bluuebunny/crossref_metadata_2025 huggingface dataset:
Cracking Analysis of Intermediate Pressure Inlet Diffuser in 1000MW Steam Turbine Units
Authors: Chen Gang , Zhang Junhui , Ye Xingzhu , Ma Chunlei
Published: August 2017

In 2013, with the operation of 1000MW steam turbine unit in a power plant, the exhaust steam temperature of intermediate pressure (IP) steam turbine exceeded the normal value. After overhaul of the IP steam turbine, a long crack was found through the drain hole of the IP inlet diffuser. The reheat steam leaked out from inside the diffuser to the exhaust cavity. It caused the exhaust temperature to exceed the design value, and reduced the efficiency of the units. Also, if the high temperature steam, which is close to 600°C, came into contact with the outer casing, a significant reduction in life would be obtained. In order to find the root cause of the crack, many efforts have been done within each department of the shanghai turbine plant (STP). Such as material detection, design, manufacture, assembling, etc.

In this paper, a three-dimensional finite element diffuser model was built and the stress state during startup and operation was obtain. It was found that the drain hole at the inside and the groove at the outside of the diffuser are dangerous regions because of the stress concentration. That’s the primary reason for causing the diffuser crack. Then the fracture mechanics software ZenCrack was used to analyze the diffuser crack route. This crack route consistently matched the actual diffuser crack.
A Selective Fast Fourier Filtering Approach Applied to High Frequency Thermoacoustic Instability Analysis
Authors: Grimm Felix , Lourier Jean-Michel , Lammel Oliver , Noll Berthold , Aigner Manfred
Published: August 2017

A method for selective, frequency-resolved analysis of spatially distributed, time-coherent data is introduced. It relies on filtering of Fourier-processed signals with periodic structures in frequency-domain. Therefrom extracted information can be analyzed in both, frequency- and time-domain using an inverse transformation ansatz.

In the presented paper, the approach is applied to a laboratory scale, twelve nozzle FLOX®-GT-burner for the investigation of high-frequency thermoacoustic pressure oscillations and limit-cycle mechanisms. The burner is operated at elevated pressure for partially premixed combustion of a hydrogen and natural gas mixture with air. At a certain amount of hydrogen addition to fuel injection, the burner exhibits self-sustained high-frequency thermoacoustic oscillation. This unstable operation is simulated with the fractional step approach SICS (Semi Implicit Characteristic Splitting), a pressure based solver extension of the Finite Volume based research code THETA (Turbulent Heat Release Extension for the TAU Code) for the treatment of weakly compressible flows with combustion. A hybrid LES/URANS simulation delivers time-resolved simulation data of the thermoacoustically unstable operation condition, which is analyzed with the presented SFFFA (Selective Fast Fourier Filtering Approach).

Acoustic pressure distribution in the combustion chamber is explicitly resolved and assigned to different characteristic modes by signal decomposition. Furthermore, the SFFFA is used for the analysis of acoustic feedback mechanism by investigating filtered transient heat release, acoustic pressure, velocity and mixture fraction. Coherent structures in flow field and combustion as well as periodic convective processes are resolved and linked to transient acoustic pressure, extensively describing the acoustic feedback of the examined burner configuration.
Large-Eddy Simulation and Detailed Modeling of Soot Evolution in a Model Aero Engine Combustor
Authors: Wick Achim , Priesack Frederic , Pitsch Heinz
Published: August 2017

In order to exploit the potential of computational modeling for the reduction of particulate emissions in future aero engines, reliable modeling approaches applicable in system scale simulations are required. Achieving this goal crucially depends on bridging the gap between academic test cases often used for model validation and real world applications. In this work, Large-Eddy Simulations of a model aero engine combustor experimentally investigated at the German Aerospace Center (DLR) are performed using an integrated modeling approach based on the Radiation Flamelet/Progress Variable model and a detailed bivariate soot particle description combined with the Hybrid Method of Moments. First, a non-reacting flow case is simulated to validate the computational setup in absence of the complex interaction of turbulence, chemistry, and soot. Then, the reacting flow is analyzed in terms of velocity, temperature, and soot volume fraction predictions. Measured velocity profiles for the non-reactive case are very well predicted. For the fired combustor, the velocity and temperature fields are well predicted. Soot is overpredicted by the simulation, but qualitatively in reasonable to good agreement with the experimental data.
Development and Applications of a Coupled Particle Deposition Dynamic Mesh Morphing Approach for the Numerical Simulation of Gas Turbine Flows
Authors: Forsyth Peter , Gillespie David R. H. , McGilvray Matthew
Published: August 2017

The presence and accretion of airborne particulates, including ash, sand, dust, and other compounds, in gas turbine engines can adversely affect performance and life of components. Engine experience and experimental work has shown that the thickness of accreted layers of these particulates can become large relative to the engine components on which they form. Numerical simulation to date, using a variety of flow coupling models, has largely ignored the effects of resultant changes in the passage geometry due to the build-up of deposited particles. This paper will focus on updating the boundaries of the flow volume geometry by integrating the deposited volume of particulates on the solid surface. Numerical models of small particulate turbulent motion and stick/bounce models are developed and integrated within commercial software to perform 3D fluid simulations to capture the deposition behaviour. The technique is implemented using a novel, coupled deposition-dynamic mesh morphing approach to the simulation of particulate-laden flows using RANS modelling of the bulk fluid, and Lagrangian-based particulate tracking. On an iterative basis the calculated particle deposition distributions are used to modify the surface topology by altering the locations of surface nodes. The mesh, continuous phase solution, and particle tracking are then recalculated, from which the mesh is again modified. The sensitivity to the modelling time steps employed is explored. This mesh morphing technique is further refined through the application of the particle stick-bounce model of Bons et al. [1] and the Continuous Random Walk model. An impingement geometry case is used to assess the validity of the technique, and a passage with film cooling holes is interrogated. The paper illustrates that for engine realistic levels of internal deposition this can lead to a significant disparity in the local aerodynamic flow field. Modelling of several internal flow fields have been investigated to illustrate the use of the technique. Differences are seen for all of the sticking and solid phase motion models employed. Notably, there are real discrepancies in using commercial and bespoke models. At small solid particle sizes considerable disparity is observed between the discrete and continuous random walk modelling approaches, while the position and level of accretion is altered through the use of a non-isotropic stick and bounce model.
A Machine Learning Approach for Determining the Turbulent Diffusivity in Film Cooling Flows
Authors: Milani Pedro M. , Ling Julia , Saez-Mischlich Gonzalo , Bodart Julien , Eaton John K.
Published: August 2017

In film cooling flows, it is important to know the temperature distribution resulting from the interaction between a hot main flow and a cooler jet. However, current Reynolds-averaged Navier-Stokes (RANS) models yield poor temperature predictions. A novel approach for RANS modeling of the turbulent heat flux is proposed, in which the simple gradient diffusion hypothesis (GDH) is assumed and a machine learning algorithm is used to infer an improved turbulent diffusivity field. This approach is implemented using three distinct data sets: two are used to train the model and the third is used for validation. The results show that the proposed method produces significant improvement compared to the common RANS closure, especially in the prediction of film cooling effectiveness.
Implicit LES for Shaped-Hole Film Cooling Flow
Authors: Oliver Todd A. , Anderson Joshua B. , Bogard David G. , Moser Robert D. , Laskowski Gregory
Published: August 2017

Results of a recent joint experimental and computational investigation of the flow through a plenum-fed 7-7-7 shaped film cooling hole are presented. In particular, we compare the measured adiabatic effectiveness and mean temperature against implicit large eddy simulation (iLES) for blowing ratio approximately 2, density ratio 1.6, and Reynolds number 6000. The results overall show reasonable agreement between the iLES and the experimental results for the adiabatic effectiveness and gross features of the mean temperature field. Notable discrepancies include the centerline adiabatic effectiveness near the hole, where the iLES under-predicts the measurements by Δη ≈ 0.05, and the near-wall temperature, where the simulation results show features not present in the measurements. After showing this comparison, the iLES results are used to examine features that were not measured in the experiments, including the in-hole flow and the dominant fluxes in the mean internal energy equation downstream of the hole. Key findings include that the flow near the entrance to the hole is highly turbulent and that there is a large region of backflow near the exit of the hole. Further, the well-known counter-rotating vortex pair downstream of the hole is observed. Finally, the typical gradient diffusion hypothesis for the Reynolds heat flux is evaluated and found to be incorrect.
Computational Analysis of a Novel Cooling Scheme for Ultra Compact Combustor Turbine Vanes
Authors: Bohan Brian T. , Polanka Marc D. , Rutledge James L.
Published: August 2017

The Ultra Compact Combustor (UCC) has the potential to improve overall engine efficiency at a reduced size, while offering a unique component configuration that can allow for novel cooling of turbine vanes located below the circumferential cavity. In this configuration the leading edge of the turbine vane is located upstream of the combustor, with hot gases impinging near 1/5-chord and aft to the trailing edge. Therefore the leading edge remains in a cold region of the flow allowing openings in the stagnation region of the vane to ingest cool core flow. A computational fluid dynamics (CFD) analysis is presented that analyzed stagnation fed cooling variations for the current UCC turbine vane. The variants included several internal only cooling schemes and one external film cooling scheme. The internal only variants showed that with proper component geometry the internal pressure could exceed the external pressure downstream from the leading edge. The film cooling hole variant showed that coolant did in fact exit the vane through 3 of the 8 cooling holes in a similar fashion as a compressor fed scheme. The determination if coolant would exit the holes was highly dependent on the external pressure gradient on the vane.
A Numerical Investigation on the Differences Between Annular and Flat Film Cooled Endwalls
Authors: Yao Ran , Wang Jianhua , Yang Wenshuo , Wang Wei , Du Zhineng , Wang Ming
Published: August 2017

Models simplified from real annular turbine cascades into linear cascades have been widely used in the experimental investigations on the cooling performances of turbine blade and endwall (including hub and shroud), but errors caused by the simplifications are seldom considered and discussed. This paper presents a numerical comparison of film cooled endwall between real annular and linear cascade. The model used in this work is derived from a real gas turbine stator, which consists of 46 vanes. Numerical simulations are carried out by the commercial software ANSYS CFX 15.0 and ICEM 15.0. Conjugate Heat Transfer (CHT) analysis is used to solve pressure field and temperature field through a fully implicit multi-grid coupling algorithm, and the two-equation turbulence model, Shear Stress Transport (SST) k-ω, is selected as closed equations. To validate the numerical strategy, a series of experiments is conducted by a flat endwall model, in the hot gas wind tunnel at University of Science and Technology of China (USTC). Using the validated numerical strategy, the fluid flow and heat transfer characteristics of the real annular and flat endwalls models are simulated and compared. The differences in static pressure, temperature and overall cooling effectiveness between the two models are exhibited, and the reliability and reasonability of the simplification from a real annular cascade to a linear cascade are discussed. The results show the following important conclusion: If the pressure problems of hub endwall are considered only, the flat endwall simplification is acceptable, but at experimental conditions, the cooling effectiveness of the flat endwall could be 10% higher than that of the real annular endwall, while at realistic condition, the difference decreases obviously.
Efficient Lifetime Prediction of High Pressure Turbine Blades in Real Life Conditions
Authors: van Enkhuizen Marinus Johannus , Dresbach Christian , Reh Stefan , Kuntzagk Stefan
Published: August 2017

Jet engines of airplanes are designed such that in some components damage occurs and grows in service without being critical up to a certain level. Since maintenance, repair and component exchange are cost-intensive and limit the operating life of the engine, it is necessary to predict the component lifetime using an acceptable computational effort.

To efficiently calculate the lifetime consumption of turbine components with sufficient accuracy under operational conditions, we developed a hybrid approach, which is based on the following three steps: First, the possible operation space is analyzed and reduced to define a manageable Design-of-Experiments (DoE) space. Subsequently, precise aerodynamic and structural mechanic simulations of the component are performed at each DoE support point and the results are stored in a database. Next, the lifetime consumption of the component for the operation profile of interest is calculated based on interpolated stress and temperature fields using suitable lifetime prediction models. The implemented lifetime models are based on accepted lifetime prediction models for creep, fatigue and combined loading, which were extended to incorporate the loading situation on a high pressure turbine (HPT) blade.

Due to efficient data management, the computational time for calculating the lifetime consumption of a whole HPT blade is approximately four seconds for one take-off. Consequently, a full three dimensional lifetime consumption analysis of the lifespan of a HPT blade is possible within a few hours. Using the developed approach, it is now possible to predict the lifetime of a HPT blade for different operators with the necessary precision in an acceptable time. To demonstrate the developed approach, a HPT blade of an exemplarily chosen jet engine with known flight history and documented borescope inspections will be used. Comparing the calculated lifetime of the HPT blade with the documented findings from shop visits reveals that the simulation is in good agreement for the investigated flight mission of the chosen engine.
Towards High-Order Large Eddy Simulation of Aero-Thermal Flows for Turbomachinery Applications
Authors: Bhaskaran R. , Jia Feilin , Laskowski Gregory M. , Wang Z. J. , Paliath Umesh
Published: August 2017

The solution accuracy and computational efficiency of high order Large Eddy Simulation (LES) solvers are evaluated on two benchmark open literature blade cascade problems. The first problem concerns wake development in the T106A low pressure turbine cascade [1]. The second problem examines the effect of free-stream turbulence on heat transfer from the VKI first stage high pressure turbine vane [2]. The calculations are performed with two independently developed high order LES solvers using completely different numerical algorithms. The first solver FDL3Di [3] was originally developed at the Airforce Research Laboratory (AFRL) and employs structured overset grids. It uses a sixth order compact finite difference scheme in space along with an implicit Beam-Warming scheme for time marching. The second solver, hpMusic, is developed at the University of Kansas [4]. This is a variable order (up to sixth order) unstructured grid solver employing a discontinuous formulation known as flux reconstruction (FR) / correction procedure via reconstruction (CPR) [5]. The computational grids used are independently tuned for each application. The solvers are benchmarked against experimental data for wake development and blade heat transfer coefficient. Further physical insights in to the test cases are also obtained, filling gaps in experimental results, especially for the VKI problem.
Experimental Study to Enhance Resistance for Boundary Layer Flashback in Swirl Burners Using Microsurfaces
Authors: Al-Fahham Mohammed , Hatem Fares Amer , Alsaegh Ali Safa , Valera Medina Agustin , Bigot Samuel , Marsh Richard
Published: August 2017

Flame flashback has been one of the major instability problems in premixed gas turbine combustion with the potential to cause considerable damage to the combustion system hardware in addition to significant increase in pollutant levels. Swirl combustion has been proven as an effective flame stabilizer over a wide range of operation conditions, although swirling systems can be prone to various types of flashback under fuel premixed conditions. Unfortunately, using methodologies for the mitigation of one flashback mechanism will lead to another one in these systems. Therefore, this paper focuses on improving Boundary Layer Flashback (BLF) while trying to mitigate Combustion Induced Vortex Breakdown (CIVB) in a medium swirl combustion system. A new technique inspired by Biomimetic Engineering has been developed to use micro-surfaces for this aim. The use of these biologically designed shapes for successful flow stabilisation allows improved control of the boundary layer, thus reducing outflow drag while resisting the random propagation of flashback. Therefore, boundary layer flashback resistance using this concept was investigated numerically and experimentally in a 150 kW tangential swirl burner to determine the effects of using a micro-surface in swirling flows with and without central air injection. Various techniques were used, including Hot Wire Anemometry, LDA measurements, LES CFD, and RANS CFD. The results showed enhancement of the system resistance to boundary layer flashback, and a new combustion stability map was generated with a wider operational region when using central injection combined with micro-surfaces, thus avoiding two types of flashback mechanisms, i.e. BLF and CIVB.
Highly Resolved LES Study of Gap Size Effect on Low-Pressure Turbine Stage
Authors: Pichler R. , Michelassi V. , Sandberg R. , Ong J.
Published: August 2017

Blade-to-blade interactions in a low-pressure turbine were investigated using highly resolved compressible large eddy simulations. For a realistic setup, a stator and rotor configuration with profiles typical of low-pressure turbines was used. Simulations were conducted with an in-house solver varying the gap size between stator and rotor from 21.5% to 43% rotor chord. To investigate the effect of the gap size on the prevailing loss mechanisms, a loss breakdown was conducted. It was found that in the large gap size case, the turbulence kinetic energy levels of the stator wake close to the rotor leading edge were only one third of those in the small gap case, due to the longer distance of constant area mixing. The small time averaged suction side separation on the blade, found in the large gap case, disappeared in the small gap calculations, confirming how stronger wakes can keep the boundary layer attached. The higher intensity wake impinging on the blade, however, did not affect the time averaged losses calculated using the control volume approach of Denton. On the other hand, losses computed by taking cross sections upstream and downstream of the blade revealed a greater distortion loss generated by the stator wakes in the small gap case. Despite the suction side separation suppression, the small gap case gave higher losses overall due to the incoming wake turbulent kinetic energy amplification along the blade passage.
Assessment of the Effect of Environmental Conditions on Rotorcraft Pollutant Emissions at Mission Level
Authors: Ortiz-Carretero Jesus , Castillo Pardo Alejandro , Pachidis Vassilios , Goulos Ioannis
Published: August 2017

It is anticipated that the contribution of rotorcraft activities to the environmental impact of civil aviation will increase in the forthcoming future. Due to their versatility and robustness, helicopters are often operated in harsh environments with extreme ambient conditions and dusty air. These severe conditions affect not only the engine operation but also the performance of helicopter rotors. This impact is reflected in the fuel burn and pollutants emitted by the helicopter during a mission. The aim of this paper is to introduce an exhaustive methodology to quantify the influence of the environment in the mission fuel consumption and the associated emissions of nitrogen oxides (NOx). An Emergency Medical Service (EMS) and a Search and Rescue (SAR) mission were used as a case study to simulate the effects of extreme temperatures, high altitude and compressor degradation on a representative Twin-Engine Medium (TEM) weight helicopter, the Sikorsky UH-60A Black Hawk. A simulation tool for helicopter mission performance analysis developed and validated at Cranfield University was employed. This software comprises different modules that enable the analysis of helicopter flight dynamics, powerplant performance and exhaust emissions over a user defined flight path profile. The results obtained show that the environmental effects on mission fuel and emissions are mainly driven by the modification of the engine performance for the particular missions simulated. Fluctuations as high as 12% and 40% in mission fuel and NOx emissions, respectively, were observed under the environmental conditions simulated in the present study.
Experimental Investigation Into Crater Morphology for Droplets Impinging on a Moving Film
Authors: Mitchell Antony J. , Hann David , Simmons Kathy
Published: August 2017

The behaviour of impinging droplets is a field that has been studied for over 100 years mostly focused on impingements upon solid substrates or static films. Few studies report cases when the moving film might influence the impact outcomes. In many situations where droplet impact is industrially relevant there is film motion and relying on observations and correlations for impacts on static films might not be reliable.

The University of Nottingham’s Gas Turbine and Transmissions Research Centre is conducting a research program investigating impact outcomes and crater morphology for water droplets of around 2–3 mm falling under the influence of gravity and impacting on films created by water flow down an inclined plane. In the investigation reported here dimensionless film heights were in the range 0.77 to 1.8 and the plane was inclined at 10° to the horizontal. This paper details the investigation into the morphology of the crater formed during an impingement event. The properties of the impinging droplet are measured using a high-speed camera to provide a side-view of the impingement. Brightness-Based Laser-Induced Fluorescence (BB-LIF) is used to provide three-dimensional measurements of the crater during the self-similar inertial regime. This is accomplished by doping the fluid with Rhodamine 6G, and exciting the fluorescence with a 527 nm pulsed Nd-Yag laser. A second high-speed camera observes the impingement from below in order to provide information about the behaviour of the film.

The development of cavity depth is compared to published models from work on both deep and thin static films. Further, the development of cavity width with time is compared against existing models from static film research. A modification to these models is proposed that includes the effects of film velocity. The effect of film movement on the cavity footprint is examined; both the equivalent radius and the cavity width are investigated and the differences compared to static film experiments are quantified. Some modifications to an established width model are suggested, and an effect of droplet diameter upon this cavity width is noted. The work shows that static film models are not universally applicable for moving films.
Aerodynamic Optimization of a Transonic Centrifugal Compressor by Using Arbitrary Blade Surfaces
Authors: Hehn Alexander , Mosdzien Moritz , Grates Daniel , Jeschke Peter
Published: August 2017

A transonic centrifugal compressor was aerodynamically optimized by means of a numerical optimization process. The objectives were to increase the isentropic efficiency and to reduce the acoustic signature by decreasing the amplitude of pre shock pressure waves at the inlet of the compressor. The optimization was performed at three operating points on the 100% speed line in order to maintain choke mass flow and surge margin. At the design point, the specific work input was kept equal. The baseline impeller was designed by using ruled surfaces due to requirements for flank milling. To investigate the benefits of arbitrary blade surfaces, the restrictions of ruled surfaces were abolished and fully 3D blade profiles allowed. In total therefore, 45 parameters were varied during the optimization. The combined geometric and aerodynamic analysis reveals that a forward swept leading edge and a concave suction side at the tip of the leading edge are effective design features for reducing the shock strength. Beyond that the blade shape of the optimized compressor creates a favorable impeller outlet flow, which is the main reason why the performance of the vaneless diffuser improves. In total a gain of 1.4%-points in isentropic total-to-static efficiency, evaluated by CFD at the exit plane of the vaneless diffuser, is achieved.
Impingement/Effusion Cooling With Low Coolant Mass Flow
Authors: Oguntade H. I. , Andrews G. E. , Burns A. D. , Ingham D. B. , Pourkashanian M.
Published: August 2017

A low coolant mass flow impingement/effusion design for a low NOx combustor wall cooling application was predicted, using conjugate heat transfer (CHT) computational fluid dynamics (CFD). The effusion geometry had 4306/m2 effusion holes in a square array with a hole diameter of D and pitch of X and X/D of 1.9. It had previously been shown experimentally and using CHT/CFD to have the highest adiabatic and overall cooling effectiveness for this number of effusion holes. The effect of adding an X/D of 4.7 impingement jet wall with a 6.6 mm impingement gap, Z, and Z/D of 2.0, on the overall cooling effectiveness was predicted for several coolant mass flow rates, G kg/sm2bar. At low G the internal wall heat transfer dominated the overall cooling effectiveness. The addition of impingement cooling to effusion cooling gave only a small increase in the overall cooling effectiveness at all G at 127mm downstream of the start of effusion cooling. An overall cooling effectiveness >0.7 was predicted for a low G of 0.30 kg/sm2bar. This represents about 15% of the combustion air for a typical industrial gas turbine combustor and design changes to reduce this further were suggested based on the predictions of this geometry. The main benefit of the impingement cooling was at the start of the effusion cooling, where the overall cooling effectiveness was dominated by the internal wall impingement and effusion cooling. The separate effusion and impingement cooling were also predicted for comparison with their combination. This showed that the combination of impingement and effusion was not the sum of the individual effusion and impingement heat transfer. The predictions showed that the aerodynamic interactions decreased the effusion and impingement internal wall heat transfer.
Predicting Efficiency of a Turbine Driven by Pulsing Flow
Authors: Fernelius Mark H. , Gorrell Steven E.
Published: August 2017

One of the challenges of integrating pressure gain combustion into a gas turbine engine is that a turbine driven by pulsing flow experiences a decrease in efficiency. Computational fluid dynamic simulations validated with experiments showed that pulse amplitude is the driving factor for decreased turbine efficiency and not the pulsing frequency. A quadratic correlation between turbine efficiency and corrected pulse amplitude is presented. Incidence variation is shown to cause the change in turbine efficiency and a correlation between corrected incidence and corrected amplitude is shown to predict turbine efficiency.
Transport of Microparticles in a Turbulated Serpentine Passage
Authors: Borup Daniel D. , Elkins Christopher J. , Eaton John K.
Published: August 2017

Quantitative, fully three-dimensional particle concentration data were obtained for a streak of ∼30 micron titanium micro-spheres injected isokinetically into the center of flow at Re = 20,000 through a ribbed serpentine passage. The rib height to channel height ratio was 10% and the pitch was 60% channel height. The ribs were oriented at 45° to the flow and staggered on opposite walls. Each passage was 10 ribs long. Concentration measurements were made using a newly developed Magnetic Resonance Imaging (MRI) based technique with an uncertainty of ±0.018% particles by volume. Three-component mean velocity data were also obtained using an existing MRI technique. The concentration data are in good agreement with the expected large-scale particle transport based on the mean flow field. Quantitative analysis is performed in the high-concentration portion of the streak where turbulent dispersion plays a significant role. Particles also tend to concentrate just upstream of the angled ribs, forming rivulets that persist as the flow returns to the channel center. These results suggest the potential for improved design of dust-resistant cooling systems based on experimental data. It is also concluded that the data set comprises a suitable validation case for Computational Fluid Dynamics (CFD) simulations.
Impingement/Effusion Cooling Wall Heat Transfer: Reduced Number of Impingement Jet Holes Relative to the Effusion Holes
Authors: El-Jummah Abubakar M. , Nazari Ahmad , Andrews Gordon E. , Staggs John E. J.
Published: August 2017

Internal wall heat transfer for impingement/effusion cooling was measured and predicted using conjugate heat transfer (CHT) computational fluid dynamics (CFD). The work was only concerned with the internal wall heat transfer and not with the effusion film cooling and there was no hot gas crossflow. Previous work had predicted impingement/effusion internal wall cooling with equal number of holes. The present work investigated a small number of impingement holes and a larger number of effusion holes. The aim was to see if the effusion holes acted as a suction surface to the impingement surface flow and thus enhanced the wall heat transfer. Hole ratios of 1/4, 1/9 and 1/25 were studied by varying the number of effusion holes for a fixed array of impingement holes and a fixed impingement gap, Z, of 8 mm. The Z/D for the impingement holes was 2.7. The impingement hole pitch, X, to diameter, D ratio X/D was 10.6 at a constant effusion hole X/D of 4.7 for all the configurations. The impingement holes were aligned on the midpoint of four effusion holes. The results were computed for a mass flux G from 0.1–0.94 kg/sm2bar for all n. This gave 26 separate CFD/CHT computations. Locally surface, X2, average heat transfer coefficient (HTC), hx, values were determined using the lumped capacitance method. Nimonic 75 metal walls with imbedded thermocouples were used to determine hx from the time constant in a transient cooling experiment following electrical heating to about 80°C. The CHT/CFD predictions showed good agreement with measured data and the highest number of effusion holes for the 1/25 hole ratio gave the highest h. However, comparison with the predicted and experimental results for equal number of impingement and effusion holes for the same Z, showed that there was little advantage of decreasing the number of impingement holes, apart from that of decreasing the Z/D significantly for the 1/15 hole ratio, which increased the heat transfer. The largest number of effusion holes had the highest heat transfer due to the greater internal surface area of the holes and their closer spacing. This was present irrespective of the number of impingement holes and there was no evidence of any benefit of the 25 effusion holes enhancing the single impingement jet heat transfer. For the lowest number of effusion hole there was predicted to be a small disadvantage of reducing the number of impingement jets.
Aerodynamic Optimization Design of Last Stage Long Blade for Steam Turbine Using Self-Adaptive Differential Evolution Algorithms and RANS Solutions
Authors: Yin Mingyan , Li Jun , Song Liming , Li Bin , Zhong Gangyun , Fan Xiaoping , Sun Qi , Feng Zhenping
Published: August 2017

High performance of the last stage long blade plays an important role on the aerodynamic performance of low pressure cylinder for steam turbines. Aerodynamic optimization design of the last stage long blade for the maximization total-total isentropic efficiency with constraints of mass flow rate and leaving velocity using self-adaptive differential evolution algorithm is presented in this work. The aerodynamic performance of last stage is evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) computations. Six two-dimensional airfoils along the span and three controlling points for the radial foil of blade using B-Spline functions are used to parameterize the three-dimensional profiles of the stator and rotor blade of the last stage, respectively. Self-adaptive differential evolution algorithms is developed to optimize the maximization total-total isentropic efficiency of last stage. The results show that the total-total isentropic efficiency of the optimized last stage is higher 1.68% than that of the referenced design. Furthermore, the aerodynamic performance of the five stages low pressure cylinder with three extractions coupled with the optimized last stage and referenced design is analyzed and compared. The detailed flow field and aerodynamic parameters of the optimized last stage are also illustrated.
Investigation on the Highly Loaded Helium Compressor Based on Helium Thermophysical Properties: Part A — The Design of Highly Loaded Axial Helium Compressor
Authors: Tian Zhitao , Zheng Qun , Jiang Bin , Zhu Qingfang
Published: August 2017

Helium is hard to be compressed with the traditional way of air compression because of thermophysical properties differences between helium and air, which would result in helium compressor being of much more stages and shorter blades. In this paper, based on the flowing features of helium, that is, the higher sound speed, the lower Mach number etc. which are also due to the specific thermophysical properties of helium, the design method of a highly loaded helium compressor is investigated in detail. The relationships between the highly loaded helium compressor flow coefficient, load coefficient, reaction degree and its efficiency and pressure ratio are systematically discussed. Then, to meet the higher efficiency and reliability requirements, unequal spanwise work distribution technique is implemented. The results indicate that a 16 stages helium compressor of a 300MW HTGR can be reduced to a 3 stages compressor by the highly loaded design method proposed in this paper, under the condition of the same tip tangential velocity. The polytropic efficiency is 90%, which is higher than that of the previous 16 stages compressor.
A Rim Seal Ingress Model Based on Turbulent Transport
Authors: Savov Svilen S. , Atkins Nicholas R.
Published: August 2017

Recent experimental work from the present authors demonstrated that interactions between the mainstream and cavity/rim seal flows lead to ingestion mechanisms with a range of length scales. In addition to the (well known) effect of the vane and blade pressure fields, it was demonstrated that the shear layer instabilities between the mainstream and rim seal flows can affect ingress. Building upon these observations and the understanding in the literature, this paper presents a model which relates rotor-stator cavity seal effectiveness to purge flow rate based on turbulent transport. The main assumption is that all length scales of ingress lead to an effective eddy diffusivity. This eddy diffusivity drives ingress across the seal concentration gradient. Following Prandtl’s mixing length hypothesis for eddy viscosity, the model uses an empirical constant representing an equivalent mixing length. This assumption is shown to be sufficient across a limited range of dimensionless flow rates. An extension of the model is presented to account for the reduction in turbulent mixing in the rim seal recirculation region as it becomes washed out with increasing purge flow. The rate at which the effect of the rim seal recirculation region gets washed out is modelled with a purge-to-mainstream blowing ratio term and the volume fraction of the seal occupied by the rim seal recirculation. The differences in volume fraction and blowing ratio between the different experiments in literature are defined by the geometry and flow condition only. By fitting, it is shown that the model is sufficient to capture a wide variety of experimental data in the literature and that of the present authors. The results and the model derivation provide an encouraging first step and a framework towards a model that is sensitized to both geometry and flow conditions.
Optimum Aerodynamic Design of Centrifugal Compressor Impeller Using an Inverse Method Based on Meridional Viscous Flow Analysis
Authors: Oka Nobuhito , Furukawa Masato , Yamada Kazutoyo , Itou Sasuga , Ibaraki Seiichi , Iwakiri Kenichiro , Hayashi Yoshihiro
Published: August 2017

An optimum aerodynamic design method for centrifugal compressor impeller has been developed. The present optimum design method is using a genetic algorithm (GA) and a two-dimensional inverse blade design method based on a meridional viscous flow analysis. In the meridional viscous flow analysis, an axisymmetric viscous flow is numerically analyzed on a two-dimensional meridional grid to determine the flow distribution around the impeller. Full and splitter blade effects to the flow field are successfully evaluated in the meridional viscous flow analysis by a blade force modeling. In the inverse blade design procedure, blade loading distribution is given as the design variable. In the optimization procedure, the total pressure rise and adiabatic efficiency obtained from the meridional viscous flow analysis are employed as objective functions. Aerodynamic performance and three-dimensional flow fields in the Pareto-optimum design and conventional design cases have been investigated by three-dimensional Reynolds averaged Navier-Stokes (3D-RANS) and experimental analyses. The analyses results show performance improvements and suppressions of flow separations on the suction surfaces in the optimum design cases. Therefore, the present aerodynamic optimization using the inverse method based on the meridional viscous flow analysis is successfully achieved.
Integrated Approach for Steam Turbine Thermo-Structural Analysis and Lifetime Prediction at Transient Operations
Authors: Moroz Leonid , Doerksen Glenn , Romero Fernando , Kochurov Roman , Frolov Boris
Published: August 2017

In order to achieve the highest power plant efficiency, original equipment manufacturers (OEMs) continuously increase turbine working parameters (steam temperatures and pressures), improve components design and modify start-up cycles to reduce time while providing more frequent start-up events. All these actions result in much higher levels of thermo-stresses, a lifetime consumption of primary components and an increased demand for accurate thermo-structural and LCF simulations.

In this study, some aspects of methodological improvement are analyzed and proposed in the frame of an integrated approach for steam turbine components thermo-structural analysis, reliability and lifetime prediction. The full scope of the engineering tasks includes aero/thermodynamic flow path and secondary flows analysis to determine thermal boundary conditions, detailed thermal/structural 2D and 3D FE models preparation, components thermal and stress-strain simulation, rotor-casing differential expansion and clearances analysis, and finally, turbine unit lifetime estimation. Special attention is paid to some of the key factors influencing the accuracy of thermal stresses prediction, specifically, the effect of ‘steam condensation’ on thermal BC, the level of detailing for thermal zones definition, thermal contacts and mesh quality in mechanical models. These aspects have been studied and validated against test data, obtained via a 30 MW steam turbine for combined cycle application based on actual start-up data measured from the power plant. The casing temperatures and rotor-stator differential expansion, measured during the commissioning phase of the turbine, were used for methodology validation. Finally, the evaluation of the steam turbine HPIP rotor lifetime by means of a low cycle fatigue approach is performed.
Numerical Investigation of the Heat Transfer and Flow Phenomena in an IP Steam Turbine in Warm-Keeping Operation With Hot Air
Authors: Toebben Dennis , Łuczyński Piotr , Diefenthal Mathias , Wirsum Manfred , Reitschmidt Stefan , Mohr Wolfgang F. D. , Helbig Klaus
Published: August 2017

Nowadays, steam turbines in conventional power plants deal with an increasing number of startups due to the high share of fluctuating power input of renewable generation. Thus, the development of new methods for flexibility improvements, such as reduction of the start-up time and its costs, have become more and more important. At the same time, fast start-up and flexible steam turbine operation increase the lifetime consumption and reduce the inspection intervals. One possible option to prevent these negative impacts of a flexible operation is to keep the steam turbine warm during a shut down and a startup. In order to do so, General Electric has developed a concept for warm-keeping respectively pre-warming of a high-pressure (HP) / intermediate-pressure (IP) steam turbine with hot air: After a certain cool-down phase, air is passed through the turbine while the turbine is rotated by the turning engine. The flow and the rotational direction can be inverted to optimize the warming operation. In order to fulfill the requirements of high flexibility in combination with reduced costs and thermal stresses during the start-up, a detailed investigation of the dominant heat transfer effects and the corresponding flow structure is necessary: Complex numerical approaches, such as Conjugate Heat Transfer (CHT), can provide this corresponding information and help to understand the physical impact of the flow phenomena.

The aim of the present work is thus to understand the predominant heat transport phenomena in warm-keeping operation and to gain detailed heat transfer coefficients within the flow channel for blade, vane and shrouds. A multitude of steady-state simulations were performed to investigate the different warm-keeping operation points. Data from literature was recomputed in good agreement to qualitatively validate the numerical model in windage operation. Furthermore, the steady-state simulations were compared with transient Computational Fluid Dynamics (CFD) simulations to verify that the flow in warming operation can be simulated with a steady-state case. The transient calculations confirm the steady-state results. A variation of the mass flow rate and the rotational speed was conducted to calculate a characteristic map of heat transfer coefficients. The Conjugate Heat Transfer simulations provide an insight into the flow structure and offer a comparison with the flow phenomena in conventional operation. In addition, the impact of the flow phenomena on the local heat transfer was investigated.
CFD Simulation of Blade Flows With High Amplitude Pitching
Authors: Kumar Ramesh , Chew John W. , Amirante Dario , Murua Joseba , Hills Nicholas J.
Published: August 2017

Large and flexible wind turbine blades may be susceptible to severe blade deformations coupled with dynamic stall. To advance prediction capability for this problem a general deforming mesh computational fluid dynamics (CFD) method has been developed for calculating flows with moving or deforming boundaries using an elastic spring analogy. The method has been evaluated against experimental data for flow around a pitching NACA0012 airfoil in the deep dynamic stall regime where flow is highly separated, and compared with other authors’ CFD simulations for pitching airfoil. The effects of varying the reduced frequency are also investigated. During the upstroke the present results are in generally good agreement with experiment and other CFD studies. During the downstroke some differences with experiment and other CFD models are apparent. This may be due to the sensitivity of the separated flow to modelling assumptions and experimental conditions. Overall, the degree of agreement between CFD and experiment is considered encouraging.
A Review of Inlet-Fan Coupling Methodologies
Authors: Godard Benjamin , De Jaeghere Edouard , Ben Nasr Nabil , Marty Julien , Barrier Raphael , Gourdain Nicolas
Published: August 2017

With the rise of ultra high bypass ratio turbofan and shorter and slimmer inlet geometries compared to classical architectures, designers face new challenges as nacelle and fan design cannot anymore be addressed independently. This paper reviews CFD methods developed to simulate inlet-fan interactions and suitable for industrial design cycles. In addition to the reference isolated fan and nacelle models, the methodologies evaluated in this study consist of two fan modeling approaches, an actuator disc and body-force source terms.

The configuration is a modern turbofan with a high bypass ratio under cross-wind. Results are compared to experimental data. As to be predicted, the body-force modeling approach enables early inlet reattachment. In addition, it provides a representative flow deviation across the fan zone which enables performance and stability assessments.