bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and Characterization of Additive Manufactured Nickel-Based ODS Coating Layer for High Temperature Application
Authors: Min Zheng , Parbat Sarwesh Narayan , Yang Li , Kang Bruce , Chyu Minking K.
Published: August 2017

Increasing turbine inlet temperature (TIT) is important for improving the efficiency of gas turbine engine. Elevated thermal load causes severe oxidation and corrosion for base alloy in turbine airfoils. To survive in this extreme high temperature and harsh oxidation environment, both outside protection like thermal barrier coatings (TBC) and inside air cooling have been applied to turbine blades. Significantly more protection can be achieved if the cooling channels are embedded near surface, constructed partially by the coating system and partially by the superalloy substrate. However, neither the ceramic coating layer nor the metallic bond coating layer in current TBC system can provide structural support to such internal cooling channels. Development of structural bond coating layers consequently becomes one of the key technologies to achieve this goal.

Present study proposed a method to fabricate structural coating layers on top of turbine blades with the aid of additive manufacturing (AM) and oxide dispersion strengthened (ODS) nickel based alloy. ODS powder comprised of evenly distributed host composite particles (Ni, Al, Cr) with oxide coating layers (Y2O3) was subjected to a direct metal laser sintering (DMLS) process to fabricate a desirable structural coating layer above Nickel based superalloy substrates. Systematic experimental tests were carried out focusing on the interface adhesion, mechanical strength, microstructure and surface finish of the ODS coating layer. Based on characterization results from indentation tests and microscopy observations, an optimal coating quality was obtained under ∼250W laser power.

The selected samples were then characterized under isothermal conditions of 1200 °C for 2000 hours. SEM observations and Energy-dispersive X-ray spectroscopy (EDX) analysis were conducted in different stages of the oxidation process. Results indicated a formation of Al2O3 scale on top of the ODS coating layer at early stage, which showed long term stability throughout the oxidation test. The formation of a stable alumina scale is acting as a protective layer to prevent oxygen penetrating the top surface. Spallation of part of nickel oxide and chromium oxide is observed but the thickness of oxide scale is almost no change. In addition, the observed adhesion between ODS coating layer and substrate was tight and stable throughout the entire oxidation test. Present study has provided strong proof that additive manufacturing has the capability to fabricate structural and protective coating layers for turbine airfoils.
Interaction of Flow and Film-Cooling Effectiveness Between Double-Jet Film-Cooling Holes With Various Spanwise Distances
Authors: Yao Jiaxu , Xu Jin , Zhang Ke , Lei Jiang , Wright Lesley M.
Published: August 2017

The interaction of flow and film-cooling effectiveness between jets of double-jet film-cooling (DJFC) holes on a flat plate is studied experimentally. The time-averaged secondary flow field in several axial positions (X/d = −2.0, 1.0, and 5.0) is obtained through a seven-hole probe. The downstream film-cooling effectiveness on the flat plate is achieved by Pressure Sensitive Paint (PSP). The inclination angle (θ) of all holes is 35°, and the compound angle (β) is ±45°. Effects of spanwise distance (p = 0, 0.5d, 1.0d, 1.5d, 2.0d) between the two interacting jets of DJFC holes are studied while streamwise distance (s) is kept as 3d. The blowing ratio (M) varies as 0.5, 1.0, 1.5, and 2.0. The density ratio (DR) is maintained at 1.0. Results show that the interaction between two jets of DJFC holes has different effects for different spanwise distance. For a small spanwise distance (p/d = 0), the interaction between jets presents a pressing effect. The downstream jet is pressed down and kept attached to the surface by the upstream one. The effectiveness is not sensitive to blowing ratios. For mid spanwise distances (p/d = 0.5 and 1.0), the anti-kidney vortex pair dominates the interaction, and pushes both of the jets down, thus leads to better coolant coverage and higher effectiveness. As spanwise distance becomes larger (p/d≥1.5), the pressing effect almost disappears, and the anti-kidney vortex pair effect is weaker. The jets separate from each other and the coolant coverage decreases. At higher blowing ratio, the interaction between the two jets of DJFC holes moves more downstream.
Effect of Density Ratio on Film-Cooling Effectiveness Distribution and its Uniformity for Several Hole Geometries on a Flat Plate
Authors: Yao Jiaxu , Xu Jin , Zhang Ke , Lei Jiang , Wright Lesley M.
Published: August 2017

Film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by Pressure Sensitive Paint (PSP) under different density ratios. Several hole geometries are studied, including a streamwise cylindrical hole, a compound-angled cylindrical hole, a streamwise fan-shape hole, a compound-angled fan-shape hole, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35°.The compound angle (β) is 45°. The fan-shape hole has a 10° expansion in the spanwise direction. In order to have a fair comparison, the pitches are kept as 4d for the cylindrical and the fan-shape holes, and 8d for the double-jet film-cooling holes. The investigated uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. Effects of density ratios (DR = 1.0, 1.5 and 2.5) on film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. Results show that at higher density ratios, the lateral spread for discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, and the DJFC holes is more advantageous, and the high effectiveness region near the downstream hole exit is larger. Mostly, increased lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of density ratios on lateral-uniformity are not monotonic in some cases. Utilizing compound angle configuration leads to increased lateral-uniformity due to stronger spanwise motion of the jet. Generally, with higher blowing ratio, the lateral-uniformity for the discrete-hole geometries decreases due to narrower traces, while it for the DJFC holes increases due to stronger spanwise movement.
Performance Evaluation of a SOFC-GT Hybrid System With Ejectors for the Anode and Cathode Recirculations
Authors: Chen Jinwei , Gao Kuanying , Liang Maozong , Zhang Huisheng
Published: August 2017

The recirculation of the anode and cathode exhaust has huge benefits on the fuel cell system, for instance, keeping proper operating conditions of the reformer and preheating the inlet air which reduces the recuperator size. Furthermore, the ejectors used for the fuel cell recirculation are more reliable and low-cost in maintenance than high temperature blowers. In this paper, an anode and cathode recirculation scheme, both equipped with ejectors, was designed in a Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT) hybrid system. Additionally, a blower was added between the compressor and the heat exchanger to overcome the significant pressure loss caused by the cathode ejector. This configuration separates the compressor from the fuel cell and turbine components, introducing more flexibility in system modification. The investigations were conducted to analyze the performance of the hybrid system with anode and cathode ejectors in this paper. Firstly, the ejector model was established based on the energy, mass and momentum balance equations. Furthermore, it was validated that the ejector model was consistent with the reference data. Secondly, the stand-alone performance of the anode and cathode ejectors was analyzed. The geometry parameters of the ejectors were determined based on the design conditions. Then the off-design performance was analyzed based on the designed ejectors geometry. The results show that the performance of the ejectors is greatly influenced by the inlet conditions of the primary and secondary fluid mass flow rate. Finally, the anode and cathode ejectors were integrated into the SOFC-GT hybrid system. Meanwhile, the off-design and dynamic behaviors of the whole SOFC-GT hybrid system with anode and cathode ejectors for recirculation loops were analyzed. In the end, the results show that the designed ejectors can effectively satisfy the demands of the SOFC-GT system with anode and cathode recirculation loops. And the safety range of relative fuel flow rate is from 0.42 to 1.22 when the rotator speed is constant.
A CFD Method Study on the Resistance Performance of the Axial Flow Cyclone Separator
Authors: Luan Yigang , Yang Lianfeng , Sun Tao
Published: August 2017

Axial flow cyclone separator with guide blade has been widely used, due to its low resistance, huge gas processing and small volume. Although its structure is simple, three-dimension strong rotating turbulent flow forms which involves many complex interactions such as dual-phase separation, adsorption and electrostatic interference. This paper is focused on studying the resistance performance of the axial flow cyclone separator. Numerical simulation methods are carried out to acquire the internal flow field characteristics under different operating pressure and temperature conditions. The result shows that the pressure drop decreases under the same operating pressure, as the operating temperature increases. When the operating temperature is the same, the higher operating pressure enhances the value of the pressure drop. Velocity distribution, pressure contours and turbulent viscosity contours have been presented, to analyze the characteristics of the internal airflow, so as to help optimize the design. Experiments are intended to verify the results of numerical simulation and explore the internal flow field of the cyclone separator further. The cyclone separator has 8 rotary blades which are split into 8 parts, namely one blade is 45° in the tangential direction. 0° and 22.5° are chosen in the experiment. The dimensionless pressure distribution is shown. A comparison of the CFD results and the experimental results is made to prove that the numerical simulation methods are correct and accurate. The curve of the numerical simulation results is very close to that of the experimental results with the similar trend. It is concluded that the methods can predict the internal flow field characteristics of the axial flow cyclone separator.
Investigation of In-Stall Behavior in a Transonic Compressor Rotor
Authors: Lang Jinhua , Chu Wuli , Zhang Haoguang , Ma Shan , Chen Xiangyi
Published: August 2017

This paper shows the results of three-dimensional multi-passage numerical simulations on a transonic compressor, NASA compressor Rotor 37. The aim is to investigate the unsteady flow on the stall condition and elucidate the dynamic evolution mechanism of the rotating stall. Three-dimensional Reynolds-averaged Navier-Stokes equations with the Spalart-Allmaras turbulence model were solved to analyze the fluid flow in the transonic axial compressor. Before the study of the stall flow, grid independence and data correctness were well validated.

A new parameter B is defined to assess the blockage effect during the stall development. As shown in the results, with the development of the rotating stall, the blockage effect increases slowly before the 18th revolution in unsteady numerical simulation, and then increases dramatically in the following revolutions. Thus, the whole process of stall evolution can be divided into two stages, i.e. stall stage I and stall stage II. The stall stage I is the first 18th revolutions, while the stall stage II refers to the period after the18th revolution.

Further analyses of the instantaneous flow field show that the interaction between the tip leakage flow and the detached shock wave induces the breakdown of the leakage vortex. As the broken leakage vortex moves downstream, the low energy flow is rolled up. At the middle of the channel, the trajectory of the vortex core inclines to the PS of adjacent blade under the influence of the adverse pressure gradient, and an obvious new vortex is formed. During the development process of the rotating stall, the blockage is primarily induced by the tip leakage vortex and the new vortex. In the stall stage I, the evolution of the blockage area near the tip is periodic affected by the self-sustaineed process of tip leakage vortex. The self-sustained phenomenon will be illustrated in detail later. In the stall stage II, the whole passage is blocked at 99% blade span, and the spillage flow is observed throughout the whole stage. These flow charicteristics are regarded as signs of a rapid deterioration of the flow field. A vicious cycle is seen as the main reason for the rapid deterioration of the flow field, and the vicious cycle will be explained in detail later.
Numerical Investigation of Effect of Recess Vane Casing Treatments on an Axial Lift Fan Performance
Authors: Chen Xiangyi , Chu Wuli , Zhang Haoguang , Li Jinge , Lang Jinhua
Published: August 2017

Lift fans fitted on hovercraft are often subjected to pressure pulse generated by the sea waves. With a high pressure from the pressure pulse, the fan is driven transiently to a low mass flow rate operating point. The probability that a stall can happen is relatively high. The recess vane casing treatment (RVCT) is used to improve the axial lift fan’s stall margin in this paper.

Using the NUMECA software, the fan with solid casing and different RVTC geometry and its flow field are analyzed. The geometry modifications include blade chord exposure variation and cavity outlet axial span. Compared with the solid case, all casing treatments result in a reduction in efficiency. The blade chord exposure is a key factor that affects the efficiency. The RVCT with minimum blade chord exposure provides an inferior stall margin of −0.293% while the others provide 6% to 15% stall margin improvement, respectively.

In the study of the physical flow mechanisms, visualization can provide an insight into the flow field. This reveals that characteristics of the mainstream flow are different between near stall point and design point for the solid casing fan. The three-dimensional (3D) flow field suggests that the flow capacity near the blade tip is damaged by the blockage. The rotor blade is considered as a critical tip based on its stalling behavior. By applying RVCT, the flow field near blade tip is modified, and local mass flow ahead of blade leading edge increases while flow distribution of blade downstream along spanwise is almost the same with the solid casing fan. Also, the flow exchange between RVCT and mainstream is established through the introduction of RVCT. In quantitative analysis, the flow exchange is quantified based on the mass flow passing through the cavity. The ability of RVCT to stabilize the fan is based on the size of cavity, the more mass flow passes through cavity, the more stall margin enhancement can be obtained by the fan. However, the flow exchange between RVCT and mainstream can cause intense mixing, which can lead to efficiency loss.
Investigation of 3D Blade Design on Flow Field and Performance of a Low Pressure Turbine Stage
Authors: Zhao Zhiyuan , Du Xin , Wen Fengbo , Wang Zhongqi
Published: August 2017

To investigate the effect of blade geometry profiling by 3D bowing and twisting independently and jointly on entropy, efficiency and performance for the turbine cascades, the paper describes the mechanism of how bowed and twisted blades affect the secondary flow. The efficiency of the turbine stage improves considerably and flow structure has been optimized by applying the bowed and twisted blade.

An optimization of low pressure turbine with bowed stator has been performed using steady and transient RANS simulations. Cases with varying bow angles including both positive bow angle and negative bow angle have been discussed to show how bow angle influence the performance of rotor and stator. An optimal case with positive 18-degree bow angle was obtained. It indicates that the entropy increase rises slightly in the region near mid-span, while it reduces distinctly near the hub and shroud in the stator.

In addition to the varying bow angles, further deliberate modification has been made to present a detailed study on the effect of twisted and bowed blade with different stator exit angles. Due to the varying exit flow angles of stator, the mass flow in the spanwise direction has been changed. Meanwhile, the circumferential mass-averaged efficiency in spanwise direction is different. Therefore, the mass flow changing in the spanwise direction leads to redistribution of low energy fluid in the flow passage. The variation of exit flow angles also affects secondary flow and it can be controlled actively by changing the angles. A considerable increase of efficiency has been achieved in this part of investigation.

Considering the unsteady interaction of rotor and stator influenced by applying bowed and twisted stator, the flow through the LPT with relatively low aspect ratio was numerically simulated. It shows clearly how the secondary flow develops in the passage of the stage with bowed and twisted stator and proves several results achieved previously. At the same time, it shows how wakes of the stator and passage vortex develop in the rotor passage.
Analytical Model for the Performance Estimation of Pre-Cooled Pulse Detonation Turbofan Engines
Authors: Xisto Carlos , Ali Fakhre , Petit Olivier , Grönstedt Tomas , Rolt Andrew , Lundbladh Anders
Published: August 2017

This paper proposes a pulse detonation combustion (PDC) model integrated within Chalmers University’s gas turbine simulation tool GESTPAN (GEneral Stationary and Transient Propulsion ANalsysis). The model will support the development of novel aircraft engine architectures exploiting the synergies between intercooling, aftercooling and PDC. The proposed engine architectures are based on a reference high bypass ratio geared-turbofan engine model with performance levels estimated to be available by year 2050. Parametric studies have been carried out for each proposed advanced architecture, providing engine cycle mid-cruise design point parameters. Design sensitivity studies related to intercooling technology in combination with a PDC are further explored for a number of heat-exchanger design effectiveness values and associated pressure loss levels. The acquired results suggest that the incorporation of PDC technology within a conventional core has the potential to significantly improve engine thermal efficiency. Incorporating intercooling improves the cycle performance for any pre-combustion OPR above 10 and contributes to an increase in specific power over the entire range of OPR. Finally, the results demonstrate that aftercooling the high pressure compressor delivery air further improves core specific power, but cancels out any SFC and thermal efficiency benefits arising from pulse detonation.
Numerical Investigation of Stall Mechanism of an Axial Compressor at Three Different Rotating Speeds
Authors: Zhang HaoGuang , Tan Feng , An Kang , Wu YanHui , Chu WuLi
Published: August 2017

For some axial flow compressors, the compressor stall is a result of the blade tip blockage caused by the complex flows, which include the boundary layer flow separation (BLFS), tip leakage flow (TLF), and shock wave. Owing to the difference of the design rotating speed and aerodynamic load in the axial flow compressor, these complex flows might exist in isolation or occur at the same time in practical application. Aiming at the stall mechanism in the axial flow compressors, a great deal of experimental and numerical investigations have been carried out at the design rotating speed. However, the investigation for off-design rotating speed in the axial flow compressors is seldom. Therefore, a transonic axial flow compressor rotor, which is NASA Rotor67, was chosen to investigate the stall mechanism at 100%, 80% and 60% design rotating speeds with the help of the numerical method. Moreover, the guiding suggestions for selecting the measures of increasing the transonic axial flow compressors stability are presented for the later investigation. The compared results show that the variation tendency of the experimental total performance lines are finely repeated by the numerical results at the three design rotating speeds. The fundamental flow mechanism of the rotor is obtained by analyzing the flow field in the blade passage in details. With the decrease of the rotor mass flow at the three design rotating speeds, the starting position of the tip leakage vortex (TLV) moves to the blade leading edge gradually, and the tip leakage vortex also deviates to the pressure surface of the adjacent blade. The deviated angle, which is the angle between the trajectory of the tip leakage vortex core and rotor rotating axis, for near stall point (NS) are about three degree, five degree and nine degree than that for near peak efficiency point (NPE) at 100%, 80% and 60% design rotating speeds respectively. The blockage resulted from the interaction between the tip leakage vortex and shock wave is the cause of the rotor stall at 100% and 80% design rotating speeds. Besides, the breakdown of the tip leakage vortex and leading edge spilled flow (LESF) occur at 80% design rotating speed. At 60% design rotating speed, the blockage caused by the leading edge spilled flow resulted from the tip leakage vortex is the main cause of bringing about the compressor stall, and the boundary layer flow separation (BLFS) in a small scope appears at the blade tip suction surface near the trailing edge.
Vortex Structures for Highly-Loaded Subsonic Compressor Cascades With Slot Injection
Authors: Chen Huanlong , Liu Huaping , Zhang Dongfei , Li Linxi
Published: August 2017

A promising flow analytical way to offset the respective shortcomings for the experimental measure and numerical simulation methods is presented. First, general topological rules which are applicable to the skin-friction vector lines on the passage surface, to the flow patterns in the cross-section of the cascade as well as on the blade-to-blade surface were deduced for the turbomachinery cascades with/without suction/blowing slots in this paper. Second, the qualitative analysis theory of the differential equation was used to investigate the distribution feature of the flow singular points for the limiting streamlines equation. The topological structure of the flow pattern on the cascade passage surfaces was discussed in detail. Third, the experiment and numerical simulations results for a linear compressor cascade passage with highly-loaded compound-lean slotted blade, which were combined to topologically examine the flow structure with penetrating slot injections through the blade pressure side and suction side. The results showed that the general topological rules are applicable and effective for flow diagnosis in highly-loaded compressor blade passage with slots. Finally, an integrated vortex control model, in which the blade compound-lean effect and the injection flow through the slots were coupled, was presented. The model shows that reasonable slot injection configurations can effectively control the concentrated shedding vortices from the suction surface of a highly-loaded compressor cascades passage, thereby the aerodynamic performance for the blade passage is remarkably improved. The present work provides a novel theoretical analysis method and insights of the flow for the turbine blade passage with cooling structures, aspirated compressor blade passage and other applications with new flow control configurations in turbomachinery field.
Numerical Investigation of Self-Driven Fan Performance With Tip-Jet
Authors: Li Lei , Huang GuoPing , Chen Jie , Wang JinChun
Published: August 2017

Tip-jet rotor system has unique potential value in the area of vertical take-off and landing (VTOL) or short take-off and landing (STOL) concept aircraft. The main objective of the current work is to investigate the aerodynamic properties of a self-driven fan with tip-jet (SDF_TJ) in hover by numerical experiments. In order to obtain the detailed flow phenomena of SDF_TJ, CFD method is performed, which is conducted by solving three-dimensional Reynolds-averaged Navier-Stokes equations using the shear stress transport turbulence model. For the purpose of investigation, the analysis of SDF_TJ performances with different nozzle configurations have been carried out. Current results indicate the conformal tip-jet not only provide the reaction torque, but also augment the fan lift via entraining the main flow above the suction surface of blade. The rotation speed of fan is mainly determined by bleed air parameters and nozzle area, so as to torque self-balance. The total torque produced by jets contains rotor required torque and penalty torque induced by Coriolis force. The blade lift coefficient and the ratio with jet momentum coefficient are influenced by the distance from the nozzle downstream edge to blade trailing. As the lift of SDF_TJ is larger than the thrust generated by jets alone, which could benefit the take-off and landing capability of VTOL concept aircraft.
Numerical Study of Flow Control in a Diffuser by Vibration Wall and Mechanism Analysis by Establishment of a Nonlinear Simplified Model
Authors: Weiyu Lu , Guoping Huang , Xin Fu , Jinchun Wang , Shuli Hong
Published: August 2017

Vibration wall is a kind of important active flow control method, while the interaction between the vibration wall and unsteady separation flow is so complex for researchers to discover the corresponding mechanism. Current researches imply that the better controlled flow is the more ordered flow. At first, the effect of the different control parameters of vibration wall on the total pressure loss was studied by numerical simulation to reveal the control mechanism of vibration wall. Numerical results show that when the vibration frequency reaches the separation vortex frequency, with the amplitude of 0.1 characteristic length, the best flow control is resulted. Furthermore, it can be seen that, the vibration wall with effective parameters can make the large-scale vortices more dominant, while small-scales ones (or clutters) appear less in the pattern. This observation indicates that the flow field tends to be more orderly. Moreover, to further explain this ordering mechanism, a simplified model is established and analyzed, showing that valid external excitement can strengthen the dominated frequency of K-H wave which forms the large-scale separation vortices, and restrains small-scale ones. The flow field is then more orderly and less chaotic, resulting in reduction of flow loss.
Size and Temperature Dependent Deposition Model of Micro-Sized Sand Particles
Authors: Yu Kuahai , Tafti Danesh
Published: August 2017

Sand ingestion and deposition in gas turbine engine components can lead to several operational hazards. This paper discusses a physics based model for modeling the impact and deposition of sand particles. The collision model divides the impact process into three stages, the elastic stage, the elastic-plastic stage, and full plastic stage. The recovery stage is assumed to be fully elastic. The contact force, contact radius and work of contact force are conformed to the Hertzian theory, using “Young’s modulus similarity” rule to predict the recovery displacement. The adhesion loss in the recovery stage is considered using Dunn’s model, which describes the adhesion force as an idealized line force with the contact radius. The validation case of steel spherical particle impact on a glass surface with the maximum Stokes number of 10000, shows that the adhesion model with elastoplastic impact model describes the experimental result well. When the Stokes number is less than 12, the particle deposits on the surface. Sand properties are characterized by size and temperature dependencies. Model predictions for particle sizes ranging from 0.5 to 50 micron, impact velocities up to 80 m/s, and temperatures above 1300 K are given and discussed. It is shown that both size and temperature have an effect on the deposition characteristics.
1-D Model Analysis of Tesla Turbine for Small Scale Organic Rankine Cycle (ORC) System
Authors: Song Jian , Gu Chun-wei
Published: August 2017

Energy shortage and environmental deterioration are two crucial issues that the developing world has to face. In order to solve these problems, conversion of low grade energy is attracting broad attention. Among all of the existing technologies, Organic Rankine Cycle (ORC) has been proven to be one of the most effective methods for the utilization of low grade heat sources. Turbine is a key component in ORC system and it plays an important role in system performance. Traditional turbine expanders, the axial flow turbine and the radial inflow turbine are typically selected in large scale ORC systems. However, in small and micro scale systems, traditional turbine expanders are not suitable due to large flow loss and high rotation speed. In this case, Tesla turbine allows a low-cost and reliable design for the organic expander that could be an attractive option for small scale ORC systems. A 1-D model of Tesla turbine is presented in this paper, which mainly focuses on the flow characteristics and the momentum transfer. This study improves the 1-D model, taking the nozzle limit expansion ratio into consideration, which is related to the installation angle of the nozzle and the specific heat ratio of the working fluid. The improved model is used to analyze Tesla turbine performance and predict turbine efficiency. Thermodynamic analysis is conducted for a small scale ORC system. The simulation results reveal that the ORC system can generate a considerable net power output. Therefore, Tesla turbine can be regarded as a potential choice to be applied in small scale ORC systems.
A CFD Simulation of Coal Syngas Oxy-Combustion in a High-Pressure Supercritical CO2 Environment
Authors: Abdul-Sater Hassan , Lenertz James , Bonilha Chris , Lu Xijia , Fetvedt Jeremy
Published: August 2017

The Allam Cycle is an oxy-fuel supercritical CO2 power cycle that generates low-cost electricity from fossil fuels while producing near-zero air emissions. The turbine exhaust (sCO2) is then available for partial injection into underground storage while remainder is reused in the power cycle. Novel combustors required by this and other sCO2 cycles are critical to their commercialization. A conceptual design was developed for a coal syngas-fueled oxy-fuel combustor that meets the conditions of the Allam Cycle. The design of this combustor utilizes a 300MWe coal syngas-fired Allam Cycle thermodynamic analyses and ASPEN process models as inputs to the combustor. The primary inputs for design of the combustor included the fuel mixture compositions and respective flow rates for the constituent gases, pressures, and operating temperatures which were scaled to a 5MWth test article. The combustor was sized to accommodate the required pressures, heat release rate, flow rates, and residence times to produce well mixed turbine inlet flows with complete combustion. A preliminary design for a 5MWth test scale combustor was then developed, and a numerical study using Computational Fluid Dynamics (CFD) simulations was carried out to demonstrate the feasibility of that combustor. Steady-state RANS simulations were used to qualitatively examine the preliminary design of the 5MWth combustor and predict the fluid mechanics, heat transfer, and combustion. The purpose of the analysis was to verify the following criteria: 1) good mixing of the fuel and oxidizer in the primary zone, 2) uniform exhaust gas temperature and 3) efficient combustion with complete CO burnout. Additionally, the analysis investigated wall temperature and the impact of varying the fuel composition on combustion performance. The CFD model results were in good agreement with the equilibrium one-dimensional (1D) Aspen model results. The CFD predictions of the current conceptual design verified the identified key criteria for the combustor and demonstrated its feasibility.
Multistage Blisk and Large Mistuning Modeling Using Fourier Constraint Modes and PRIME
Authors: Kurstak Eric , D’Souza Kiran
Published: August 2017

Current efforts to model multistage turbomachinery systems rely on calculating independent constraint modes for each degree of freedom on the boundary between stages. While this approach works, it is computationally expensive to calculate all the required constraint modes. This paper presents a new way to calculate a reduced set of constraint modes referred to as Fourier constraint modes (FCMs). These FCMs greatly reduce the number of computations required to construct a multistage reduced order model (ROM). The FCM method can also be integrated readily with the component mode mistuning method to handle small mistuning and the pristine rogue interface modal expansion method to handle large and/or geometric mistuning. These methods all use sector level models and calculations, which makes them very efficient. This paper demonstrates the efficiency of the FCM method on a multistage system that is tuned and, for the first time, creates a multistage ROM with large mistuning using only sector level quantities and calculations. The results of the multistage ROM for the tuned and large mistuning cases are compared with full finite element results and are found in good agreement.
Numerical Investigation on Mist/Air Cooling in Rectangular Ribbed Channels With Various Aspect Ratios
Authors: Zeng Junxiong , Gao Tieyu , Li Jun , Gong Jianying
Published: August 2017

Continuously increasing gas turbine inlet temperature to further improve thermal efficiency and power output of gas turbines leads to acquiring a higher cooling effectiveness of gas turbine blades and vanes to protect them from high temperature corrosion and creeping damage. One of the new and promising technologies to greatly increase heat transfer is mist cooling by injecting a small amount of tiny droplets into coolant flow. This paper aims to numerically study the flow and heat transfer behaviors of mist/air coolant in rectangular ribbed channels with various aspect ratios of 1/4, 1/2, 1/1, 2/1 and rib angle of 60°. In addition, the distribution of secondary flows in the four ribbed channels and its effect on heat transfer are analyzed in detail. The effects of Reynolds number ranging from 10,000 to 60,000, mist mass ratios ranging from 1% to 4%, and droplet sizes ranging from 5 μm to 20 μm on heat transfer characteristics of mist/air cooling are investigated. As a comparison, the air-only coolant is also considered in the present study.

The Eulerian-Lagrangian particle tracking method is adopted in this study to simulate the two-phase flow mist/air cooling. Turbulence model validation has been conducted for air-only, indicating that the numerical results with SST k-ω model are fairly consistent with experimental data. The results show that the aspect ratio has insignificant influence on longitudinal secondary flow distribution in the four ribbed channels, but greatly affects the size of main secondary flows. The channel with a smaller aspect ratio obtains a larger size of main secondary flow, which may result in decreasing the heat transfer coefficient. The average Nu on ribbed surfaces presents an increasing trend with Reynolds number and mist mass ratio for mist/air cooling. The heat transfer enhancement of mist/air as compared to air-only increases from 12.3% to 91.86% when Reynolds number ranges from 10,000 to 60,000 with injecting 2% mist into air coolant, while that increases from 7.96% to 113.15% when mist mass ratio increases from 1% to 4%. The average Nu initially increases with droplet size and then decreases. A peak value of average Nu is obtained in the case of 15μm mist among all the sizes of droplets. The case of AR = 2/1 obtains the highest average Nu, followed by the cases of AR = 1/2, 1/1 and 1/4 for both air-only and mist/air. The channel with aspect ratio of 1/2 obtains the best thermal performance in mist/air cooling channel.
Unsteady Pressure Characteristics in the Mainstream/Disc Cavity of a Turbine-Stage
Authors: Mirzamoghadam A. V. , Balasubramanian J. , Michael M. , Roy R. P.
Published: August 2017

The interaction between the mainstream and disc cavity purge flows in a turbine stage is an unsteady 360° phenomenon. Most of the current rotating rigs have used steady pressure transducers to measure the mainstream annulus pressure distributions as well as the pressure distribution in the disc cavity. Unsteady static pressure measurements in these regions using fast-response transducers have also been reported but to a much lesser degree, mainly at ASU, OSU, VKI, and ETH. To gain better insight into the prevailing unsteady flow phenomena, and to assess the difference between steady and time-averaged unsteady pressure data, new unsteady static pressure measurements were recently carried out at three locations in an ASU-Honeywell turbine stage, namely, in the main gas path on the outer shroud near vane trailing edge as well as on the vane platform lip, and on the stator surface rim seal. They are reported in this paper along with the comparative results of the corresponding URANS CFD simulation reported in an earlier publication. Experiments were carried out at five different purge air flow conditions for each of the two mainstream air flow rate and rotor speed combinations. The current unsteady measurements indicate that the rim cavity pressure frequency is governed by the blade passage frequency. The unsteadiness amplitude increases with purge flow in the main gas path, but decreases with increase in purge flow for the rim cavity where the sensitivity to change in purge flow is smaller at the lower mainstream flow rate. The difference in the ambient-corrected time-averaged static pressures between those evaluated from the current unsteady measurements and the previously published steady measurements are found to be within the measurement uncertainties.
Modeling and Optimal Operation of a Network of Energy Hubs System With Distributed Energy Resources
Authors: Ma Shixi , Zhou Dengji , Zhang Huisheng , Lu Zhenhua
Published: August 2017

Energy hubs is a functional unit which is capable of transporting transforming and storing of several kinds of energy. Several hubs can be combined as a network and achieve higher efficiency by exchanging energy with each other. A framework to assist the decision-making process towards the optimal integration of independent small scale distributed energy systems and traditional large scale CHP power plants is presented using an energy supply system in Shanghai as a case study. A model of this complex network of energy hubs with renewable energy resources is presented based on energy flow between its constituent elements. Furthermore, GA optimization method is presented for short term 24-hour optimal operation. Case study are undertaken on a 7-node energy system which comprises 4 energy hubs and 3 load hubs. Results validate the high efficiency of this system. Two cases with and without internal-combustion engine failure within the network are considered. The results showed that the proposed system can enhance the energy utilization efficiency and reduce the system operation cost, even under a system contingency.
A Two-Dimensional Analytical Method for Turbine Blade Cooling Design
Authors: Li Chen , Liu Jian-jun , An Bai-tao , Yu Zhi-qiang
Published: August 2017

Turbine blade cooling design involves many complex fluid-thermal coupling issues. Using complete 3D CFD and FEA method would increase the cost of computing; on the other hand, the simplified 1D analytical method would lose too much important blade geometric information when employed in preliminary cooling design. In order to shorten design period and improve the design efficiency, the current 2D analytical method has been developed from a conceptual design that stacking a series of 2D radial sections to shape a quasi-3D blade model attached with the internal fluid flow network. Each of those 2D radial sections could maximally retain the actual blade profile, thus making it more authentic for accomplishing the numerical calculations of turbine cascade flow and heat transfer. For the gas side, methods for calculating external heat transfer coefficients have been investigated, and a simple method for considering the effect of thermal barrier coating on 2D conduction model is proposed. For internal cooling channels, a general calculation method of compressible pipe flow under rotating condition has been derived for fast solving coolant mass flow rates and internal heat transfer coefficients supported by empirical correlations of Darcy resistance coefficient and Nusselt number. Those work are significant to achieve the parametric cooling design by means of modifying and controlling geometric parameters and boundary conditions. Consequently, a real turbine blade case by applying the current 2D analytical method to obtain a quasi-3D blade temperature distribution is presented, demonstrating that this 2D analytical method is effective for turbine cooling design.
Plastic Effects on High Cycle Fatigue at the Edge of Contact of Turbine Blade Fixtures
Authors: Richter C. H. , Krupp U. , Zeißig M. , Telljohann G.
Published: August 2017

Slender turbine blades are susceptible to excitation. Resulting vibrations stress the blade’s fixture to the rotor or stator. In this paper, high cycle fatigue at the edge of contact between blade and rotor/stator of such fixtures is investigated both experimentally and numerically. Plasticity in the contact zone and its effects on e.g. contact tractions, fatigue determinative quantities and fatigue itself are shown to be of considerable relevance. The accuracy of the finite element analysis is demonstrated by comparing the predicted utilizations and slip region widths with data gained from tests. For the evaluation of edge of contact fatigue, tests on simple notched specimens provide the limit data. Predictions on the utilization are made for the edge of contact of a dovetail set-up. Tests with this set-up provide the experimental fatigue limit to be compared to. The comparisons carried out show a good agreement between the experimental results and the plasticity-based calculations of the demonstrated approach.
Fan Similarity Model for the Fan-Intake Interaction Problem
Authors: Carnevale Mauro , Wang Feng , Parry Anthony B. , Green Jeffrey S. , di Mare Luca
Published: August 2017

Very high-bypass ratio turbofans with large fan tip diameter are an effective way of improving the propulsive efficiency of civil aero-engines. Such engines, however, require larger and heavier nacelles, which partially offset any gains in specific fuel consumptions. This drawback can be mitigated by adopting thinner walls for the nacelle and by shortening the intake section. This binds the success of very high-bypass ratio technologies to the problem of designing an intake with thin lips and short diffuser section which is well matched to a low speed fan. Consequently the prediction of the mutual influence between the fan and the intake flow represents a crucial step in the design process.

Considerable effort has been devoted in recent years to the study of models for the effects of the fan on the lip stall characteristics and the operability of the whole installation. The study of such models is motivated by the wish to avoid the costs incurred by full, three-dimensional CFD computations. The present contribution documents a fan model for fan-intake computations based on the solution of the double linearization problem for unsteady, transonic flow past a cascade of aerofoils with finite mean load. The computation of the flow in the intake is reduced to a steady problem, whereas the computation of the flow in the fan is reduced to one steady problem and a set of solutions of the linearised model in the frequency domain. The nature of the approximations introduced in the fan representation is such that numerical solutions can be computed inexpensively, whilst the main feature of the flow in the fan passage, namely the shock system and an approximation of the unsteady flow encountered by the fan are retained. The model is applied to a well-documented test case and compares favourably with much more expensive three-dimensional, time domain computations.
Effects of the Injector Design on the Transfer Function of Premixed Swirling Flames
Authors: Gatti M. , Gaudron R. , Mirat C. , Schuller T.
Published: August 2017

This article reports a series of experiments on the dynamics of lean-premixed swirl-stabilized flames submitted to harmonic flowrate modulations. The flame transfer function is analyzed for different injector designs with a specific focus on conditions leading to the lowest heat release rate response for a given flowrate perturbation. Experiments are carried out at a fixed equivalence ratio and fixed thermal power. Transfer functions are measured for radial swirling vanes by modifying the diameter of the swirler injection holes, the diameter of the injection tube at the top of the swirler and the end piece diameter of a central insert serving as a bluff body. It is found that the lowest response depends on the forcing frequency and is obtained when the injector design features the largest swirl number. The transfer function of the studied flames features a minimum gain value which decreases for increasing swirl levels. This minimum value is found to be independent of the velocity forcing level and is only controlled by the level of swirl. An excessive swirl level however leads to flash-back of the perturbed flames inside the injector. The way the flame behaves at this forcing frequency is analyzed for a set of injectors featuring the same radial swirling vane design and different injection tube diameters or conical end pieces. It is found that at the condition corresponding to the lowest FTF gain, i.e. the injector with the largest swirl number, the upper and lower parts of the flame contribute to out of phase heat release oscillations, but they also both feature a reduced level of fluctuations. When the swirl number decreases, the FTF gain increases due to a reduction of the phase lag between heat release rate oscillations in the lower and the upper parts of the flame and more importantly due to a general increase of the level of heat release oscillations in both parts of the flame.