bluuebunny/crossref_metadata_2025 huggingface dataset:
An Enhanced Off-Design Performance Model for Single Stage Fans
Authors: Kurzke Joachim
Published: September 2014

Modern high bypass turbofan engines have single stage fans with a low hub-tip radius ratio. The fan map is a very important element for off-design performance simulations. Such a map consists of tables with corrected mass flow, pressure ratio and efficiency for a range of corrected spool speeds.

Applying the data read from a fan map to both the core and the bypass stream is inaccurate because the transonic flow field of the bypass stream is very different to the subsonic flow field of the core stream. A better approximation of reality is to use a hybrid map with total mass flow, bypass pressure ratio and efficiency. Constant factors are employed to derive the core stream pressure ratio and efficiency.

For more accurate simulations two maps may be employed, one for the core and another one for the bypass stream. The total mass flow of the fan is the same in these two maps while pressure ratio and efficiency are different for the two streams. The data for each point in this so-called “Split Map” are valid for a pre-defined bypass ratio.

This paper describes an alternative to the split map methodology which takes the variability of the bypass ratio into account in a different way. The hypothesis is that the overall fan performance is not affected by variations in bypass ratio. The fan performance map is completed by an additional table with core stream efficiency.

This enhanced map is used as follows. When scaling the map, the bypass ratio as well as the pressure ratio and efficiencies for the core and bypass streams are known. Assumed values for fan tip speed, hub-tip radius ratio and fan inlet Mach number yield the core stream velocity triangle. The rotor blade exit flow angle from this triangle remains the same in all other operating conditions.

The core flow velocity triangle analysis with known rotor blade exit angle yields the work done on the core stream during off-design. The pressure ratio is calculated from this work and the efficiency read from the core stream efficiency table mentioned above.

Finally, the bypass stream pressure ratio and efficiency are calculated from the overall map and the core stream data applying the actual bypass ratio.
Research of Temperature Characteristics of Non-Equilibrium Condensation in Transonic Steam Flow
Authors: Chun Wang , Xie Danmei , Yangheng Xiong , Xinggang Yu , Chu Nie , Zhang Hengliang
Published: September 2014

The non-equilibrium phase transition model in CFX is used to simulate the non-equilibrium condensation flow in Laval nozzles. The Eulerian-Eulerian governing equation of multi-phase computational fluid dynamics model is utilized to solve the two-phase flow with k-ε turbulence model. By simulating the spontaneous condensation flow in 2D and 3D models Laval nozzles with different geometries, non-equilibrium phase transition and condensation shock are captured. Our numerical results indicate that the pressure distributions and water droplet diameters are compared with the experimental ones under the same situation. It is shown that the results of 3D model agree with the experimental results better, while the pressure distribution curve of 2D model exhibits the “2D effect”, which may cause calculated errors. Finally, the temperature characteristics of non-equilibrium condensation in transonic steam flow are computed with 3D model and the influence of the inlet temperature on the condensation characteristics and position of shock wave is analyzed.
Hybrid RANS/ILES for Aero Engine Intake
Authors: Oriji Ugochukwu R. , Yang Xiaoyu , Tucker Paul G.
Published: September 2014

Hybrid, Implicit Large Eddy Simulations (ILES) for an idealized aero engine intake in a crosswind is performed. The ILES zone is smoothly blended to a near wall Reynolds Averaged Navier-Stokes (RANS) zone. The flow has a region of high favourable pressure gradient (FPG) where the streamwise acceleration parameter (KS) is found to be greater than 3×10−6. This is sufficient to laminarize the boundary layer (BL). As a consequence, the turbulence in the boundary is severely suppressed and this interacts with a shock causing separation and distortion at the engine fan face. This is known to be undesirable for aero engines. The separated shear layer reenergizes turbulence and this promotes reattachment. The calculation in the RANS zone has been enhanced with a novel three-component RANS model and this is used in the hybrid RANS/ILES framework. Simulations also consider the modelling of roughness. The turbulent statistics and the engineering relevance of these are also discussed in this work. Broadly, encouraging agreement is found with measurements. Substantial accuracy improvements are found relative to standard RANS model simulations. The accuracy of the hybrid simulations is also contrasted with pure ILES and the critical need for the RANS layer shown for modest grids.
Aerodynamic Performance of a Transonic Turbine Blade Passage in Presence of Upstream Slot and Mateface Gap With Endwall Contouring
Authors: Jain Sakshi , Roy Arnab , Ng Wing , Ekkad Srinath , Lohaus Andrew S. , Taremi Farzad
Published: September 2014

The present article investigates mixed out aerodynamic loss coefficient measurements for a high turning, contoured endwall passage under transonic operating conditions in presence of upstream purge slot and mateface gap. The upstream purge slot represents the gap between stator-rotor interface and the mateface gap simulates the assembly feature between adjacent airfoils in an actual high pressure turbine stage. While the performance of the mateface and upstream slot has been studied for lower Mach number, no studies exist in literature for transonic flow conditions. Experiments were performed at the Virginia Tech’s linear, transonic blow down cascade facility. Measurements were carried out at design conditions (isentropic exit Mach number of 0.88, design incidence) without and with coolant blowing. Upstream leakage flow of 1.0% coolant to mainstream mass flow ratio (MFR) was considered with the presence of mateface gap. There was no coolant blowing through the mateface gap itself. Cascade exit pressure measurements were carried out using a 5-hole probe traverse at a plane 1.0-Cax downstream of the trailing edge. Spanwise measurements were performed to complete the entire 2D loss plane from endwall to midspan, which were used to plot pitchwise averaged losses for different span locations and loss contours for the passage. Results reveal significant reduction in aerodynamic losses using the contoured endwall due to the modification of flow physics compared to a non-contoured planar endwall. The heat transfer experiments, designed to find the heat transfer coefficient and the film cooling effectiveness are described in detail in a separate paper [1].
Design and Development of Advanced Three-Dimensional Non-Periodic Diffusers for Centrifugal Compressors
Authors: Grigoriev Mikhail , Swiatek Chet , Hitt Jim
Published: September 2014

Recent changes in the global economy have significantly impacted the air separation market. Companies traditionally focused upon initial capital expenditures, have shifted their mindset towards total life cycle costs. As a primary component in the air separation process, the compressor has been recognized as a significant contributor to life cycle costs of an air separation facility. Accordingly, market expectations have shifted towards more efficient compressor designs to reduce the overall power consumption.

This paper highlights the development efforts at Cameron’s Compression Systems to design advanced 3D cascade diffusers, leading to the development of compressors with higher aerodynamic efficiencies.

While the concept of matching the diffuser design towards the local flow field is not new, the implementation of this concept has been significantly hindered by a lack of understanding with regard to impeller discharge conditions. Furthermore, the tools necessary to explore these specifics either did not exist, or where prohibitive in terms of both cost and time.

Over the past 20 years, great advances have been made in the area of computational engineering. The advancements in Computational Fluid Dynamics (CFD) tools have led to a better understanding of the transitional impeller flow fields. Furthermore, the dramatic progress in cheaper high-end computers has facilitated the design and development of sculpted three-dimensional diffusers within reasonable time frames and at relatively low cost.

Recently, Cameron has deployed advanced sculpted 3D diffusers on limited production designs. This process involves a heavy utilization of STAR-CCM+ for performance analyses of centrifugal stages with various diffuser geometries. The CFD analyses vary from relatively simple steady state analyses with single impeller and single diffuser passages using indirect (mixing plane) interfaces to full stage unsteady simulations involving full inlet, impeller, diffuser and volute with a discharge pipe. This paper discusses a range of issues involved in performing CFD analyses for complex diffuser geometries. We show how CFD analyses are used to improve the aerodynamic performance of stages with respect to the regular low solidity cascade 2D diffusers. The paper provides results of comparative studies of the computational analyses with the aerodynamically tested data for the stages using both the regular low solidity 2D diffusers and sculpted non-periodic 3D diffusers. The test results confirm predicted improvements in compressor efficiency using sculpted non-periodic 3D diffusers over regular 2D diffusers by as much as 2% for peak efficiency. The paper discusses stage improvements due to use of 3D sculpted non-periodic diffusers.
An Experimental Study of Detailed Flow and Heat Transfer Analysis in a Single Row Narrow Impingement Channel
Authors: Hossain Jahed , Tran Lucky V. , Kapat Jayanta S. , Fernandez Erik , Kumar Rajan
Published: September 2014

An experimental investigation of detailed flow and heat transfer in a narrow impingement channel was studied; the channel included 15 inline jets in a single row with a jet-to-target wall distance of 3 jet diameters. The spanwise length of the channel was 4 jet diameters, and a streamwise jet spacing of 5 jet diameters was considered for the current study. Both the flow physics and heat transfer tests were run at an average jet Reynolds number of 30,000. Temperature sensitive paint was used to study heat transfer at the target wall. Along with other parameters, jet-to-jet interaction in a narrow row impingement channel plays a significant role on heat transfer distribution at the side and target walls as the self-induced jet cross flow tends to bend the downstream jets. The present work shows detailed information of flow physics using Particle Image Velocimetry (PIV). PIV measurements were taken at planes normal to the target wall along the jet centerline for several jets. The flow field and heat transfer data was compared between the experiment and CFD in order to understand the relationship between flow characteristics and heat transfer. The experimental data gathered from PIV can be used as benchmark data for validating the current state of the art RANS turbulence models as well as for Large Eddy Simulation (LES).
Time-Resolved Stereo PIV Measurements of Flow Fields Inside a Rotating Cavity
Authors: Kouwa Junya , Nagao Takahisa , Matsuno Shinsuke , Sasaki Yukie , Hisaeda Koutarou
Published: September 2014

This paper describes the experimental and numerical results of flow fields inside a rotor-stator rotating cavity. The rotational speeds and the axial throughflow are varied as experimental conditions. In the experiment, 3-components velocity vectors on the r–θ and r–z sections are obtained by a stereo dynamic PIV system to understand complex flow fields in detail such as flow structure and unsteadiness. A large eddy simulation (LES) is also carried out to confirm the analytical capability for the rotating cavity and to complement the understanding of the flow field. From the results, axisymmetric steady flow fields are observed under high Rossby number conditions, while several vortices are captured in the cavity in the r – θ section under low Rossby number conditions. The visualization results with seeding tracers for PIV show the flow structure of flow fields. LES can predict the flow field of the experimental result and the behavior of vortices which are varied as to the change of Ro conditions.
Through Flow Calculations for Convective Cooling Turbines
Authors: Haibo Li , Gu Chunwei
Published: September 2014

Conjugate heat transfer is a key feature of modern gas turbine, as cooling technology is widely applied to improve the turbine inlet temperature for high efficiency. Impact of conjugate heat transfer on heat loads and thermodynamic efficiency is a key issue in gas turbine design. This paper presented a through flow calculation method to predict the impact of heat transfer on the design process of a convective cooled turbine. A cooling model was applied in the through flow calculations to predict the coolant requirements, as well as a one-dimensional mixing model to evaluate some key parameters such as pressure losses, deviation angles and velocity triangles because of the injection cooling air. Numerical simulations were performed for verification of the method and investigation on conjugate heat transfer within the blades. By comparing these two calculations, it is shown that the through flow calculation method is a useful tool for the blade design of convective cooled turbines because of its simplicity and flexibility.
Performance Analysis of Savonius-Style Wind Turbines Under Concentrated and Oriented Jets
Authors: Roy Sukanta , Saha Ujjwal K.
Published: September 2014

With the rapid growth of renewable energy sector, vertical axis wind turbines are finding their applications in the small-scale distributed wind energy system, particularly in rural areas. These turbines are simple in construction and easy to install with comparatively lower cost. However, the efficiency of these turbines is not competitive to that of horizontal axis wind turbines. In this paper, an attempt has been made to improve the efficiency of a Savonius-style vertical axis wind turbine under concentrated and oriented jets through installation of deflectors at different positions ahead of the turbine. The aim is to make the major portion of the flow to be incident on the concave part of the blades. Experiments are conducted in a low speed wind tunnel with an open test section facility. For all the experiments, the wind speed in the tunnel is kept constant at 6.2 m/s. The mechanical loads are varied to analyze the performance of the turbine at various tip speed ratios. In each case, both power and torque coefficients are calculated in order to estimate the performance indices of the turbine. Moreover, a suitable operating range of this turbine is specified. The present investigation demonstrates that with the installation of deflectors, the performance of the Savonius-style wind turbines can be sufficiently improved under concentrated and oriented jets. The peak power coefficient of 0.32 is achieved with an optimized position of the deflectors in front of both the advancing and returning blades.
Numerical Investigation of Influence of Radial Inlet Distortion on Compressor Performance in 2-Stage Turbocharging System
Authors: Chen Jinke , Zheng Xinqian , Wang Chenfang , Zhuge Weilin , Zhang Yangjun
Published: September 2014

As the result of strict emission regulations and the demand of fuel reduction, an increasing number of engines are highly boosted with complex two-stage turbocharging systems.

In a two-stage turbocharging system, an additional intercooler between LP compressor and HP compressor is usually used to reduce the inlet temperature of the HP compressor for extending its life and reducing the compression work. Spatial restrictions of the turbocharging system lead to reduced distances between different components of the two-stage turbocharging system. Consequently, each component’s performance is influenced by the upstream and downstream ones. The high pressure compressor performance is affected by the inlet flow condition, which is significantly distorted by the intercooler.

In this paper, the characteristics of flow distortion caused by the intercooler and its evolution process are analyzed. Performances of the downstream high pressure compressor under uniform inlet condition and distorted inlet condition caused by the intercooler are analyzed and compared. The results show that the inlet distortion caused by intercooler deteriorates the compressor pressure ratio, flow range, and efficiency.
Effect of Vaned Diffuser on a Small Centrifugal Impeller Performance
Authors: Chen Jie , Yue Yang , Huang Guoping
Published: September 2014

A small transonic centrifugal compressor with 3D vaned diffuser has been developed for a turbine engine by Nanjing University of Aeronautics and Astronautics. The centrifugal impeller’s diameter is approximately 80 mm. The impeller was improved by reducing the static pressure gradient in spanwise direction. But the improvement is reduced by the interaction between the impeller and the diffuser, when it works with the diffuser. So, the effect of the vaned diffuser on the performance and flow structure of the impeller was studied by steady and unsteady numerical simulations.

The total pressure ratio and efficiency of the impeller with a vaned diffuser are lower than those with a vaneless diffuser. Further, the difference decreases as the operation point moves from the surge to the choke. Analysis of steady flow proves that the meridional bend and the vanes in the 3D vaned diffuser are the main causes. When the impeller operates with the vaned diffuser, the vortex at the shroud of the impeller exit is pushed toward the trailing edge of the impeller blade, which leads to an altered flow structure in the impeller passages. As a result, the loss of the impeller increases, and consequently the efficiency as well as the pressure ratio drops. On the other hand, the unsteady analysis shows that the flow pattern at the impeller exit is circularly affected by features of the stagnation, the local acceleration, and the shock wave in the semi-vaneless space of the diffuser. The flow at the different spanwise location in the trailing edge of the impeller blade can be influenced by the different flow feature, therefore, the spanwise distributions of the flow parameters is disturbed.
Thermodynamic Analysis and Comparison Study of an Organic Rankine Cycle (ORC) and a Kalina Cycle for Waste Heat Recovery of Compressor Intercooling
Authors: Wang Jianyong , Wang Jiangfeng , Zhao Pan , Dai Yiping , Peng Yan
Published: September 2014

The intercooling of multi-stage compressors contributes to reducing the power consumption of compressors and the waste heat is generally taken away by cooling water, which is a great waste of energy. This paper employs an organic Rankine cycle (ORC) or a Kalina cycle to recover the waste heat of compressor intercooling. The mathematical models of ORC and Kalina cycle are established by MATLAB software to simulate the ORC system and the Kalina cycle system under steady-state conditions. A parametric analysis is conducted to evaluate the effects of several key thermodynamic parameters on the system performance. In addition, a parametric optimization is carried out to find the optimum performance of waste heat recovery system from thermodynamic aspect. The results showed that, for the ORC system, there is an optimum value of turbine inlet pressure with the state of working fluid being saturated vapor that yields the minimum net power consumption of the system; whereas for the Kalina cycle system, in some ranges of accessible operation conditions, a higher turbine inlet pressure, a lower turbine inlet temperature and a lower ammonia mass fraction of basic solution could obtain a less net power consumption of the system. The optimization results indicated that the Kalina cycle system shows a better performance than the ORC system.
Study on the Effects of Upstream Flow Conditions and Clearance Sizes to Tip Leakage Flow in a Subsonic Large-Scale Rotor
Authors: Zhang Chenkai , Hu Jun , Wang Zhiqiang , Ding Ning , Mao Zhiming , Chen Zehua
Published: September 2014

To clearly clarify how it affects the detailed tip clearance flow and flow mechanism by varying the upstream boundary layer thickness and tip clearance size, numerical studies were performed on a subsonic rotor, which is used for low-speed model testing of one rear stage embedded in a modern high-pressure compressor. Firstly, available experimental data were adopted to validate the numerical method. Second, comparisons were made for tip leakage vortex structure, the interface of leakage flow/mainflow, endwall loss, isentropic efficiency and pressure-rise between different operating conditions. Then, effects of different clearance sizes and inlet boundary layer thicknesses were investigated. At last, the self-induced unsteadiness at one near-stall operating condition was studied for different cases. Results show that increasing the tip clearance size has a deleterious effect on rotor efficiency and pressure-rise performance over the whole operating range, while thickening the inflow boundary layer is almost the same except that its pressure-rise performance will be increased at mass flow rate larger than design operating condition. Self-induced unsteadiness occurs at near-stall operating conditions, and its appearance depends largely on tip clearance size, while upstream boundary layer thickness has little effect.
Wind Power Output Performance Horizontal and Vertical Axis Wind Turbines for Isolated Small Applications in Saudi Arabia
Authors: Al-Hadhrami Luai M. , Rehman Shafiqur
Published: September 2014

The study evaluated the energy output and plant capacity factor of small wind turbines in the category of 3–10 kW rated power. The effects of hub height on energy output and the PCF have been studied. To achieve the set objectives, hourly average wind speed data measured at 10, 20, 30, and 40 meter and wind direction at 30 and 40 meter above ground level during July 01, 2006 to July 10, 2008 has been utilized. The highest percentage change in annual energy yield (AEY) was obtained for an increase in hub height from 20 to 30 m for both horizontal and vertical wind turbines used in this study. Horizontal axis wind turbines HAWT-1, HAWT-2, and HAWT-6; and vertical axis wind turbines VAWT-1, VAWT-2, and VAWT-4 are recommended for various ranges of loads. Horizontal axis wind turbines were found generally more efficient than the vertical axis wind turbine in the present case. In general, all the turbines showed a maximum increase in energy yield for an increase of 10 m in hub height from 20 to 30m and the annual mean energy yield usually followed the load pattern in the study area. Lastly, the mean turbulence intensity was always less than the value recommended in IEC64100-1 standard.
Vibration of Bi-Periodic Bladed Disk
Authors: Wang Peiyi , Li Lin
Published: September 2014

The dynamic behavior of bi-periodic bladed disk has been studied systematically. Bi-periodicity in bladed disk means that two types of structural subassemblies, alternating in circumferential direction, make up the structure. Based on a lumped parameter model, the dynamic behaviors of mono- and bi-periodic structures were compared. The nodal diameter spectrum was proposed to compare the difference of modes between mono- and bi-periodic bladed disk. The modified modal assurance criterion was proposed to evaluate the vibration suppression ability of bi-periodic bladed disk. The results showed that the generalized force and infinity norm are two most effective factors in altering modal dynamics. At the end, an improved Monte Carlo simulation is performed to show the resonance attenuation ability of bi-periodic bladed disk with mistuning considered.
Experimental Investigation of Compressor Aerodynamic Instability Induced by Rotating Disturbance
Authors: Yan Wei , Zhang Huan , Mao Zhi-ming , Yin Chao , Zhang Chen-kai , Hu Jun
Published: September 2014

In twin-spool engines, there will be a rotating disturbance at the inlet of the downstream compressor when rotating stall occurs in the upstream compressor. It will lead the downstream compressor to aerodynamic instability if the speed difference between the two spools is not designed reasonably. In order to investigate how the rotating disturbance affects, a two-stage compressor is operated with a newly designed rotating disturbance generator running upstream. The generator is able to produce disturbances with different circumferential extent. It can also produce a disturbance with more than one cell. The rotating speed of the generated disturbances is designed up to 100 percent of the compressor speed. The experiments show that the compressor experiences significant degradation in its stall margin when the disturbance rotates at the “dangerous speed”. The circumferential extent of the rotating disturbance also has an influence on the stall margin. Rotating disturbances with larger circumferential extent lead to severer loss of stall margin. However, it does not affect the “dangerous speed”. The twin-cell disturbance affects the stall boundary of the compressor in a similar manner as the single-cell disturbance does. It is the rotating speed of each cell acts on the stall boundary. Based on the analysis of stall inception under different rotating disturbances, an explanation is given to interpret the mechanism of the “dangerous speed”. The “dangerous speed” is associated with the propagating speed of stall inception. When the disturbance is rotating at this speed, it will intensify the flow separation and accelerate the growth of rotating stall, thus aggravates the compressor aerodynamic stability.
Preliminary Design of Axial Fans at Off-Design Working Points
Authors: Semel Matthias , Grilliat Julien , Delgado Antonio
Published: September 2014

An analytical formulation for axial fan performances at and off design point is proposed for an arbitrary work distribution. It is shown that the total pressure, total-to-static pressure and hydraulic efficiency characteristics can be described by means of hyperbola, straight lines and parabola. This formulation is applied to axial fans with free vortex work distributions, allowing a theoretical study onto the influence of the hub-to-tip ratio. Theoretical predictions are compared with numerical simulations. Good qualitative agreements are found. Conclusions onto the best practice guidelines for the design of axial fan according to a free vortex work distributions are presented.
Two Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers
Authors: Mayo Ignacio , El-Habib Ahmed , Arts Tony , Parres Benjamin
Published: September 2014

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different Rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with 8 ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10 per cent. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state Liquid Crystal Thermography was employed to quantify a detailed two dimensional distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the 6th and 8th rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15000, 20000, 30000 and 40000. The maximum Rotation number values were ranging between 0.12 (Re = 40000) and 0.30 (Re = 15000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the Rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case the secondary flows are responsible for high heat transfer gradients on the investigated area.
Computational Study of a Transonic Turbine Cascade: Validation and Comparison of Griding Approaches and Challenges
Authors: Abo El Ella H. M. , Kibsey M. , Sjolander S. A.
Published: September 2014

This paper presents a computational study, with some experimental validation, of a low-turning transonic turbine cascade. A comparison is presented between the time-consuming and difficult to generate hexa-structured meshing approach, and the mostly automated tetra-unstructured meshing approach. The paper compares the predicted flow physics and losses, with discussion of the challenges in griding and convergence between both approaches.

Computations were carried out using a commercial RANS solver (ANSYS CFX 12) using the Shear Stress Transport turbulence model, and the Gamma-Theta transition model. The computational domain encompassed a half blade span, and one blade pitch with periodic boundary conditions; griding for both approaches was done using ANSYS ICEM CFD. Computational results from both griding approaches were compared to corresponding experimental data. The outlet Mach number was 0.90. The experiment was carried out using a linear cascade in a blow-down type wind tunnel. Downstream seven-hole pressure probe measurements at 1.8 axial chord lengths from the leading edge provided loss, streamwise vorticity, and secondary kinetic energy distributions and integrated coefficient values.

It was found that both griding approaches predicted similar downstream endwall flow structures to those observed in the experiment. The tetra-unstructured mesh solution predicted higher losses, but both predicted lower losses than the experiment. Overall results suggest that for capturing of the basic flow physics, both approaches suffice, with the tetra-unstructured being the much easier approach, but with limitations on the level of grid refinement. For more accurate capturing of the flow physics, the time-consuming and difficult to generate hexa-structured meshing approach can be justified.
Effects of Gas-Ingestion Through Turbine Rim Seals on Flow and Heat Transfer in the Wheel-Space
Authors: Tian Shuqing , Zhang Ying , Su Wei
Published: September 2014

This paper presents numerical simulations of the gas-ingress into turbine wheel-space through the rim seal. The objective is to reveal the physical mechanism of gas-ingress flow in the wheel-space and its effects on the heat transfer in the cavity. Firstly, the wheel-space without mainstream passage is simulated to get the baseline of the case without ingress, and the windage heat in the cavity is investigated. Secondly, the gas-ingestion is conducted, and its effects on the flow and heat transfer in the wheel-space are studied.

The results reveal that in the absence of ingress into the wheel-space, the windage heating pays an important contribution to the stator/rotor temperatures because of the high rotational speed of the engine. When ingress occurs, the ingested gas mixes with the sealing air at the seal clearance and then inward flows into the wheel-space along the stator wall, and thus leads to the stator wall heated. The rotor wall is relatively less heated by the invaded gas than the stator wall because of the thermal buffering of the sealing air on the rotor wall. The thermal buffer ratio, which is defined as the ratio of the sealing effectiveness on the stator wall to that on the rotor wall, is shown dependent on the sealing flow rate. It is increased as the sealing flow rate increases.
Thermodynamic Analysis of Low-Temperature Power Generation Transcritical Rankine Cycle With R41 and CO2
Authors: Liao Jixiang , Zheng Qun
Published: September 2014

The performances of the transcritical Rankine cycles using R41 and CO2 as working fluids for power generation with lower temperature renewable energy are analyzed respectively and presented in this paper. The results show that the R41 cycle displays better comprehensive performance than that of the CO2 cycle. Compared with the CO2 cycle under the same specified conditions, the average value of the maximum net power output increased by more than 52.6%, the optimum inlet pressure decreased by over 41.6% and the second law efficiency increased by 24.8%. Moreover, the system thermal efficiency of R41 cycle is slightly higher than that of the CO2 cycle.
Last Stage Blade Coupled Shaft Torsional Vibration Analysis of 1000 MW Steam Turbine Generator Set by a Reduced 3D Finite Element Method
Authors: Xu Zi-Li , Dou Baitong , Fan Xiaoping , Fang Yu , Cao Shouhong , Wang Jianlu
Published: September 2014

To increase output and efficiency of steam turbine, long or ultra-long blades are used for last stage blades of low pressure rotors. The application of long blades enhance the coupled effect between the shaft torsional vibration and nodal diameter zero umbrella vibration mode of shrouded blade. In order to precisely calculate the shaft-blade coupled vibration characteristics for large steam turbine generator sets, a reduced method consisted of the three dimensional finite element method and the component mode synthesis method is studied. The study shows that the precision of the reduction method can be guaranteed if the maximum frequency of high order mode used in the coordinate transformation matrix of substructure is higher than 5 times of the maximum frequency of the whole system that one hopes to calculate. The last-stage, the next to last stage blades, and the whole shaft of a 1000MW steam turbine generator set are described by the three dimensional finite element method. The degrees of freedom of the whole system are reduced by using the component mode synthesis method. The coupled vibration of the steam turbine generator set is computed. The vibration of the shaft neglecting the coupled effect is also calculated, and only the moment of inertia of disk-blades is considered. The results by two models are compared with each other. The results show that there exist 4 extra torsional coupled vibration modes when the structural flexibility influence of last-stage and the next to last stage blades is considered.
Performance of IGFC With Exergy Recuperation
Authors: Iki Norihiko , Kurata Osamu , Tsutsumi Atsushi
Published: September 2014

The Integrated coal Gasification Combined Cycle (IGCC) is considered to be a very clean and efficient system for coal-fired power generation. And given the development of 100 MW-scale solid oxide fuels cells (SOFCs), the integrated coal Gasification Fuel Cell combined cycle (IGFC) would be the most efficient coal-fired power generation system. However, more energy efficient power generation systems must be developed in order to reduce CO2 emissions over the middle and long term. Thus, the authors have proposed the Advanced Integrated coal Gasification Combined Cycle (A-IGCC) and Advanced IGFC (A-IGFC) systems, which utilize exhaust heat from solid oxide fuel cells (SOFCs) and/or gas turbines as a heat source for gasification (exergy recuperation).

The A-IGCC and A-IGFC systems utilize a twin circulating fluidized bed coal gasifier consisting of three primary components: a pyrolyzer, steam reformer and partial combustor. The temperature of the steam reformer is 800 °C, and that of the partial oxidizer is 950 °C. Since the syngas, produced by pyrolysis and the reforming process involving volatile hydrocarbons, tar and char, contains carbon monoxide and hydrogen, the A-IGCC technology has considerable potential for higher thermal efficiency while utilizing low-grade coals. The coal types utilized in the study were bituminous Taiheiyo, sub-bituminous Adaro and Loy Yang coal. Milewski’s formula was used to model the circuit voltage of the SOFC.

Cool gas efficiency increases, in order, from Taiheiyo coal to Adaro coal to Loy Yang coal. The A-IGFC system has the potential to achieve high thermal efficiency using various coals, with Loy Yang coal achieving the highest thermal efficiency. However, the drying process for Loy Yang and Adaro coal is an important issue.
Fatigue Crack Growth of Multiple Load Path Structure Under Combined Fatigue Loading: Part II — Experiment Study
Authors: Liu Huawei , Hu Dianyin , Wang Rongqiao , Shen Xiuli , Fan Jiang
Published: September 2014

The fir-tree mortise of a turbine is a typical multiple load path structure which can reallocate the loading during operation. Performing experiments on a full scale turbine blade attached to a part of actual turbine disc at elevated temperature can present the reallocation phenomenon and accurately predict the crack growth of the fir-tree mortise under combined cycle fatigue (CCF). The purpose of this experiment is to determine the allowable crack size of this multiple load path structure under the circumstance of a firm overhaul period. The experimental load spectrum was determined by using a linear cumulative damage rule based on the flight load spectrum. And three turbine components were tested by using a Ferris Wheel system to access the effect of HCF loading amplitude on life. Then the experiments on crack growth were carried out to investigate crack growth lives of the actual mortise teeth with a pre-crack under combined cycle fatigue at elevated temperature. The effects of the contact state of the turbine mortise on crack propagation rates were investigated by comparing the turbine components with nominal dimensions and limiting dimensions. Fatigue fracture analysis by SEM certified that the failure was owing to combined cycle fatigue. Combined with numerical simulations, the crack growth behavior of the turbine components under combined cycle fatigue loading was estimated. Based on the above work, this paper provides a new way to establish a life-time criterion for withdrawal from service of turbine components.
A Seismic Analysis on Steam Turbine Considering Turbine and Foundation Interaction
Authors: Hu Zhiqiang , Wang Wei , Jiang Puning , Huang Qinghua , Wang Jianhua , Xu Sihua , He Jin , Xiao Lei
Published: September 2014

This paper presents a seismic analysis on steam turbine within a Nuclear Power Plant. Firstly, considering that steam turbine is a kind of large equipment with complex structure, high precision and tightly connected with other equipments and structure, this paper coupled together the steam turbine, condenser and its spring foundation as a whole structure for analysis, and created detailed finite analysis models for almost each part. Secondly, the detailed model of steam turbine, condenser and spring foundation was analyzed separately to obtain their dynamic properties (inertia, eigenvalues etc.) to verify whether the detailed finite analysis models were correct and proper. Thirdly, with seismic analysis on the whole structure with time-history method, relative displacement time history curves of some places, as well as stress response of LP (low pressure) outer and inner case, was extracted. Finally, the anti-seismic performance of steam turbine, such as rotor gaps using those relative displacement and stress response results, was analyzed and evaluated.
Alternative Fuels Based on Biomass: An Experimental and Modeling Study of Ethanol Co-Firing to Natural Gas
Authors: Braun-Unkhoff Marina , Dembowski Jens , Herzler Jürgen , Karle Jürgen , Naumann Clemens , Riedel Uwe
Published: September 2014

In response to the limited resources of fossil fuels as well as to their combustion contributing to global warming through CO2 emissions, it is currently discussed to which extent future energy demands can be satisfied by using biomass and biogenic by-products, e.g. by co-firing. However, new concepts and new unconventional fuels for electric power generation require a re-investigation of at least the gas turbine burner if not the gas turbine itself to ensure a safe operation and a maximum range in tolerating fuel variations and combustion conditions.

Within this context, alcohols, in particular ethanol, are of high interest as alternative fuel. Presently, the use of ethanol for power generation — in decentralized (micro gas turbines) or centralized gas turbine units, neat, or co-fired with gaseous fuels like natural gas and biogas — is discussed, besides its role within the transport sector.

Chemical kinetic modeling has become an important tool for interpreting and understanding the combustion phenomena observed; for example, focusing on heat release (burning velocities) and reactivity (ignition delay times). Furthermore, a chemical kinetic reaction model validated by relevant experiments performed within a large parameter range allows a more sophisticated computer assisted design of burners as well as of combustion chambers, when used within CFD (computational fluid dynamics) codes.

Therefore, a detailed experimental and modeling study of ethanol co-firing to natural gas will be presented focusing on two major combustion properties within a relevant parameter range: (i) ignition delay times measured in a shock tube device, at ambient (p = 1 bar) and elevated (p = 4 bar) pressures, for lean (φ = 0.5) and stoichiometric fuel-air mixtures, and (ii) laminar flame speed data at several preheat temperatures, also for ambient and elevated pressure, gathered from literature. Chemical kinetic modeling will be used for an in-depth characterization of ignition delays and flame speeds at technical relevant conditions.

An extensive database will be presented identifying the characteristic differences of the combustion properties of natural gas, ethanol, and ethanol co-fired to natural gas.
Enhancing the Centrifugal Compressor Performance Map Measurements Through a Developed One–Dimensional Calculation Tool to Analyse Local Flow Phenomena
Authors: Hamann Matthias , Chebli Elias , Müller Markus , Krampitz Alexander
Published: September 2014

Centrifugal compressors for automotive turbochargers have large influence on the operation characteristic of combustion engines. Especially the improvement of the surge margin is one of the most important development targets. Thereby, a reliable detection of local flow phenomena within the compressor stage is necessary and a procedure to gain this information from standard measurement data is discussed in this paper.

A one–dimensional calculation methodology for a single-stage centrifugal compressor with a vaneless diffuser and casing treatment is presented. The tool calculates the flow properties at the impeller inlet and exit as well as at diffuser exit, based on the measured inlet and outlet data and the geometry information of the compressor. The calculated flow characteristics are plotted within the measured compressor performance map to show local flow parameters. The unsteady recirculation flow within the casing treatment, the inflow angle and the total pressure losses are considered.

The tool is validated on different compressor sizes. Thereby the compressor is equipped with static pressure measuring points at the impeller inlet and exit as well as at the diffuser exit. The calculated static pressure correlated well with the measured data with an accuracy of 2 % to 5 % on 95 % of the operating range.

In this paper an experimental parameter study is executed in order to improve the surge margin. Thereby the geometry of the diffuser and the casing treatment is varied and the compressor performance is measured on a turbocharger test rig. The calculation of the flow angles and other flow characteristics within the diffuser enables one to find out whether surge is triggered through the diffuser or the impeller.
Secondary Flow and Heat Transfer Coefficient Distributions in the Developing Flow Region of Ribbed Turbine Blade Cooling Passages
Authors: Forsyth Peter R. , McGilvray Matthew , Gillespie David R. H.
Published: September 2014

This paper reports an experimental and numerical study of the development and coupling of aerodynamic flows and heat transfer within a model ribbed internal cooling passage to provide insight into the development of secondary flows. Static instrumentation was installed at the end of a long smooth passage, and used to measure local flow features in a series of experiments where ribs were incrementally added upstream. This improves test turnaround time while ensuring that the aerodynamic probe was non-invasive. Local heat transfer coefficient distributions were similarly captured using a hybrid transient liquid crystal technique. A composite heat transfer coefficient distribution for a 12 rib-pitch passage is reported: notably the behaviour is dominated by the development of the secondary flow in the passage throughout. Both the aerodynamic and heat transfer test data were compared to numerical simulations developed using a commercial computational fluid dynamics solver. By conducting a number of simulations it was possible to interrogate the validity of the underlying assumptions of the experimental strategy — their validity is discussed. The results capture the developing size and strength of the vortical structures in secondary flow. The local flow field was sensibly shown to be strongly coupled to the enhancement of heat transfer coefficient. Comparison of the experimental and numerical data generally show excellent agreement in the level of heat transfer coefficient predicted, though the numerical simulations fail to capture some local enhancement on the ribbed surfaces. Where this was the case the coupled flow and heat transfer measurements were able to identify missing velocity field characteristics.
The Effect of Impingement Jet Heat Transfer on Casing Contraction in a Turbine Case Cooling System
Authors: Tapanlis Orpheas , Choi Myeonggeun , Gillespie David R. H. , Lewis Leo V. , Ciccomascolo Carlo
Published: September 2014

This paper reports full local Nusselt number distributions under an array of impinging jets typical of those used for thermal tip clearance control through casing contraction.

Characteristic features of this type of application are sparse arrays of short cooling holes flowing at low jet Reynolds numbers (700–11,000) and large stand-off distances from the surface into a semi-confined passage with multiple exits. These features are captured in a large scale model, approximately ten times engine scale. Heat transfer measurements are made using the transient thermochromic liquid crystal technique. The measurement domain was extended far downstream of the impingement array. This allowed the entire heat transfer coefficient distribution contributing to the contraction of the liner around the rotor blades to be captured. CFD studies were conducted to characterize the flow field obtained, which in turn is helpful in understanding the drivers of heat transfer.

The results are compared to existing industry standard correlations, which are generally outside the geometric and Reynolds number range of interest. It was shown that, for the tested geometries, the heat transfer was sensibly unaffected by whether the flow was exhausted through one side of the exit passage or equally in both directions, and the bulk flow field could be predicted using a modified distributed injection model.

The heat transfer coefficient distributions are linked to a thermal-mechanical finite element model to provide thermal boundary conditions on an idealized representation of the casing for casing contraction in the presence of cooling scheme.

For one of the geometries tested, data from an engine casing thermocouple survey have been compared to predictions of casing temperature determined using the measured heat transfer coefficient distributions and these show reasonable agreement.