bluuebunny/crossref_metadata_2025 huggingface dataset:
Superalloy Cooling System for the Composite Rim of an Inside-Out Ceramic Turbine
Authors: Courtois N. , Ebacher F. , Dubois P. K. , Kochrad N. , Landry C. , Charette M. , Landry-Blais A. , Fréchette L. G. , Plante J.-S. , Picard M. , Picard B.
Published: August 2017

The use of ceramics in gas turbines potentially allows for very high cycle efficiency and power density, by increasing operating temperatures. This is especially relevant for sub-megawatt gas turbines, where the integration of complex blade cooling greatly affects machine capital cost. However, ceramics are brittle and prone to fragile, catastrophic failure, making their current use limited to static and low-stress parts. Using the inside-out ceramic turbine (ICT) configuration solves this issue by converting the centrifugal blade loading to compressive stress, by using an external high-strength carbon-polymer composite rim. This paper presents a superalloy cooling system designed to protect the composite rim and allow it to withstand operating temperatures up to 1600 K. The cooling system was designed using one-dimensional (1D) models, developed to predict flow conditions as well as the temperatures of its critical components. These models were subsequently supported with computational fluid dynamics and used to conduct a power scalability study on a single stage ICT. Results suggest that the ICT configuration should achieve a turbine inlet temperature (TIT) of 1600 K with a composite rim cooling-to-main mass flow rate ratio under 5.2% for power levels above 350 kW. A proof of concept was performed by experimental validation of a small-scale 15 kW prototype, using a commercially available bismaleimide-carbon (BMI-carbon) composite rim and Inconel® 718 nickel-based alloy. The combination of numerical and experimental results show that the ICT can operate at a TIT of 1100 K without damage to the composite rim.
Assessment of the Severity of Unsteady Mach Number Effects in a 3-Stage Transonic Compressor
Authors: Dent Anthony , Xu Liping , Wells Roger
Published: August 2017

In this paper results from steady and unsteady CFD simulations of an industrial transonic compressor are compared, in order to gain a better understanding of the cause of the differences in the predicted efficiencies between the steady and unsteady simulations. Initially the first stage is simulated as an isolated compressor stage with inlet guide vanes in order to analyse the effect of individual blade rows on the stage performance. It is found that the rotor efficiency is lower for steady simulations than for unsteady simulations due to stronger shock waves. The stator efficiency is greater in the steady simulations due to not being able to model the interaction of the rotor wakes with the stator blade leading edge and boundary layers. Greater variation between steady and unsteady predictions is found at higher operating speeds. In the 3-stage unsteady simulations, the front stage efficiency characteristic is the same as the efficiency calculated from the isolated unsteady simulations. This shows that the unsteady pressure potential propagating from the downstream stages has no significant effect on the front stage efficiency meaning that the designer does not need to give great consideration to the downstream blade rows when predicting the characteristics of the front stage.
Influence of the Steady Deformation on Numerical Flutter Prediction for Highly Loaded and Flexible Fan Blades
Authors: Schuff Matthias , Lengyel-Kampmann Timea , Forsthofer Nicolai
Published: August 2017

Deflections at off-design conditions can change the aeroelastic behavior of turbomachinery blades significantly. Therefore, steady-state deformations at each operating point cannot be neglected and need to be captured by CFD-CSM coupling.

The implementation of an automated toolchain for the generation of a compressor map is presented. It includes steady FSC and is preceded by aflutter analysis. The CFD mesh is adapted to steady surface deflections via a mesh deformation using radial basis functions interpolation. Mode shape vibrations are computed at each operating point. Aerodynamic damping for each mode and IBPA is than assessed by unsteady RANS computations with time-linearization around the steady flow field.

A detailed compressor map of a highly flexible CFRP fan, that was optimized within a multidisciplinary toolchain, is generated based on the geometry for design conditions. Elastic deformations affect a shift of the speedlines especially in near-choked conditions. At the surge line, some cases did not reach a steady-state deformation, oscillating between two deflections and indicating possible stall flutter.

The impact of the steady deformation on predicting flutter boundaries for very elastic blades is pointed out by the comparison to a rigid setup. Significant differences are identified in the region of near-surged and stalled conditions and are due to large deformations, especially torsional deflections. The results of the underlying work of this paper will assist in identifying critical designs during optimization runs more quickly.
Simulation of CHP System Based on Micro Gas Turbine With Inverted Brayton Cycle
Authors: Abrosimov Kirill Alexandrovich , Galkin Dmitrii Igorevich , Tumashev Ramil Zarifovich , Ustinov Alexander Alexandrovich
Published: August 2017

In the present work mathematical modeling of a CHP system based on Micro Gas Turbine (MGT) with Inverted Brayton Cycle (IBC) (also known as subatmospheric) is provided. Nominal electric power of the facility is 10 kW. Engineering calculation based modeling is conducted to determine optimal parameters of each component, electrical and total efficiency at full load. Further dynamic modeling is provided for the components with determined optimal parameters. With chosen optimal parameters of the scheme components and coolant temperature the dynamic (time-dependent) modeling of disturbance from the nominal state with no control, ramp down and ramp up of power load (a) and heat load (b) with the activated control system was provided. An iteration based approach of MGT modeling is suggested. The difficulties in the system control under reduction of heat consumption are revealed and challenged.

The final objectives of the research are comparison of the IBC with the conventional Brayton cycle for MGT application from the electric efficiency, dynamic behavior and controllability points of view, creation of the control system for such a facility.
On the Choice of Suitable Parameters for the Assessment of Industrial Fans Performance and Efficiency
Authors: Masi Massimo , Fontana Federico , Lazzaretto Andrea
Published: August 2017

More than half a century has been spent by technicians involved in fans testing to suggest and fix best practice procedures including also the definitions of several performance and efficiency parameters (e.g., ISO, AMCA, ASHRAE Standards...). However, the huge amount of energy used by ventilation systems and the recent introduction of the stringent European Community regulations on Energy Related Products, suggests to spend additional time on the ancient question about which and how many should be the parameters best suited to classify the performance of fans and their capability to properly use the energy input. This also because there are some attempts to fix the fan total-to-static pressure rise and the related total-to-static efficiency as the only two parameters required to assess the fan quality.

Starting from basic thermodynamic principles, this paper tries to shed light on the parameters that are best suited to assess fan performance and efficiency.

The general layout of a ventilation system is discussed to clearly show which and how many are the parameters required for the optimal matching between fan and system. Finally, some comments on practical advantages and drawbacks in the operation of the fan at the total-to-static best efficiency point are presented as well.
Scaling Heat-Transfer Coefficients Measured Under Laboratory Conditions to Engine Conditions
Authors: Shih T. I.-P. , Lee C.-S. , Bryden K. M.
Published: August 2017

Almost all measurements of the heat-transfer coefficient (HTC) or Nusselt number (Nu) in gas-turbine cooling passages with heat-transfer enhancement features such as pin fins and ribs have been made under conditions, where the wall-to-bulk temperature, Tw/Tb, is near unity. Since Tw/Tb in gas-turbine cooling passages can be as high as 2.2 and vary appreciably along the passage, this study examines if it is necessary to match the rate of change in Tw/Tb when measuring Nu, whether Nu measured at Tw/Tb near unity needs to be scaled before used in design and analysis of turbine cooling, and could that scaling for ducts with heat-transfer enhancement features be obtained from scaling factors for smooth ducts because those scaling factors exist in the literature. In this study, a review of the data in the literature shows that it is unnecessary to match the rate of change in Tw/Tb for smooth ducts at least for the rates that occur in gas turbines. For ducts with heat-transfer enhancement features, it is still an open question. This study also shows Nu measured at Tw/Tb near unity needs to be scale to the correct Tw/Tb before it can be used for engine conditions. By using steady RANS analysis of the flow and heat transfer in a cooling channel with a staggered array of pin fins, the usefulness of the scaling factor, (Tw/Tb)r, from the literature for smooth ducts was examined. Nuengine, computed under engine conditions, was compared with those computed under laboratory conditions, Nulab, and scaled by (Tw/Tb)r; i.e., Nulab,scaled = Nulab (Tw/Tb)r. Results obtained show the error in Nulab,scaled relative to Nuengine can be as high as 36.6% if r = −0.7 and Tw/Tb = 1.573 in the “fully” developed region. Thus, (Tw/Tb)r based on smooth duct should not be used as a scaling factor for Nu in cooling passages with heat-transfer enhancement features. To address this inadequacy, a method is proposed for generating scaling factors, and a scaling factor was developed to scale the heat transfer from laboratory to engine conditions for a channel with pin fins.
Effect of Multicomponent Mixtures on Cycles With Supercritical Carbon Dioxide
Authors: Vesely Ladislav , Dostal Vaclav
Published: August 2017

With the increasing interest in solar and geothermal power plants as well as waste heat recovery systems from many technologies, the whole world is more focused on gas power cycles. Especially, the supercritical carbon dioxide (S-CO2) cycles are very interesting for these applications. This is due to many advantages of the S-CO2 cycles over the other cycles such as a steam-water cycle or helium cycle. On the other hand, S-CO2 cycles have also disadvantages. One of the disadvantages is presence of impurities in the cycles. The big question is the effect of these impurities in the CO2, which can occur as impurities or can be suitably added to the pure CO2. From the previous research, it is obvious that binary mixtures affect the cycle as they influence cycle component design and thus the overall efficiency of the power cycle. The biggest effect of mixtures is on the heat exchangers and compressor, which operate close to the critical point. The positive effect of the binary mixtures is observed in the recuperative heat exchanger. On the other hand, negative effects occurs in the cooler. Therefore, the Czech Technical University in Prague (CTU) conducted research on supercritical carbon dioxide cycles, which is focused on the effect of the gaseous admixtures in S-CO2 on the different cycle components. The main goal of this paper is to describe the effect of gaseous admixtures on the efficiency of the cycles and their effect on each component. The first part of the study is focused on the calculation of the basic cycles for binary mixtures and description of the effect on the compressor and the cycle efficiency. The second part of the study is focused on the calculation of the basic cycles for multicomponent mixtures. In this part, the effect of the mixtures for different compositions and amounts of the individual mixture components will be presented. The calculations are performed for pure CO2 and then for selected multicomponent mixtures. A basic multicomponent mixture includes mixtures from technology of carbon capture and storage. Other multicomponent mixtures are combinations of previously investigated gaseous admixtures such as He, CO, O2, N2, H2, CH4 and H2S. The last part of the study is focused on the optimization of individual basic cycles for different amount of admixtures in CO2. The result of this study defines the optimum composition of multicomponent mixtures and describes their effect on the cycle efficiency for the particular utilization of S-CO2 cycle.
Development of Highly Durable Thermal Barrier Coating by Suppression of Thermally Grown Oxide
Authors: Negami Masahiro , Hibino Shinya , Kawano Akihito , Nomura Yoshimichi , Tanaka Ryozo , Igashira Kenichiroh
Published: August 2017

Durability of thermal barrier coating (TBC) systems is important because of recent rising of TIT (Turbine inlet temperature) for improved efficiency of industrial gas turbine engines. However, high-temperature environment accelerates the degradation of the TBC as well as causes spalling of the top coat.

Spalling of the top coat may be attributed to several factors, but evidently the growth of thermally grown oxide (TGO) should be considered as an important factor. One method for reducing the growth rate of TGO is to provide a dense α-Al2O3 layer at the boundary of the bond coat and top coat. This α-Al2O3 layer will protect the bond coat against oxidation and prevent outward diffusion of aluminum of the bond coat which causes further oxidation.

In this study, we focused on thermal pre-oxidation of the bond coat as a means for forming an α-Al2O3 barrier layer that would be effective at reducing the growth rate of TGO and we studied the suitable pre-oxidation conditions. In the primary stage we analyzed the oxidation behavior of the bond coat surface during pre-oxidation heat treatment by means of in-situ synchrotron X-ray diffraction (XRD) analysis. As a result, we learned that during oxidation in ambient air environment, in the initial stage of oxidation metastable alumina is produced in addition to α-Al2O3, but if the thermal treatment is conducted under some specific low oxygen partial pressure condition, unlike in the ambient air environment, only α-Al2O3 is formed with suppressing formation of metastable alumina.

We also conducted TEM and XRD analysis of oxide scale formed after pre-oxidation heat treatment of the bond coat. As a result, we learned that if pre-oxidation is performed under specific oxygen partial pressure conditions, a monolithic α-Al2O3 layer is formed on the bond coat.

We performed a durability evaluation test of TBC with the monolithic α-Al2O3 layer formed by pre-oxidation of the bond coat. An isothermal oxidation test confirmed that the growth of TGO in the TBC that had undergone pre-oxidation was suppressed more thoroughly than that in the TBC that had not undergone pre-oxidation. Cyclic thermal shock test by hydrogen burner rig was also carried out. TBC with the monolithic α-Al2O3 layer has resistance to >2000 cycle thermal shock at a load equivalent to that of actual gas turbine.
Experimental Investigation of the Grouped Blade Vibration for Steam Turbine by Non-Contact Sensors
Authors: Nakajima Tomomi , Segawa Kiyoshi , Kitahara Hiromichi , Seo Akimitsu , Yamashita Yutaka , Kudo Takeshi
Published: August 2017

All turbine blades have mistuned structures caused by manufacturing variations within the manufacturing tolerance, such as the geometrical deviations and variance of material properties. The mistuning effect has a known tendency to increase the dynamic stress, but it is also known to be difficult to predict the maximum vibration response before the operation. This paper studies the blade vibration of grouped blades in a low-pressure steam turbine. The study objectives are to characterize the vibration behavior of the grouped blade structure and to evaluate the maximum response of all blades in a stage by experiments.

An experimental investigation is carried out in a vacuum chamber, and blades are excited by an air jet during start-up and shut-down. The circumferential blade amplitude distribution is measured by non-contact sensors and strain gauges. The circumferential blade amplitude distribution is found to differ depending on vibration modes and nodal diameters, but the relative tendency is almost the same for all types of operation at each mode and all nodal diameters.

Therefore, the median of all experimental results obtained with the non-contact sensors are used in a comparison with calculation results and two theoretical curves obtained using equations from the literature. In comparing the measurement results and the calculation results, the circumferential blade amplitude distribution is not the same with all modes and nodal diameters. However, the maximum amplitude magnification is about 1.5–1.8, and all measurement results are lower than the results for the two theoretical equations. This means the maximum response compared to the tuned blade can be evaluated on the safe side by the two theoretical equations.
Performance and Cost Reduction of Permanent Magnet Biased Magnetic Bearings
Authors: Nichols B. R. , Allaire P. E. , Dimond T. , Cao J. , Dousti S.
Published: August 2017

Active magnetic bearings (AMBs) have the well-documented advantage of reduced operational power losses when compared to conventional fluid-film bearings; however, they have yet to be widely adopted in industry due to the high initial costs of manufacturing and supporting power electronics. As AMBs look to become more cost competitive in more widely based applications, permanent magnet biased designs seek to reduce both the operating electrical power losses and the power electronic hardware costs while maintaining normal load and maximum load capacities. In these new designs, permanent magnet components are used to provide the necessary bias magnetic flux in the bearing usually provided by an electrical bias current in traditional all electromagnetic AMB designs. By eliminating electrical bias currents, operating electrical power losses can be significantly reduced while allowing for smaller, cheaper electronic components. This paper provides a comparison of the performance of permanent magnet biased thrust and radial bearing designs with conventional, all electromagnetic bearing designs. The thrust bearings are designed with nominal and maximum load capacities of 1,333 N and 4,000 N, while the radial bearings are designed with nominal and maximum load capacities of 1,000 N and 3,000 N. The shaft diameter is considered to be 70 mm for all bearings. Finite element modeling is used to calculate load capacities and operating electrical power requirements. Power requirements for a number of loads ranging from nominal to maximum capacity are presented for the permanent magnet biased and all electromagnetic bearing designs. A significant reduction in electrical power requirements under maximum load conditions is shown in the permanent magnet biased designs. This reduction is further magnified under nominal load conditions. Additionally, the number of pole wire turns and maximum wire currents are adjusted to realize even greater electrical power losses. The required bias magnetic flux can be generated with reduced wire currents by increasing the number of wire turns. While reducing wire currents also reduces electrical power requirements, the increase in wire turns increases the circuit induction. This increase in induction decreases the bearing slew rate and, in turn, the bandwidth. This study looks at a number of wire turns and current combinations. Tradeoffs between reduced electrical power losses and bearing bandwidth are presented and discussed. The permanent magnet biased AMB designs are shown to significantly reduce electrical power losses having the potential to improve overall machine efficiency. Implications of adopting this technology to both operating and manufacturing costs are discussed. The use of permanent magnets in AMBs is shown to make the costs of these systems more competitive with oil lubricated bearings when compared to conventional AMB designs.
Investigations of Single Jet Impinging on Plates With Circular Dimples
Authors: Guo Zhiqiang , Zheng Mei , Liu Yinze , Dong Wei
Published: August 2017

In this paper, experimental and numerical investigations are both conducted to study the effect of circular dimples on the heat transfer performance of jets impingement. The circular dimples, set as one kind of surface structures on flat plate, have the same diameter of 3 mm but with different depths: 1.2 mm, 0.9 mm and 0.6 mm. Furthermore, in order to understand the mechanism of impingement heat transfer with circular dimples deeply, three different jet locations are studied in this paper. For the experimental investigations, the infrared thermography is applied to gain the temperature distributions on the flat plate. A comparison is made between the numerical results and experimental data, which indicates that they are in good agreement. The numerical results show that the dimples on the plates have significant effects on the impingement heat transfer. The overall averaged and local heat transfer coefficient in a single jet impingement on the smooth and dimpled plates are obtained and compared, as well as the flow structure. The effect of the dimples on the heat transfer performance of the target plates is different for different locations of dimples. Velocity distributions and streamlines near the target plates are also shown to explain the heat transfer characteristics. From the investigations, for the dimpled plates with different depths, the deeper dimples have the better averaged heat transfer on the target plates. The dimpled surface enhances the heat transfer performance obviously with H/D of 1.5. However, with the distance between the impinging hole and the target plate increasing, the transition location of the impact zone and the wall jet zone advances and the enhancement effect decreases. Moreover, further downstream region on the dimpled plates shows lower heat transfer enhancement effect and the effect becomes approximately invisible after X/D is larger than 3. The fluid in the dimples with different depths has the same streamline. The heat transfer enhancement at the downstream of dimples is better than the upstream.
Fuel Utilization Effects on System Efficiency and Solid Oxide Fuel Cell Performance in Gas Turbine Hybrid Systems
Authors: Harun Nor Farida , Shadle Lawrence , Oryshchyn Danylo , Tucker David
Published: August 2017

The simulation work presented herein characterizes the performance of a recuperated gas turbine (GT) hybrid systems in response to different levels of fuel utilization (Uf) by the SOFC. The SOFC performance was compared with and without anode recycle (AR), operating at 90% total stack Uf (Uf.stack). A study at 65% Uf was also considered as a reference case for the hybrid power system without anode recycle, i.e. using single-pass cell fuel utilization (Uf.cell). All three cases in this paper were evaluated at design points for a 550 MW hybrid system using coal-derived syngas feed with zero methane.

A previously developed one-dimensional (1D) fuel cell model was used to simulate the distributed profile of thermal and electrochemical properties along the fuel cell length. Fuel cell total current density, average solid temperature, and cathode inlet temperature were maintained identical at each fuel utilization to avoid confounding the results with the impacts of SOFC degradation.

The maximum system efficiency of 71.1% was achieved by SOFC/GT non-recycle systems at 90% Uf.cell (with 90% Uf.stack). The case at 65% Uf.cell (with 65% Uf.stack) demonstrated 70.7% total efficiency, only 0.4% point lower than at 90% Uf.cell. However, integrating anode recycle to the system significantly reduced the maximum total efficiency to 55.5%. Although the distributed SOFC performance across the cell length for 65% Uf.cell with AR at 90% Uf.stack was similar to the 65% Uf.cell (with 65% Uf.stack), recycling anode off-gas resulted in lower fuel cell Nernst potential that caused further drop in both stack and total system efficiency.
Design of Turbine System for Positive Mud-Pulse Telemetry
Authors: Amini Andrew , Peng Xiaobo
Published: August 2017

This paper presents the design of a turbine system that powers an alternator in a Positive Mud Pulse Telemetry (P-MPT) system, a Measurement While Drilling tool (MWD) used in the petroleum industry. With rig rates exceeding $1 million per day and wells that are drilled at depths of over 30,000 ft (9144 m), operators need to have an MWD tool that can provide continuous power while drilling without interruption. With our design of the turbine component for the P-MPT system, it allows the signals of directional drilling information to be continuously transmitted while concurrently drilling.

This paper presents the turbine system for a P-MPT system with the testing and analysis for operational conditions. The turbine system consists of a stationary vein positioned 0.25 inches (0.635 centimeters) apart from a rotating vein that is connected to the shaft-alternator system. The turbine system was manufactured with 3D printing. An experimental wind tunnel was built to simulate a downhole drilling environment by applying density scaling techniques to model flow in drilling fluid. The testing results of the turbine system are presented and discussed, including differential pressure, no-load rotation speed (RPM), stall torque, and power. CFD analyses were performed. The wind tunnel experimental data were validated by the CFD analyses. The results show that the turbine system design is functional for the P-MPT system.
A Multi-Scale Data Fusion Method for Damage Detection of Rod Fastening Rotor in Modal Strain Energy
Authors: Guo Tian , Xu Zili
Published: August 2017

A new methodology is proposed for damage detection of rod fastening rotor in gas turbine. Rod fastening rotor is a vibration sensitive structure that exhibit complex and multi-modal vibration, it can show some characteristics of vibration when suffered local damage. Due to this fact, the vibration-based method could face a challenge when used for damage detection in these structures. The proposed methodology applies multi-scale space theory and data fusion approach to detect the damage from changes in modal strain energy (MSE). The multi-scale space theory is utilized to cope with the measurement noise, which is inevitable in the process of actual measurement. Based on the multi-scale space data, the proposed methodology finally uses Dempster-Shafer’s evidence theory to detect and locate single and multiple damage. The effectiveness of the methodology is analytically verified using two rod fastening rotor with various types of damage scenarios. The analytical results demonstrate that the proposed methodology has superior noise tolerant ability as well as damage detectability, with knowledge of neither the material properties nor boundary conditions. The proposed methodology can make a contribution to ensure safety and performance of gas turbines which play an important role in the power systems.
Numerical Investigation Into the Mechanism of Tip Flow Unsteadiness in a Transonic Compressor
Authors: An Guangyao , Wu Yanhui , Lang Jinhua , Chen Zhiyang , Wang Bo , Yang Guowei
Published: August 2017

It is well known that tip flow unsteadiness has profound effects on both performance and stability of axial compressors. A number of numerical simulations have been performed in transonic compressors to uncover the nature of tip flow unsteadiness. From this research, tip flow unsteadiness can be attributed to many factors, such as the movement of the primary and secondary leakage flow, the interaction between shock and vortex, and the tip leakage vortex breakdown. However, no final conclusion has yet been reached on this matter. The current investigation is carried out to explore the origin of tip flow unsteadiness from the perspective of the evolution and development of tip leakage vortex breakdown.

In this paper, unsteady RANS simulations have been performed to investigate the fluid dynamic processes in a tip-critical transonic compressor, NASA Rotor 35. A vortex core visualization method based on an eigenvector method is introduced as an important tool to identify the vortex arising from tip leakage flow. As the flow rate varies, three critical operating points with distinctive features of flow unsteadiness are observed.

At the first critical operating point, bubble-type breakdown occurs, and gives rise to a weak unsteadiness with high frequency in the rotor passage due to the oscillation of the recirculation region induced by the tip leakage vortex breakdown.

At the second critical operating point, the vortex breakdown has transformed from bubble-type to spiral-type, which leads to the frequency of the pressure oscillation reduced almost by half and the amplitude increased significantly.

At the third critical operating point, a new vortex that is perpendicular to the pressure surface comes into being in the tip region, which leads to a prominent pressure oscillation of the tip flow and another jump in amplitude.

As a result, the evolution and development of tip leakage vortex breakdown are closely related to the tip flow unsteadiness of the investigated rotor.
Prediction of the Turbine Tip Convective Heat Flux Using Discrete Green Functions
Authors: Andreoli Valeria , G. Cuadrado David , Paniagua Guillermo
Published: August 2017

The complex heat and mass transfer across the turbine tip gap requires a detailed analysis which cannot be expressed using the classical Newton heat convection approach. In this portion of the turbine, characterized by tight moving clearances, pressure gradients are counterbalanced by viscous effects. Hence, non-dimensional analysis, based on the boundary layer, is inadequate and therefore the use of an adiabatic wall temperature is questionable. In this paper, we propose an alternative approach to predict the convective heat transfer problem across the turbine rotor tip using Discrete Green Functions.

The linearity of the energy equation can be applied with a superposition technique to measure the data extracted from flow simulations to determine the Green’s function distribution. The Discrete Green Function is a matrix of coefficients that relate the increment of temperature observed in a surface with the heat flux integrated on the same surface. These coefficients are independent on the inlet temperature of the flow and are associated to the geometry. The controlled surface is discretized into cells and each cell is associated to a vector of coefficients. The Discrete Green Function coefficients are calculated using the temperature response of the cell to a heat flux pulse imposed at different locations.

The methodology was previously applied to a backward facing step to prove its validity. Several simulations were performed applying a representative pulse of heat flux in different locations in the bottom wall of the backward facing step. From these simulations, the increment of temperature in each node of the geometry was retrieved and the Discrete Green Function coefficients associated to the bottom wall were calculated. A numerical validation was performed imposing a random pattern of heat flux and predicting the increment of temperature on the bottom wall under different inlet flow conditions. The final aim of this paper is to demonstrate the method in the rotor turbine tip.

A turbine stage at engine-like conditions was assessed using a CFD software. The heat flux pulses were applied at different locations in the rotor tip geometry, and the increment of temperature in this zone was evaluated for different clearances, with a consequent variation of the Discrete Green Function coefficients. A validation of the rotor tip heat flux was accomplished by imposing different heat flux distributions in the studied region. Ultimately, a detailed uncertainty analysis of the methodology was included based in the magnitude of the heat flux pulses used in the Discrete Green Function coefficients calculation and the uncertainty in the experimental measurements of the wall temperature.
Effect of Missing Fin on Endwall Heat Transfer in a Rotating Cooling Channel
Authors: Wang Chen-Chih , Huang Szu-Chi , Liu Yao-Hsien
Published: August 2017

This paper experimentally investigated the endwall heat transfer distribution in a rotating rectangular cooling channel (Aspect ratio = 4:1) using a newly developed steady-state liquid crystal thermography. Three Reynolds numbers (5000, 10000 and 20000) were tested, and the highest rotation number was 0.65. The buoyancy parameter ranged from 0 to 1.0 at a fixed density ratio of 0.1. Effect of missing fin (one fin missing) on heat transfer in a staggered pin-fin array was studied. For the stationary case, absence of the fin contributed to an undisturbed wake region from the adjacent upstream fins. Both leading and trailing surfaces produced the asymmetric heat transfer distribution along the spanwise direction because of the channel orientation (150 degrees) and rotation. At the highest rotation number, a highly irregular Nusselt number contour was observed on the missing fin region. This was mainly attributed to the intensified rotation induced secondary flow from the enlarged fin spacing, and the heat transfer enhancement of the missing fin case was 20% higher than the full fin case on the trailing surface.
Effect of Density Ratio on Multi-Row Film Cooling Performance
Authors: Voet Michael T. , Fernandes Craig P. , Little Zachary , Fernandez Erik , Kapat Jay
Published: August 2017

This study is an investigation into the effects of density ratio on the jet structure of different film cooling configurations. A simple-shaped cylindrical hole is tested at a tight spacing, which has a lateral and streamwise pitch-to-hole-diameter ratio of 7.5. Each of the holes are 3.8mm in diameter, and have a hole length-to-diameter ratio of 11.2. The holes are inclined at 20°. The cylindrical hole shapes were machined from an aluminum plate.

Two different density ratios of nominally 1 and 1.5, are achieved by alternating the coolant gas between air and CO2 respectively, while maintaining a constant freestream velocity of 36.2 m/s. In order to compare cases between different densities, various ratios are independently matched for both density ratios. Blowing ratios comparisons made at 0.3 and 0.5, accompanied by comparisons of momentum flux ratio and velocity ratio at 0.1 and 0.3, respectively.

Particle image velocimetry (PIV) is utilized to measure the flow field of the centerline planes of the film cooling arrays over the two density ratios. This data is then used to investigate flow interactions as coolant leaves the film cooling hole, and structure of the jet as it enters and mixes with the freestream.

When comparing density ratio effects at low blowing and momentum flux ratios, increased turbulence intensities are seen closer to the surface for CO2 injection. This suggests that the overall performance of the film decreases with increasing density ratio at these low mass flux and momentum flux cases. However, when increasing blowing ratio, the higher density injection is seen to have lower levels of turbulence in the near wall region, when compared to that of the lower density fluid. This suggests that as blowing ratio increases, the higher density fluid out performs the lower density fluid. When a low constant velocity ratio is observed, the higher density fluid is seen to have decreased levels of turbulence, again suggesting that the higher density fluid out performs the low density fluid.
Morphological Changes in γ’ Phase by Creep, Aging and Aging After Creep for Polycrystalline Nickel-Based Superalloy
Authors: Shigeyama Haruhisa , Okada Mitsutoshi , Takahashi Toshihiko , Yamada Susumu , Sakai Takayuki , Fujioka Terutaka
Published: August 2017

This study investigates the relationship between the amount of creep pre-strain and morphological changes in γ’ phase during thermal aging in conventionally cast nickel-based superalloy GTD-111.

In the interrupted creep sample with creep strain of 0.4%, rafting of the γ’ phase was not observed, but it was caused by additional thermal aging. This indicated that the rafting of the γ’ phase during thermal aging was affected by the amount of creep pre-strain. Furthermore, in the samples prepared near an in-service blade surface, rafting of the γ’ phase was not observed, but it was caused by thermal aging. This suggested that a comparatively large amount of creep strain accumulated near the blade surface during service. This result qualitatively corresponded to the creep strain distribution of the blade portion obtained by conjugate heat transfer analysis and finite element analysis. Thus, it clarified that the small amounts of creep strain can be evaluated by aging the samples taken from in-service blades in the gas turbine, which can lead to the creep life assessment.
Comparison of Stall Characteristics of Multi-Stage and Single-Stage Transonic Axial Compressors
Authors: Kang Young Seok , Park Tae Choon , Lim Byeung Jun , Lim Hyung Soo
Published: August 2017

This study experimentally investigated compressor instability characteristics of two transonic axial compressors. From the stall precursors when their operating points are approaching the stall line, stall initiation and its development and its transition to compressor surge were measured with high frequency pressure transducers, step by step.

First part of this paper describes three-stage transonic axial compressor instability characteristics. The compressor has been designed to have positive incidence angle in order from third stage to first stage as compressor outlet throttle valve closes at the design speed. Then periodic modal signal appeared from the third stage before it spread toward the first stage as a precursor of the compressor stall. However, the actual compressor stall took place from the first stage and developed toward the third stage. Interestingly, the stall cell spread toward downstream by spiral direction, which means stall cell moves with axial and circumferential velocity components. When the stall cell reached the collector through the third stage, sudden strong one-dimensional fluctuation, system surge, appeared. Then operating point revolved along the hysteresis loop on the compressor map repeatedly before anti-surge valve opened.

Second part of this paper describes a single stage transonic compressor instability characteristics. Different from the three-stage compressor, spike type stall precursor was detected just ahead of rotating stall cell appearance. Before spike initiation there was no warning signal of compressor stall. When the spike was fully developed to the rotating stall, the operating points deviated from the operating line and settled at deteriorated operating points until the anti-surge valve opened. Also a weak compressor system Helmholtz frequency was detected regardless of the rotating speed.

To identify the overall compressor instability behavior and difference between two axial compressors, Greizter’s B parameter was found to be very useful. B parameter of the three stage compressor was about 0.83, it means classic surge could occur at the final stage of instability. On the other hand, B parameter of the single stage compressor was 0.62. According to this B parameter, the single stage compressor stall would no longer develop to compressor surge and it well agrees with experimental results.
Numerical and Experimental Investigations of the Siemens SGT-800 Burner Fitted to a Water Rig
Authors: Moëll Daniel , Lörstad Daniel , Lindholm Annika , Christensen David , Bai Xue-Song
Published: August 2017

DLE (Dry Low Emission) technology is widely used in land based gas turbines due to the increasing demands on low NOx levels. One of the key aspects in DLE combustion is achieving a good fuel and air mixing where the desired flame temperature is achieved without too high levels of combustion instabilities. To experimentally study fuel and air mixing it is convenient to use water along with a tracer instead of air and fuel. In this study fuel and air mixing and flow field inside an industrial gas turbine burner fitted to a water rig has been studied experimentally and numerically. The Reynolds number is approximately 75000 and the amount of fuel tracer is scaled to represent real engine conditions. The fuel concentration in the rig is experimentally visualized using a fluorescing dye in the water passing through the fuel system of the burner and recorded using a laser along with a CCD (Charge Couple Device) camera. The flow and concentration field in the burner is numerically studied using both the scale resolving SAS (Scale Adaptive Simulation) method and the LES (Large Eddy Simulation) method as well as using a traditional two equation URANS (Unsteady Reynolds Average Navier Stokes) approach. The aim of this study is to explore the differences and similarities between the URANS, SAS and LES models when applied to industrial geometries as well as their capabilities to accurately predict relevant features of an industrial burner such as concentration and velocity profiles. Both steady and unsteady RANS along with a standard two equation turbulence model fail to accurately predict the concentration field within the burner, instead they predict a concentration field with too sharp gradients, regions with almost no fuel tracer as well as regions with far too high concentration of the fuel tracer. The SAS and LES approach both predict a more smooth time averaged concentration field with the main difference that the tracer profile predicted by the LES has smoother gradients as compared to the tracer profile predicted by the SAS. The concentration predictions by the SAS model is in reasonable agreement with the measured concentration fields while the agreement for the LES model is excellent. The LES shows stronger fluctuations in velocity over time as compared to both URANS and SAS which is due to the reduced amounts of eddy viscosity in the LES model as compared to both URANS and SAS. This study shows that numerical methods are capable of predicting both velocity and concentration in a gas turbine burner. It is clear that both time and scale resolved methods are required to accurately capture the flow features of this and probably most industrial DLE gas turbine burners.
InterTurb: High-Pressure Turbine Rig for the Investigation of Combustor-Turbine Interaction
Authors: Wolf T. , Lehmann K. , Willer L. , Pahs A. , Rößling M. , Dorn L.
Published: August 2017

This paper introduces a new 2-stage high-pressure turbine rig for aerodynamic investigations. It is operated by DLR Göttingen (Germany) and installed in DLR’s new testing facility NG-Turb. The rig’s geometrical size as well as the non-dimensional parameters are comparable to a modern engine in the small to medium thrust range. The turbine rig closely resembles engine hardware and features all relevant blade and vane cooling as well as secondary air-system flows. The effect of variations of each individual flow and different tip clearances on overall turbine efficiency will be studied. While the first part of the testing program will be based on uniform inlet conditions the second part will be run with a combustor simulator, which is based on electrical heaters and delivers a flow field similar to a rich-burn combustor. In order to find the optimum relative position for maximum turbine efficiency the combustor simulator can be rotated relative to the HPT inlet (clocking). For the same reasons the stators can also be clocked.

The paper gives a brief overview of the testing facility and from there on focuses on the HPT rig features such as aerodynamic design, cooling and sealing flows. The aerodynamic optimisation of the stator vanes and shroudless rotor blades will be outlined. Further topics are the aerodynamic design of the combustor simulator, a comparison with engine combustors as well as the implementation in the rig. The paper also describes the rig instrumentation in the stationary and rotating system which most importantly focuses on measurements of efficiency and capturing of traverse data. The topic of blade and vane manufacturing via direct metal laser sintering will be briefly covered. The discussion of test results and comparison with numerical simulations will be the subject of a follow-up paper.
Mixture Quality of a Vortex Generator Premixer and Alternative Premixer Designs in the Auto-Ignition Regime of Hydrogen Air Flames
Authors: Bauer Stefan , Bäßler Simon , Hampel Balbina , Hirsch Christoph , Sattelmayer Thomas
Published: August 2017

The application of vortex generator premixers (VGPs) is particularly challenging for highly reactive fuels in recuperated gas turbines, because high combustor inlet temperature leads to a potential risk of premature self-ignition and flame flashback. As current knowledge does not extend to the temperature range far above the self-ignition temperature, an experimental investigation of the operational limits of VGPs is conducted at the Thermodynamics Institute of the Technical University of Munich. The study is particularly focused on highly reactive fuels and the thermodynamic conditions present in recuperated gas turbines with pressure ratios of 4–5. The present study is focuses on fuel-air mixing at the corresponding high air temperatures. A fuel-air mixing device is required to achieve sufficient mixing quality without excessive premixer length. Vortex generators are known to be effective in augmenting the distribution of fuel injected from the tube wall over the cross section of the tube. In the range of typical gas turbine combustor inlet temperatures, the performance of VGPs has already been investigated for methane as well as for hydrogen-methane blends. The limits of operating a VGP under auto-ignition relevant conditions were presented in a previous study. In this study, the VGP’s mixture quality under these conditions is experimentally investigated. For this purpose, the existing test rig has been modified to conduct high speed PIV and MixPIV measurements. Measurements at different positions inside and downstream of the injector have been performed. Two other mixer types in addition to the VGP are investigated to determine the influence of mixture quality on auto-ignition behavior in a future study and to validate MixPIV measurements. The influence of the momentum flux ratio on mixture quality is presented for the three mixer types. Comparison shows that the VGP exhibits significantly better mixture homogeneity at the mixer exit than do the two other mixer types.