the Reduction of Trailing Edge Shock Losses for a Highly Loaded Transonic Turbine
Authors: Zhao Wei , Luo Weiwei , Zhao Qingjun , Xu Jianzhong
Published: September 2016

A shock loss reduction method for highly loaded transonic turbine blades with convergent passages is presented. The method is illustrated with an improved blade profile that employs a negative curvature curve on its uncovered suction side. The improved profile and a conventional baseline profile are applied to two cascades with the same solidity, chord and aspect ratio respectively. The numerical simulation results for the two cascades show that a reduction of 4.58% in the total pressure loss coefficient is obtained for the improved profile at the design condition. The effects of back pressures on the performance of both cascades are also presented, and the improved blade profile shows a much better part-load performance. The paper compares the flow fields of the baseline and the improved blade profiles to understand loss reduction mechanism especially by analyzing the shock interactions downstream of the trailing edge. It is found that, for the improved profile, the reflected shock of pressure side leg of the trailing-edge shock rotates forward and the suction side leg of the trailing-edge shock rotates backward. Therefore, the two shocks delay their intersection points where they merge into a relatively strong shock, and consequently produce less shock losses than those of the baseline profile.
The Effect of a Meter-Diffuser Offset on Shaped Film Cooling Hole Adiabatic Effectiveness
Authors: Haydt Shane , Lynch Stephen , Lewis Scott
Published: September 2016

Shaped film cooling holes are used extensively in gas turbines to reduce component temperatures. These holes generally consist of a metering section through the material and a diffuser to spread coolant over the surface. These two hole features are created separately using electrical discharge machining, and occasionally an offset can occur between the meter and diffuser due to misalignment. The current study examines the potential impact of this manufacturing defect to the film cooling effectiveness for a well-characterized shaped hole known as the 7-7-7 hole. Five meter-diffuser offset directions and two offset sizes were examined, both computationally and experimentally. Adiabatic effectiveness measurements were obtained at a density ratio of 1.2 and blowing ratios ranging from 0.5 to 3. The detriment in cooling relative to the baseline 7-7-7 hole was worst when the diffuser was shifted upstream (aft meter-diffuser offset), and least when the diffuser was shifted downstream (fore meter-diffuser offset). At some blowing ratios and offset sizes, the fore meter-diffuser offset resulted in slightly higher adiabatic effectiveness than the baseline hole, due to a reduction in the high-momentum region of the coolant jet caused by a separation region created inside the hole by the fore meter-diffuser offset. Steady RANS predictions did not accurately capture the levels of adiabatic effectiveness or the trend in the offsets, but it did predict the fore offset’s improved performance.
Blade Damage in PowerGen Turbine Losses and Blade Health Monitoring
Authors: Zhou Bin
Published: September 2016

Losses of gas turbines and steam turbines in the power generation industry are often due to mechanical breakdowns associated with flow-path component damage, especially on rotating blades. Advanced condition monitoring technologies, such as Noncontact Blade Vibration Monitoring (NBVM), have been shown to effectively detect abnormal behaviors of blades during turbine operation, and thus help to mitigate the turbine loss. Following a brief review of the technology, this paper focuses on results of analyses performed using FM Global’s turbine loss data. Loss events were categorized according to different blade damage mechanisms, turbine types and damage locations; and analyzed in order to identify the realizable benefits through noncontact blade monitoring. Based on the results of the analysis, field applications of the technology for improvement of long-term turbine condition monitoring are discussed.
Experimental Study of the Interaction of Water Sprays With Swirling Premixed Natural Gas Flames
Authors: Lellek Stephan , Barfuß Christoph , Sattelmayer Thomas
Published: September 2016

Water injection is often used to control NOx emissions or to increase power output from non-premixed combustion of gaseous and liquid fuels. Since the emission level in premixed natural gas combustion is significantly lower than for non-premixed combustion, water injection for emission reduction is usually not an issue. However, the increasing share of fluctuating power output from renewables motivates research activities on the improvement of the operational flexibility of combined cycle power plants. One aspect in that context is power augmentation by injection of liquid water in premixed combustors without drawbacks regarding emissions and flame stability. For research purposes, water injection technology has therefore recently been transferred to premixed combustors burning natural gas. In order to investigate the influence of water injection on premixed combustion of natural gas, an atmospheric single burner test rig has been set up at Lehrstuhl für Thermodynamik, TU München. The test rig is equipped with a highly flexible water injection system to study the influence of water atomization behavior on flame shape, position and stabilization. Presented investigations are conducted at gas turbine like preheating temperatures (673K) and flame temperatures (1800–1950K) to ensure high technical relevance. In this paper, the interaction between water injection, atomization and macroscopic flame behavior is outlined. Favorable and non-favorable operating conditions of the water injection system are presented in order to clarify the influence of water atomization and vaporization on flame stability and the emission behavior of the test rig. Water spray quality is assessed externally with a Malvern laser diffraction spectrometer whereas spray distribution in the test rig is determined by means of Mie scattering images at reacting conditions. The flame shape is analyzed using time-averaged OH* chemiluminescence images while the efficiency of water injection at various operating points is evaluated using global emission concentration measurements. Finally, the important influence of the water injection system design on the combustor performance will be shown using combined Mie scattering and OH* chemiluminescence images.

At constant adiabatic flame temperatures, a stable flame could be established for water-to-fuel ratios of up to 2.25. While only minor changes could be detected for the heat release distribution in the combustion chamber, the water distribution changes significantly while increasing the amount of water. Finaly, changes in NOx emission concentrations can directly be related to water droplet sizes and the global water distribution in the combustion chamber.
Film Cooling Investigation of a Slot-Based Diffusion Hole
Authors: An Bai-Tao , Liu Jian-Jun , Zhou Si-Jing , Zhang Xiao-Dong , Zhang Chao
Published: September 2016

This paper presents a new configuration of discrete film hole, i.e., the slot-based diffusion hole. Retaining the similar diffusion features to a traditional diffusion hole, the slot-based diffusion hole transforms the cross section of circle for the traditional diffusion hole to a flattened rectangle with respect to the equivalent cross-sectional area. Consequently, the exit width of the new hole is effectively enlarged. To verify the film cooling effectiveness, a low speed flat plate experimental facility incorporated with Pressure Sensitive Paint (PSP) measurement technique was employed to obtain the adiabatic film cooling effectiveness. The experiments were performed with hole pitch to diameter ratio p/D=6 and density ratio DR=1.38. The blowing ratio was varied from M=0.5 to M=2.5. A fan-shaped hole and two slot-based diffusion holes were tested and compared. Three-dimensional numerical simulation was employed to analyze the flow field in detail. The experimental results showed that the area averaged effectiveness of two slot-based diffusion holes is significantly higher than that of the fan-shaped hole when the blowing ratio exceeds 1.0. The slot-based diffusion hole demonstrates the great advantage over the fan-shaped hole at hole exit and maintains this to far downstream. The numerical results showed that the ends shape of the flattened rectangular cross section has large influences on film distribution patterns and downstream vortex structures. The semi-circle and straight line ends shapes lead to a bi-peak and a single-peak effectiveness pattern, respectively. The optimal ends shape can regulate the vortex structures and improve the film cooling effectiveness further.
Design of Highly Loaded Turbine Stage for Small Gas Turbine Engine
Authors: Rajeevalochanam Prathapanayaka , Sunkara S. N. Agnimitra , Mayandi Balamurugan , Banda Bala Venkata Ganesh , Chappati Veera Sesha Kumar , Kumar Kishor
Published: September 2016

Aero-thermodynamic and mechanical design of a single stage axial turbine stage has been carried out for small gas turbine engine in Propulsion Division, CSIR-NAL. From the engine design configuration extract, it is envisaged that the single stage axial gas turbine operating close to 50500 rpm and at an elevated temperature of 1095K would meet the power requirement of mixed flow compressor of 385kW. This paper presents the aero-thermodynamic, mechanical design and analysis of a single stage highly loaded axial turbine stage with a stage loading coefficient of 1.45 and a flow coefficient of 0.67. The mean-line and detailed 3D aero-thermodynamic design is carried out using commercially available dedicated turbomachinery design codes Axial® and Axcent™ of Concepts NREC. The number of blades of the rotor and stator are 50 & 19 respectively. The turbine stage has undergone a series of design improvements. The final configuration of single stage turbine is analyzed using commercially available RANS CFD software ANSYS-CFX™ and NUMECAFINE™/Turbo flow solver. The design is carried out by aiming 88% total-to-total efficiency. Detailed 3D-RANS CFD analysis of the turbine shows that, the design requirements of turbine are achieved with enhanced efficiency of 90%. Mechanical design & analysis of the turbine stage is carried out using ANSYS-Mechanical™ software. Nimonic-90 material is selected for fabrication. Detailed non-linear steady thermal-structural analysis is carried out for both stator assembly and rotor BLISK. Burst margin of rotor disk is estimated to be around 63% at design speed.
Uncertainty Analysis and Data-Driven Model Advances for a Jet-in-Crossflow
Authors: Ling Julia , Ruiz Anthony , Lacaze Guilhem , Oefelein Joseph
Published: September 2016

For film cooling of combustor linings and turbine blades, it is critical to be able to accurately model jets-in-crossflow. Current Reynolds Averaged Navier Stokes (RANS) models often give unsatisfactory predictions in these flows, due in large part to model form error, which cannot be resolved through calibration or tuning of model coefficients. The Boussinesq hypothesis, upon which most two-equation RANS models rely, posits the existence of a non-negative scalar eddy viscosity, which gives a linear relation between the Reynolds stresses and the mean strain rate. This model is rigorously analyzed in the context of a jet-in-crossflow using the high fidelity Large Eddy Simulation data of Ruiz et al. (2015), as well as RANS k-ε results for the same flow. It is shown that the RANS models fail to accurately represent the Reynolds stress anisotropy in the injection hole, along the wall, and on the lee side of the jet. Machine learning methods are developed to provide improved predictions of the Reynolds stress anisotropy in this flow.
Robust Optimization of the HPT Blade Cooling and Aerodynamic Efficiency
Authors: Vinogradov Kirill A. , Kretinin Gennady V. , Otryahina Kseniya V. , Didenko Roman A. , Karelin Dmitry V. , Shmotin Yury N.
Published: September 2016

Constant rise of hot gas temperature is crucial for the creation of modern gas-turbines engines requiring considerable improvement of cooling configurations. A high pressure turbine blade is one of the most crucial and loaded details in gas-turbine engines. A HPT blade is affected by different operational deviations: stochastic fluctuations of inlet parameters and difference in operational parameters for manufactured engines. Combination of these factors makes the task of uncertainty quantification and robust optimization of the HPT blade relevant in modern science.

The authors make an attempt to implement robust optimization to the HPT blade of the gas-turbine engine. The two most important areas of the cooling blade (the leading edge (LE) and the blade tip) were taken into account. The operational and the aleatoric uncertainties were analyzed. These uncertainties represent the fluctuations in the operational parameters and the random-unknown conditions such as the boundary values and or geometrical variations.

Industrial HPT blade with a serpentary cooling system and film cooling at the LE was considered. Results of many engine tests were applied to construct probability density function distributions for operational uncertainties. More than 100 real gas-turbines were examined. The following operational uncertainties were reviewed: inlet hot gas pressure and temperature together with cooling air pressure. The tip gap was used as geometrical variation. Conjugate Heat Transfer computations were carried out for the temperature distribution obtained.

Geometrical variations of the LE film cooling rows and the tip gap are variables in the robust optimization process. The authors developed a special technology for full parameterization of the LE film-cooling rows only by two parameters.

A surrogate model technique (the response surface and the Monte-Carlo method) was applied for the uncertainty quantification and the robust optimization processes. The IOSO technology was employed as one of the robust optimization tools. This technology is also based on the widespread application of the response surface technique.

Robust optimal solution (the Pareto set) between cooling effectiveness of the leading edge and the blade tip and aerodynamic efficiency was obtained as the result. At chosen point from the Pareto set (angle point) we calculated necessary levels of robust criteria characterized LE and blade tip cooling effectiveness and kinetic energy losses.
Heat Transfer and Flow Characteristics of Two-Pass Parallelogram Channels With Attached and Detached Transverse Ribs
Authors: Liou Tong-Miin , Chang Shyy-Woei , Lan Yi-An , Chan Shu-Po , Liu Yu-Shuai
Published: September 2016

The full-field endwall Nusselt number (Nu) distributions and flow field are presented respectively using steady-state infrared thermography and particle image velocimetry (PIV) for the two-pass parallelogram channels with attached and detached transverse ribs. These square transverse ribs on two opposite channel endwalls are in-line arranged with rib-height to duct-height ratio of 0.1 and rib-pitch to rib-height ratio of 10. For the detached ribs, the detached distance between rib and channel endwall is 0.38 rib height. With the measurements of Fanning friction factor (f), heat transfer distributions and flow field features, the thermal performance factors (TPF) for the attached and detached rib cases are comparatively examined. A set of Nu, f and TPF results with the associated flow measurements at the test conditions of 5,000≤Re≤20,000 is selected to disclose the differential heat transfer enhancement mechanisms and heat transfer efficiencies between the attached and detached ribbed channels. Empirical correlations evaluating the endwall area-averaged Nusselt numbers (Nu) and f factors are devised to assist the relevant design activities.
A Multi-Scale Approach for Nonlinear Dynamic Response Predictions With Fretting Wear
Authors: Armand J. , Pesaresi L. , Salles L. , Schwingshackl C. W.
Published: September 2016

Accurate prediction of the vibration response of aircraft engine assemblies is of great importance when estimating both the performance and the lifetime of its individual components. In the case of underplatform dampers, for example, the motion at the frictional interfaces can lead to a highly nonlinear dynamic response and cause fretting wear at the contact. The latter will change the contact conditions of the interface and consequently impact the nonlinear dynamic response of the entire assembly. Accurate prediction of the nonlinear dynamic response over the lifetime of the assembly must include the impact of fretting wear. A multi-scale approach that incorporates wear into the nonlinear dynamic analysis is proposed, and its viability is demonstrated for an underplatform damper system. The nonlinear dynamic response is calculated with a multiharmonic balance approach, and a newly developed semi-analytical contact solver is used to obtain the contact conditions at the blade-damper interface with high accuracy and low computational cost. The calculated contact conditions are used in combination with the energy wear approach to compute the fretting wear at the contact interface. The nonlinear dynamic model of the blade-damper system is then updated with the worn profile and its dynamic response is recomputed. A significant impact of fretting wear on the nonlinear dynamic behaviour of the blade-damper system was observed, highlighting the sensitivity of the nonlinear dynamic response to changes at the contact interface. The computational speed and robustness of the adopted multi-scale approach are demonstrated.
Origins and Structure of Rotating Instability: Part 1 — Experimental and Numerical Observations in a Subsonic Axial Compressor Rotor
Authors: Wu Yanhui , Chen Zhiyang , An Guangyao , Liu Jun , Yang Guowei
Published: September 2016

Rotating instability (RI) is an obvious unsteady flow phenomenon occurring in the tip region of compressors, which is potentially linked to tip clearance flow noise, blade vibration and rotating stall/surge. The existing investigations for RI indicate the origins of RI are closely related to unsteady flow behaviors in given blade passages in the rotating reference frame, which depend on the design specifics of axial machines. However, no efforts are made to set up a quantitative link between the time scale of unsteady behavior in a given passage and the characteristic parameters of RI, let alone to define the fluid dynamic processes/events which are causally linked with the RI inception. This is the motivation for the current investigations.

In Part I, the experimental and numerical investigations are carried out to investigate tip flow unsteadiness in a subsonic axial compressor rotor. The measurement results show RI appears at operating points near the stability limit of the test rotor. It becomes more pronounced with mass flow rate decreased. The corresponding computational experiments show that flow unsteadiness in given passages also appears close to the stability limit with its initial origination confined to the tip region. The appearance of tip flow unsteadiness is accompanied by a phase lag pattern in different passages across the circumference similar to the detection of stall flutter. The well-developed Fourier-decomposed method is thus used to evaluate the mode characteristics of circumferential traveling waves. It turns out the circumferential traveling wave rotating against the rotor rotation direction with the mode order of 4 is prominent in the flow field with its frequency in the absolute frame equivalent to the mean frequency value of RI detected in measurements. The further analyses of the simulated flow fields indicate that tip flow unsteadiness in a given passage attributes to the periodic oscillation of “secondary clearance flow”, which induces a blockage tranfer across the passage. The mode order and propagation speed of RI depend on the blockage transfer induced by the periodic oscillation of “secondary clearance flow” between two neighbouring passages along the whole circumference. The investigation results presented in the paper implies that one of early ideas to interpret the origin of RI might be altered to such an extent that it contains any unsteady behavior associated with tip leakage flow, rather than limited to “periodical oscillation of tip leakage vortex”.