bluuebunny/crossref_metadata_2025 huggingface dataset:
Performances of Gas Turbines in Oil and Gas Applications: Simple Thermodynamic Methods Help Predict Major Trends
Authors: Schuhler Thierry , Riche Mai , Orhon Dominique , Zoughaïb Assaad , Busco Alessia , Moliere Michel
Published: August 2018

While reliability stays the most critical requirement for power generation in the Oil & Gas sector, energy effectiveness is becoming an increasingly important topic. Gas turbines are efficient and flexible tools both in electrical and mechanical drive applications as they cope with the multiple energy demand profiles of this sector. Aeroderivative gas turbines boast fast response and fast O&M procedures which fits with the exploitation of hydrocarbon fields. Heavy duty machines are robust and very popular in refinery utilities or as large mechanical drivers. However, it is sometimes desirable to boost GT performances: operators of the Oil & Gas sector may need to increase power output or wish to improve efficiency, especially during part load operation where the latter is degraded. While a number of commercial hardware, service and software products cover these needs, the operators may want to keep their own control on their production tools. To that end resorting to simple thermodynamic considerations enables rule-of-thumb evaluations of the impact of cycle changes on GT performances but this possibility is often unexploited.

This joint paper is intended to provide the energy community, especially the engineers of the Oil & Gas sector, with some basic methods for the estimation/anticipation of gas turbine performance changes.
Assessing the Feasibility of Micro-Plasma Technology for Additive Manufacturing
Authors: Nagy Jason , Huang Xiao
Published: August 2018

In this research, a micro-plasma system was investigated for its capability in additive manufacturing (AM). Micro-plasma AM system has the advantage of lower cost and higher deposition rate over laser based AM systems, and generates leaner and cleaner weld deposit than other arc based AM systems. However, the micro-plasma system is complex and involves a large number of process variables. In this study, the feasibility of using a micro-plasma system for additive manufacturing was assessed based on surface features, mechanical properties and microstructure. In addition, two arc and wire feed modes were examined to understand the effects of these two variables. Each was used to produce IN 718 superalloy samples for macro- and microstructure evaluation, hardness, wear, and tensile tests along both long and transverse directions. Preliminary results showed that crack free samples, measured up to 100 mm × 40 mm, can be generated without measurable distortion. Some surface discoloration was observed, ranging from light straw to a purple tint. After heat treatment, the hardness of the samples varies from 403 to 440 HV, with the transverse surface showing slightly lower hardness values. Pin-on-disk wear test yielded consistent wear volume for three sets of the samples produced using different process parameters; however, samples produced with no modifications to the current and wire feed mode showed marginally higher wear rate. Microstructural analysis with SEM and EDS revealed presence of small pinholes, measured from submicron up to 22 μm in diameter, and no indication of any cracks or boundary layers between passes. SEM analysis revealed the presence of high contrast Nb/Mo rich carbides along with γ″-Ni3Nb in the γ matrix. Finally, tensile test was carried out to understand the anisotropic behavior; the results showed that transverse direction had lower tensile strength and ductility. Samples produced with pulsed current and wire feed mode had lower yield/tensile strength but higher ductility than that without current and wire feed mode modification.
Emission of Carbonyl and Polyaromatic Hydrocarbon Pollutants From the Combustion of Liquid Fuels: Impact of Biofuel Blending
Authors: Dagaut Philippe , Bedjanian Yuri , Dayma Guillaume , Foucher Fabrice , Grosselin Benoît , Romanias Manolis , Shahla Roya
Published: August 2018

The combustion of conventional fuels (Diesel and Jet A-1) with 10–20% vol. oxygenated biofuels (ethanol, 1-butanol, methyl octanoate, rapeseed oil methyl ester, diethyl carbonate, tri(propylene glycol)methyl ether, i.e., CH3(OC3H6)3OH, and 2,5-dimethylfuran) and a synthetic paraffinic kerosene was studied. The experiments were performed using an atmospheric pressure laboratory premixed flame and a four-cylinder four-stroke Diesel engine operating at 1500 rpm. Soot samples from kerosene blends were collected above a premixed flame for analysis. Polyaromatic hydrocarbons (PAHs) were extracted from the soot samples. After fractioning, they were analyzed by high-pressure liquid chromatography (HPLC) with UV and fluorescence detectors. C1 to C8 carbonyl compounds were collected at the Diesel engine exhaust on 2,4-dinitrophenylhydrazine coated cartridges (DNPH) and analyzed by HPLC with UV detection. The data indicated that blending conventional fuels with biofuels has a significant impact on the emission of both carbonyl compounds and PAHs adsorbed on soot. The global concentration of 18 PAHs (1-methyl-naphthalene, 2-methyl-naphthalene, and the 16 US priority EPA PAHs) on soot was considerably lowered using oxygenated fuels, except 2,5-dimethylfuran. Conversely, the total carbonyl emission increased by oxygenated biofuels blending. Among them, ethanol and 1-butanol were found to increase considerably the emissions of carbonyl compounds.
Investigations on the Heat Transfer and Flow Characteristics in a Trapezoid Duct for Turbine Blade Leading Edge
Authors: Liu Hai-yong , Liu Cun-liang , Ye Lin
Published: August 2018

To evaluate the application of the impingement cooling in a trapezoidal duct, particularly the influence on internal cooling of the cross flow and swirl flow. Experimental and numerical studies have been performed. The experiment focuses on the heat transfer characteristics in the duct, when the numerical simulation focuses on the flow characteristics. Four Reynolds numbers (10000, 20000, 30000 and 40000), six cross flow mass flow ratios (0, 0.1, 0.2, 0.3, 0.4 and 0.5) and two impingement angle (35° and 45°) are considered in both the experiment and the numerical simulation. The temperature on the target wall and the exit side wall is measured by the thermocouples, when the realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. The results show that only part of the jets contribute in the heat transfer enhancement on the target wall, the other jets improve a large anticlockwise vortex occupied the upper part of the duct and drive strong swirl flow. The heat transfer on the exit side wall is enhanced by the swirl flow. The cross flow is induced in the duct by the outflow of the end exit hole. It deflects the jets and abates the impingement cooling on the target wall in the downstream region but has no evidently effect on the heat transfer on the exit side wall. Higher impingement angle helps to augment the impingement cooling on the target wall and improves the resistance ability of the jets against the effect of the cross flow. The heat transfer enhancement ability on the target wall and exit side wall in the present duct is compared to that of a smooth duct. The Nusselt number of the former is about 3 times higher than that of the latter. It indicates that the impingement and swirl play equally important roles in the heat transfer enhancement in the present duct. Empirical dimensionless correlations based on the present experiment data are presented in the paper.
On the Application of the Bay Model for Vortex Generator Flows
Authors: Manolesos Marinos , Papadakis Giorgos , Voutsinas Spyros G.
Published: August 2018

Today, Vortex Generators (VGs) are becoming an integral part of a Wind Turbine blade design. However, the challenges that are involved in the computation of the flow around VGs are yet to be dealt with in a satisfactory manner. A large number of VG models for flow solvers have been proposed and among them, the BAY model is one of the most popular for its ease of use and relatively low requirements for user input.

In the present paper, a thorough investigation on the performance and application of the BAY model for aerodynamic Vortex Generator flows is presented. A Fully Resolved Reynolds Averaged Navier Stokes simulation is validated against experiments and then used as the benchmark for the BAY model simulations. The Benchmark case is the flow past a wind turbine airfoil at Reynolds number 0.87e6. When the grid related errors are excluded, it is found that in the model simulations, the generated vortices are weaker than in the fully resolved computation. The latter finding is linked to an inherent deficiency of the model, which is explained in detail. As the vortex generation mechanism is different between the fully resolved and the BAY model simulation, so is the vortex evolution and interaction, even on the same numerical mesh. With regards to grid dependence, the integral BAY force depends on both grid density and grid architecture.
Evaluation of Impact on Lean Blowout Limit and Ignition Delay While Using Alternative Fuels on Gas Turbine Combustor
Authors: Ahmed Ihab , Zheng Lukai , Ubogu Emamode A. , Khandelwal Bhupendra
Published: August 2018

Burning leaner is an effective way to reduce emissions and improve efficiency. However, this increases the instability of the combustion and hence, increases the tendency of the flame to blowout. On the other hand, the ignition delay of a jet fuel is a crucial factor of the instability feedback loop. Shorter ignition delay results in faster feedback loop, and longer ignition delay results in slower feedback loop. This study investigates the potential effect of ignition delay on the lean blowout limit of a gas turbine combustion chamber.

At the Low Carbon Combustion Centre of The University of Sheffield, a range of tests were carried out for a range of jet fuels on a Rolls-Royce Tay combustor rig. The ignition delay for each fuel was tested using Advanced Fuel Ignition Delay Analyser (AFIDA 2805).

Lean blowout tests (LBO) was conducted on various air flows rates. High speed imaging was recorded using a high speed camera to give further details of the flame behavior near blowout limit for various fuels. The instability level was observed using the pressure, vibration and acoustic fluctuation. This paper presents results from an experimental study performed on a small gas turbine combustor, comparing Lean Blowout limit of different conventional, alternative and novel jet fuels with various ignition delay characteristics. It was observed that at higher cetane number, the blowout is improved remarkably. The Ignition plays an important role in determining the average instability level, and as result determines the Lean Blowout limit of a fuel.
Coupled Analysis of the Rotor-Dynamic Fluid Forces in the Annular Plain Seal and the Shaft Vibration
Authors: Miyake K. , Ikemoto A. , Uchiumi M. , Inoue T.
Published: August 2018

In recent years, along with demands for higher rotational speed and higher efficiency in the rotating machinery, shaft vibration has been a serious problem. One of the causes of this shaft vibration problem is the rotor-dynamic fluid force (RD fluid force) generated by working fluid at turbo machinery parts. It is important in the design stage of rotating machines to estimate the RD fluid force and predict the stability of the rotor system accurately. Therefore, many researches have been conducted to clarify the characteristics of RD fluid force. One of the traditional methods for analyzing the RD fluid force is the bulk flow theory. However, in conventional bulk flow analysis, it is assumed that the amplitude of the shaft displacement is sufficiently smaller than the clearance. Therefore, influence of nonlinearity in the large amplitude whirl may not be included in this analysis. Accordingly, this paper focuses on constructing a coupled analysis of the fluid force and the shaft vibration that describes each behavior of fluid and shaft at the same time. By using this coupled analysis, the interaction between fluid and shaft systems can be taken into consideration more accurately. Regarding the fluid region, finite difference method is used for bulk flow continuity and momentum transport equations. Incompressible fluid is assumed, and the pressure field is calculated by solving the Poisson equation of pressure. In solving the Poisson equation of pressure, a specific problem for this coupled analysis relating unknown shaft acceleration arises. In this paper, this problem is solved by obtaining the approximated acceleration based on Newmark-beta technique. This coupled analysis is conducted for a simple flexible rotor system with annular plain seal, and the frequency response is obtained. First, the case with isotropic support stiffness and with no gravitational force is considered. Then, the case with the constant load and the case with anisotropic support stiffness are analyzed. These analytical results show that both the constant load and structural anisotropy may affect the stability of the rotor system. As a result, the usefulness of the proposed coupled analysis procedure of the fluid force and the shaft vibration is validated.
Uncertainty Quantification of NOx Emission due to Operating Conditions and Chemical Kinetic Parameters in a Premixed Burner
Authors: Yousefian Sajjad , Bourque Gilles , Monaghan Rory F. D.
Published: August 2018

Many sources of uncertainty exist when emissions are modelled for a gas turbine combustion system. They originate from uncertain inputs, boundary conditions, calibration, or lack of sufficient fidelity in the model. In this paper, a non-intrusive polynomial chaos expansion (NIPCE) method is coupled with a chemical reactor network (CRN) model using Python to rigorously quantify uncertainties of NOx emission in a premixed burner. The first objective of the uncertainty quantification (UQ) in this study is development of a global sensitivity analysis method based on NIPCE to capture aleatory uncertainty due to the variation of operating conditions and input parameters. The second objective is uncertainty analysis of Arrhenius parameters in the chemical kinetic mechanism to study the epistemic uncertainty in the modelling of NOx emission. A two-reactor CRN consisting of a perfectly stirred reactor (PSR) and a plug flow reactor (PFR) is constructed in this study using Cantera to model NOx for natural gas at the relevant operating conditions for a benchmark premixed burner. UQ is performed through the use of a number of packages in Python. The results of uncertainty and sensitivity analysis using NIPCE based on point collocation method (PCM) are then compared with the results of advanced Monte Carlo simulation (MCS). Surrogate models are also developed based on the NIPCE approach and compared with the forward model in Cantera to predict NOx emissions. The results show the capability of NIPCE approach for UQ using a limited number of evaluations to develop a UQ-enabled emission prediction tool for gas turbine combustion systems.
Experimental Application of a Boundary Layer Control Strategy in a Radial Vaned Diffuser
Authors: Moënne-Loccoz V. , Trébinjac I. , Laucher P.
Published: August 2018

A boundary layer suction strategy is tested in a centrifugal compressor stage designed and built by Safran Helicopter Engines. According to previous numerical results, suction slots are disposed in the radial diffuser at the hub and the shroud near the vane suction side. Experimental results performed in the compressor without any boundary layer suction at partial speed showed a specific feature consisting in a two-channel pattern in the radial diffuser characterized by one stalled passage over two. If throttled the compressor experiences mild surge during which both rotating instabilities and alternate stall co-exist, the latter being then highly unsteady. When the boundary layer suction is activated no surge margin improvement is registered. However, the boundary layer suction allows to revert the pattern in the radial diffuser and to improve the compressor performance both at design and off-design operating points depending on the location of the boundary layer strategy.
Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer
Authors: Fraas Marc , Glasenapp Tobias , Schulz Achmed , Bauer Hans-Jörg
Published: August 2018

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10-10-10deg laidback fan-shaped cooling hole are discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit.

First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.
Development and Use of Machine-Learnt Algebraic Reynolds Stress Models for Enhanced Prediction of Wake Mixing in LPTs
Authors: Akolekar Harshal D. , Weatheritt Jack , Hutchins Nicholas , Sandberg Richard D. , Laskowski Gregory , Michelassi Vittorio
Published: August 2018

Non-linear turbulence closures were developed that improve the prediction accuracy of wake mixing in low-pressure turbine (LPT) flows. First, Reynolds-averaged Navier–Stokes (RANS) calculations using five linear turbulence closures were performed for the T106A LPT profile at exit Mach number 0.4 and isentropic exit Reynolds numbers 60,000 and 100,000. None of these RANS models were able to accurately reproduce wake loss profiles, a crucial parameter in LPT design, from direct numerical simulation (DNS) reference data. However, the recently proposed kv2¯ω transition model was found to produce the best agreement with DNS data in terms of blade loading and boundary layer behavior and thus was selected as baseline model for turbulence closure development. Analysis of the DNS data revealed that the linear stress-strain coupling constitutes one of the main model form errors. Hence, a gene-expression programming (GEP) based machine-learning technique was applied to the high-fidelity DNS data to train non-linear explicit algebraic Reynolds stress models (EARSM). In particular, the GEP algorithm was tasked to minimize the weighted difference between the DNS and RANS anisotropy tensors, using different training regions. The trained models were first assessed in an a priori sense (without running any CFD) and showed much improved alignment of the trained models in the region of training. Additional RANS calculations were then performed using the trained models. Importantly, to assess their robustness, the trained models were tested both on the cases they were trained for and on testing, i.e. previously not seen, cases with different flow features. The developed models improved prediction of the Reynolds stress, TKE production, wake-loss profiles and wake maturity, across all cases, in particular those trained on just the wake region.
Three-Dimensional Blade Shape Optimization for a Transonic Axial Flow Compressor Through Incorporating Surrogate Model and Sequential Sampling
Authors: Wang Xuesong , Sun Jinju , Song Peng , He Youwei , Xu Da
Published: August 2018

High level aerodynamic performance has been always expected for the axial flow compressors, and it is the consistent goal for axial flow compressor research. To achieve such a goal, the incorporation of CFD with optimization algorithm and surrogate model in blade geometry optimization has become a common practice and been used extensively. But the conventional surrogate model based on merely initial sampling often deviates from the real optimization problem during optimization process and then brings the optimizer to search locally, leading to the compromised optimal results. There are yet much to do to improve such optimization design method.

An optimization method of surrogate model being updated by sequential sampling strategy is developed to achieve global optimal design geometry and permit high-level of aerodynamic performance for axial flow compressor. Preliminary Kriging surrogate model is constructed with a small number of selected DOE samplings, where the multiple optimization objective functions are obtained based on CFD simulations. The optimization is performed on the surrogate model with NSGA-II optimization algorithm and Pareto fronts successively obtained. To improve the surrogate model, the MSE (Mean Squared Error) criteria is used to select the refinement point from the newest Pareto front, and it is used to update and improve the surrogate model gradually during the optimization. Such adaptive feature of the surrogate model has enabled the optimizer to search globally.

The method is used to optimize transonic Rotor 37 at design flow rate, where the blade shape is varied simultaneously in terms of sweep and lean, and the geometry is optimized. In the converged Pareto front, abundant candidate designs with significant performance gains are produced. Three points over the Pareto front are selected and analyzed to take an insight into the optimization effectiveness. Overall performance curves of optimized geometries are predicted over the entire flow range and they are significantly improved compared with the original ones. Significant overall performance gains arising from the blade optimization are supported by the improved flow behavior. The overall pressure ratio or efficiency gains of the optimized blades are attributed to the significant improvement in the radial distribution of aerodynamic parameters. Further research shows that the shock structure is changed and separation zone is reduced with the optimized blades, which are the major reasons for the improvement of the aerodynamic performance of optimized blades.
Effects of Streamwise Distance and Density Ratio on Film-Cooling Effectiveness for Double-Jet Film-Cooling on a Flat Plate
Authors: Yao Jiaxu , Lei Jiang , Wu Junmei , Fang Yu , Wright Lesley M.
Published: August 2018

Several double-jet film-cooling (DJFC) hole geometries on a flat plate are investigated in this paper. Pressure sensitive paint (PSP) is used to measure the film-cooling effectiveness on the flat plate. The streamwise distance between the DJFC holes varies as s/d = 3.0, 4.0, 5.0, and 6.0, while three different spanwise distance conditions are considered (p/d = 0, 0.5, and 1.0). The diameter (d) of the DJFC holes is 7 mm, and the pitch (P) between each set of the DJFC holes is 8d. The holes have an inclination angle (θ) of 35°, and a compound angle (β) of ± 45°. The density ratio (DR) varies as 1.0, 1.5, and 2.5, and the blowing ratio (M) is 0.5, 1.0, 1.5, and 2.0. Both effects of the streamwise distance between DJFC holes, and the density ratio on film-cooling effectiveness are focused. Results show, though the effect of the streamwise distance is not monotonic all the time, a general trend exists when comparing with the baseline case of s/d = 3.0. For p/d = 0, increasing the streamwise distance leads to wider lateral coverage and higher laterally averaged effectiveness; however, for p/d = 0.5 and 1.0, an increased s/d may weaken the interaction between the two jets, thus the film coverage and effectiveness decrease. A higher density ratio reduces the jet momentum, therefore better attachment and higher effectiveness are obtained. Effects of the streamwise distance and the density ratio on double-jet film-cooling are more distinct when the blowing ratio rises. However, in most cases, both of them show minor influence on the range of lateral coverage, as it is mainly dominated by the spanwise distance. For each operation condition (DR and M), an optimal DJFC configuration (among the geometries in this study) is identified by comparing the area averaged effectiveness.
Evolution Process of Diffuser Stall in a Centrifugal Compressor With Vaned Diffuser
Authors: Fujisawa Nobumichi , Inui Tetsuya , Ohta Yutaka
Published: August 2018

The evolution process of a diffuser rotating stall in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analyses. From velocity measurements, it was found that the diffuser stall propagated near the shroud side in the vaneless space. As the mass flow decreased, a stage stall rotated within both the impeller and diffuser passages, instead of a diffuser stall. The evolution process of the diffuser stall had three stall forms. First, the diffuser stall, which was rotating on the shroud side, shifted to the hub side. Then, the diffuser stall moved into the impeller passages and evolved to a stage stall. From computational fluid dynamics (CFD) analysis, a tornado-type vortex was generated first, near the hub side of the diffuser leading edge, when the diffuser stall was shifted to the hub side. Next, a throat area blockage was formed near the hub side because of the boundary layer separation in the vaneless space. Finally, the blockage within the diffuser passages expanded to the impeller passages and developed into a stage stall. From the pressure measurements along the impeller and diffuser passages, the magnitude of pressure fluctuation on the casing wall of the diffuser throat area also suddenly increased when the diffuser stall shifted to the hub side. Therefore, the evolution area of the diffuser stall was caused by the evolution of the blockage near the throat area of the diffuser passage.
The Impact of Inlet Distortion and Reduced Frequency on the Performance of Centrifugal Compressors
Authors: Grimaldi A. , Michelassi V.
Published: August 2018

This paper discusses the impact of inlet flow distortions on centrifugal compressors based upon a large experimental data base in which the performance of several impellers in a range of corrected flows and corrected speeds have been measured after been coupled with different inlet plenums technologies. The analysis extends to centrifugal compressor inlets including a side stream, typical of Liquefied Natural Gas (LNG) applications. The detailed measurements allow a thorough characterization of the flow field and associated performance. The results suggest that distortions can alter the head by as much as 3% and efficiency of around 1%. A theoretical analysis allowed to identify the design features that are responsible for this deviation. In particular, an extension of the so-called “reduced-frequency”, a coefficient routinely used in axial compressors and turbine aerodynamics to weigh the unsteadiness generated by upstream to downstream blade rows, allowed to determine a plenum-to-impeller reduced frequency that correlates very well with the measured performance. The theory behind the new coefficient is discussed together with the measurement details, and validate the correlation that can be used in the design phase to determine the best compromise between the inlet plenum complexity and impact on the first stage.
On the Development of Harmonic Balance Methods for Multiple Fundamental Frequencies
Authors: Junge Laura , Ashcroft Graham , Kersken Hans-Peter , Frey Christian
Published: August 2018

Due to the relative motion between adjacent blade rows the aerodynamic flow fields within turbomachinery are usually 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 modelling flow nonlinearities. A nontrivial issue in the application of frequency-domain methods to turbomachinery flows is to simultaneously capture disturbances with multiple fundamental frequencies in one relative system. In case of harmonically related frequencies, the interval spanned by the sampling points typically resolves the common fundamental frequency. To avoid signal aliasing the highest harmonic of the common frequency should be sampled with an appropriate number of sampling points. However, when the common fundamental frequency is very low in relation to the frequencies of primary interest, equidistant time sampling leads to a high number of sampling points, hence frequency-domain methods can become computationally inefficient. Furthermore, when a problem can no longer be described by harmonic perturbations that are integer multiples of one fundamental frequency, as it may occur in two-shaft configurations, the standard discrete Fourier transform is no longer suitable and the basic harmonic balance method requires extension. In this article two nonlinear frequency-domain approaches for dealing with the accounted issues are demonstrated and compared. The first approach is a generalized harmonic balance method based on almost periodic Fourier transforms with non-equidistant time sampling. Then the so-called harmonic set approach, developed by the authors, is evaluated. Based on the neglection of the nonlinear, quadratic cross-coupling terms between higher harmonics of different fundamental frequencies, the harmonic set approach allows the superposition of periodic disturbances with different fundamental frequencies as well as the separated, equidistant sampling of the highest harmonic of each base frequency. The aim of this paper is to compare the computational efficiency and accuracy of the two methods and assess the impact of neglecting the quadratic cross-coupling terms.
Surface Roughness Impact on Secondary Flow and Losses in a Turbine Exhaust Casing
Authors: Jonsson Isak , Chernoray Valery , Rojo Borja
Published: August 2018

This paper experimentally addresses the impact of surface roughness on losses and secondary flow in a Turbine Rear Structure (TRS). Experiments were performed in the Chalmers LPT-OGV facility, at an engine representative Reynolds number with a realistic shrouded rotating low-pressure turbine (LPT). Outlet Guide Vanes (OGV) were manufactured to achieve three different surface roughnesses tested at two Reynolds numbers, Re = 235000 and Re = 465000. The experiments were performed at on-design inlet swirl conditions. The inlet and outlet flow of the TRS were measured in 2D planes with a 5-hole probe and 7-hole probe accordingly. The static pressure distributions on the OGVs were measured and boundary layer studies were performed at the OGV midspan on the suction side with a time-resolved total pressure probe. Turbulence decay was measured within the TRS with a single hot-wire.

The results showed a surprisingly significant increase in the losses for the high level of surface roughness (25–30 Ra) of the OGVs and Re = 465000. The increased losses were primary revealed as a result of the flow separation on the OGV suction side near the hub. The loss increase was seen but was less substantial for the intermediate roughness case (4–8 Ra). Experimental results presented in this work provide support for the further development of more advanced TRS and data for the validation of new CFD prediction methods for TRS.
Aerodynamic Design and Testing of an Imbedded Forward Swept Rotor in a Two-Stage Transonic Fan
Authors: Wadia A. R. , Niedermeier J. D. , Szucs P. N. , Cormier N. G. , Crall D. W. , Rabe D. C.
Published: August 2018

Previous experimental and analytical studies comparing the performance of transonic swept rotors in single and multistage fans have demonstrated the potential of large improvements in clean inlet performance and substantial improvements in fan sensitivity with inlet distortion with forward swept blading. A two-stage, low-aspect ratio transonic fan investigation was previously conducted in the Air Force’s Compressor Research Facility, in two builds on a back-to-back test basis, using a radial and a forward swept stage 1 blade. While the forward swept stage 1 blade configuration did demonstrate superior front stage efficiency and tolerance to inlet distortion, the common second stage among the two builds prevented the overall fan from showing clean inlet performance and stability benefits with the forward swept Rotor 1. To address this measured overall performance shortfall, this paper reports on the design of a new second stage blade tested in the same two-stage fan rig with the forward swept stage 1 blade configuration. The new second stage blade was designed with forward sweep to improve efficiency and operability while replicating the baseline radial Rotor 2’s aerodynamic design conditions within the same flow path. The design point requirements of the forward swept Rotor 2 were selected to preserve the internal stage matching with the radially stacked Rotor 2. As the new stage 2 blade had to fit within the existing radial Rotor 2’s physical envelope, the new blade was designed with forward sweep through lean only, which proved to be quite challenging from a mechanical growth and deflection view point. The first attempt to run the fan rig with the new stage 2 blade resulted in a leading-edge tip rub during a part speed stall event. However, even with this unfortunate event, fan mapping test results with clean inlet from part speed to 97.5 percent design speed showed a significant improvement in overall fan efficiency and stall margin, validating the hypothesis that in the earlier tests stage 2 was indeed the limiting stage that prevented the fan from reaching its overall performance goals. Based on this experience and the test data acquired with unstable leadingedge tip rubs during stall deflections with forward swept airfoils leaned in the direction of rotation, a process was developed to determine the acceptability criteria of such blading.
Uncertainty Quantification of NOx Emissions Induced Through the Prompt Route in Premixed Alkane Flames
Authors: Durocher Antoine , Versailles Philippe , Bourque Gilles , Bergthorson Jeffrey M.
Published: August 2018

Increasingly stringent regulations on emissions in the gas turbine industry require novel designs to minimize the environmental impact of oxides of nitrogen (NOx). The development of advanced low-NOx technologies depends on accurate and reliable thermochemical mechanisms to achieve emissions targets. However, current combustion models have high levels of uncertainty in kinetic rates that, when propagated through calculations, yield significant variations in predictions. A recent study identified and optimized nine elementary reactions involved in CH formation to accurately capture its concentration and improve prompt-NO predictions. The current work quantifies the uncertainty on peak CH concentration and NOx emissions generated by these nine reaction rates only, when propagated through the San Diego mechanism. Various non-intrusive spectral methods are used to study atmospheric alkane-air flames. 1st- and 2nd-order total-order expansions and tensor-product expansions are compared against a reference Monte Carlo analysis to assess the ability of the different techniques to accurately quantify the effect of uncertainties on the quantities of interest. Sparse grids, subsets of the full tensor-product expansion, are shown to retain the advantages of tensor formulation compared to total-order expansions while requiring significantly fewer collocation points to develop a surrogate model. The high resolution per dimension can capture complex probability distributions witnessed in radical species concentrations. The uncertainty analysis of lean to rich flames demonstrated a high variability in NOx predictions reaching up to 400 % of nominal predictions. Wider concentration intervals were observed in rich conditions where prompt-NOx is the dominant contributor to emissions. The high variability and scale of uncertainty in NOx emissions originating from these nine elementary reactions demonstrate the need for future experiments and data assimilation to constrain current models to accurately capture CH for robust NOx emissions predictions.
The Counteractive Flow and Heat Transfer in a Narrow Straight Channel With Sidewall Bleeding Slots
Authors: Qiu Lu , Chen Yanan , Deng Hongwu , Zhu Jianqin
Published: August 2018

In the internal cooling passages of the first stage turbine blade in the modern advanced gas turbines, the dense bleeding holes are arranged in order to supply the cold air for the external film cooling. The fluid extractions dramatically vary the flow field and convective heat transfer in the internal channels. In the current work, the flow and heat transfer in a high aspect ratio channel (AR = 4) with the side wall bleeding slots are investigated. Unlike the traditional single inlet channel, the cooling air is supplied into the channel from two entrances located at the both ends of the long straight channel. Therefore, a counteractive flow pattern is generated. The effects of the flow rate ratio of the two streams (MR = ṁ2/ṁ1) on the flow and heat transfer inside the channel are investigated, where ṁ1 and ṁ2, are the flow rate of the two streams at the two entrances. The local heat transfer is found to be zigzagging with an increase in the flow rate ratio. Interestingly, once a local flow ratio, MRx, is defined, which is based on the predicted local flow rate, all the data at different locations are converged to the same trend in the Nu/Nu0 - MRx space, where Nu is the measured local Nusselt number normalized with the Dittus-Boelter correlation, Nu0. Based on the numerical simulations, the detailed flow structure is analyzed and reported. The thermal boundary conditions in the simulations mimic the heating scheme in the experiments, where the channel wall is segmented into a matrix of copper plates which are separated by the insulations. It shows that the segmental heating scheme influences the heat transfer significantly.
Comparison of Linear and Nonlinear Frequency Domain Methods for Flutter Analysis
Authors: Kersken Hans-Peter , Ashcroft Graham , Frey Christian , Wolfrum Nina , Pütz Oliver
Published: August 2018

Both linear and nonlinear frequency domain methods have been applied successfully to the investigation of time-periodic phenomena in turbomachinery. Linear methods allow to perform flutter analysis of turbomachinery blade rows very efficiently. Nonlinear frequency domain method can be applied to flutter analysis as well. If a pseudo-time solution algorithm is employed as a solver the nonlinear frequency domain method takes advantage of the stabilizing effect of the nonlinear coupling of the harmonics. Additionally, it allows studying the influence of nonlinear effects on the flutter stability. A linear GMRes based method and a harmonic balance method using a pseudo-time solution approach are compared with respect to computational efficiency when applied to the flutter analysis of blades of a stationary gas turbine and a low pressure turbine of a jet engine. It is shown that both methods have their merits and limitation depending on the type of problem at hand.
Measurement of Pressures and Temperatures in a Cover-Plate Pre-Swirl System
Authors: Wu Heng , Liu Gaowen , Wu Zhipeng , Feng Qing , Yangang Wang
Published: August 2018

A Pre-swirl system is used to supply cooling air to the rotating turbine blades where the pressure and temperature of the supplied air is crucial for blade cooling.

A test rig was designed to simulate the flow in a cover-plate Pre-swirl system. Some important performance parameters of a pre-swirl system were measured at different mass flow rate (Cw is up to 1.35 × 105), rotation speed (Maϕ is up to 0.744) and outlet pressure (210 kPa and 310 kPa). These parameters include discharge coefficient of pre-swirl nozzle, pressure ratios, temperature drop and rotor work consumption. To get rotor pressure boost ratio and temperature drop, pressures and temperatures on the rotating turbine disc were measured respectively by tiny pressure transducers and thermo-couples co-rotating with the axis and recorded by a customized data recorder co-rotating also. By measuring the inlet and outlet total temperature of the test rig, work consumption was estimated approximately with heat transfer ignored.
Single-Point Optimization of the LS89 Turbine Cascade Using a Hybrid Algorithm
Authors: Châtel Arnaud , Verstraete Tom , Coussement Grégory , Mueller Lasse
Published: August 2018

This paper presents a single point optimization of the LS89 turbine vane cascade for a downstream isentropic Mach number of 0.9. The objective of the optimization is to minimize the entropy generation through the cascade while maintaining the flow turning of the baseline geometry. The optimization is performed using a hybrid optimization algorithm which combines two main families of optimization methods, namely an evolutionary algorithm and a gradient-based method. The combination of these two methods aims to correct their respective main disadvantage which are the poor convergence performance of the evolutionary and the trend to get trapped in local minima of the gradient-based method. The hybrid algorithm implemented in this work is based on the Lamarckian evolution and consists in incorporating directly the gradient-based method inside the loop of the evolutionary algorithm. In this approach, the evolutionary algorithm performs a global exploration of the design space while the gradient-based method improves the convergence rate of the evolutionary algorithm. The better performance of the developed hybrid method, compared to a classical evolutionary algorithm, is first demonstrated on two analitycal functions used as benchmark problems. Subsequently, the hybrid algorithm is used to optimize LS89 turbine vane, resulting in a new design with about 20 percent lower entropy production compared to baseline geometry. A thorough flow analysis shows that the improvements are largely due to a significant decrease in trailing edge losses, which is characterized by a higher base pressure. A previous optimization of the LS89 cascade has been already realized using a classical gradient-based method. This optimization converged towards a new design which reduces the entropy rise by a factor of 11 percent. Therefore, the comparison between this optimum and the one found using the proposed method demonstrates that the hybrid algorithm allows to locate a better minimum by performing a global exploration of the design space.
Large Eddy Simulations of a Highly Loaded Transonic Blade With Separated Flow
Authors: Harnieh Mael , Gicquel Laurent , Duchaine Florent
Published: August 2018

Efficient design of highly loaded pressure blades often leads to the generation of a separation bubble on the pressure side of highly curved blades. For this specific region, fundamental, numerical and experimental studies have indicated the importance of the turbulence present in the main stream in determining the size of the bubble before its reattachment to the blade. Despite this important finding, many complex phenomena remain and are still present and can influence the overall flow response. In this paper, explorations of high-fidelity unsteady Large Eddy Simulations of a separated flow are studied for the high pressure T120 blade from the European project AITEB II (Aerothermal Investigation on Turbine Endwalls and Blades). For this investigation, simulations are carried out at the nominal operating point with and without synthetic turbulence injection at the inlet condition to comply with the specification from the experiment. Based on these predictions, the near wall flow structure and turbulent fields are specifically investigated in an attempt to identify the key mechanisms introduced by the turbulent main stream flow. Results show that the turbulence specification at the inlet enables the recovery of the correct pressure distribution on the blade surface contrary to the laminar inlet condition if compared to the experiment. Investigations of the boundary layer profiles show a strong impact of the freestream turbulence on the shape factor from the leading edge. As a consequence, the recirculation bubble located downstream on the pressure side is impacted and reduced when turbulence is injected. Due to this change in mean flow topology, the mass flow distribution in the passage appears strongly affected. Investigations of loss fields furthermore show that the freestream turbulence dramatically increases the loss production within the computational domain.
Performance Simulation and Analysis of a Gas Turbine Engine Using Drop-In Bio-Fuels
Authors: Rubie J. S. , Li Y. G. , Jackson A. J. B.
Published: August 2018

There is an increasing dependence on conventional fuels for aviation. In order for a country’s air force to sustain a steady and a secure supply of fuel for aircraft with foresight into the future, alternate sources of fuels must be considered. This paper describes a thermodynamic performance simulation method and analysis of a model military aero gas turbine engine operating in several off-design modes while employing various types of blended fuels between Jet A and alternate bio-fuels, including Synthetic Paraffinic Kerosene (SPK) from Algae (Bio-Algae), Jatropha (JSPK) and Camelina (CSPK). These fuels are already approved by American Society for Testing and Materials (AS™) for blending with 50% Jet A fuel. A thermodynamic performance model for the model engine similar to GE F404-400 turbofan engine has been set up using Pythia, a Cranfield University created performance simulation software implemented with multiple fuel capabilities. The simulated performance and a comparative study shows that the performance of the model engine using blended fuels between Jet A and a bio-fuel were found to be equal or better than that using pure conventional fuel Jet A. The key hot section temperatures, pressures and the fuel consumption of the model engine were found to be slightly lower with the blended fuels than that using Jet A.
High Frequency Measurement of Temperature and Composition Spots With LITGS
Authors: De Domenico Francesca , Shah Priyav , Williams Benjamin A. O. , Ewart Paul , Lowe Steven M. , Fan Luming , Hochgreb Simone
Published: August 2018

Temperature and composition spots in a turbulent flow are detected and time-resolved using Laser Induced Thermal Grating Spectroscopy (LITGS). A 355 nm wavelength PIV laser is operated at 0.5–1 kHz to generate the thermal grating using biacetyl as an absorber in trace amounts. In a open laminar jet, a feasibility study shows that small (≃ 3%) fluctuations in the mean flow properties are well captured with LITGS. However, corrections of the mean flow properties by the presence of the trace biacetyl are necessary to properly capture the fluctuations. The actual density and temperature variation in the flow are determined using a calibration procedure validated using a laminar jet flow. Finally, travelling entropy and composition spots are directly measured at different locations along a quartz tube, obtaining good agreement with expected values. This study demonstrates that LITGS can be used as a technique to obtain instantaneous, unsteady temperature and density variations in a combustion chamber, requiring only limited optical access.