bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental and Numerical Investigation of Effect of Center Offset Degree on Compressor Stability With Circumferential Grooved Casing Treatment
Authors: Zhang HaoGuang , Tan Feng , Wu YanHui , Chu WuLi , Wang Wei , An Kang 
Published: September 2016

For compressor blade tip stall, one effective way of extending stable operating range is with the application of circumferential grooved casing treatment and its validity was proved by a lot of experimental and numerical investigations. The emphases of most circumferential grooved investigations are focused on the influence of groove depth and groove number on compressor stability, and there is few investigations dealt with the center offset degree of circumferential grooves casing treatment. Hence, an axial compressor rotor with casing treatment (CT) was investigated with experimental and numerical methods to explore the effect of center offset degree on compressor stability and performance.
In the work reported here, The center offset degree is defined as the ratio of the central difference between rotor tip axial chord and CT to the axial chord length of rotor tip. When the center of CT is located within the upstream direction of the center of rotor tip axial chord, the value of center offset degree is positive. The experimental and numerical results show that stall margin improvement gained with CT is reduced as the value of center offset degree varies from 0 to 0.33 or −0.33, and the CT with −0.33 center offset degree achieves the lowest value of stall margin improvement at 53% and 73% design rotational speed. The detailed analysis of the flow-field in compressor tip indicates that there is not positive effect made by grooves on leading edge of rotor blade tip when the value of center offset degree is −0.33. As the mass flow of compressor reduces further, tip clearance leakage flow results in the outlet blockage due to the absence of the positive action of grooves near blade tip tail when the value of center offset degree is 0.33. Blockage does not appear in rotor tip passage owing to utilizing the function of all grooves with CT of 0 center offset degree.
Experimental Observations of Thermal Bow due to Natural Convection on a Gas Turbine Compressor Rotor Shaft Analogue
Authors: Smith E. O. , Neely A. J. , Butcher A. P. 
Published: September 2016

This study describes the development of an experimental apparatus designed to provide initial validation of numerical simulations of a gas turbine compressor rotor shaft under thermal bow due to natural convection. The experimental analogue represents a simplified model developed by the authors in previous works, designed to represent the basic elements of a compressor rotor shaft, as part of an ongoing parametric study into the influence of compressor design and integration on the onset time, duration, and severity of thermal bow, and the propensity of an engine to suffer from the Newkirk Effect.
The semi-enclosed steel shaft, mounted on a support frame, was heated to approximately 600K in a convective oven before being removed and allowed to cool under ambient conditions. Observations of the shaft under natural cooling were made using several experimental techniques, including temperature profiling using thermographic imaging and a thermocouple array, and physical distortion measurement using linear variable displacement transducer (LVDT) probes. The behaviour of the buoyant plume was also observed using background oriented schlieren (BOS). Using these techniques, the natural convection-driven thermal gradient and resultant physical deformation were measured and recorded over a period of 60 minutes.
The observed thermal gradients and resultant thermal bow distortions were then compared to a one-way fluid thermal structural interaction (FTSI) 3D conjugate heat transfer (CHT) computational fluid dynamics (CFD) and finite element analysis (FEA) model developed by the authors, in order to validate the numerical model. The behaviour of the thermal plume from the BOS imagery was also used as a qualitative validation method. The temperature measurements and overall cooling rate measured on the experimental model showed good agreement with the numerical predictions (within 1%); however, uncertainties in the initial phase of the experiment led to error in the numerical prediction of the thermal gradient and resultant thermal bow measurements (error of up to 63%). Noting the uncertainties in the experiment, the agreement between numerical and experimental results with respect to the overall cooling rate indicates that the numerical approach being employed as part of the larger parametric study into gas turbine compressor rotor shaft thermal bow is appropriate and valid.
Heat Transfer of Winglet Tips in a Transonic Turbine Cascade
Authors: Zhong Fangpan , Zhou Chao , Ma H. , Zhang Q. 
Published: September 2016

Understanding the heat transfer of winglet tips is crucial for their applications in high pressure turbines. The current paper investigates the heat transfer performance of three different winglet-cavity tips in a transonic turbine cascade at a tip gap of 2.1% chord. A cavity tip was studied as the baseline case. The cascade operates at engine representative conditions of an exit Mach number of 1.2 and an exit Reynolds number of 1.7×106. Transient infrared thermography technique was used to obtain the tip distributions of heat transfer coefficient for different tips in the experiment. The CFD results were validated with the measured tip heat transfer coefficients, and then used to explain the flow physics related to heat transfer. It is found that on the pressure side winglet, the flow reattaches on the top winglet surface and results in high heat transfer coefficient. On the suction side winglet, the heat transfer coefficient is low near the blade leading edge, but is higher from the mid-chord to the trailing edge. The suction side winglet pushes the tip leakage vortex further away from the blade suction surface and reduces the heat transfer coefficient from 85% to 96% span on the blade suction surface. However, the heat transfer coefficient is higher for the winglet tips from 96% span to the tip. This is because the tip leakage vortex attaches on the side surface of the suction side winglet and results in quite high heat transfer coefficient on the front protrusive part of the winglet.
The effects of relative endwall motion between the blade tip and the casing were investigated by CFD methods. The endwall motion has a significant effect on the flow physics within the tip gap and near tip region in the blade passage, thus affects the heat transfer coefficient distributions. With relative endwall motion, a scraping vortex forms inside the tip gap and near the casing, and the cavity vortex gets closer to the pressure side squealer/winglet. The tip leakage vortex in the blade passage becomes closer to the blade suction surface, resulting in an increase of the heat transfer coefficient.
Unsteady Aerodynamics of a Flat Tip and a Winglet Tip in a High-Pressure Turbine
Authors: Zhou Kai , Zhou Chao 
Published: September 2016

In an unshrouded high-pressure turbine, tip leakage flow results in a loss of efficiency. In this paper, the aerodynamic performance of the tip leakage flow is investigated in a turbine stage by numerical methods. A flat tip and a closed squealer tip combined with a suction side winglet are used for the rotor tips, and the two turbines are named as ‘Flat Configuration’ and ‘Winglet Configuration’. The ability of the CFD methods in predicting the unsteady flow and the tip leakage flow is validated. The steady calculations using a mixing plane between the stator and the rotor are presented first. Then, the unsteady flows of the turbine stage with a flat rotor tip and a winglet rotor tip are simulated by solving Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations.
Compared with the ‘Flat Configuration’, the ‘Winglet Configuration’ reduces the size of the passage vortex and the tip leakage vortex. A surprising observation is that although the ‘Winglet Configuration’ reduces the size of the tip leakage vortex, its maximum swirl strength of the tip leakage vortex is about 40% higher than that for the ‘Flat Configuration’. The steady calculation shows that the entropy generation for the turbine stage is 12.1% lower with the ‘Winglet Configuration’ than that with the ‘Flat Configuration’.
The mixed-out entropy predicted in the unsteady calculation is higher than that of the steady calculation for both tips. The stator casing passage vortex has a periodic effect on the vortex near the tip gap of the rotor. The unsteady interaction of the vortices seems to be beneficial in terms of the loss. As a result, the ‘Winglet Configuration’ produces 9.4% less entropy than the ‘Flat Configuration’, which is lower than that in the case of the steady calculation.
Comparison of 2D and 3D Airfoils in Combination With Non Axisymmetric End Wall Contouring: Part 2 — Numerical Investigations
Authors: Curkovic Oliver , Zimmermann Tobias W. , Wirsum Manfred , Fowler Andrew , Patel Kush 
Published: September 2016

Secondary flow phenomena have a considerable part in the efficiency loss in turbomachinery. A potential method to reduce these secondary flow losses is tangential end wall contouring inside the blade passages. The present paper is the second of two papers which investigate the impact of tangential end wall contouring on 2D and 3D airfoils compared to a baseline configuration. The first paper summarizes the experimental investigation on a 2-stage air driven turbine test rig located at the Institute of Power Plant Technology, Steam and Gas Turbines RWTH Aachen University. To enhance the impact of the tangential end wall contours (TEWC) on the near wall flow, the rotor cavities are sealed by means of combined brush- and labyrinth seals. The stator cavities are sealed by labyrinth seals, only.
This paper investigates the flow phenomena using CFD with the commercial software package ANSYS 15.0©. The brush seals are modeled by using the porous body approach and are calibrated using pressure drop measurements across the first rotor cavity. The experimental data will be presented and is used to validate the numerical model. For this, circumferential plots for the measurement planes are shown. In addition a detailed description of the changes in vortex formations as well as blade loading will be given for the various configurations. Finally a discussion of the impact on the turbine’s efficiency is given. It has been found, that for steady CFD simulations the use of stage interfaces suppresses the positive effects of the tangential end wall contour onto the downstream blade row.
Conjugate Heat Transfer Simulation of the Intercooled Compressor Vanes Based on Discontinuous Galerkin Method
Authors: Liu Long-gang , Gu Chun-wei , Ren Xiao-dong 
Published: September 2016

Convective cooling channels are applied in a two-dimensional compressor vane to use the intercooling method to improve the efficiency of Brayton cycle and reduce the temperature of the vane. In this paper, we analyze the effect of coolant to the aerodynamic performance and heat transfer performance of the main stream and the vane.
For the case of a two-dimensional compressor vane NACA65-(12A2I8b)10, the vane which has five convective cooling channels has been numerically simulated in different test conditions by discontinuous Galerkin (DG) method. The coolant is supercritical carbon dioxide whose pressure is 10MPa. Conjugate heat transfer method has been used in this paper. The numerical simulation result is similar to the experiment data and has been compared with the result of the vane without cooling channels to prove the effect of cooling channels. Cooling channels have large effect on the distribution of temperature and heat transfer coefficient. In addition, the relationship between Nu and Re on the fluid-solid interface has been analyzed and a suitable empirical equation has been obtained.
This work analyzes the effect of intercooling system in the compressor and give several advice on future engineering applications in aero engines and gas turbines.
Difference in the Working Principle of Axial Slot and Tip Blowing Casing Treatments
Authors: Inzenhofer André , Guinet Cyril , Hupfer Andreas , Becker Bernd , Grothe Patrick , Heinichen Frank 
Published: September 2016

Tip blowing and axial slot casing treatments have shown their ability to enhance the stability of a transonic axial compressor with different effects on efficiency. For an effective application of these casing treatments, a good knowledge of the influence of the casing treatment on the rotor flow field is important. There is still a need for more detailed investigations, in order to understand the interaction between the treatment and the near casing 3D flow field. For transonic compressor rotors this interaction is more complex, as super- and subsonic flow regions alternate while interacting with the casing treatment.
In the present study, an axial slot and a tip blowing casing treatment, which have been developed and optimized for the same tip critical transonic axial compressor rotor (reference rotor) by Streit et al. [1] and Guinet et al. [2], are subject of the investigation. Both casing treatment types showed their capabilities to enhance the compressor stability without losing by means of CFD simulations. Since the higher compressor stability allows a higher blade loading, Streit et al. reduced the blade number of the rotor. Thus, the efficiency was increased due to the reduction of friction losses. However, applying the tip blowing casing treatment to the reduced rotor shows a negative effect on the efficiency.
Both casing treatment types recirculate flow from a downstream to an upstream location of the rotor and reinject it to enhance the near casing flow field. Although the working principle of the two casing treatment types are similar, the transfer of the casing treatments from the reference to the reduced rotor show different trends in efficiency. Therefore, the effect of recirculation cannot explain the difference in efficiency. Hence, applying axial slots must include additional flow features, compared to recirculation channels.
Compensating effects as in circumferential groove casing treatments and other flow interactions between the near casing flow field and the slot flow are considered. These additional mechanisms of the axial slot casing treatment will be identified and isolated by comparing the two different casing treatment types. The numerical simulations are carried out on a 1.5 stage transonic axial compressor using URANS simulations.
Unsteady Rotating Radial Load of a Single Stage Radial Inflow Turbine
Authors: Marlier Jonathan , Barbieux Virginie , Tartinville Benoît 
Published: September 2016

Radial inflow turbines with pivoting stator vanes are known to keep a high level of efficiency over a large flow range. This turbine type maintains a good efficiency level at reduced speed because the turbine wheel is not very sensitive to negative incidence. For these reasons variable geometry radial inflow turbines are used where a large operating map is required.
However, it is known from literature that impeller blades undergo significant unsteady aerodynamic forces due to upstream stator vanes, especially with transonic conditions at stator exit, which are quite common for these machines. From a mechanical point of view, the number of stator vanes is therefore crucial since it determines the excitation frequency. Over a large operating map, it is not possible to avoid all eigenmodes. The vane count shall avoid excitation of impeller critical eigenmodes, especially if their mode shape matches.
Amongst unsteady phenomena occurring in turbomachinery, rotor/stator interactions are of primary importance. Independently from impeller eigenmodes, this study discusses the unsteady rotating radial load on the impeller that can be generated under specific blade count combinations, for a single stage radial inflow turbine. This radial load can indeed be large and impact the rotordynamics. The rotating frequency of the load is given by Tyler-Sofrin theory. In order to compute its amplitude, unsteady CFD is performed, with the use of the non-linear harmonic method implemented into FINE™/Turbo software from NUMECA. The effects of the fluid, of the operating conditions and of the rotational speed are also quantified. Under specific conditions, resonance may occur and is discussed.
Investigations on the Generation and Weakening of Shock Wave in a Radial Turbine With Variable Guide Vanes
Authors: Yang Dengfeng , Lao Dazhong , Yang Ce , Hu Leon , Sun Harold 
Published: September 2016

The turbocharger, with its advantages in increasing fuel economy and reducing emission, has been widely used in internal combustion engines. Aiming to achieve both fast transient response and high boost at low engine speeds of the diesel engines, variable nozzle turbine (VNT) turbochargers are necessary to match well with the engines in various operating conditions. At different engine speeds, both the mass flow rate and expansion ratio of the exhaust gas could be controlled by changing the opening of the guide vanes to adjust the nozzle throat area. At low engine speeds, the small opening of the VNT nozzle can accelerate the exhaust gas, resulting in the increase of the compressor boost pressure. The large opening of the VNT nozzle is capable of avoiding the excessive boost pressure at high engine speeds.
The high exhaust gas pressure accompanying the small opening of the guide vane at the engine braking condition leads to shock waves. Loading fluctuation on the surface of the rotor blade, in response to the shock wave at the variable guide vanes, could increase the high cycle fatigue (HCF) risk of the rotor blade significantly. In this study, the generation and weakening mechanism of the shock wave in the VNT have been investigated by adopting three guiding vanes with different span chord ratios. Numerical simulation indicates that two shock waves are produced in the geometry throat and the trailing edge of the guide vane, named throat shock wave and trailing edge shock wave, respectively.
The trailing edge shock wave at mid-span area of the rotor-stator interface has the largest intensity, and it is gradually weakened towards both the rotor blade leading edge and the guide vane trailing edge. As the distance between the guiding vane and rotor blade changes, the trailing edge shock wave also varies in intensity, shape, and relative position to the blade, while the throat shock wave has no variations. Further analysis shows that the generation of the shock wave is mainly due to the excessive acceleration of the exhaust gas. Reduction of the gas expansion ratio across the variable guide vane and the channel shrinkage degree between the nozzle vane trailing edge and the rotor blade can eliminate the throat shock wave and weakens the trailing edge shock wave. As the trailing edge shock wave weakens, pressure fluctuation inside the rotor blade can be reduced, which will significantly reduce the turbine blades forced response and enhance the reliability of the VNT turbine.
Large-Scale DES Analysis of Stall Inception Process in a Multi-Stage Axial Flow Compressor
Authors: Yamada Kazutoyo , Furukawa Masato , Tamura Yuki , Saito Seishiro , Matsuoka Akinori , Nakayama Kentaro 
Published: September 2016

The paper describes the flow mechanism of the rotating stall inception in a multi-stage axial flow compressor for an actual gas turbine. Large-scale numerical simulations have been conducted. The compressor investigated is a test rig compressor which was used for development of the industrial gas turbine, Kawasaki L30A. While the compressor consists of 14 stages, the front half stages of the compressor were analyzed in the present study. According to the test data, it is considered that the 5th or 6th stage is the one most suspected of leading to the stall.
In order to capture precise flow physics that could happen at stall inception, a computational mesh was made dense, giving at least several million cells to each passage. It amounted to about two billion cells for the first 7 stages (three hundred million cells in each stage). Since the mesh was still not enough for the large-eddy simulation (LES), the detached-eddy simulation (DES) was employed. In the DES, a flow field is calculated by LES except near-wall and near-wall turbulent eddies are modeled by RANS. The computational resource required for such large-scale simulation was still quite large, so the computations were conducted on the K computer (RIKEN AICS in Japan). Unsteady flow phenomena at the stall inception were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method.
The present compressor has stall started from the separation on the hub side instead of the commonly observed leading-edge separation near the tip. The flow phenomenon first observed in the stalling process is the hub corner separation, which appears in some passage of the 6th stator when approaching the stall point. This hub corner separation expands with time, and eventually leads to the leading-edge separation on the hub side for the stator. Once the leading-edge separation happens, it rapidly develops into the rotating stall, causing another leading-edge separation for the neighboring blade in sequence. Finally, the rotating stall spreads to the upstream and downstream bladerows due to its large blockage effect.
Cogenerative Performance of a Wind–Gas Turbine–Organic Rankine Cycle Integrated System for Offshore Applications
Authors: Bianchi Michele , Branchini Lisa , De Pascale Andrea , Melino Francesco , Orlandini Valentina , Peretto Antonio , Haglind Fredrik , Pierobon Leonardo 
Published: September 2016

Gas Turbines (GT) are widely used for power generation in offshore oil and gas facilities, due to their high reliability, compactness and dynamic response capabilities. Small heavy duty and aeroderivative units in multiple arrangements are typically used to offer larger load flexibility, but limited efficiency of such machines is the main drawback. A solution to enhance the system performance, also in Combined Heat and Power (CHP) arrangement, is the implementation of Organic Rankine Cycle (ORC) systems at the bottom of the gas turbines. Moreover, the resulting GT-ORC combined cycle could be further integrated with additional renewable sources.
Offshore wind technology is rapidly developing and floating wind turbines could be combined with offshore GT-ORC based power plants to satisfy the platform load.
The pioneering stand alone power system, for an oil and gas platform, examined in this paper comprises a 10MW offshore wind farm and three gas turbines rated for 16.5MW, each one coupled with an 4.5MW ORC module. The ORC main parameters are observed under different wind power fluctuations. Due to the non-programmable availability of wind and power demand, the part-load and dynamic characteristics of the system should be investigated. A dynamic model of the power system based on first principles is used, developed in the Modelica language. The model is integrated with a time series-based model of two offshore wind mills. Various thermodynamic indexes, available in the literature, are identified and evaluated to compare the actual combined heat and power performances of single components and of the overall integrated system in the considered wind scenarios.