bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the Speed Control System of a Heavy-Duty Gas Turbine
Authors: Cao Yue , Wang Jiaying , Dai Yiping , Xie Danmei
Published: August 2015

Gas turbine plays an important role in both the power generation and the frequency regulation of the power grid. In this paper, we have designed a speed control system for the heavy-duty gas turbine. Specifically, the speed control can be organized into four phases, including startup frequency converter (SFC), run-up ramp controller, speed/load controller and grid control center. Firstly, SFC determines the speed during the initial start-up period as the gas turbine and SFC are coaxial. Secondly, after SFC stops, the run-up ramp controller takes over the speed control until near the rated speed. Then, the speed/load controller is selected by a minimum selector to control the speed of the gas turbine. Finally, after synchronization with the power grid, the speed of the gas turbine depends on the frequency of the grid. In order to study the dynamic characteristics of the speed control system, a model of the gas turbine with its control system has been designed in SIMULINK based on the modular modeling method. The simulation results showed that the transient responses had good performances. So it seems that the speed control system that we designed could regulate the gas turbine during a variable condition.
The Effects of Inlet Reynolds Number, Exit Mach Number and Incidence Angle on Leading Edge Film Cooling Effectiveness of a Turbine Blade in a Linear Transonic Cascade
Authors: Liu Cong , Zhu Hui-ren , Fu Zhong-yi , Xu Run-hong
Published: August 2015

This paper experimentally investigates the film cooling performance of a leading edge with three rows of film holes on an enlarged turbine blade in a linear cascade. The effects of blowing ratio, inlet Reynolds number, isentropic exit Mach number and off-design incidence angle (i<0°) are considered. Experiments were conducted in a short-duration transonic wind tunnel which can model realistic engine aerodynamic conditions and adjust inlet Reynolds number and exit Mach number independently. The surface film cooling measurements were made at the midspan of the blade using thermocouples based on transient heat transfer measurement method. The changing of blowing ratio from 1.7 to 3.3 leads to film cooling effectiveness increasing on both pressure side and suction side. The Mach number or Reynolds number has no effect on the film cooling effectiveness on pressure side nearly, while increasing these two factors has opposite effect on film cooling performance on suction side. The increasing Mach number decreases the film cooling effectiveness at the rear region mainly, while at higher Reynolds number condition, the whole suction surface has significantly higher film cooling effectiveness because of the increasing cooling air mass flow rate. When changing the incidence angle from −15° to 0°, the film cooling effectiveness of pressure side decreases, and it presents the opposite trend on suction side. At off-design incidence of −15° and −10°, there is a low peak following the leading edge on the pressure side caused by the separation bubble, but it disappears with the incidence and blowing ratio increased.
Investigation of the Compressibility Effects on Engine Transient Performance
Authors: Shi Yang , Tu Qiuye , Jiang Ping , Zheng Heng , Cai Yuanhu
Published: August 2015

Compressibility is an important feature of gas in unsteady process. This paper presents a numerical model to describe the compressibility effect of engine transient performance by solving the equations of mass flow, energy and momentum conservation.

In order to compare the difference of compressibility effect on the engine transient performance, the volume of each component was considered individually and the transient performance of a turbojet engine and a turbofan engine were simulated respectively.

The turbojet engine transient performance results showed that the component’s compressibility effect had a little effect on the engine transient performance, and the model proposed in this paper was able to capture more details than the traditional actuator-volume model. It also indicated that the influence of component’s compressibility on the engine performance depends on the relative position of the component and turbine nozzle. The volume of components such as compressors and burners before the turbine nozzle, slowed down the engine transient response; and the components such as turbines and afterburners after the turbine nozzle, influenced the turbine expansion ratio, thereby affected the engine transient performance.

The results of a turbofan engine indicated that the volume effect of the LP components hardly influenced the core. The volume effects of HP component on the core engine were similar with the turbojet.
Investigation of Corner Separation in a Linear Compressor Cascade Using DDES
Authors: Liu Yangwei , Yan Hao , Lu Lipeng
Published: August 2015

Delayed Detached Eddy Simulation (DDES) method, compared with the RANS method, can more accurately predict the complexity and unsteadiness naturally associated with the compressor flow. DDES method, which incorporates a simple modification into the initial detached eddy simulation (DES) introduces kinematic eddy viscosity into turbulence model to take both effects of grid spacing and eddy-viscosity field into considerations. An attempt is made in the present paper to apply DDES for investigating the flow field in a compressor cascade.

Three-dimension (3D) corner separation, which is also referred as corner separation, have been identified as an inherent flow feature of the corner formed by the blade suction surface and endwall of axial compressors. The flow visualization and the quantification of passage blockage expose that corner separation contribute most to the total passage blockage.

In order to accurately predict 3D corner separation by employing CFD and increase the performance in compressor routine design by controlling such phenomenon, this paper tries to figure out its mechanism and investigate the turbulence flow field by using DDES method. Numerical simulations are conducted under different incidences in a linear PVD compressor cascade. The results show passage vortex starting at mid-chord position in cascade develops into dominant secondary vortex and obviously enhances corner separation in the PVD cascade. DDES method, which can capture intensive vortex flow and predict complicated flow at the separation region, also illustrates the corner vortex breaks into small stripe vortices which mix with the mainstream flow at the blade trailing edge. The total pressure loss is high in the corner separation region.
Development of the DLE Combustor for L30A Gas Turbine
Authors: Sakurazawa Toshiaki , Oda Takeo , Takami Satoshi , Okuto Atsushi , Kinoshita Yasuhiro
Published: August 2015

This paper describes the development of the Dry Low Emission (DLE) combustor for L30A gas turbine.

Kawasaki Heavy Industries, LTD (KHI) has been producing relatively small-size gas turbines (25kW to 30MW class). L30A gas turbine, which has a rated output of 30MW, achieved the thermal efficiency of more than 40%. Most continuous operation models use DLE combustion systems to reduce the harmful emissions and to meet the emission regulation or self-imposed restrictions. KHI’s DLE combustors consist of three burners, a diffusion pilot burner, a lean premix main burner, and supplemental burners. KHI’s proven DLE technologies are also adapted to the L30A combustor design.

The development of L30 combustor is divided in four main steps. In the first step, Computational Fluid Dynamics (CFD) analyses were carried out to optimize the detail configuration of the combustor. In a second step, an experimental evaluation using single-can-combustor was conducted in-house intermediate-pressure test facility to evaluate the performances such as ignition, emissions, liner wall temperature, exhaust temperature distribution, and satisfactory results were obtained. In the third step, actual pressure and temperature rig tests were carried out at the Institute for Power Plant Technology, Steam and Gas Turbines (IKDG) of Aachen University, achieving NOx emission value of less than 15ppm (O2=15%). Finally, the L30A commercial validation engine was tested in an in-house test facility, NOx emission is achieved less than 15ppm (O2=15%) between 50% and 100% load operation point.

L30A field validation engine have been operated from September 2012 at a chemical industries in Japan.
Laminar Flame Speed Measurements of Synthetic Gas Blends With Hydrocarbon Impurities
Authors: Keesee Charles L. , Petersen Eric L. , Zhang Kuiwen , Curran Henry J.
Published: August 2015

New Laminar Flame Speed measurements have been taken for a wide range of syngas mixtures containing hydrocarbon impurities. These experiments began with two baseline syngas mixtures. The first of these baseline mixtures was a bio-syngas with a 50/50 H2/CO split, and the second baseline mixture was a coal syngas with a 40/60 H2/CO split. Experiments were conducted over a range of equivalence ratios from ϕ = 0.5 to 3 at initial conditions of 1 atm and 300 K. Upon completion of the baseline experiments, two different hydrocarbons were added to the fuel mixtures at levels ranging from 0.8 to 15% by volume, keeping the H2/CO ratio locked for the bio-syngas and coal syngas mixtures. The addition of these light hydrocarbons, namely CH4 and C2H6, had been shown in recent calculations by the authors to have significant impacts on the laminar flame speed, and the present experiments validated the suspected trends. For example, a 7% addition of methane to the coal-syngas blend decreased the peak flame speed by about 25% and shifted it from ϕ = 2.2 to a leaner value near ϕ = 1.5. Also, the addition of ethane at 1.7% reduced the mixture flame speed more than a similar addition of methane (1.6%). In general, the authors’ chemical kinetic model over predicted the laminar flame speed by about 10–20% for the mixtures containing the hydrocarbons. The decrease in laminar flame speed with the addition of the hydrocarbons can be explained by the increased importance of the inhibiting reaction CH3 + H (+M) ↔ CH4 (+M), which also explains the enhanced effect of C2H6 compared to CH4, where the former produces more CH3 radicals, particularly at fuel rich conditions.
Control of Blow-Down Wind Tunnel Using Combined Extended and Nonlinear Predictive Filters
Authors: Zheng Ruixiang , Li Mian , Wang Zhaoguang , Zhang Qiang
Published: August 2015

A blow-down wind tunnel is a typical nonlinear time-variant system facing the coupling of the pressure and temperature during a short duration. The control of blow-down wind tunnels has been discussed for long time and a satisfactory general solution to this problem is still under developing. This paper aims to model the internal relationship of the state variables of the wind tunnel by using thermodynamic theories. With the developed model, a new control method combining Extended Kalman Filter (EKF) together with auxiliary Nonlinear Predictive Filter (NPF) is proposed to improve the control performance of the blow-down wind tunnel controller in terms of precision and robustness. The transient coupling effects between the pressure and temperature are fully considered by the proposed approach. The results both from the simulation and experiments are consistent and prove that the EKF combined together with NPF can work better than previously proposed EKF-based method.
Intermittency Route to Combustion Instability in a Laboratory Spray Combustor
Authors: Pawar S. A. , Vishnu R. , Vadivukkarasan M. , Panchagnula M. V. , Raman Sujith
Published: August 2015

In the present study, we investigate the phenomenon of transition of a thermoacoustic system involving two-phase flow, from aperiodic oscillations to limit cycle oscillations. Experiments were performed in a laboratory scale model of a spray combustor. A needle spray injector is used to generate a droplet spray having one dimensional velocity field. This simplified design of the injector helps in keeping away the geometric complexities involved in the real spray atomizers. We investigate the stability of the spray combustor in response to the variation of the flame location inside the combustor. Equivalence ratio is maintained constant throughout the experiment. The dynamics of the system is captured by measuring the unsteady pressure fluctuations present in the system. As the flame location is gradually varied, self-excited high amplitude acoustic oscillations are observed in the combustor. We observe the transition of the system behaviour from low amplitude aperiodic oscillations to large amplitude limit cycle oscillations occurring through intermittency. This intermittent state mainly consists of a sequence of high-amplitude periodic bursts separated by low amplitude aperiodic regions. Moreover, the experimental results highlight that during intermittency, the maximum amplitude of bursts oscillations, near to the onset of intermittency, is as much as three times higher than the maximum amplitude of the limit cycle oscillations. These high amplitude intermittent loads can have stronger adverse effects on the structural properties of the engine than the low amplitude cyclic loading caused by the sustained limit cycle oscillations. Evolution of the three different dynamical states of the spray combustion system (viz. stable, intermittency and limit cycle) are studied in three-dimensional phase space by using a phase space reconstruction tool from the dynamical system theory. We report the first experimental observation of type-II intermittency in a spray combustion system. The statistical distributions of the length of aperiodic (turbulent) phase with respect to the control parameter, first return map and recurrence plot techniques are employed to confirm the type of intermittency.
Constraint Mechanical Model and Investigation for Rub-Impact in Aero-Engine System
Authors: Ma Yanhong , Cao Chong , Zhang Dayi , Liang Zhichao , Hong Jie
Published: August 2015

A mechanical model for rub-impact was proposed considering the additional constraints caused by rubbing. Based on the constraint mechanical model, some characteristics of response such as resonant range expansion, contact unstability and amplitude jump during rubbing were studied. The influences of typical parameters on rotor’s vibration response with rub constraint were also evaluated. The result reveals that additional constraint stiffness causes the unstable contact range and the resonant range to be wider. While greater friction coefficient between rotor and casing results in smaller response and narrower resonant range.

A simplified dynamic model for the aero-engine was built, which takes the constraint effect into account. The numerical simulation result shows that in addition to the resonant range expansion caused by the constraint, the rotor response is also closely related to rubbing location and mode shapes. The rotor response shows a feature of quasi-periodic in slight rubbing, while the rotor motion tends unstable in heavy rubbing.
On the Application of Frequency-Domain Methods to Multistage Turbomachinery
Authors: Junge Laura , Ashcroft Graham , Jeschke Peter , Frey Christian
Published: August 2015

Due to the relative motion between adjacent blade rows the aerodynamic flow fields within turbomachinery are normally dominated by deterministic, periodic phenomena. In the numerical simulation of such unsteady flows (nonlinear) frequency-domain methods are therefore attractive as they are capable of fully exploiting the given spatial and temporal periodicity, as well as capturing or modelling flow nonlinearity. Central to the efficiency and accuracy of such frequency-domain methods is the selection of the frequencies and the circumferential modes to be resolved in simulations. Whilst trivial in the context of the simulation of a single compressor- or turbine-stage, the choice of solution modes becomes substantially more involved in multi-stage configurations. In this work the importance of mode scattering, in the context of the unsteady aerodynamic field, is investigated and quantified. It is shown that scattered modes can substantially impact the unsteady flow field and are essential for the accurate modelling of wake propagation within multistage configurations. Furthermore, an iterative approach is outlined, based on the spectral analysis of the circumferential modes at the interfaces between blade rows, to identify the dominant solution modes that should be resolved in the adjacent blade row. To demonstrate the importance of mode scattering and validate the approach for their identification the unsteady blade row interaction within a 4.5 stage axial compressor is computed using both the harmonic balance method and, based on a full annulus midspan simulation, a time-domain method. Through the inclusion of scattered modes it is shown that the solution quality of the harmonic balance results is comparable to that of the nonlinear time-domain simulation.
Computational Investigation of Heat Transfer Characteristics of Counter-Rotating Turbine Disks With Annulus
Authors: Liu Dongdong , Luo Xiang , Tao Zhi
Published: August 2015

The heat transfer characteristics of counter-rotating disks with annulus flow were investigated numerically in this paper, in which the effects of coolant inlet conditions (inlet geometry, turbulent parameter and inlet preswirl) of the cavity were emphasized. The axial Reynolds number of annulus Rew was set to be 5.99×105 and rotating Reynolds number Reϕ was set to be 2.35×105. Two kinds of cooling air inlet, radial inlet from the middle of cavity and axial inlet from one side of cavity, were adopted and investigated. The turbulent parameter and preswil ratio varied from 0.028 to 0.197 and −1.5 to 1.5, respectively. According to the calculation results:a vortex pair that generated by the radial inlet and non-preswirling cooling air is somehow unstable which rendered a complex flow field and wall heat transfer pattern in the cavity. For the influence of pumping effect of rotating disks, preswirling of cooling air led to uneven division of cooling air for two counter-rotating disks in radial cooling air inlet type. More cooling air flows towards the disk with same rotating direction of preswirl cooling air and leads to higher Nu in that wall which was enhanced by the increase of preswirl ratio. Axial cooling air inlet results in a much more stable flow than that with radial inlet. The Nu of the wall that cooling air flow towards was higher than that of the other one and this difference increased with the increase of turbulent parameter λT.
Reduced-Order Modeling of Compressor Blades by 1D Finite Elements
Authors: Carassale Luigi , Maurici Mirko , Traversone Laura
Published: August 2015

The concept design of new gas turbines requires fast computational tools able to predict the modal characteristics of the blades on the basis of some incomplete description of their geometry. This paper investigates the potentials of a 1D Finite-Element (FE) formulation based on the beam theory to achieve this result. The key-point of the method is the construction of the FE mesh and the determination of the FE parameters starting from the knowledge of a set of blade cross sections. A typical compressor blade of a large gas turbine is used as a case study to validate the procedure.
Discrete Adjoint Solution of Unsteady Turbulent Flow in Compressor
Authors: Ma Can , Su Xinrong , Yuan Xin
Published: August 2015

Unsteady blade row interactions play an important role in the performance of the compressor stages. However, due to the large cost of the unsteady flow simulation, most aerodynamic optimizations of the compressor are based on the steady flow simulation. This paper adopts the time spectral method to reduce the cost of the unsteady flow simulation and a discrete adjoint solver based on the unsteady flow solver has been developed. The unsteady flow equations and the adjoint equations are solved using an in-house code. The in-house code is based on the finite volume method and solves the URANS (Unsteady Reynolds Averaged Navier-Stokes) equations on the multi-block structured mesh. For spatial discretization the 3rd order WENO (Weighted Essentially Nonoscillatory) upwind scheme is used for reconstruction and the convective flux is computed with Roe’s approximate Riemann solver. The widely used one-equation Spalart-Allmaras turbulence model is adopted for the flow simulation. For the adjoint solution, the constant-eddy viscosity assumption is adopted and only the main flow adjoint equations are solved. The adjoint equations are formed in a discrete manner, which leads to more accurate discrete objective function sensitivity than the continuous adjoint method. The present work serves as an essential part of the system for efficient unsteady aerodynamic optimization of turbomachinery.
Numerical Investigation of Non-Axisymmetric Endwalls in a High Pressure Axial Flow Turbine
Authors: Na Zhenzhe , Liu Bo
Published: August 2015

In this paper, an optimization system was applied to design the non-axisymmetric endwalls for the stator of a high pressure axial flow turbine. This optimization system combines the endwall parameterization, 3D Navier-Stokes flow field calculation and genetic algorithm based on artificial neural network, which has the advantages of flexible geometry representation and automatic design of the optimal non-axisymmetric endwalls.

And, the 3D steady flow field calculation was carried out to analyze the detailed behavior of complex flow structures pre and post optimization and to examine the influences of the optimized endwalls on the stage performance as well. The results of investigation show that the optimized non-axisymmetric endwalls can significantly decrease the flow loss in the stator, but also affect other aerodynamic parameters at the stator exit, especially the flow angle, and then the flow loss at the rotor exit caused by both the passage vortex in the rotor passage and the tip leakage vortex were increased by changing the incidence angle of the rotor due to the non-axisymmetric endwalls. Finally, the stage performance of the HP turbine is not improved as expected.
Aerodynamic and Heat Transfer Optimization of One Stage Air-Cooled Turbine
Authors: Lu Shaopeng , Qiang Xiaoqing , Wen Fengbo , Teng Jinfang
Published: August 2015

In this paper, we present a study on the aerodynamic and heat transfer performance optimization of one stage air-cooled turbine. In order to tackle the high cost associated with both CFD simulations and the large number of design variables involved, 28 parameters are chosen as the optimization variables including the blade profiles and the direction of film cooling holes. Multiple Pareto Fronts are constructed using the optimization algorithm NSGA-II. A new objective function is proposed to reflect the worst heat transfer condition of the blade except the objective function which is used to reflect the aerodynamic performance. Then three solutions are chosen according to design requirements to compare with the original scheme. The aerodynamic efficiency is improved by 1.5%, and the second objective function is improved by 110.48%. The maximum temperature and the area of the high temperature region is decreased significantly. The result shows that the shock loss is decreased in the stator passage, and the increase of the reaction degree increased the rotor load and changed the separation structure. All the reasons mentioned above can improve the aerodynamic efficiency. The heat transfer effect improvement mainly due to the direction change of the film holes. The direction change makes the coolant distribution more reasonable than the original scheme, so the coolant could cover the blade directly. Meanwhile, the double-jet ejection plays an important role in the improvement of film cooling.
Scaling of Adiabatic Effectiveness and Net Heat Flux Reduction From Near Ambient to Engine Temperatures
Authors: Greiner Nathan J. , Polanka Marc D. , Rutledge James L.
Published: August 2015

The present work computationally examines the scaling of a fan-shaped hole’s film-cooling performance from a near ambient temperature to an engine temperature on a flat plate. Heat flux distributions for both film-cooled and non-film-cooled cases were computed for several isothermal boundary conditions. Cases with engine representative freestream temperatures and near ambient temperatures were examined.

This study first shows that the adiabatic wall temperatures interpolated from the isothermal results were lower than those measured directly using an adiabatic wall boundary condition. This was due to the presence of a thermal boundary layer in the isothermal results, which would not develop for the adiabatic case. As a result, the adiabatic effectiveness found with adiabatic models will not represent the true thermal condition found in the engine. Finally, this study shows that both the adiabatic effectiveness interpolated from the isothermal results and Net Heat Flux Reduction can be scaled from low temperature to high temperature by proper non-dimensional matching.
Experimental Investigation of Net Heat Flux Reduction at Combustion Temperatures
Authors: Greiner Nathan J. , Polanka Marc D. , Rutledge James L. , Shewhart Andrew T.
Published: August 2015

The present work examines film cooling on a flat plate surface with a freestream temperature between 1430K and 1600K and a coolant to freestream density ratio of approximately two. Since the objective of film cooling is to reduce heat flux to a surface, Net Heat Flux Reduction (NHFR) is used to quantify film cooling performance. It is first demonstrated that non-dimensional matching can be used to scale NHFR between freestream temperature conditions of 1490K and 1600K. Next, the NHFR of a single row of cylindrical holes, fan-shaped holes, holes embedded in a trench, and a slot are compared at a blowing ratio of unity. Finally, the NHFR of five rows of cylindrical holes, holes embedded in trenches, and slots are compared to show the effect of a build-up of coolant near the wall.
The Determination of Fan Blade Aerodynamic Loading From a Measured Response
Authors: Muiyser Jacques , Els Daniel N. J. , van der Spuy Sybrand J. , Zapke Albert
Published: August 2015

Large-scale cooling system fans often operate under distorted inlet air flow conditions due to the presence of other fans and the prevalent wind conditions. Strain gauge measurements have been used to determine the blade loading as a result of the unsteady aerodynamic forces. However, these measurements are of the blade’s response to the aerodynamic forces and include the deformation as a result of the first natural frequency being excited. When considering the dominant first natural frequency and bending mode of the fan blade, one can approximate the fan blade as a cantilever beam that acts as a single degree-of-freedom system. The response of a single degree-of-freedom system can be calculated analytically for any excitation if the system’s properties are known. The current investigation focuses on using these equations to create an algorithm that can be applied to the measured response of a fan blade to then extract the aerodynamic forces exciting it. This is performed by using a simple non-linear, least-squares optimization algorithm to fit a complex Fourier series to the response and using the coefficients of each harmonic term to determine the Fourier series representing the excitation function. The algorithm was first tested by applying it to the response of a finite element cantilever beam representing a simplified model of the fan blade. Good results were obtained for a variety of excitation forces and as such the algorithm was then applied to the measured response of a full-scale fan blade. The full-scale blade was excited with a shaker where the forcing function could be accurately controlled. Once validated, the algorithm was applied to a set of strain gauge measurements that were recorded at a full-scale fan while in operation. The reconstructed aerodynamic loading showed increased forces when the blade passed beneath the fan bridge as well as when it approached the windward side of the casing.
Effects of Composition on the Flame Stabilization of Alternative Aviation Fuels in a Toroidal Well Stirred Reactor
Authors: Vijlee Shazib Z. , Novosselov Igor V. , Kramlich John C.
Published: August 2015

The use of alternative/synthetic fuels in jet engines requires improved understanding and prediction of flame stabilization envelopes relative to the behavior of conventional fuels. Previous studies using the Toroidal Well Stirred Reactor (TWSR) found that synthetic alternatives to JP8 behave similarly in terms of lean flameout, but there is significant difference in the flameout behavior of a highly aliphatic fuel versus that of a highly aromatic fuel. Detailed computational fluid dynamics (CFD) and chemical reactor modeling (CRM) is necessary to understand differences in flame stabilization.

The first portion of this study employs CFD models of the TWSR with reduced methane combustion chemistry. The models provide insight into the mechanism of flame stabilization inside the reactor as equivalence ratio is decreased to flameout. The CFD domain is expanded over earlier published TWSR CFD studies to capture previously unknown asymmetrical flame behavior. The Reynolds Stress Model (RSM) is used for turbulence closure, and the Eddy Dissipation Concept (EDC) model is used to include turbulence-chemistry interaction. The CFD results show that radical species (specifically OH) are transported around the reactor to interact with the incoming premixed fuel-air jet and initiate chain branching reactions. As the equivalence ratio decreases, and flameout is approached, the species concentration in the reactor becomes less homogenous. Radical production is delayed and eventually insufficient radical concentrations are available to ignite the incoming jet. The production and transport of radical species throughout the reactor are, thus, responsible for stabilizing the flame. CFD and PSR studies with methane agree that the radical behavior dictates blowout.

The second portion of this study focuses on the importance of radical species in flame stabilization, but now employs a single perfectly stirred reactor (PSR) model, which allows the study of detailed chemistry for individual components of jet fuel. An aliphatic compound (iso-octane) and an aromatic compound (toluene) are used as investigative fuels to compare the differences in the chemical kinetic behavior of blowout for aliphatic versus aromatic fuel classes. The models show that the rates at which radical species (O, H, and OH) destroy the original fuel molecule are significantly different for iso-octane and toluene. During combustion, the radical destruction of toluene is much slower than for iso-octane at a constant temperature. In PSR systems, the toluene flame blows out at a higher temperature because a higher temperature is needed to provide sufficient radical concentrations and reaction rates to maintain a stable flame.
Stall Inception in a Boundary Layer Ingesting Fan
Authors: Perovic D. , Hall C. A. , Gunn E. J.
Published: August 2015

Jet engines with Boundary Layer Ingestion (BLI) could offer significant reductions in aircraft fuel burn compared with podded turbofans. However, the engine fans must run continuously with severe inlet distortion, which is known to reduce stability. In this paper an experimental study has been completed on a low-speed rig fan operating with a BLI-type inlet distortion. Unsteady casing static pressure measurements have been made at multiple locations during stall events. Steady-state, full-annulus area traverses have also been performed at rotor inlet and exit at a near-stall operating point. The reduction in stability caused by BLI is found to be small. It is found that with BLI the fan can operate stably despite the presence of localised regions where the rotor operating point lies beyond the stability boundary measured in clean flow. With the BLI-type distortion applied, the measured rotor incidence varies around the annulus due to non-uniform upstream velocity and swirl. The measured amplitude of unsteady casing pressure fluctuations just prior to stall is found to correlate with the circumferential variation of rotor incidence, suggesting that rotor incidence is a key variable affecting the creation and growth of flow disturbances. In regions of high incidence, disturbances resembling local flow separations are initiated. However, in regions of low or negative incidence, any disturbances decay rapidly. Full rotating stall with BLI occurs when high incidence regions are widespread enough to sustain disturbances which can propagate around the entire annulus.
A Simplified Theory to Justify Forward Sweep in Low Hub-to-Tip Ratio Axial Fan
Authors: Masi Massimo , Lazzaretto Andrea
Published: August 2015

Many modern axial flow compressor and fan rotors feature forward swept blades. However, there was no general consensus on advantages due to blade forward sweep until some years ago, also because of the difficulties in isolating the effect of blade sweep alone from the global aerodynamic blading behaviour. Thus, while some researchers try to collect in a “sweep package” all modifications connected to the introduction of blade sweep, there is no attempt in the recent literature to formalise a theory on the aerodynamic effect of sweep angle on axial flow fan blades.

This paper first recalls the swept wing concept suggested by Adolf Busemann, then the original swept wing meaning is reinterpreted to present a simplified theory of blade forward sweep. This theory allows to explain the not yet completely understood changes in total pressure and efficiency due to the inclusion of sweep in the design of high circulation gradient controlled vortex design rotors.

A methodology to select the degree of forward sweep to be chosen in the preliminary design of constant-swirl bladings for rotor-only axial flow fan featuring low hub-to-tip ratio is suggested as well.

A specifically designed unswept fan and its modified configurations according to the suggested theory has been verified by using CFD.

The forward swept design increases the unswept fan total pressure in the whole operation range from about 1% to 4% and expands the stall margin at throttling by more than 10% of the design flow rate leaving efficiency and duty unchanged.
Simulation of Tip-Clearance Effects in a Transonic Compressor
Authors: Lejon Marcus , Andersson Niklas , Eriksson Lars-Erik , Ellbrant Lars
Published: August 2015

Tip clearance flow can have a large impact on compressor performance and is therefore important to consider in compressor design. A wide range of computational approaches can be used for modeling tip clearance flow. The different modeling strategies reflect compromises between accuracy and computational time. The present study investigates a large tip gap configuration (1.65% of the rotor tip chord) of the highly loaded transonic 1.5 stage compressor Hulda. The aim of the study is to evaluate different modeling approaches and find a method that can predict the effects of a large tip clearance on compressor performance. The modeling approaches investigated are the SAS-SST model in CFX and the k-ε turbulence model using a wall function and Chien’s low-Reynolds model in the in-house CFD solver VolSol++. Results obtained using the chosen solvers and turbulence models are compared with experimental data, and all approaches are shown to predict the overall performance trends. However, the turbulence kinetic energy in the tip clearance flow and the trajectory of the vortex are shown to vary depending on the method. The SAS-SST model predicts the performance well in terms of total pressure ratio, polytropic efficiency as well as radial distribution of total pressure downstream the rotor. Based on the results from the study, SAS-SST is concluded to be a good candidate for detailed studies of transonic compressors with large tip gaps.
Numerical Investigation of Effect of Geometry Changes in a Model Combustor on Swirl Dominated Flow and Heat Transfer
Authors: Kedukodi Sandeep , Ekkad Srinath , Moon Hee Koo , Kim Yong , Srinivasan Ram
Published: August 2015

Numerical computations are performed on three configurations of a model gas turbine combustor geometry for cold flow conditions. The purpose of this study is to understand the effect of changes to combustor passage section on the location of peak convective heat transfer along the combustor liner. A Reynolds Averaged Navier-Stokes equations based turbulence model is used for all the numerical computations. Simulations are performed on a 3D sector geometry. The first geometry is a straight cylindrical combustor section. The second model has an upstream diverging section before the cylindrical section. Third one has a converging section following the upstream cylindrical section. The inlet air flow has a Reynolds number of 50000 and a swirl number of 0.7. The combustor liner is subjected to a constant heat flux. Finally, liner heat transfer characteristics for the three geometries are compared. It is found that the peak liner heat transfer occurs far downstream of the combustor for full cylinder and downstream convergent cases compared to that in the upstream divergent case. This behavior may be attributed to the resultant pressure distribution due to the combustor passage area changes. Also the magnitude of peak liner heat transfer is reduced for the former two cases since the high turbulent kinetic energy regions within the combustor are oriented axially instead of expanding radially outward. As a consequence, the thermal load on the liner is found to reduce.
Evaluation of Effects of Different Design Parameters on Axial Fan Performance Using CFD
Authors: Matai Racheet , Yavuzkurt Savas
Published: August 2015

The performance of an industrial fan was simulated using CFD and results were compared with the experimental data. The fan is used to cool a row of resistor networks which dissipate excess energy generated by regenerative power in an inverter application. It has a diameter of 24 inches (0.6096m) and rotates at different speeds ranging from 2500 to 3900 RPM depending on the requirements. CFD simulation results were also verified by simulating performance of the same fan at different speeds and comparing the results with what was expected from fan affinity laws. The CFD results matched almost exactly (with ∼0.2% difference for pressure at a given flow rate) with the performance being predicted by the affinity laws. The effect of variation of different parameters such as the blade length, number of blades, and blade chord length was studied. Increasing the blade length at the same RPM increased the mass flow rate (by ∼17%) for the same pressure. Increasing the chord length while keeping the same number of blades, at a given RPM, made the performance curve (pressure versus flow rate, i.e. PV curve) steeper and blades stalled at a higher mass flow rate (8.77 kg/sec compared to the previous 8.44 kg/sec). For the same total blade surface area, less number of blades with longer chords stalled at lower mass flow rates (9.22 kg/sec for a 33% shorter chord and 36 blades compared to 8.3 kg/sec for the original rotor which had 24 blades).
Development and Validation of a Partially Coupled Soot Model for Turbulent Kerosene Combustion in View of Application to Gas Turbines
Authors: Shahriari Bijan , Thomson Murray , Dworkin Seth
Published: August 2015

Soot emissions are by-products of combustion that are well documented to have adverse effects on human health and the environment. Consequently, these emissions are becoming a target for stricter regulations. However, obstacles exist in the implementation of soot models in Computational Fluid Dynamics codes with complex geometry, such as ensuring carbon mass conservation as soot forms. This challenge is due to the thermochemistry interactions in turbulent codes being preprocessed (included in look-up tables), and not solved for directly. This study considers the development of a soot model for kerosene combustion. Coupling is introduced between the soot and gas phase by including nucleation rates within the flamelet library, and by adjusting the concentrations of key soot precursors through additional transport equations. Validation has been performed for turbulent coflow kerosene flames at pressures of 1 and 4.8 bar. This simplified model reasonably predicts the soot volume fraction without tuning of the inception rate.
Unsteady Structure and Development of a Row of Impingement Jets, Including Shear Layer and Vortex Development: Part 1 — Turbulent Jets
Authors: Yang L. , Ligrani P. M. , Ren J. , Jiang H.
Published: August 2015

Considered is a cylinder channel with a single row of 10 aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, an unsteady RANS solver is employed for predictions of flow characteristics within and nearby the 10 impingement jets, where the jet Reynolds number is 15,000. Spectrum analysis of different flow quantities is also utilized to provide data on associated frequency content. Visualizations of three-dimensional, unsteady flow structural characteristics are also included, including instantaneous distributions of Y-component of vorticity, three-dimensional streamlines, a shear layer parameter, and local static pressure. Kelvin-Helmholtz vortex development is then related to local, instantaneous variations of these quantities. Of particular importance are the cumulative influences of cross flows, which result in locally increased shear stress magnitudes, enhanced Kelvin-Helmholtz vortex generation instabilities, and increased magnitudes and frequencies of local flow unsteadiness, as subsequent jets are encountered with streamwise development.
An Experimental and Numerical Study on the Aerothermal Characteristics of a Ribbed Transonic Squealer-Tip Turbine Blade With Purge Flow
Authors: Arisi A. , Phillips J. , Ng W. F. , Xue S. , Moon H. K. , Zhang L.
Published: August 2015

Detailed heat transfer coefficient (HTC) and film cooling effectiveness (Eta) distribution on a squealer tipped first stage rotor blade were measured using an infrared (IR) technique. The blade tip design, obtained from a Solar Turbines Inc. gas turbine, consisted of double purge hole exits and four ribs within the squealer cavity, with a bleeder exit port on the pressure side close to the trailing edge. The tests were carried out in a transient linear transonic wind tunnel facility under land-based engine representative Mach/Reynolds number. Measurements were taken at an inlet turbulent intensity of Tu = 12%, with exit Mach numbers of 0.85 (Reexit=9.75×105) and 1.0 (Reexit = 1.15×106) with the Reynolds number based on the blade axial chord and the cascade exit velocity. The tip clearance was fixed at 1% (based on engine blade span) with a purge flow blowing ratio BR = 1.0. At each test condition, an accompanying numerical study was performed using Reynolds Averaged Navier Stokes (RANS) equations solver ANSYS Fluent to further understand the tip flow characteristics. The results showed that the tip purge flow has a blocking effect on the leakage flow path. Furthermore, the ribs significantly altered the flow (and consequently heat transfer) characteristics within the squealer tip cavity resulting in a significant reduction in film cooling effectiveness. This was attributed to increased coolant-leakage flow mixing due to increased recirculation within the squealer cavity. Overall, the peak heat transfer coefficient on the cavity floor increased with exit Mach/Reynolds number.
Experimental Results and CFD Simulations of Labyrinth and Pocket Damper Seals for Wet Gas Compression
Authors: Vannini Giuseppe , Bertoneri Matteo , Nielsen Kenny Krogh , Iudiciani Piero , Stronach Robert
Published: August 2015

The most recent development in centrifugal compressor technology is towards wet gas operating conditions. This means the centrifugal compressor has to manage a liquid phase which is varying between 0 to 3% Liquid Volume Fraction (LVF) according to the most widely agreed definition. The centrifugal compressor operation is challenged by the liquid presence with respect to all the main aspects (e.g. thermodynamics, material selection, thrust load) and especially from a rotordynamic viewpoint. The main test results of a centrifugal compressor tested in a special wet gas loop [1] show that wet gas compression (without an upstream separation) is a viable technology. In wet gas conditions the rotordynamic behavior could be impacted by the liquid presence both from a critical speed viewpoint and stability wise. Moreover the major rotordynamic results from the previous mentioned test campaign [2] show that both vibrations when crossing the rotor first critical speed and stability (tested through a magnetic exciter) are not critically affected by the liquid phase. Additionally it was found that the liquid may affect the vibration behavior by partially flooding the internal annular seals and causing a sort of forced excitation phenomenon.

In order to better understand the wet gas test outcomes, the authors performed an extensive CFD analysis simulating all the different types of balance piston annular seals used (namely a Tooth on Stator Labyrinth Seal and a Pocket Damper Seal). They were simulated in both steady state and transient conditions and finally compared in terms of liquid management capability.

CFD simulation after a proper tuning (especially in terms of LVF level) showed interesting results which are mostly consistent with the experimental outcome. The results also provide a physical explanation of the behavior of both seals, which was observed during testing.
Investigation of Water Film Formation on Blade Surfaces of a Wet Compression Transonic Compressor Rotor
Authors: Zhang Hai , Jiang Bin , Luo Mingcong , Liu Xiangkun , Fan Shuangming , Yang Lu , Zheng Qun
Published: August 2015

As is known, when water injected at the inlet of the compressor, the water droplets will move onto the blade where water film could form on the blade surface. In this paper, the movement and formation of the water film on a transonic rotor, NASA Rotor 37, are simulated and analyzed by using unsteady numerical methods under different water injecting conditions.

The motions of water droplets and flows in the blade passage are presented in detail. Tearing process of water film on the blade surface is also a key point of this research. The preliminary results indicate that the movement of water droplets is tending to deviate from the suction surface and pile on the pressure surface due to the effect of inertia force, and water film could be formed on the pressure surface. Continuity and scope of the water film on the blade surface will develop with the increasing of droplet sizes and water injection rate. Based on the simulation, it is found that more discrete water films are formed on the pressure side of blade when the droplets move onto the pressure surface, tearing phenomenon may occur where the area is of lower water film thickness. Smaller enough sprayed droplet size can not only ensure the compressor performance of wet compression, but also avoid the erosion caused by water film accumulation.