Accepted Manuscripts

Robert G. Laycock and Thomas H. Fletcher
J. Turbomach   doi: 10.1115/1.4037911
The reported mole fractions of oxides in the ash were calculated incorrectly from the elemental composition, resulting in significant errors in the sticking probability. These errors are corrected in this Errata, and the corrected sticking probabilities are shown.
TOPICS: Turbochargers, Coal, Gas turbines, Errors, Fly ash, Probability
Arnab Roy, Sakshi Jain, Srinath V. Ekkad, Wing Ng, Andrew Lohaus, Michael Crawford and Santosh Abraham
J. Turbomach   doi: 10.1115/1.4037909
Comparison of heat transfer performance of a non-axisymmetric contoured endwall to a planar baseline endwall in presence of leakage flow through stator-rotor rim seal interface and mateface gap is reported in this paper. Heat transfer experiments were performed on a high turning turbine airfoil passage at Virginia Tech's transonic blow down cascade facility under design conditions for two leakage flow configurations - 1) mateface blowing only, 2) simultaneous coolant injection from the upstream slot and mateface gap. Coolant to mainstream mass flow ratios (MFR) were 0.35% for mateface blowing only, whereas for combination blowing, a 1.0% MFR was chosen from upstream slot and 0.35% MFR from mateface. A common source of coolant supply to the upstream slot and mateface plenum made sure the coolant temperatures were identical at both upstream slot and mateface gap at the injection location. The contoured endwall geometry was generated to minimize secondary aerodynamic losses. Transient Infrared thermography technique was used to measure endwall surface temperature and a linear regression method was developed for simultaneous calculation of heat transfer coefficient (HTC) and adiabatic cooling effectiveness (ETA), assuming a 1D semi-infinite transient conduction. Results indicate reduction in local hot spot regions near suction side as well as area averaged HTC using the contoured endwall compared to baseline endwall for all coolant blowing cases. Contoured geometry also shows better coolant coverage further along the passage. Detailed interpretation of the heat transfer results along with near endwall flow physics has also been discussed.
TOPICS: Heat transfer, Turbochargers, Turbine blades, Leakage flows, Coolants, Flow (Dynamics), Temperature, Geometry, Stators, Transient heat transfer, Heat transfer coefficients, Airfoils, Cascades (Fluid dynamics), Transients (Dynamics), Design, Rotors, Turbines, Physics, Suction, Adiabatic cooling, Thermography
Huang Chen, Yuanchao Li, Subhra Shankha Koley, Nick Doeller and Joseph Katz
J. Turbomach   doi: 10.1115/1.4037910
The effects of axial casing grooves on the performance and flow structures in the tip region of an axial low speed fan rotor are studied experimentally in the JHU refractive index-matched liquid facility. The four-per-passage semicircular grooves are skewed by 45°, overlapping partially with the blade leading edge and extending upstream. They reduce the stall flow rate by 40% compared to the same machine with a smooth endwall. Stereo-PIV measurements show that the inflow into the downstream side of the grooves and the outflow from their upstream side varies periodically, peaking when the inlet is aligned with the blade pressure side. This periodic suction has three effects: First, substantial fractions of the leakage flow and the tip leakage vortex (TLV) are entrained into the groove, causing a reduction in TLV strength starting from mid-chord. Second, the grooves prevent the formation of large scale backflow vortices (BFVs), which are associated with the TLV, propagate from one blade passage to the next, and play a key role in the onset of rotating stall in the untreated fan. Third, the flow exiting from the grooves causes periodic variations of the relative flow angle around the blade leading edge, presumably affecting the blade loading. The distributions of turbulent kinetic energy provide statistical evidence that in contrast to the untreated casing, very little turbulence originating from the TLV and BFV of one blade propagates across the tip gap to the next passage.
TOPICS: Flow (Dynamics), Turbochargers, Rotors, Blades, Vortices, Turbulence, Suction, Kinetic energy, Machinery, Chords (Trusses), Leakage flows, Leakage, Inflow, Outflow, Pressure
Davide Lengani, Daniele Simoni, Marina Ubaldi, Pietro Zunino, Francesco Bertini and Vittorio Michelassi
J. Turbomach   doi: 10.1115/1.4037858
The paper analyzes losses and the loss generation mechanisms in a low-pressure turbine cascade by Proper-Orthogonal-Decomposition (POD) applied to measurements. Total pressure probes and time resolved particle image velocimetry (TR-PIV) are used to determine the flow field and performance of the blade with steady and unsteady inflow conditions varying the flow incidence. The total pressure loss coefficient is computed by traversing two Kiel probes upstream and downstream of the cascade simultaneously. This procedure allows a very accurate estimation of the total pressure loss coefficient also in the potential flow region affected by incoming wake migration. The TR-PIV investigation concentrates on the aft portion of the suction side boundary layer downstream of peak suction. POD applied to this portion of the domain provides a statistical representation of the flow oscillations by splitting the effects induced by the different dynamics. The paper also describes how POD can dissect the loss generation mechanisms by separating the contributions to the Reynolds stress tensor from the different modes. The steady condition loss generation, driven by boundary layer streaks and separation is augmented in presence of incoming wakes by the wake-boundary layer interaction and by the wake dilation mechanism. Wake migration losses have been found to be almost insensitive to incidence variation between nominal and negative (up to -9deg), while at positive incidence the losses have a steep increase due to the alteration of the wake path induced by the different loading distribution.
TOPICS: Turbochargers, Cascades (Fluid dynamics), Turbines, Wakes, Pressure, Flow (Dynamics), Boundary layers, Probes, Suction, Stress tensors, Inflow, Blades, Principal component analysis, Oscillations, Dynamics (Mechanics), Separation (Technology), Particulate matter
Xinguo Lei, Mingxu QI, Harold Sun and Liangjun Hu
J. Turbomach   doi: 10.1115/1.4037860
Radial flow Variable Nozzle Turbine (VNT) enables better matching between a turbocharger and engine, and can improve the engine performance as well as decrease the engine emissions, especially when the engine works at low-end operation points. With increased nozzle loading, stronger shock wave and clearance leakage flow may be generated and consequently introduces strong rotor-stator interaction between turbine nozzle and rotor, which is a key concern of rotor HCF failure. With the purpose of developing a low shock wave intensity turbine nozzle, the influence of grooved vane on the shock wave characteristics is investigated in present paper. A Schlieren visualization experiment was first carried out on a linear turbine nozzle with smooth surface and the behavior of the shock wave was studied. Numerical simulations were also performed on the turbine nozzle. Guided by the visualization and numerical simulation, grooves were designed on the nozzle surface where the shock wave was originated and numerical simulations were performed to investigate the influence of grooves on the shock wave characteristics. Results indicate that for a smooth nozzle configuration, the intensity of the shock wave increases as the expansion ratios increase, while the onset position is shifted downstream to the nozzle trailing edge. For a nozzle configuration with grooved vane, the position of the shock wave onset is shifted upstream compared to the one with a smooth surface configuration, and the intensity of the shock wave as well as the static pressure distortion at the nozzle vane exit plane are significantly depressed.
TOPICS: Turbochargers, Shock (Mechanics), Turbines, Nozzles, Shock waves, Engines, Computer simulation, Rotors, Pressure, Clearances (Engineering), Schlieren methods, Visualization, Failure, Radial flow, Stators, Leakage flows, Emissions, High cycle fatigue
Matthias Rolfes, Martin Lange, Konrad Vogeler and Ronald Mailach
J. Turbomach   doi: 10.1115/1.4037822
The demand of increasing pressure ratios for modern high pressure compressors leads to decreasing blade heights in the last stages. As tip clearances cannot be reduced to any amount, the tip clearance ratios of the last stages can reach values notably higher than current norms. This can be intensified by a compressor running in transient operations. The ability of circumferential casing grooves in the rotor casing to improve the compressor's operating range has been in the focus of research for many years. Their simplicity is one reason for their continuing popularity nowadays. In a previous paper, three different circumferential groove CTs were investigated in a single stage environment in the LSRC at TUDresden. One groove was able to notably improve the operating range and the efficiency of the compressor at very large rotor tip clearances (5% chord). In this paper, tests with this particular groove type in a 3 stage environment in the LSRC are presented. Two different rotor tip clearance sizes of 1.2% and 5% of chord were investigated. At the small tip clearance, the grooves are almost neutral. If the compressor runs with large tip clearances, both, total pressure and efficiency can be improved by the grooves in a similar extent as in single stage tests. Five-hole probe measurements and unsteady wall pressure measurements show the influence of the groove on the flow field. With the help of numerical investigations the different behavior of the grooves at the two tip clearance sizes will be discussed.
TOPICS: Compressors, Turbochargers, Clearances (Engineering), Rotors, Chords (Trusses), Pressure, Flow (Dynamics), Pressure measurement, High pressure (Physics), Transients (Dynamics), Blades, Probes
Simon Jacobi and Budimir Rosic
J. Turbomach   doi: 10.1115/1.4037820
The integrated combustor vane concept for power genera- tion gas turbines with can combustors has been shown to have significant benefits compared to conventional nozzle guide vanes. Aerodynamic loss, heat transfer levels and cooling requirements are reduced while stage efficiency is improved by approximately 1.5% (for a no-swirl scenario). Engine realistic combustor flow with swirl however leads to increased turning non-uniformity downstream of the integrated vanes. This paper thus illustrates the altered integrated vane stage performance caused by inlet swirl. The study shows a distinct performance penalty for the in- tegrated vane rotor as a result of increased rotor incidence and the rotor's interaction with the residual swirl core. The stage effi- ciency advantage of the integrated combustor vane concept com- pared to the conventional design is thus reduced to 0.7%. It is furthermore illustrated how integrated vane profiling is suitable to reduce the turning variation across the span downstream of the vane, further improve stage efficiency (in this case by 0.23%) and thus mitigate the distinct impact of inlet swirl on integrated vane stage performance.
TOPICS: Flow (Dynamics), Turbochargers, Combustion chambers, Rotors, Nozzle guide vanes, Design, Gas turbines, Heat transfer, Cooling, Engines
Technical Brief  
Santosh Patil, Ivana D. Atanasovska and Saravanan Karuppanan
J. Turbomach   doi: 10.1115/1.4030242
The aim of this paper is to provide a new viewpoint of friction factor for contact stress calculations of gears. The idea of friction factor has been coined, for the calculation of contact stresses along the tooth contact for different helical gear pairs. Friction factors were developed by evaluating contact stresses with and without friction for different gear pairs. In this paper, 3D Finite Element Method (FEM) and Lagrange Multiplier algorithm has been used to evaluate the contact stresses. Initially, a spur gear FE model was validated with the theoretical analysis under frictionless condition, which is based on Hertz's contact theory. Then, similar FE models were constructed for 5, 15, 25 and 35 deg. helical gear pairs. The contact stresses of these models were evaluated for different coefficients of friction. These results were employed for the development of friction factor.

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