bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of Surface Curvature in Modelling Droplet Impingement on Fan Blades
Authors: Burson-Thomas Charles B. , Wellman Richard , Harvey Terry J. , Wood Robert J. K.
Published: August 2018

When modelling a droplet impingement, it is reasonable to assume a surface is flat when the radius of curvature of the surface is significantly larger than the droplet radius. In other contexts where Water Droplet Erosion (WDE) has been investigated, the typical droplet size has either been sufficiently small, or the radius of curvature of the surface sufficiently large, that it has been sensible to make this assumption. The equations describing the kinematics of an impinging water droplet on a flat surface were reformulated for a curved surface. The results suggest the relatively similar radii of curvature, of the leading-edge of a fan blade and the impinging water droplet, will significantly affect the application of the initial high-pressures, along with the onset of lateral outflow jetting. Jetting is predicted to commence substantially sooner and not in unison along the contact periphery, leading to an asymmetric flow stage. This is likely to have significant implications for the WDE that occurs, and thus, the engineering approaches to minimise the WDE of fan blades.
The Inner Workings of Axial Casing Grooves in a One and a Half Stage Axial Compressor With a Large Rotor Tip Gap: Changes in Stall Margin and Efficiency
Authors: Hah Chunill
Published: August 2018

Effects of axial casing grooves (ACGs) on the stall margin and efficiency of a one and a half stage low-speed axial compressor with a large rotor tip gap are investigated in detail. The primary focus of the current paper is to identify the flow mechanisms behind the changes in stall margin and on the efficiency of the compressor stage with a large rotor tip gap. Semicircular axial grooves installed in the rotor’s leading edge area are investigated. A large eddy simulation (LES) is applied to calculate the unsteady flow field in a compressor stage with ACGs. The calculated flow fields are first validated with previously reported flow visualizations and stereo PIV (SPIV) measurements. An in-depth examination of the calculated flow field indicates that the primary mechanism of the ACG is the prevention of full tip leakage vortex (TLV) formation when the rotor blade passes under the axial grooves periodically. The TLV is formed when the incoming main flow boundary layer collides with the tip clearance flow boundary layer coming from the opposite direction near the casing and rolls up around the rotor tip vortex. When the rotor passes directly under the axial groove, the tip clearance flow boundary layer on the casing moves into the ACGs and no roll-up of the incoming main flow boundary layer can occur. Consequently, the full TLV is not formed periodically as the rotor passes under the open casing of the axial grooves. Axial grooves prevent the formation of the full TLV. This periodic prevention of the full TLV generation is the main mechanism explaining how the ACGs extend the compressor stall margin by reducing the total blockage near the rotor tip area. Flows coming out from the front of the grooves affect the overall performance as it increases the flow incidence near the leading edge and the blade loading with the current ACGs. The primary flow mechanism of the ACGs is periodic prevention of the full TLV formation.

Lower efficiency and reduced pressure rise at higher flow rates for the current casing groove configuration are due to additional mixing between the main passage flow and the flow from the grooves. At higher flow rates, blockage generation due to this additional mixing is larger than any removal of the flow blockage by the grooves. Furthermore, stronger double-leakage tip clearance flow is generated with this additional mixing with the ACGs at a higher flow rate than that of the smooth wall.
Influence of a Non-Axisymmetric Endwall on the Flow Field in a Turbine Passage: High-Resolution LDV
Authors: Schmid Jonas , Schulz Achmed , Bauer Hans-Jörg
Published: August 2018

The present paper focuses on the influence of a non-axisymmetric endwall on the flow field in a turbine passage. Therefore, laser Doppler velocimetry (LDV) is applied to both a non-axisymmetric endwall and a flat endwall as reference. Time mean values and fluctuating components of the velocity field are evaluated.

Three-component LDV with up to 38000 valid coincident events per second is carried out up- and downstream of a linear cascade with high resolution, especially in the near-wall region of the suction surface, where secondary vortices are expected. The three velocity components recorded by the LDV are transformed into the orthogonal coordinate system of the turbine cascade, and several flow quantities, like turbulence parameters and parameters describing the secondary regime, are assessed. By comparing the data for the non-axisymmetric endwall and the flat endwall, the influence of the contouring on the secondary flow field is shown. To substantiate the measurements and gain a deeper insight, the data are compared to previous surface oil flow visualizations and specific results of former thermal studies.
Influence of Leakage Flows on Hot Gas Ingress
Authors: Patinios Marios , Ong Irvin L. , Scobie James A. , Lock Gary D. , Sangan Carl M.
Published: August 2018

One of the most important problems facing gas turbine designers today is the ingestion of hot mainstream gases into the wheel-space between the turbine disc (rotor) and its adjacent casing (stator). A rim seal is fitted at the periphery and a superposed sealant flow — typically fed through the bore of the stator — is used to prevent ingress. The majority of research studies investigating ingress do so in the absence of any leakage paths that exist throughout the engine’s architecture. These inevitable pathways are found between the mating interfaces of adjacent pieces of hardware. In an environment where the turbine is subjected to aggressive thermal and centrifugal loading these interface gaps can be difficult to predict and the resulting leakage flows which pass through them even harder to account for.

This paper describes experimental results from a research facility which experimentally models hot gas ingestion into the wheel-space of an axial turbine stage. The facility was specifically designed to incorporate leakage flows through the stator disc; leakage flows were introduced axially through the stator shroud or directly underneath the vane carrier ring. Measurements of CO2 gas concentration, static pressure and total pressure were used to examine the wheel-space flow structure with and without ingress from the mainstream gas-path. Data is presented for a simple axial-clearance rim-seal. The results support two distinct flow-structures, which are shown to be dependent on the mass-flow ratio of bore and leakage flows. Once the leakage flow was increased above a certain threshold, the flow structure is shown to transition from a classical Batchelor-type rotor-stator system to a vortex-dominated structure. The existence of a toroidal vortex immediately inboard of the outer rim-seal is shown to encourage ingestion.
Aerothermal Optimization of Fully Cooled Turbine Blade Tips
Authors: Andreoli V. , Braun J. , Paniagua G. , De Maesschalck C. , Bloxham M. , Cummings W. , Langford L.
Published: August 2018

Optimal turbine blade tip designs have the potential to enhance aerodynamic performance while reducing the thermal loads on one of the most vulnerable parts of the gas turbine. This paper describes a novel strategy to perform a multi-objective optimization of the tip geometry of a cooled turbine blade. The parameterization strategy generates arbitrary rim shapes around the coolant holes on the blade tip. The tip geometry performance is assessed using steady Reynolds-Averaged Navier-Stokes simulations with the k-ω SST model for the turbulence closure. The fluid domain is discretized with hexahedral elements, and the entire optimization is performed using identical mesh characteristics in all simulations. This is done to ensure an adequate comparison among all investigated designs. Isothermal walls were imposed at engine-representative levels to compute the convective heat flux for each case. The optimization objectives were a reduction in heat load and an increase in turbine row efficiency. The multi-objective optimization is performed using a differential evolution strategy. Improvements were achieved in both the aerodynamic efficiency and heat load reduction, relative to a conventional squealer tip arrangement. Furthermore, this work demonstrates that the inclusion of over-tip coolant flows impacts the over-tip flow field, and that the rim-coolant interaction can be used to create a synergistic performance enhancement.
Calculation of Intake-Fan-Bypass Interaction With a Fan Similarity Model
Authors: Carnevale Mauro , Wang Feng , di Mare Luca
Published: August 2018

Modern trend in installation design is moving towards very high-bypass ratio turbofans. Very high-bypass turbofans represent an effective way of improving the propulsive efficiency of civil aero-engines. Such engines require larger and heavier nacelles, which partially offset the gains in specific fuel consumption. The penalty associated with a larger installation can be mitigated by adopting thinner walls for the nacelle and by shortening the intake section. Such inlet sections are characterized by more restrictive operation condition because they are more prone to separation at high incidence flight conditions. Moreover, in short nacelle installations the by-pass guide vanes and pylon are closer to the fan blades and consequently the distortion due to potential effects induced by the presence of the pylon and non-axisymmetric OGV stage play a significant role in terms of unsteady interaction in the entire system. It is mandatory to consider the inlet, fan, bypass and pylon as a unique coupled system also at the design stage, for assessment of fan force. This kind of assessment is usually carried on by expensive URANS calculation. The factors leading to high computational demands are the spatial resolution required in the fan domain and the time resolution required to sample the fan blade passing frequency. Large savings are therefore possible if simplifications are introduced which relax the resolution requirements in the fan passages and change the nature of the computation into a steady-state computation for the ducts. The present contribution documents a simplified fan model for fan-intake computations based on the solution of the double linearization problem for unsteady, transonic flow past a cascade of thin aerofoils with finite mean load. The coupling with the intake flow and the bypass is performed by using the flow patterns at fan face and fan exit as boundary conditions for the fan model and computing circumferentially non-uniform boundary conditions for the intake and the bypass from the fan model. The computation of the flow in the intake, bypass and pylon is therefore reduced to a steady problem, whereas the computation of the flow in the fan is reduced to one steady problem and a set of linearised models in the frequency domain. The model is applied to a well-documented test case and compares favourably with experimental data and much more expensive three-dimensional, time domain computations.
Turbomachine Design for Supercritical Carbon Dioxide Within the sCO2-HeRo.EU Project
Authors: Hacks Alexander , Schuster Sebastian , Dohmen Hans Josef , Benra Friedrich-Karl , Brillert Dieter
Published: August 2018

The paper aims to give an overview over the keystones of design of the turbomachine for a supercritical CO2 (sCO2) Brayton cycle. The described turbomachine is developed as part of a demonstration cycle on a laboratory scale with a low through flow. Therefore the turbomachine is small and operates at high rotational speed. To give an overview on the development the paper is divided into two parts regarding the aerodynamic and mechanical design. The aerodynamic design includes a detailed description on the steps from choosing an appropriate rotational speed to the design of the compressor impeller. For setting the rotational speed the expected high windage losses are evaluated considering the reachable efficiencies of the compressor. The final impeller design includes a description of the blading development together with the final geometry parameters and calculated performance. The mechanical analysis shows the important considerations for building a turbomachine with integrated design of the three major components turbine, alternator and compressor (TAC). It includes different manufacturing techniques of the impellers, the bearing strategy, the sealing components and the cooling of the generator utilising the compressor leakage. Concluding the final design of the TAC is shown and future work on the machine is introduced.
A High Fidelity Quality Assessment of High Pressure Turbine Blades Using Surface Curvature and Gradient-Based Adjoint
Authors: Mulloth Akhil , Banks Gabriel , Zamboni Giulio , Bather Simon
Published: August 2018

Gas turbine performance is highly dependent on the quality of the manufactured parts. Manufacturing variations in the parts can significantly alter the performance, especially efficiency and thus SFC. The legacy process is to accept variations within predefined profile tolerance limits and a few other qualitative parameters, mostly at a few, key two-dimensional aerofoil sections. With the widespread use of White light scans and other similar three-dimensional scans, this has improved to include the three-dimensional profile. The future however may lie with performance based quality assessment of manufactured parts, combined with quantitative surface quality assessment to implement an intelligent screening process for the parts. The adjoint method, typically used for shape optimization is adapted to provide a prediction of the impact on performance due to manufacturing variations. The work presented outlines a three stage quality assessment process for manufactured parts, involving three-dimensional profile tolerance based screening, followed by a surface curvature based screening and finally an Adjoint based performance prediction.
Numerical Study on Film Cooling Characteristics of C3X Vane With Wave-Trench Hole
Authors: Zhang Bo-lun , Zhang Li , Zhu Hui-ren , Wei Jian-sheng , Fu Zhong-yi , Yao Chun-yi
Published: August 2018

To get wider laterally coverage of the cooling jet, the single-wave trench and double-wave trench were further studied on the vane. The film cooling characteristics of different film cooling structures were numerically studied using Reynolds Averaged Navier Stokes (RANS) equations. The SST turbulence model with γ-θ transition model was applied for the present simulation. The film cooling effectiveness and heat transfer coefficient of different film cooling structures were investigated, and the distribution of temperature field and flow field were analyzed. Four different blowing ratios (M) from 0.5 to 2.0 were studied. The results show that compared with the transverse trench structure, the span-wise averaged film cooling effectiveness of the double-wave trench increases 0.1–0.35. The single-wave trench and double-wave trench film cooling structures significantly improve the uniformity of the jet and increase the film cooling effectiveness. The span-wise averaged film cooling effectiveness of the double-wave trench is higher than that of the single-wave trench at high blowing ratio conditions. The anti-counter-rotating vortices which can press the cooling jet on near-wall are formed at the downstream single-wave trench and double-wave trench. Both of the double-wave trench and the single-wave trench structure can effectively improve the film cooling effectiveness of the vane in the case of a little increase in the heat transfer coefficient compared to the cylindrical hole. The guidance action of the double-wave trench is more reasonable, therefore the film cooling characteristics is better than that of the single-wave trench.
Improvement in the Rapid Startup Performance for the Solar Steam Turbine
Authors: Wang Peng , Chen Gang , Li WenFu
Published: August 2018

In the latest several years, concentrated solar plants (CSP) have been rapidly developed. Steam turbines employed in these plants are subjected to daily start up and continuous load variations. There is a general increase in demand for operation flexibility and rapid start up capability for solar steam turbines. Accordingly, how to decrease the low cyclic fatigue life consumption during the daily start up process is a hot researched topic at present, and this greatly depends on the transient thermal stress. A number of studies show that the startup schemes and the unit’s structural form decide the LCF life consumption directly.

In this paper, a 50MW double cylinder (HP and ILP Section) reheat solar steam turbine is studied, and it is operated continuously with inlet steam conditions of 540[°C], 140[bar], reheat steam conditions of 540[°C], 24[bar] and exhaust conditions of 41.5[°C], 0.08[bar]. A number of comparisons are made with the FEM numerical simulation, and some optimal designs which are applied to improve the rapid start up performance and decrease the LCF life consumption during the startup are presented.
Assessment of Different Technology Chains for Fir Tree Manufacturing: A Case Study
Authors: Klocke Fritz , Seimann Martin , Binder Marvin , Doebbeler Benjamin
Published: August 2018

Multiple technology chains are able to manufacture fir tree slots for the mounting of turbine blades including broaching, milling, non-conventional machining strategies and combinations of the named technologies. The advantageousness of the possible technology chains depends on many boundary conditions such as the capacity, the floor space, scheduled delivery, material, shape of the fir tree slots and many more. Within this paper different technology chains are assessed considering productivity and costs under the assumptions of different scenarios. The manufacturing technologies as well as their interdependencies have been investigated within a project providing technological boundary conditions for the assessment like tool lifes and required manufacturing times. The data was combined with organizational and financial data from a manufacturing OEM to enable a proper and holistic assessment. The technologies include broaching with HSS and cemented carbide as well as milling with ceramic and cemented carbide. The scenarios include different assumptions regarding the slot shape and size, the capacity and the demand for discs as well as a comparison of a brown field and green field approach. Based on the results, key parameters are deducted affecting the advantage of the considered technologies. For reasons of confidentiality, the results are obtained in a relative manner.
Optimal Design of Flexible Power Cycles Through Kriging-Based Surrogate Models
Authors: Riboldi Luca , Nord Lars O.
Published: August 2018

The paper presents a novel technique to define the optimal design of a power cycle considering design and off-design performance. A Kriging-based surrogate model is developed in order to simulate the power cycle at design conditions, while decreasing the computational effort. For each design considered, the performance at relevant off-design points is additionally evaluated by means of specific off-design models, developed for the main components of the system. The combination of design and off-design models allows the optimization process to take into account the performance at a selected set of operating conditions. The resulting optimal design will, thus, be characterized by a high degree of flexibility, intended as the ability to work efficiently in the several modes of operations to which the plant will be subjected to. The presented technique was tested on a case study. The optimal design of an offshore combined cycle was evaluated by using a multi-objective approach, where the two objective functions to minimize were the cumulative CO2 emissions and the weight of the bottoming cycle. The resulting designs showed to outperform those defined by a standard optimization procedure, demonstrating the effectiveness of the novel design technique.
Gas Turbine Bearing Wear Monitoring Method Based on Magnetic Plug Inductance Sensor
Authors: Cao Yunpeng , Liu Rui , Du Jianwei , Yu Fang , Yang Qingcai , He Yinghui , Li Shuying
Published: August 2018

In this paper, a gas turbine bearing wear monitoring method based on the magnetic plug inductance sensor is presented. Using the induced magnetic field of the magnetic pulse generated by the inductance coil, this method is applied to measure ferromagnetic wear debris in the oil, and the condition of bearing wear can be monitored and predicted on line. To estimate the mass of different particle size of ferromagnetic debris, the sample databases of debris mass were built, the oil capturing experiment was conducted, and the mapping model for the voltage signal of the sensor and the captured accumulation of ferromagnetic wear debris based on the BP (Error Back Propagation) neural network was established. Moreover, the kernel method was used to calculate the voltage distribution of the debris sensor in the step time of wear prediction, and the mean value and confidence boundary value of the signals in the expected step time were obtained. Moreover, the prediction model of the bearing wear was established by a linear regression method to predict the mass of ferromagnetic wear debris generated by bearing wear. Finally, a lubricating oil debris detection system was designed, and the bearing wear test was conducted on the bearing wear testing rig. The results showed that the monitoring method can continuously monitor and dynamically predict the condition of bearing wear online with the advantages of stability and automatic purifying lubricant oil.
Numerical Prediction of Tonal Noise in Centrifugal Blowers
Authors: Cravero Carlo , Marsano Davide
Published: August 2018

Centrifugal blowers are widely used in automotive, heating, ventilating, air-conditioning and other industrial purposes. In fact, they allow high-pressure increase to a moderately high mass flow rate, despite the reduced overall dimensions of the system. Numerous authors have worked to increase the fluid dynamic efficiency of the impeller and the volute. However, the recent sound emission standards have imposed tighter constraints, making the noise reduction one of the most challenging target for the design. The reduction of the tonal noise is the main concern for these blowers because the noise at the first harmonic is clearly distinguishable in the noise spectrum. Techniques to reduce this peak generally rely on experimental measurements in aeroacoustics laboratory. In this work, a CFD procedure has been developed to accurately predict the tonal noise in radial bowers. The approach has been validated using real geometries and experimental data. Various turbulence models have been tested to find the best results without the use of excessive computational resources. Moreover, unsteady simulations of the 3D blower have been carried out to analyze the influence of the main geometric parameters on the tonal noise reduction. A parametric design code developed by the authors have been used to change the geometry in order to identify the effect of the main geometrical design parameters on both fluid dynamic and aeroacoustics performance.
POD and Extended-POD Analysis of Pressure Fluctuations and Vortex Structures Inside a Steam Turbine Control Valve
Authors: Wang Peng , Ma Hongyu , Liu Yingzheng
Published: August 2018

In steam turbine control valves, pressure fluctuations coupled with vortex structures in highly unsteady three-dimensional flows make essential contributions to aerodynamic forcing on the valve components, and are major sources of flow-induced vibration and acoustic effects. Advanced turbulence models, such as scale adaptive simulation (SAS), detached eddy simulation (DES) and large eddy simulation (LES), can capture detailed flow information of the control valve, but it is challenging to identify the primary flow structures due to the massive flow database. The present study used state-of-the-art data-driven analysis, namely proper orthogonal decomposition (POD) and extended-POD, to extract the energetic pressure fluctuations and dominant vortex structures of the control valve. To this end, the typical annular attachment flow inside a steam turbine control valve was investigated by performing a DES study. Subsequently, the energetic pressure fluctuation modes were extracted by performing POD analysis on the valve’s pressure field. The vortex structures contributing to these energetic pressure fluctuation modes were extracted by performing extended-POD analysis on the pressure-velocity coupling field. Finally, the dominant vortex structures were revealed directly by POD analysis of the valve’s velocity field. The results demonstrated that the flow instabilities inside the control valve were mainly induced by oscillations of the annular wall-attached jet and the derivative flow separations and reattachments. In POD analysis of the pressure field, the axial, antisymmetric and asymmetric pressure modes occupied most of the pressure fluctuation intensity. By further conducting extended-POD analysis, the vortex structures’ incorporation with the energetic pressure modes was identified as mainly attributed to the synchronous, alternating and single-sided oscillation behaviors of the annular attachment flow. However, based on POD analysis of the unsteady velocity fields, the vortex structures, buried in the dominant modes at St = 0.017, were found to result from alternating oscillations of the annular wall-attached jet.
A New Spin on Small-Scale Combustor Geometry
Authors: Bohan Brian T. , Polanka Marc D.
Published: August 2018

The Ultra Compact Combustor (UCC) is an innovative combustor system alternative to traditional turbine engine combustors with the potential for engine efficiency improvements with a reduced volume. Historically, the UCC cavity had been configured such that highly centrifugally loaded combustion took place in a recessed circumferential cavity positioned around the outside diameter of the engine. One of the obstacles with this design was that the combustion products had to migrate radially across the span of a vane while being pushed downstream by a central core flow. This configuration proved difficult to produce a uniform temperature distribution at the first turbine rotor. The present study has taken a different spin on the implementation of circumferential combustion. Namely, it aims to combine the combustion and space saving benefits of the highly centrifugally loaded combustion of the UCC in a new combustor orientation that places the combustor axially upstream of the turbine versus radially outboard. An iterative design approach was used to computationally analyze this new geometry configuration with the goal of fitting within the casing of a JetCat P90RXi. This investigation revealed techniques for implementation of this concept including small-scale combustor centrifugal air loading development, maintaining combustor circumferential swirl, combustion stability, and fuel distribution are reported. Furthermore, dramatic improvements in the uniformity of the turbine inlet temperature profiles are revealed over historical UCC concepts.
An Efficient Transient Simulation Method for a Volume Dynamics Model
Authors: Kurosaki Masahiro , Sasamoto Minoru , Asaka Kentaro , Nakamura Keiko , Kakiuchi Daiki
Published: August 2018

This paper presents an efficient numerical integration method for a volume dynamics model in gas turbine engine transient simulations. It is a modified implicit Euler method that allows a time increment that would not be stable with the explicit Euler method. The Jacobian matrix of a nonlinear engine model is evaluated along the steady state engine operation line and scheduled as a function of the corrected shaft speed in advance, eliminating the necessity of computing during the simulation.

The proposed method was applied to transient simulations of a compressor rig test model composed of a compressor, a nozzle with variable geometry and a volume placed between them. The eigenvalues of the simplified volume dynamics were analytically derived. It is shown that they are functions of the characteristic time of the volume defined by mass present in the volume divided by mass flow rate flowing into and out of the volume and dimensionless influence coefficients of nearby components.
Experimental Investigation of an Inverted Brayton Cycle for Exhaust Gas Energy Recovery
Authors: Kennedy Ian , Chen Zhihang , Ceen Bob , Jones Simon , Copeland Colin D.
Published: August 2018

Exhaust gases from an internal combustion engine (ICE) contain approximately 30% of the total energy released from combustion of the fuel. In order to improve fuel economy and reduce emissions, there are a number of technologies available to recover some of the otherwise wasted energy. The inverted Brayton cycle (IBC) is one such technology.

The purpose of the study is to conduct a parametric experimental investigation of the IBC. Hot air from a turbocharger test facility is used. The system is sized to operate using the exhaust gases produced by a 2 litre turbocharged engine at motorway cruise conditions. A number of parameters are investigated that impact the performance of the system such as turbine inlet temperature, system pressure drop and compressor inlet temperature.

The results confirm that the output power is strongly affected by the turbine inlet temperature and system pressure drop. The study also highlights the packaging and performance advantages of using a 3D printed heat exchanger to reject the excess heat. Due to rotordynamic issues, the speed of the system was limited to 80,000 rpm rather than the target 120,000 rpm. However, the results show that the system can generate a specific work of up to 17 kJ/kg at 80,000 rpm. At full speed it is estimated that the system can develop approximately 47 kJ/kg, which represents a thermal efficiency of approximately 5%.
Design of a Variable Geometry Axial-Inflow Turbine Turbocharger Equipped With a Diffuser-Collector System
Authors: Pesyridis Apostolos , Cappiello Alessandro , Tuccillo Raffaele
Published: August 2018

The fluid-dynamic design of a bespoke variable geometry axial inflow turbine, equipped with a diffuser-collector system for turbocharging applications, was numerically investigated with the purpose of replacing the radial flow turbine in a commercial turbocharger.

The paper aims to investigate the suitability of axial turbines for turbocharging applications in the automotive field. The turbine outflow is linked to a diffuser-collector system in order to obtain a kinetic energy recovery together with a correct flow direction to the discharge system.

Additionally, once completed the turbine design, the operating maps for three different stator positions were numerically obtained.

Finally, a turbocharger–engine matching model allowed comparison of the new axial and conventional radial flow turbine in terms of turbine power and efficiency, compressor pressure ratio, engine torque and BSFC.
Characterizing Static and Dynamic Mechanical Properties for Additive Manufactured ULTEM 9085 Used to Construct Flow Control Devices for Turbomachinery Applications
Authors: Pham Khang D. , O’Brien Walter F. , Case Scott W.
Published: August 2018

Extrusion additive manufacturing technologies may be utilized to fabricate complex geometry devices to control the flow distortions at the inlets of gas turbine engines. However, the success of these devices depends upon their ability to withstand the dynamic mechanical loads experienced in service. One such device is a StreamVane®. A current candidate material for StreamVane fabrication is ULTEM 9085 — a thermoplastic polymer material. ULTEM 9085 was selected as the material of choice for StreamVane production because of its high strength-to-weight ratio. In this study, quasi-static and cyclic fatigue tests were performed on ULTEM 9085 samples fabricated by fused deposition modeling. First, ASTM D638 tensile-tensile material tests were conducted on three different build orientations to verify the mechanical strength of ULTEM 9085 listed by Stratasys. The three different orientations that were tested were Orientation XZZ, Orientation XYZ, and Orientation ZXY with measured ultimate tensile strengths of 69.6 MPa, 56.3 MPa, and 37.6 MPa, respectively. Fatigue properties were investigated utilizing the procedure outlined in ASTM D7791. S-N curves were generated using data collected at stress levels of 80%, 60%, 30% and 20% of the ultimate tensile stress with an R-ratio of 0.1 for the build orientation XZY. Next, the modified Goodman approach was used to estimate the fully reversed (R = −1) fatigue life. The initial data suggested that the modified Goodman approach was very conservative. Therefore, four different stress levels of 25%, 20%, 15% and 10% of ultimate tensile stress were used to characterize the fully reversed fatigue properties. Because of the extreme conservatism of the modified Goodman model for this material, a simple phenomenological model was developed to estimate the fatigue life of ULTEM 9085 subjected to fatigue at different R-ratios. The calculated fatigue life using the model and the data collected for the fully reversed test correlated very well. The data from this investigation demonstrated that StreamVane designs using ULTEM 9085 are more than capable of withstanding the static and dynamic loads in currently planned turbomachinery applications.
Effects of Oscillations in the Main Flow on Film Cooling at Various Frequencies at a Low Blowing Ratio
Authors: Baek Seung Il , Yavuzkurt Savas
Published: August 2018

The objective of this study was to investigate the effects of oscillations in the main flow on film cooling at various single frequencies at a low average blowing ratio of M = 0.5. The oscillations in the main flow could be a result of combustion instabilities that have been one of the major concerns for gas turbine industry. Understanding the effect of the instabilities on film cooling is important for better design of the gas turbine engines. The frequencies from 268 to 2144 Hz were identified as the dominant frequencies from a Fourier analysis of a combustor instability data on pressure oscillations. Lastly, the experimental data on gas turbine combustor instabilities is applied to the main flow using Fourier Series and the results are compared to those at single frequencies. Numerical simulations are carried out using LES Smagorinsky-Lilly and URANS k-epsilon models. This study is focused on film cooling effectiveness and heat transfer coefficient which are very important in calculation of the blade temperatures. The results show that as the frequency of the main flow goes from 0 to 180 Hz, the film cooling effectiveness is decreased due to enhancement of jet lift off with increasing frequency. However, when the frequency goes from 180 to 268 Hz, the film cooling effectiveness climbs up sharply because a thin coolant film near the wall is overlapped by large vortices containing the coolant. If the frequency changes from 268 to 1072 Hz, the effectiveness drops because the large vortices generated catch up with each other and they start overlapping and they are moved away from the wall. Main flow frequencies from 1072 to 2144 Hz cause an increase of the film cooling effectiveness since the coolant jet could not respond to these very high frequencies and the coolant behavior starts to return to that at 0 Hz gradually along with the effectiveness. In terms of heat transfer coefficients, when the oscillation frequency climbs from 0 to 536 Hz, the spanwise-averaged Stanton number ratio (Stm/Sto) increases due to growing disturbances in the flow. If the frequency is increased from 536 to 2144, the spanwise-averaged Stanton number ratio is decreased. When the oscillation frequency exceeds 536 Hz, the mixing between the hot mainstream and the coolant is reduced because jets do not respond to the flow oscillations as quickly by very short period.
Investigation of Flow-Induced Radial Force and its Influence on Rotor Dynamics for a Cryogenic Liquid Turbine Expander
Authors: Yuan Ningbo , Sun Jinju , Song Peng , Huo Changjiang , Sun Shan
Published: August 2018

To improve the operating stability of a cryogenic liquid turbine expander, the influence of flow behavior on rotor radial force and critical speed is investigated numerically. At both design and off-design conditions, unsteady flow simulation is conducted in the entire expander environment where the physical model is constituted by a volute, nozzle, impeller and diffuser duct. The asymmetric flow characteristics are captured at both design and off-design conditions and they are responsible for the significant radial force on rotor. The radial component of flow-induced resultant force is calculated with direct integration approach and it is significant due to apparent asymmetric impeller flow. The influence of such radial component of flow-induced resultant force on the rotor critical speed is further investigated, where the flow-induced radial force is considered as an equivalent mass and superposed on the impeller mass integrity to obtain a resultant mass of impeller, which is used in the prediction of rotor critical speed.

To predict rotor critical speed, a finite element method is developed and incorporated into a FORTRAN code, and it is validated and then used to predict the rotor critical speed with and without consideration of the radial component of flow-induced resultant force respectively. The following is described: at both design condition and off-design conditions, the predicted critical speeds with consideration of flow-induced radial force are significantly below that without flow-induced radial force. The influence of impeller flow behavior on rotor dynamics of the turbine expander is not negligible.
Coupled Thermal-Structural-Fluid Numerical Analysis of Gas Lubricated Mechanical Seals
Authors: Luo Jingjing , Dohmen Hans Josef , Benra Friedrich-Karl
Published: August 2018

With the increase of the operating pressure of gas compressors, the demand for a robust and reliable shaft end sealing solution, namely dry gas seal, has risen. The narrow sealing gap formed between the rotating and the stationary rings, about 2–5 micrometers wide, is subject to the hydrodynamic pressure on sealing surfaces and deflections on both rings due to mechanical forces and thermal loads. In order to estimate the seal performance in terms of film thicknesses, leakage flows and radial tapers, a numerical program which automatically couples the simulation of the pressure field in micro-scale based on the Reynolds equation for compressible fluids, the heat generation and transfer model between the fluid and solids as well as the structural and thermal distortion of both rings, has been developed by the authors to address the mechanical seal problem as a whole system. In this way, the interaction of all arising forces, mechanical deformations and thermal deviations is taken into account in the design process of the seals. The choked flow exit boundary is also taken into considerations for high pressure conditions.

The method to solve this interactive problem as a whole is discussed. The paper presents the numerical analysis carried out with various groove parameters, seal geometries and operating conditions. Results are compared and show a good agreement with actual experimental data. Design parameters which have strong influences on the seal performance are as well discussed.
Performance Evaluation of a Tandem Rotor Under Design and Off-Design Operation
Authors: Kumar Amit , Pradeep A. M.
Published: August 2018

The inherent risk of flow separation limits the extent of diffusion that can be achieved in a single stage axial compressor. Tandem blading is a promising concept that has drawn the attention of designers and researchers. Tandem blading permits higher blade turning and hence higher diffusion factor and blade loading with lower risk of flow separation. The present study explores the feasibility of using a tandem rotor in a low speed compressor stage. Computational analysis of the performance and flow behavior of the stage is presented at design and off-design conditions. The results are initially validated with experimental test data. A higher percentage pitch of 85% and lower axial overlap of 5% is selected for the tandem rotor. Results of the tandem rotor stage is compared with a baseline stage comprising a single bladed rotor. The results indicate tandem blading offers better diffusion characteristics than the single rotor. Some interesting observations pertaining to the interaction between the gap-nozzle flow and the 3D flow features are also discussed.
Influence of Autoignition Kernel Development on the Flame Stabilisation of Hydrogen-Nitrogen Mixtures in Vitiated Air of High Temperature
Authors: Schmalhofer Christoph A. , Griebel Peter , Aigner Manfred
Published: August 2018

Autoignition and flame stabilisation in a gas turbine combustor presents severe challenges for safe and reliable gas turbine operation as soon as they occur in parts of the combustor that are not designed to sustain higher thermal loads. Especially when operating on highly-reactive fuels like hydrogen, higher autoignition and flashback risk associated with these fuels have to be taken into account. In the present study, flame stabilisation initiated by autoignition events is investigated in an optically accessible mixing duct of a generic reheat combustor at typical reheat conditions. The experiments were conducted at pressures of 15 bar, vitiated air temperatures higher than 1100 K and bulk velocity of 200 m/s. The fuel was a hydrogen-nitrogen mixture with up to 70 vol. % hydrogen and was injected by a coflow inline injector along with preheated carrier air of temperatures up to 623 K. The autoignition-driven flame stabilisation process was investigated by recording the luminescence signal with high-speed cameras and by tracking the temporal and spatial development of autoignition kernels in the mixing duct. A detailed and comprehensive data set could be generated providing the basis for an in-depth analysis of the stabilisation process on time scales down to 0.3 milliseconds, which is fast enough to disclose the small timescales at which the autoignition kernels develop in the mixing section. A stabilising sequence was found to lead to the stabilised flames due to a non-interrupted sequence of autoignition kernels. The stabilising sequence was found behave differently in two different temperature regimes where sequence durations and amounts of kernels differed significantly from each other. A state in which the cross section of the mixing section is fully blocked by one or more kernels in vertical direction could be identified for all operating conditions and the development of subsequent autoignition kernels after the section blockage changed clearly once this state was reached.
Experimental Investigation and Numerical Validation of the Bearing Face Flow of an Adaptive Seal
Authors: Zimmermann Anna-L. , Guemmer Volker , Nguyen Tue , Giepman Rogier H. M.
Published: August 2018

This paper is dedicated to experimental and numerical investigations of self-adaptive seals under 2D static conditions. Besides the leakage flow across the seal / rotor combination, the distribution of static pressures within the air bearing clearance is measured. The bearing face flow is studied extensively, focusing on its dependency to the differential pressure and the axial clearance. Unchoked and choked flow regimes are tested and analyzed independently from each other. Correlation curves are established to describe the dependency of the test parameters to either the leakage rate or the mean static pressure in the bearing clearance. Furthermore, numerical predictions gained from CFD simulations are presented and validated and provide a better understanding of the flow physic processes within the bearing face.
Numerical Simulation of ITD Flows in the Presence of HP Blade and LP Vane
Authors: Gao Jie , Liu Xuezheng , Xiao Weiyan , Fu Weiliang , Meng Fusheng , Yue Guoqiang , Zheng Qun
Published: August 2018

Flows in an intermediate turbine duct (ITD) connecting high-pressure turbines (HPT) and low-pressure turbines (LPT) are highly complex, influenced by the upstream HP turbine flow structures. Non-uniformities originating from the duct with struts of different sizes also affect the LPT inflow conditions, resulting in reduced efficiency. The goal of this paper is to provide detailed understanding of the flow physics and loss mechanisms within the ITDs for highly efficient ITD designs. Steady and unsteady numerical simulations of flows through the ITDs in the presence of HP blade and LP vane were conducted. Effects of upstream HP blade on flow fields and loss characteristics within the ITDs are explored. The generation and propagation of wake and secondary flows through the whole configuration is described, including the fast Fourier transformation (FFT) analyses of the flow in the ITD. Results from the numerical simulations show complex flow patterns resulted from blade-strut-vane flow interactions in a high-endwall-angle duct, which are not obtainable from ITD-only simulations. Moreover, the ITD has a strong amplifying effect on the distorted inflow, and the inflow with the upstream wake and secondary flows introduces a high loss area along the casing at ITD exit. Detailed results are presented and discussed for the flow physics and loss mechanisms within the ITD.
Steady RANS of Flow and Heat Transfer in a Smooth and Pin-Finned U-Duct With a Trapezoidal Cross Section
Authors: Hu Kenny S.-Y. , Chi Xingkai , Shih Tom I-P. , Chyu Minking , Crawford Michael
Published: August 2018

Steady RANS were performed to examine the ability of four turbulence models — realizable k-ε (k-ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSAM (RSM-τω) — to predict the turbulent flow and heat transfer in a U-duct with a trapezoidal cross section and with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimentally measured values.

For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k-ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, that maximum is 14.5% for RSM-τω, 29% for SST, and 50% for k-ε and RSM-LPS. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the secondary flow in the turn region and the separated flow downstream of the turn dominated in how well the models predict the HTC.

For the U-duct with pin fins, k-ε predicted the lowest and the least accurate HTCs, and SST and RSM-τω predicted the best. For k-ε, the maximum relative error in the averaged HTC is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.
T63 Turbine Response to Rotating Detonation Combustor Exhaust Flow
Authors: Naples Andrew , Battelle Ryan , Hoke John , Schauer Fred
Published: August 2018

This paper describes testing an axial turbine response when driven by a Rotating Detonation Combustor (RDC). A T63 (C20-250) gas turbine is modified by replacing the combustor with a RDC. The stator vanes of the T63 are heavily instrumented for measurement of flow enthalpy and pressure. The engine is run at multiple power levels with the stock combustor using JetA and hydrogen fuel. The engine is then modified to have an open loop configuration, and is run with both the RDC and the stock combustor hardware with hydrogen fuel. Temperature pattern factor, flow unsteadiness, and turbine component efficiency are measured for all setups. High speed pressure transducers show substantially higher unsteadiness generated by the RDC than the conventional combustor. RDC turbine component efficiencies are compared to the conventional combustor. Results suggest that RDC unsteadiness does not significantly impact turbine efficiency.