bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation on the Influence of Geometrical Parameters on the Frictional Heat Input and Leakage Performance of Brush Seals
Authors: Hildebrandt Manuel , Schwitzke Corina , Bauer Hans-Jörg
Published: August 2017

Because of the superior sealing characteristics compared to labyrinth seals, brush seals found an increased spread in turbomachinery in recent years. Their outstanding sealing performance results mainly from their flexibility. Thus, a very small gap between the rotor and bristle package can be obtained without running the risk of severe detrimental deterioration in case of rubbing. Rubbing between rotor and seal during operation might occur as a result of e.g. an unequal thermal expansion of the rotor and stator or a rotor elongation due to centrifugal forces or manoeuvre forces. Thanks to the flexible structure of the brush seal the contact forces during a rubbing event are reduced, however the frictional heat input can still be considerable. Particularly in aircraft engines with their thin and lightweight rotor structures the permissible material stresses can easily be exceeded by an increased heat input and thus harm the engine’s integrity. The geometry of the seal has a decisive influence on the resulting contact forces and consequently the heat input. The complex interactions between the geometric parameters of the seal and the heat input and leakage characteristics are not yet fully understood. This paper presents the investigation of the influence of the geometric parameters of a brush seal on the heat input into the rotor and the leakage behaviour. Two seals with different packing densities were tested under relevant engine conditions with pressure differences ranging from 1 to 7 bar, relative surface speeds ranging from 30 to 180 m/s and radial overlaps ranging from 0.1 to 0.4 mm. The transient temperature rise during the rub event was recorded with 24 thermocouples in close proximity to the rub contact embedded in the rotor structure. By comparing the temperature curves with the results of a thermal finite element analysis of the rotor the heat input into the rotor was calculated iteratively. It could be shown that the packing density has a decisive influence on the overall operating behaviour of a brush seal. Furthermore, results are obtained for the heat flux distribution between seal and rotor are shown.
Inlet Compatibility and Fan Aeromechanics of HBP Turbofan Engine
Authors: Wang Zhonglin , Chen Jingjing , Chen Yong
Published: August 2017

As an integrated system, turbofan engine airworthiness certification is a complex network because design, operating conditions and multi-disciplines are interlaced. Inlet compatibility specified in FAR regulations is to demonstrate satisfactory of engine operating characteristics throughout the flight envelope, which can be affected by engine installation and operation conditions. One limited operating condition is the high crosswind on the ground. Flow separated at engine inlet, unsteady and non-uniform, passing through the diffuser to the fan face, stimulated the fan blade at a broad frequency range, which could lead to high cycle fatigue.

A ground crosswind test was conducted by an airplane company to demonstrate the engine inlet compatibility with engine mounted on the rear of the aircraft under various crosswind conditions [1] including 90-degree crosswind, quarterly headwind (315-degree) and quarterly tailwind (225-degree). Results showed that among all tested ambient wind conditions, the engine was the least stable under quarterly tailwind (225-degree).

To predict the fan blade response driven by inlet separation, a process of evaluating inlet separation induced stimulus was illustrated in this paper. The stimuli were classified in two parts, i) synchronous stimulus induced by inlet distortion, and ii) non-synchronous stimulus induced by turbulence. Vibration of a wide-chord fan blade was evaluated by modal analysis and Campbell diagram. Test data of total pressure distortion at fan face were analyzed by Fast Fourier Transform (FFT), and the excitations in frequency domain were applied to fan blade for harmonic analysis. Results revealed that the synchronous excitation caused the blade resonating at an elevated stress level, as expected. This study provided a preliminary assessment and a better understanding of fan aeromechanics, when the engine is operating at the unsteady, unstable, and non-uniform flow environment. Discussions of how to control and how to decrease the vibration level were given in the study.
Experimental Investigation of Stall Inception and its Propagation in a Contra Rotating Axial Fan Under Radial Inflow Distortion
Authors: Dejene Toge Tegegn , Pradeep A. M.
Published: August 2017

Radial inflow distortion is encountered by any turbomachine in some form or the other. Radial inflow distortion alters the design blade loading distribution by redistributing the velocity along the blade span. The present experimental study is aimed to understand the influence of radially distorted inflow on the stall inception and propagation in a low speed contra rotating axial flow fan (CRAF). The study is carried out near-stall and at stall mass flow conditions for the design speed and off-design rotational speed combinations of the rotors. Total pressure rakes and Kiel probe rakes are used for flow characterization at the inlet of rotor-1 and rotor-2. Data from seven-hole probe measurement is also used to calculate the incidence angle at rotors inlet and the total press loss at relative frame of reference. Unsteady pressure data from the casing wall mounted sensors is used to understand the stall inception mechanism. The unsteady pressure data is analyzed using wavelet transforms and Fast Fourier Transforms (FFT). Wavelet transform is used to identify the stall inception mechanism, whereas FFT is used for quantification of the stall parameters. The study reveals that the performance and the stability of the CRAF stage is highly affected in case of hub covered radial distorted inflow condition and the stall incepts at a higher mass flow compared with the undistorted flow. However, the effect of tip covered radial distorted inflow on the performance and stability is negligible, and the stall incepts at nearly the same mass flow rate as that of the undistorted flow. Moreover, the CRAF stage gives better performance at higher mass flow for tip radially distorted inflow compared with the undistorted case. The wavelet transform clearly indicates that stall inception occurs mainly through long length-scale disturbances (LLSDs) for both the rotors. It is also observed that in some cases, spikes are embedded within LLSDs. The combined effect of stall initiated due to inflow distortion and direct interaction of the wake and the tip leakage vortex from rotor-1 with rotor-2 made the LLSDs and spikes type disturbances much stronger for rotor-2 compared with rotor-1.
The Influence of Mistuning and Coriolis Effects on the Modal Parameters of Bladed Discs: An Experimental Study
Authors: Ruffini Valentina , Green Jeffrey S. , Schwingshackl Christoph W.
Published: August 2017

A very detailed experimental analysis at several different rotational speeds was conducted on a simplified blisk to gain in-depth understanding of how the Coriolis effects and their interaction with mistuning evolve with speed to provide a better understanding for future designs. Two different nodal diameter families, characterised by different levels of mistuning, were investigated in greater detail. The blisk dynamics were found to depend both on mistuning levels and speed. Split Campbell diagrams were observed, together with the appearance of Coriolis-induced forward and backward travelling wave modes in the blisk. Three speed ranges characterised by different behaviours were identified at a high level of detail, with a gradual transition from mistuning-dominated behaviour at low speed to Coriolis-dominated features at higher speeds. The evolution of the mode shapes with speed, and the differences between low- and high-mistuning modes were particularly examined. The evolution of the mode shapes with speed, and the differences between low- and high-mistuning modes were particularly examined. An accurate comparison was conducted between the measurement data and finite element results, and confirmed the reliability of the new approach.
Gas Dynamic Simulation of Shockless Explosion Combustion for Gas Turbine Power Cycles
Authors: Rähse T. S. , Paschereit C. O. , Stathopoulos P. , Berndt P. , Klein R.
Published: August 2017

With the ongoing stagnation of the progress towards higher efficiency gas turbines, alternative approaches in combustion receive more attention than ever before. Besides, increasing efficiency and reducing emissions at the same time has become a first priority of the industry in the last few decades. Constant volume combustion is considered a technology capable of achieving a significant increase in thermal efficiency when applied in gas turbines. In this work, models of gas turbine cycles with two different combustion methods, being a shockless explosion combustion and an isobaric homogeneous combustion, will be simulated and compared. A code based on the one dimensional Euler equations is utilized to calculate the exhaust gas outlet parameters of the shockless explosion combustion chamber, while taking into account all the gas dynamic phenomena in it. The efficiency of the turbine is computed by steady state operational maps. The simulations provide numerous detailed results with a focus on the dependency of the SEC cycle’s thermal efficiency to the compressor pressure ratio and the turbine inlet temperature. Evaluating the kinetic energy in the total enthalpy of the turbine inlet flow is also an essential investigation.
Dynamic Characterization of an Integral Squeeze Film Bearing Support Damper for a Supercritical CO2 Expander
Authors: Ertas Bugra , Delgado Adolfo , Moore Jeffrey
Published: August 2017

The present work advances experimental results and analytical predictions on the dynamic performance of an integral squeeze film damper (ISFD) for application in a high-speed super-critical CO2 (sCO2) expander. The test campaign focused on conducting controlled orbital motion mechanical impedance testing aimed at extracting stiffness and damping coefficients for varying end seal clearances, excitation frequencies, and vibration amplitudes. In addition to the measurement of stiffness and damping; the testing revealed the onset of cavitation for the ISFD. Results show damping behavior that is constant with vibratory velocity for each end seal clearance case until the onset of cavitation/air ingestion, while the direct stiffness measurement was shown to be linear. Measurable added inertia coefficients were also identified. The predictive model uses an isothermal finite element method to solve for dynamic pressures for an incompressible fluid using a modified Reynolds equation accounting for fluid inertia effects. The predictions revealed good correlation for experimentally measured direct damping, but resulted in grossly overpredicted inertia coefficients when compared to experiments.
Numerical and Experimental Investigation of Acoustic Characteristics of a Fan Model With Struts Integrated in a Stator
Authors: Rossikhin Anton , Druzhinin Iaroslav , Khaletskii Iurii , Mileshin Victor
Published: August 2017

The results of the high bypass ratio turbofan fan tone noise simulation performed in CIAM (Central Institute of Aviation Motors) are presented. The feature of a design of the fan is that in it support struts are integrated to the stator. This investigation is a continuation of a series of papers devoted to numerical calculation of fan tone noise done in CIAM using the 3DAS (3 Dimensional Acoustics Solver) CIAM in-house solver. The calculation was performed at the approach operational conditions of the fan. As a result of the calculation the fields of the flow pulsations in the near field and the distribution of sound pressure levels in the far field on the surface surrounding the fan was obtained. It was shown that the distribution is strongly nonuniform both in the polar and in the azimuth directions. The results of the computation are compared with the experimental data from the CIAM C-3A acoustic test facility. In general, satisfactory correspondence between the calculation and the experiment for the directivity of sound in the horizontal plane is obtained.
Methodology to Evaluate the Characteristics of a Twin-Scroll Turbocharger With Various Approaches for the Computation of Thermodynamic Properties
Authors: Mai Holger , Kaufmann André
Published: August 2017

When it comes to evaluating the thermodynamic and fluid dynamic behavior of a turbocharger (TC) and ensuring the best possible matching to the internal combustion engine, a precise measurement of the characteristic maps is required. Measured on a hot-gas test bench under steady-state conditions, the maps of the compressor and turbine give detailed information about the turbocharger performance and provide boundary conditions for simulating the engine processes of a turbocharged engine.

At the moment there is no comprehensive standard on how to measure a TC on a test bench. All existing guidelines such as SAE J1826 & J922 and ASME PTC 10 contain more general information with recommendations, but turbocharger mapping on a hot-gas test bench is highly complex and has a large dependence on heat transfer. The characteristics are not determined directly, but have to be computed using the measured quantities and the thermodynamic properties of the working fluid. For that reason, all influences that may occur during the measurement have to be taken into account for the comparability of different turbochargers or the repeatability for the same turbocharger specimen.

As a consequence, this paper deals with the methodology of thermodynamic computation for a mono-scroll and a twin-scroll turbocharger in general and the impact of different approaches for computing the thermodynamic properties of the individual species on compressor and turbine efficiencies in particular.

For computing the characteristics of a mono-scroll turbocharger, a methodology is used that matches good practice and state-of-the-art technology. For computing the characteristics of a twin-scroll turbocharger, a new methodology is developed to provide a practical approach for the evaluation of pressure ratios and efficiencies of a twin-entry turbine. The use of the closed-loop unit for the extension of the turbine is included.

Computing the thermodynamic state changes, power, and efficiencies of the compressor and turbine requires knowledge of the physicochemical properties of the involved fluids. These fluids are humid air (compressor) and exhaust gas (turbine) and depend on the gas composition, pressure, and especially temperature with respect to the relative humidity.

Turbocharger efficiencies are very sensitive to deviations in the thermodynamic properties of the individual species. Different forms of polynomials with different levels of complexity and precision are available in literature. In this paper, the most commonly used polynomials for computing the thermodynamic properties such as caloric perfect gas, humid air, VDI 4670, NASA9, CHEMKIN, NIST, and SAE J1826 will be used for the characteristic maps of a twin-scroll turbocharger. The results will be discussed in terms of the impact on turbocharger efficiencies and the relevance to achieving a desired quality level for turbocharger mapping.
Optimization Designs of Front Stage Nozzles in a LP Steam Turbine
Authors: Wu X. , Deng G. L. , Du X. Q. , Zhang P. F.
Published: August 2017

This paper presents the findings of the original nozzle of the fourth stage in a 7 stage LP steam turbine where an obvious geometric feature is the extremely thick leading edge (LE). A cascade test was carried out to investigate the mechanism of loss reduction. A detailed comparison study was carried out using a conventional thinner leading edge design and the original thicker LE profile. The studies reveal that the overall loss in the original design is significantly lower than the counterpart of the thinner LE option together with a much wider range of incidence for which the vane is of low loss. This design philosophy is then successfully cloned to the first stage and third stage nozzles in a seven stage LP steam turbine. The analysis indicates that the obvious advantages of the new designs over the conventional thinner option are on not only the reduction of the profile loss, but the reduction of the blade count which has a significant implication on manufacturing cost. The numerical studies reveal that the idea behind this thick LE design philosophy is to minimise the profile loss without incurring a significant penalty on diffusion loss or at the worst separation. A detail investigation on the stage 2 nozzle indicates that this concept only works for a reasonably high aspect ratio blading where the secondary loss is limited.
Plasma-Assisted Combustor Dynamics Control at Ambient and Realistic Gas Turbine Conditions
Authors: Kim Wookyung , Cohen Jeffrey
Published: August 2017

The central objective of this study is to investigate the effectiveness of implementing a plasma discharge to improve combustor dynamics and flame stability. Specifically, a nano-second pulsed plasma discharge (NSPD) was applied to a premixed gaseous fuel/air dump combustor for mitigation of dynamic combustion instabilities with a minimal NOX penalty. This paper addresses the scaling of this technology from ambient pressure and temperature conditions to more realistic gas turbine combustor conditions.

A model combustor operating at representative conditions of O (102) m/s flow velocity, ∼ 580 K combustor inlet temperature, and ∼ 5 atm in-combustor pressure was selected to simulate a typical low-power environment of future aero engine gas turbine combustors. Fully premixed methane or propane was utilized as a fuel. Similar to a previous ambient-pressure study, a significant reduction of pressure fluctuation level was observed, by a factor of 2X to 4X over a wide range of velocity at the baseline temperature and pressure. The plasma power required for the reduction increased linearly with increasing velocity. The change of fuel from methane to propane showed that propane requires significantly (2X) higher plasma power to achieve a similar level of noise reduction. It was also observed that the lean blowout (LBO) limit was significantly extended in the presence of the plasma, however, substantial incomplete combustion occurs in the extended regime. NOX measurements showed that the incremental NOX production due to the presence of the plasma was low (∼ < 1EINOX) in general, however, it increased with decreasing velocity and pressure, and increasing temperature.
The Effect of Transient Fuel Staging on Self-Excited Instabilities in a Multi-Nozzle Model Gas Turbine Combustor
Authors: Culler Wyatt , Samarasinghe Janith , Quay Bryan D. , Santavicca Domenic A. , O’Connor Jacqueline
Published: August 2017

Combustion instability in gas turbines can be mitigated using active techniques or passive techniques, but passive techniques are almost exclusively used in industrial settings. While fuel staging, a common passive technique, is effective in reducing the amplitude of self-excited instabilities in gas turbine combustors at steady-state conditions, the effect of transients in fuel staging on self-excited instabilities is not well understood. This paper examines the effect of fuel staging transients on a laboratory-scale five-nozzle can combustor undergoing self-excited instabilities. The five nozzles are arranged in a four-around-one configuration and fuel staging is accomplished by increasing the center nozzle equivalence ratio. When the global equivalence ratio is φ = 0.70 and all nozzles are fueled equally, the combustor undergoes self-excited oscillations. These oscillations are suppressed when the center nozzle equivalence ratio is increased to φ = 0.80 or φ = 0.85. Two transient staging schedules are used, resulting in transitions from unstable to stable operation, and vice-versa. It is found that the characteristic instability decay times are dependent on the amount of fuel staging in the center nozzle. It is also found that the decay time constants differ from the growth time constants, indicating hysteresis in stability transition points. High speed CH* chemiluminescence images in combination with dynamic pressure measurements are used to determine the instantaneous phase difference between the heat release rate fluctuation and the combustor pressure fluctuation throughout the combustor. This analysis shows that the instability onset process is different from the instability decay process.
A Computational Fluid Dynamics Modified Bulk Flow Analysis for Circumferentially Shallow Grooved Liquid Seals
Authors: San Andrés Luis , Wu Tingcheng , Maeda Hideaki , Tomoki Ono
Published: August 2017

In straight-through centrifugal pumps, a grooved seal acts as a balance piston to equilibrate the full pressure rise across the pump. As the groove pattern breaks the development of fluid swirl, this seal type offers lesser leakage and lower cross-coupled stiffnesses than a similar size and clearance annular seal. Bulk-flow models predict expediently the static and dynamic force characteristics of annular seals; however they lack accuracy for grooved seals. Computational fluid dynamics (CFD) methods give more accurate results, but are not computationally efficient. This paper presents a modified bulk-flow model to predict the rotordynamic force coefficients of shallow depth circumferentially grooved liquid seals with an accuracy comparable to a CFD solution but with a simulation time of bulk-flow analyses. The procedure utilizes the results of CFD to evaluate the bulk flow velocity field and the friction factors for a 73 grooves annular seal (depth/clearance dg/ Cr = 0.98 and length/diameter L/D = 0.9) operating under various sets of axial pressure drop and rotor speed. In a groove, the flow divides into a jet through the film land and a strong recirculation zone. The penetration angle (α), specifying the streamline separation in the groove cavity, is a function of the operating conditions; an increase in rotor speed or a lower pressure difference increases α. This angle plays a prominent role to evaluate the stator friction factor and has a marked influence on the seal direct stiffness. In the bulk-flow code the friction factor model (f = nRem) is modified with the CFD extracted penetration angle (α) to account for the flow separation in the groove cavity. The flow rate predicted by the modified bulk-flow code shows good agreement with a measured result (6% difference). A perturbation of the flow field is performed on the bulk-flow equations to evaluate the reaction forces on the rotor surface. Compared to the rotordynamic force coefficients derived from the CFD results, the modified bulk-flow code predicts rotordynamic force coefficients within 10%, except that the cross-coupled damping coefficient is over-predicted up to 14%. An example test seal with a few grooves (L/D = 0.5, dg/Cr = 2.5) serves to further validate the predictions of the modified bulk-flow model. Compared to the original bulk-flow analysis, the current method shows a significant improvement in the predicted rotordynamic force coefficients, the direct stiffness and damping coefficients in particular.
Numerical Investigation on the Effect of Slot Leakage on a NGV With 2D Contoured Endwall: Adiabatic Effectiveness and Aerodynamic Loss
Authors: Chen Pingting , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2017

Endwall 2D contouring is a typical design to reduce the strength of secondary flows within the passage. Such contouring can lead to significant changes in the passage flow. A leakage slot at the combustor-turbine interface is a typical turbine endwall design. The leakage flow can be used to cool the endwall and vane surface. Moreover, the leakage flow interacts with the main flow and results in the change of aerodynamic loss. A 3D numerical method was used to investigate endwall adiabatic effectiveness and passage total pressure loss coefficient (TPLC) on a NGV with 2D contoured endwall under a series of mass flow ratios (MFRs). The numerical method was validated by comparision with the experiment data. The results indicate that under the condition of this study, When MFR<0.625%, there is ingestion, and when 0.625%<MFR<1.0%, the TPLC is high. When 0.875%<MFR<1.0%, the area averaged adiabatic effectiveness (AAAE) decreases and the TPLC stays high as the MFR increases. When 1.0%<MFR<1.5%, the adiabatic effectiveness is high and the TPLC is low. To accomplish high adiabatic effectiveness, low aerodynamic loss and slight ingestion, the recommended range of MFR is 1.0%<MFR<1.5%.
Towards Predicting Lean Blow-Off Based on Damköhler Number and Practical Reaction Zone
Authors: Wang Zhonghao , Hu Bin , Zhao Qingjun , Xu Jianzhong
Published: August 2017

Lean Blow-off (LBO) is important in gas turbine combustion. In this paper, numerical simulation and experiment are conducted to develop a new method for LBO prediction of gas turbine combustors based on Damköhler (Da) number and practical reaction zone (PRZ). PRZ is established based on OH concentration in the reacting flow of combustor, and it is simplified to a perfectly stirred reactor (PSR) due to the drastic mixing caused by swirling flow. Flow time scale (Ft) and chemical time scale (Ct) contained in Da number are all specified based on PRZ. Flow time scale (Ft) is defined as the residence time of fuel flowing through the PRZ, and chemical time scale (Ct) is defined as the shortest time needed to trigger the chemical reaction in PRZ. Da numbers, which introduce the physical competition between Ft and Ct, are calculated under LBO conditions and design point. The average Da number at LBO is about 1, ranging from 0.6 to 1.86, and the Da number of design condition is 4.33, showing that the method proposed in the paper is reliable and has the potential for practical engineering applications.
Adjoint Aerodynamic Optimization of a Transonic Fan Rotor Blade With a Localized Two-Level Mesh Deformation Method
Authors: Tang Xiao , Luo Jiaqi , Liu Feng
Published: August 2017

We present an optimization platform for turbomachineries with complex mesh configuration in a parallel computation environment. A continuous adjoint solver for 3-D viscous internal flow is coded under the same parallel framework as the flow solver. To meet the various permitted extents of reshaping on blade surface and cut down the computation cost in grid perturbation, a localized two-level mesh deformation method is developed based on Gaussian radial basis function (RBF). This method works efficiently for both the O mesh surrounding the blade and the O-H mesh blocks inside tip gap. In optimization of the transonic NASA Rotor 67 for higher adiabatic efficiency with a mass flow rate constraint, an adjoint sensitivity analysis is conducted. The relations between the design sensitive regions and physical phenomena in internal flow are discussed. Flow fields before and after adjoint optimization are investigated, including shock system, tip leakage flow and flow separation.
Investigation on the Highly Loaded Helium Compressor Based on Helium Thermophysical Properties: Part B — The Loss Analysis of Highly Loaded Axial Helium Compressor
Authors: Tian Zhitao , Zheng Qun , Jiang Bin , Zhu Qingfang
Published: August 2017

Helium compressor is a main component of high temperature gas reactor (HTGR) helium power conversion unit, and its performance has significant effects on the power output and cycle efficiency. In this paper, the flow loss analysis of highly loaded axial helium compressor is carried out using a computational fluid dynamics (CFD) program at both design and off-design point. To understand the loss mechanism of the highly loaded helium compressor, special attention is paid to the tip clearance loss, profile loss and the end wall loss. As is well-known, when increasing the backpressure, the specific power and adverse pressure gradient of general air compressor cascade increase as well. But the specific power and adverse pressure gradient of the highly loaded design helium compressor in this paper will decrease with the backpressure increasing due to the new velocity triangle. So the loss characteristics of the highly loaded helium compressor are different from that of air compressor. From the three-dimensional viscous numerical results, the profile loss is the most important loss source of the highly loaded helium compressor. The proportion of the highly loaded helium compressor profile loss is more than 50%.
Influence of Gas-to-Wall Temperature Ratio on By-Pass Transition
Authors: Cação Ferreira Tânia S. , Arts Tony
Published: August 2017

An investigation of thermal effects on bypass transition was conducted on the highly-loaded turbine guide vane LS89 in the short-duration isentropic Compression Tube (CT-2) facility at the von Karman Institute for Fluid Dynamics (VKI).

Measurements from high response surface-mounted thin films coupled with analog circuits provided the time-resolved wall heat flux history whereas pneumatic probes, differential pressure transducers and thermocouples allowed the accurate definition of the inlet and outlet flow conditions.

The gas-to-wall temperature ratio, ranging from 1.11 to 1.55, was varied by changing the inlet total temperature. The isentropic exit Mach number ranged from 0.90 to 1.00 and the global freestream turbulence intensity value was set at 0.8, 3.9 and 5.3%. The isentropic exit Reynolds number was kept at 106.

The onset of transition was tracked through the wall heat flux signal fluctuations. Within the present operating conditions, no significant effect of the gas/wall temperature ratio was put in evidence. At the present (design) transonic exit conditions, the local free-stream pressure gradient appears to remain the main driver of the onset of transition. A wider range of operating conditions must be considered to draw final conclusions.
Aerodynamic Performances of a Centrifugal Compressor With Discrete Cavities
Authors: Ma Sang-Bum , Kim Kwang-Yong
Published: August 2017

In this study, aerodynamic performance of the centrifugal compressor was investigated by using a recirculating device called discrete cavities. A parametric study was conducted using six parameters related to the geometry of the discrete cavities, i.e., the inclined angle, the port angle and width, the length of cavity, the axial location of each cavity, and the number of cavities. Three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used for aerodynamic analysis of the centrifugal compressor with discrete cavities. The hexahedral grid was used in impeller domain and tetrahedral grid was used in volute and inclined discrete cavities. The numerical results for the adiabatic efficiency and the total pressure ratio (inlet to outlet) showed good agreements with experimental data. It was found that inclination of the discrete cavities further increased the stall margin without loss of efficiency compared to the uninclined discrete cavities.
A Physics-Based Dynamic Model for Boilers: Part 1 — Model Development and Validation
Authors: Blom Matthew J. , Brear Michael J. , Manzie Chris G. , Wiese Ashley P.
Published: August 2017

This paper is the first part of a two part study that develops, validates and integrates a one-dimensional, physics-based, dynamic boiler model suitable for application with model based control. Part 1 of this study extends and validates the existing, higher order modelling framework of Badmus et. al. [1] to boilers. This requires derivation of particular, one-dimensional forms of the equations for heat, mass and momentum transfer in single (liquid and gas) phase and two phase fluids with real fluid properties. The so-called ‘forcing term’ mapping functions in these equations only require knowledge of steady state system behaviour, and so can be obtained from steady state measurements throughout the boiler system. Additional models are also presented for other boiler components, including the steam drum in sub-critical boilers.

The overall framework is then used to develop and validate a model of a GW scale, sub-critical boiler in an operating, electrical power plant. Overall, the model achieves reasonable agreement with the power plant dynamics during normal transient operations, including acceptable tracking of the drum dynamics and the steam at the boiler outlet. As such, this modelling framework appears suitable for developing models of sufficient fidelity yet retain an appropriate form for model reduction using singular perturbation analysis techniques, as demonstrated in Part 2 [2] of this study.
Research on the Unsteady Flow in an Axial Flow Compressor Rotor Based on PVDF Piezoelectric-Film Sensor Array
Authors: Cong Jiqing , Jing Jianping
Published: August 2017

The unsteady flow in an axial flow compressor rotor is responsible for noise generation and unexpected excitation of blade vibration; therefore, compressors may suffer from fatigue failure of blades and eventually become unable to operate. At present, a set of Kulite pressure transducers mounted on the casing wall is widely used to acquire the pressure field of unsteady flow. However, it will affect the compressor structure and it is physically impossible to mount at a small spacing to capture the variation of casing wall pressure precisely because of the size of transducers. For the requirement of measurement, a self-developed PVDF (polyvinylidene fluoride) piezoelectric-film sensor array measurement system was applied to measure and capture the pressure field distribution over the compressor rotor blade tip clearance. In this system, a multi-measuring points PVDF array, in which 40 measuring points was contained in a 70mm by 40mm rectangle area, was attached on the casing wall of the rotor blade tip. This new technique has great advantages over traditional measurement technique, such as wide frequency response, high space resolution, less impact on the compressor, easy installation and so on. Based on a multistage axial compressor rig test, the unsteady flow pattern on the casing wall was well captured by the PVDF array. And it is revealed in all measuring points that the resonance occurs all over the compressor is under one single frequency, and the pressure level of the acoustic resonance exceeds the level of the usually dominated blade passing frequency when close to the stability limit. At the same time, the acoustic resonance will be modulated with the blade passing frequency.
Optimization of the Vibration Behavior at Speed-Synchronous Resonance of a Large Turbine Blade During Speed-Up and Coast-Down Under Consideration of Mistuning
Authors: Lübbe Bertold , Siewert Christian
Published: August 2017

During start-up and coast-down of the turbine train large last stage moving blades may show elevated amplitude levels. In cases where the excitation mechanism results from a rotor imbalance, it is well known that the occurring amplitude level can be influenced by the turbine set-up as well as the mode of operation during start-up and coast-down. For example, by increasing speed gradients the exposure time in which the blade row is operated at or close to speed-synchronous resonance is reduced and hence the excitation is minimized.

To evaluate the blade response during transient operation an analytical model is developed which allows for an accurate description of the exciting inertia forces resulting from rotor imbalance. In the present paper, the effect of a small-scale variation of the tuned blades’ resonance frequency and intentional mistuning of the blade row, (Siewert & Stüer, 2014), on the obtainable resonance amplitudes and the potentially accumulated fatigue is assessed. The results show a significant increase in robustness against transient excitation by application of a dedicated tuning, allowing for enhanced flexible operation of large last stage moving blades.
Evaluation of a Micro Gas Turbine With Post-Combustion CO2 Capture for Exhaust Gas Recirculation Potential With Two Experimentally Validated Models
Authors: Nikpey Somehsaraei Homam , Ali Usman , Font-Palma Carolina , Mansouri Majoumerd Mohammad , Akram Muhammad , Pourkashanian Mohamed , Assadi Mohsen
Published: August 2017

The growing global energy demand is facing concerns raised by increasing greenhouse gas emissions, predominantly CO2. Despite substantial progress in the field of renewable energy in recent years, quick balancing responses and back-up services are still necessary to maintain the grid load and stability, due to increased penetration of intermittent renewable energy sources, such as solar and wind.

In a scenario of natural gas availability, gas turbine power may be a substitute for back-up/balancing load. Rapid start-up and shut down, high ramp rate, and low emissions and maintenance have been achieved in commercial gas turbine cycles. This industry still needs innovative cycle configurations, e.g. exhaust gas recirculation (EGR), to achieve higher system performance and lower emissions in the current competitive power generation market. Together with reduced NOx emissions, EGR cycle provides an exhaust gas with higher CO2 concentration compared to the simple gas turbine/combined cycle, favorable for post-combustion carbon capture.

This paper presents an evaluation of EGR potential for improved gas turbine cycle performance and integration with a post-combustion CO2 capture process. It also highlights features of two software tools with different capabilities for performance analysis of gas turbine cycles, integrated with post-combustion capture. The study is based on a combined heat and power micro gas turbine (MGT), Turbec T100, of 100kWe output. Detailed models for the baseline MGT and amine capture plant were developed in two software tools, IPSEpro and Aspen Hysys. These models were validated against experimental work conducted at the UK PACT National Core Facilities. Characteristics maps for the compressor and the turbine were used for the MGT modeling. The performance indicators of systems with and without EGR, and when varying the EGR ratio and ambient temperature, were calculated and are presented in this paper.
Numerical Study on the Influence of Trench Width on Film Cooling Characteristics of Double-Wave Trench
Authors: Zhang Bo-lun , Zhang Li , Zhu Hui-ren , Wei Jian-sheng , Fu Zhong-yi
Published: August 2017

Film cooling performance of the double-wave trench was numerically studied to improve the film cooling characteristics. Double-wave trench was formed by changing the leading edge and trailing edge of transverse trench into cosine wave. The film cooling characteristics of transverse trench and double-wave trench were numerically studied using Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment. The film cooling effectiveness and heat transfer coefficient of double-wave trench at different trench width (W = 0.8D, 1.4D, 2.1D) conditions are investigated, and the distribution of temperature field and flow field were analyzed. The results show that double-wave trench effectively improves the film cooling effectiveness and the uniformity of jet at the downstream wall of the trench. The span-wise averaged film cooling effectiveness of the double-wave trench model increases 20–63% comparing with that of the transverse trench at high blowing ratio. The anti-counter-rotating vortices which can press the film on near-wall are formed at the downstream wall of the double-wave trench. With the double-wave trench width decreasing, the film cooling effectiveness gradually reduces at the hole center-line region of the downstream trench. With the increase of the blowing ratio, the span-wise averaged heat transfer coefficient increases. The span-wise averaged heat transfer coefficient of the double-wave trench with 0.8D and 2.1D trench width is higher than that of the double-wave trench with 1.4D trench width at the high blowing ratio conditions.
Techno-Economic Study of Wind Farm Forecast Error Compensation by Flexible Heat-Driven CHP Units
Authors: Bexten Thomas , Wirsum Manfred , Roscher Björn , Schelenz Ralf , Jacobs Georg , Weintraub Daniel , Jeschke Peter
Published: August 2017

Many energy supply systems around the world are currently undergoing a phase of transition that is mainly characterized by a continuing increase in installed renewable power generation capacities. Aiming at a better integration of these additional capacities, operators of wind farms in Germany are obliged to bindingly forecast their power production. In order to maintain the continuous stability of the electricity grid, deviations from these forecasts have to be compensated by the grid operator, who charges the wind farm operators accordingly. An alternative way to compensate for forecast errors is the utilization of flexible and dispatchable energy conversion and storage units by the wind farm operator.

Heat-driven combined heat and power (CHP) units with heat storage systems offer the potential of limited short-term load adjustments to compensate forecast errors while simultaneously fulfilling their main task of providing heat.

The main objectives of the present study are the evaluation of the main technical parameters and the economic viability of the described application.

The study utilizes a theoretical scenario incorporating a gas turbine as a CHP unit providing heat for an industrial process, a heat storage and an associated wind farm. A generic wind farm power generation forecast error model is developed, providing realistic forecast errors for the study. Detailed models of all system components are developed and integrated into a common simulation environment, allowing for simulations of the overall system operation with varying heat storage capacities. The simulation results show that the combination of a heat-driven CHP gas turbine and a heat storage system makes a significant contribution to the compensation of the wind farm power generation forecast errors. Distinct correlations between the heat storage capacity and the remaining forecast errors are identified. The net balance energy costs resulting from the remaining demand for balance energy after the partial forecast error compensation are investigated as the main parameter for the economic viability. No distinctive correlation between the heat storage capacity and the net balance energy costs can be identified. This is the result of the stochastic character of the net balance energy price.
Experimental Analysis of Angled Injection Aerostatic Hybrid Bearings
Authors: Le Rouzic Julian , Arghir Mihai
Published: August 2017

Counter-rotation angled injection employed for aerostatic hybrid bearings reduces the cross coupling stiffness that may lead to whirl-whip instabilities at high rotation speeds. The benefits of counter-rotation injection have been known for years. Theoretical investigations were performed for water or air fed hybrid bearings but experiments were conducted only for water fed bearings. The present work is the first effort dedicated to angled injection in air fed hybrid bearings. The tests were performed for a simple rotor supported by two identical hybrid bearings. The hybrid bearings are provided with small size, shallow pockets and are fed with air via counter-rotation oriented orifice type restrictors. An impulse turbine fed with air entrains the rotor. An impact gun applies dynamic excitations and the rotordynamic coefficients are identified from the equations of motion of the rotor. Different air feeding pressures are tested as well as high rotational speeds.

Compared to the dynamic characteristics of radial injection hybrid bearings, the direct stiffness of counter-rotation injection bearings has slightly lower values and the direct damping is higher but the main impact is the drastic reduction of the cross-coupling stiffness that may have even negative values.
Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios
Authors: Li Zhigang , Li Jun , Feng Zhenping
Published: August 2017

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor-stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines.

The paper deals with the leakage and static stability behavior of a fully-partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360° mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-Averaged Navier-Stokes (RANS) solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7 000 rpm, 11 000 rpm and 15 000 rpm) including the non-rotating condition, three pressure ratios (0.17, 0.35 and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions, no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal would be statically unstable.