bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative Analysis of Propulsive System in Multi-Rotor Unmanned Aerial Vehicle
Authors: Sonaimuthu Balaji , Panchalingam Prabhagaran , Raja Vijayanandh
Published: January 2020

In an advanced Multi-rotor Unmanned Aerial Vehicle (UAV), the existing methodology of the propeller and its parametric modification leads to provide the various performance characteristics by inducing the operating efficiency. The subsisting solution for obtaining the thrust, rate of climb and forward speed by proliferating the propeller configuration and modification the design aspects in propeller by varying the pitch angle and consisting parameters in a Multi-rotor UAV. Instead of adding or modifying the design aspects, this article recommends the propeller with attaching Convergent-Divergent (C-D) Nozzle duct, which leads to producing the augmented thrust efficiency than the normal functioning system. And the comparison of the propeller with and without attaching the convergent nozzle duct, divergent nozzle duct, C-D nozzle duct has been analyzed using the numerical simulation and scrutinizing the optimized conceptual design of propeller is done with the help of ANSYS Workbench, where the design methodology is modeled by CATIA. By the result of the simulation, it leads to provide the efficient characteristics and design aspects of the Multi-rotor Unmanned Aerial Vehicle.
Performance Simulation of an Engine Retrofitted With Thrust Vectoring Capabilities
Authors: Sundararaj Ramraj H. , Chandra sekar T. , Arora Rajat , Rao A. N. , Kushari Abhijit
Published: January 2020

Thrust vectoring is a requirement for fifth generation fighters, giving them super-maneuverability capabilities, allowing them to execute tactical maneuvers that are not possible using conventional aerodynamic mechanisms. The most widely used and successful method for achieving this is by using gimbaled engines or nozzles. The complexities involved in this method, have encouraged future engine designers to explore different avenues for achieving thrust vectoring, one of which is fluidic thrust vectoring. In fluidic thrust vectoring, jet deflection is achieved by fluid injection at various locations on the nozzle.

During thrust vectoring operations, the engine performance is affected. This is primarily due to the change in effective nozzle area. When a nozzle is gimbaled, as is the method used in currently operational thrust vectored engines, or during fluidic thrust vectoring operations, there is a change in effective nozzle area. This impacts the engine mass flow rate, thus affecting the engine operation. The change in performance is similar to that of an engine fitted with a variable area nozzle.

In this study, we attempted to retrofit a thrust vectoring nozzle to an existing engine designed for a fourth-generation fighter aircraft, in order to give it fifth-generation fighter aircraft capabilities. A Twin spool mixed flow turbofan engine with a convergent nozzle is selected and its performance is simulated using Gasturb 13. The baseline engine consists of a low pressure spool, high pressure spool, combustion chamber and convergent-divergent nozzle. For the sake of simplicity, the convergent-divergent nozzle is replaced with a convergent nozzle, with no loss in thrust at design point. The design point is arrived at based on engine data available in open literature. Following this, offdesign performance is simulated, for studying the effect of thrust vectoring operations, which are modeled as a nozzle area change. Suitably scaled generic maps provided in Gasturb are used for off-design simulations. The effect of nozzle area change on engine performance is studied at sea level static conditions. The nozzle area is decreased by a maximum of 15%, in steps of 1%. During thrust vectoring operations, there is a significant change in bypass ratio and fan surge margin, with the other performance parameters being relatively constant.

Following this, simulations are conducted at different flight conditions to understand the effect of nozzle area change for different flight regimes. A total of seven different flight conditions are selected to understand the operational envelope of thrust vectoring operation. It is found that at all flight conditions, thrust vectoring has a significant influence on bypass ratio and fan surge margin. While for most conditions, there is an improvement in fan surge margin, there are two conditions where fan surge margin decreases substantially.
Comparative Assessment of Savonius Water Turbine With Conventional Savonius Wind Turbine
Authors: Sarma Neelam K. , Biswas Agnimitra , Misra Rahul D.
Published: January 2020

Wind turbine has gained a keen interest in the field of research but its low efficiency due to low working fluid density triggers the need for upgradation. However, this technology will get a boost if the factor of low density fluid is eradicated. This paper is intended towards the study of performance of the same design of Savonius wind turbine when operated in high density water. The density of water is approximately 1000 times more than air. In the present study, the performance of a two bladed Savonius wind turbine and a Savonius water turbine have been analyzed both experimentally and with the aid of Computational Fluid Dynamics (CFD) using Ansys 19.0, keeping the maximum power content (Pmax) of the fluid-stream constant. Coefficient of power (Cp) is one of the deciding factors for superiority of the turbines one over the other. For the study, three cases of power contents viz. 0.61 W, 6.2 W and 16.45 W have been considered. The results obtained suggest that the Savonius water turbine with the highest Cp value of 0.343 is dominant over Savonius wind turbine. The effects of tip speed ratio and Non-dimensional factor (γ) on performance of both the turbine kinds have also been studied.
Combustor Modeling and Design Modification of a Micro Gas Turbine Combustor With a Rotating Casing for Syngas Fuel
Authors: Shih Hsin-Yi , Ajvad Maaz
Published: January 2020

This study is an extension of the previous study, which presents the rotation effects of casing on syngas combustion. When syngas was applied to achieve the power output of proposed micro gas turbine, high temperature flame moves towards the exit of the combustor. Consequently, the temperature and temperature fluctuation at combustor exit increases. In this study, geometry of the can combustor is modified for the syngas application. In modified design, diameter of the fuel injector, length of the primary zone, configuration of primary and dilution holes is modified. To perform the numerical calculation, computational model which consists of three-dimension compressible k-ε realizable turbulent flow model and presumed probability density function for combustion process invoking a laminar flamelet assumption generated by detailed chemical kinetics from GRI 3.0 is used. Two typical composition of syngas are used namely: H2-rich (H2:CO = 80:20) and equal molar (H2:CO = 50:50). The combustion characteristics and NOx emissions were investigated to understand the rotating effects of syngas combustion in the modified design of the can combustor. In the modified design, the high-temperature flame gets stabilized along the wall of the combustor for both composition of syngas. Unlike in the previous design, the high-temperature flame moves towards the exit of the combustor. The exit temperature and pattern factor dropped and reached the design requirements after the modification. The rotation of casing enhances the swirling strength, which benefits proper mixing of fuel and air and leads to reduction in pattern factor and NOx emissions.
Supercritical Carbon Dioxide Turbomachinery Options for Kilowatt to Gigawatt Level Power Generation
Authors: Seshadri Lakshminarayanan , Raja Harini Nivetha , Kumar Pramod , Nassar Abdul , Giri Gaurav , Moroz Leonid
Published: January 2020

Supercritical Carbon Dioxide Brayton cycles can be used in conjunction with a host of heat sources associated with different magnitudes of net power generation. In this paper, the overall design features of the turbomachinery, namely the turbine and compressor are evaluated for kilowatt to Gigawatt range of net cycle power using a commercial design tool — AxSTREAM®. The thermodynamic cycle considered in all cases is a simple recuperated Brayton cycle with turbine and compressor inlet temperatures of 540 °C and 45 °C respectively. The highest and lowest pressures in the cycle are 210 bar and 85 bar respectively. The preliminary design is carried out using an inverse algorithm with a meanline solver that generates many geometries for the given boundary conditions using standard loss correlations to account for different losses in turbomachines. It, thus, provides the general design features of the compressor and turbine which include — machine size, shaft speed at design point, overall efficiency, number of blades, blade heights, blade angles and number of stages for axial turbines. The choice of axial or radial impeller and initial estimates of machine size and shaft speed are made based on standard specific speed-specific diameter charts and important loss parameters are presented for each case. This study serves as a first step towards in-depth blade profiling, 3-D analysis and design of the turbomachinery required to bring this technology to the practical realm.
Conjugate Heat Transfer Analysis of Military Aero Engine Combustor Liner With Impingement and Effusion Cooling
Authors: Suresh Batchu , Panigrahi Chinmayee , Davis Antonio , Kesavan V. , Kishore Prasad D.
Published: January 2020

Improvement in specific thrust is one of the desirable requirements for Military aero-engine which has led to a tremendous increase in turbine inlet temperatures. This has resulted in combustion chambers to operate at a gas temperature of the order of 2100K, making it difficult for the thermal designers to design a liner cooling configuration to bring down its metal temperature within allowable limits with available coolant air. The present study highlights the computational prediction of cooling effectiveness for impingement-effusion cooled combustor liner. The impingement cooling is adopted to the effusion cooled liner in order to enhance its coolant side heat transfer. 1-Dimensional (1-D) analysis is carried out to obtain a suitable impingement geometry to improve the coolant side heat transfer. Suitable geometrical features like impingement hole diameter (di) and distance of the impingement plate from effusion liner (z) are arrived for enhancement of coolant side heat transfer. Conjugate Heat Transfer analysis (CHT) is carried out for three cooling configurations with different impingement hole diameter. Effusion cooled liner with porosity 1% and holes inclined at 22° and for impingement plate hole porosity of 1.6% is maintained for all the configurations. CHT analysis is carried out for effusion cooled liner using ANSYS Fluent ver.14.5. The film cooling predictions are in good agreement for effusion cooled liner plate with measurements. SST k-ω turbulence model with enhanced wall function predicted well. The effectiveness obtained for effusion cooled liner and impingement-effusion cooled liner are compared. There is an improvement of 34% in effectiveness for impingement-effusion cooled liner compared to effusion cooled liner with a reduction of coolant air mass flow by 10%. The variation of temperature for the impingement-effusion cooled liner is lower. Parametric analysis is also carried out to study the effect of blowing ratio and metal thermal conductivity on the film cooling effectiveness for impingement-effusion cooled liner.
Accurate Prediction of Buffer Air Temperatures Using Lumped Heat Transfer Method
Authors: Gandla Pavan , Nidamanuri Naresh
Published: January 2020

Buffer air system plays a vital role in gas turbine engines as it pressurizes bearing compartments, thermal conditioning of life limiting parts, purging the hot gas ingestion and antiicing. Buffer air is normally tapped from compressor section and routed to several locations of the engine through tubes, struts and ducts. Air supply is controlled though a buffer valve which sources air from different sources based on the flight condition. Accurate prediction of steady state buffer air temperature is critical in achieving gas turbine performance, durability and operability. It allows design community to determine optimum amount of buffer air which directly impacts gas turbine efficiency. As buffer air passes through different section of the engine by the time it reaches its intended destination, it losses or gains heat which eventually alter its temperature. Buffer air is currently modelled through a network of chambers and restrictors which is solved through an iterative solver for flow and energy convergence. Heat transfer is neglected in this solver and captures only enthalpy balance and pressure losses.

An effort has been made to capture buffer air convective heat transfer as it passes through many channels and ducts on its routing. Lumped heat transfer method is employed and estimated the delta temperature b/w inlet and outlet of the corresponding passage. Outside and inside heat transfer coefficients are estimated using empirical correlations. Under steady state conditions, Final temperature of the buffer air would be the surrounding air temperature at that location and initial temperature of the air is its entry temperature. This delta temperate is incorporated in the buffer air network which then predicts corrected buffer air temperature for any flight conditions.

With this methodology predicted buffer air Temperature is matched very close to thermo couple test data for various engine power conditions. Buffer air network model fidelity is greatly improved and gives greater confidence on air temperature for any flight conditions.

Design studies are carried out and made a recommendation to incorporate thermal barrier coating on passages so that buffer temperature is retained which improves its thermal conditioning capabilities.
Modeling Combustion in a Rearward-Facing Step Using a Hybrid RANS/LES Method
Authors: Verma Ishan , Yadav Rakesh , Nakod Pravin , Sharkey Patrick , Li Shaoping , Meeks Ellen
Published: January 2020

With incremental High-Performance Computing (HPC) scalability and performance improvements, hybrid Reynolds Averaged Navier Stokes (RANS)/Large Eddy Simulation (LES) have become popular for modeling reactive flow configurations. Hybrid RANS/LES methods like Stress-Blended Eddy Simulation (SBES) are presented in this paper and have been applied to model near-wall flows using two-equation k-ω RANS formulation while switching to LES in the separated flow region using a blending function. Turbulent combustion in a rearward-facing step is modeled by using Flamelet Generated Manifold (FGM) with SBES turbulence. A turbulent premixed propane/air flame (φ = 0.57) is stabilized in the turbulent mixing layer (ReH = 22, 100) formed at the rearward-facing step. The results obtained show a good agreement with the experimental data for velocity, temperature and species mass fractions at various locations in the channel.
Flamelet Generated Manifold Simulation of Turbulent Non-Premixed Bluff Body Flames
Authors: Verma Ishan , Yadav Rakesh , Nakod Pravin , Sharkey Patrick , Li Shaoping , Meeks Ellen
Published: January 2020

In this paper, the turbulent jet diffusion flame stabilized behind a bluff body (HM1) is simulated using the Flamelet Generated Manifold (FGM) model. Interactions between turbulence and chemistry are detailed in this paper. In HM1 flame, ignition mainly occurs in the outer shear layer while mixing effects dominate in the recirculation zone. Turbulence is modeled by using variants of two-equation Reynolds Averaged Navier Stokes (RANS) models (steady and unsteady RANS), whilst turbulence-chemistry closure is based on FGM approach. Results are compared with experimental data to validate the dynamics and spatial structure of bluff-body flames. Different approaches based on the variants of steady RANS and unsteady RANS are compared for three mesh resolutions. Definitive advantages and disadvantages of each approach are identified on the basis of computational cost and accuracy. The results provide important insights into the simulation of bluff-body flames approaching the blow-off limit.
A Comparative Study of Heat Transfer Characteristics and Pressure Drop in Matrix Structures
Authors: Prajapati Anjana N. , Tariq Andallib
Published: January 2020

An experimental study on local heat transfer distributions and pressure loss in the closed matrix channels with an angle 45° has been conducted using liquid crystal thermography for a Reynolds number (Re) range 5800–14000. A total of five different configurations of matrixes have been considered for investigation. The thermo-hydraulic performance of the matrix structure with angle 45° is initially compared with that of the matrixes with angles 35° and 55° for a constant sub-channel aspect ratio (ARs) 0.8. Later, the sub-channel aspect ratio of matrix with angle 45° has been varied as 0.4 and 1.2 and the comparative results are presented. While comparing the performance parameters of different angles for the sub-channel aspect ratio 0.8, it is found that for lower Reynolds numbers (Re ≤ 8100), the angle 45° offers highest augmentation Nusselt number. However, for Re > 8100, the angle 55° showed the highest augmentation Nusselt number. It has been also observed that the sub-channel aspect ratio 0.8 presents the highest augmentation Nusselt numbers as compared to ARs = 1.2 and 0.4 for Re ≤ 12400. Whereas, the friction factor fairly decreases with the increase in the sub-aspect ratio. A significant effect of angle has been found for friction factor as compared to sub-channel aspect ratio. The highest thermal performance factor (1.13) is obtained for the matrix with angle 45° and sub-channel aspect ratio 0.8 at Reynolds number 8100.
Characterization of Burner Stabilized Premixed and Non-Premixed Flame Using Digital Image Processing
Authors: Hassan Tarik , Sarkar Sourav , Mukhopadhyay Achintya , Sen Swarnendu
Published: January 2020

The present goal of combustion research is to enhance the burning efficiency resulting in minimal emission which is in fact, paves the way for a sustainable future. Researchers are investigating different parameters and factors associated with combustion to control the combustion process. Image processing is one of the most useful and safe tool for this job as it is nonintrusive and do not interfere with the combustion zone during experiment. Present work focuses on the digital image processing of the premixed and diffusion flame which has been utilized as a tool to characterize burner stabilized premixed and non-premixed Flame. The experiment is performed on a burner stabilized LPG-air flame. For premixed flame, several sets of experiments are done keeping the camera setting and image quality identical which resulted in an almost linearly increasing average RGB value with respect to equivalence ratio. Taking the relation of an experiment as standard, equivalence ratio is calculated for other experiments just by observing the average RGB value(R+G+B/3) of that image. It is found that almost in all cases the error values are lying between −10% to +10% of the actual value calculated from the flow rates of air and fuel. Diffusion flame is examined by passing fuel through the central channel of co-flow burner and air through the outer cylindrical channel. Air is used to stabilize the flame and for giving it a steady shape. Experiment is done keeping air flow constant while the fuel flow is varied and the image is captured. For diffusion flame, as the change in colour of flame is not much differentiable with the change in fuel, analysis is done to find the relation between fuel flow rate and flame area by counting the number of pixels. Finally, a direct relation of fuel amount and the image area is obtained.
Performance Evaluation of Contra-Rotating Fans Operating Under Different Speed Combinations
Authors: Joshi Navjot , Madasseri Payyappalli Manas , Pradeep A. M.
Published: January 2020

One of the advantages of a contra-rotating fan is its possibility to operate both the rotors at different speeds. Owing to this possibility, the performance of a contra-rotating fan can be controlled by operating it at different speed combinations. A numerical study of a low aspect ratio contra-rotating fan in low subsonic regime is carried out under various speed combinations of the rotors. Both steady state and Nonlinear Harmonic (NLH) simulations are performed to identify the important flow mechanisms in the contra-rotating fan. The results show that the diffusion factor of rotor-2 is significantly high towards the hub region which implies that large separations are likely to occur at the hub. The wake of rotor-1 is observed to impinge on the suction surface of rotor-2. Rotor-2 generates a strong suction effect at high rotational speeds and thereby delays the stall inception in the whole stage and shows an improvement in the stage pressure ratio. The upstream effect strongly influences the performance of rotor-1. When rotor-2 rotates at higher rotational speed, due to the suction effect, the flow angle at the exit of rotor-1 decreases which allows the fan to operate at lower flow coefficient. When the suction effect is very strong, it pulls the tip leakage vortex of rotor-1 towards the axial direction. Due to the suction effect, the location of the appearance of tip-leakage vortex moves further downstream. The tip-leakage vortex makes a higher angle with the blade chord at near stall conditions for speed combination Nd – 1.5Nd in contrast to a lower angle for speed combination Nd – 0.5Nd. In summary, the paper describes the performance changes, flow physics and the rotor-rotor interaction mechanisms for different speed combinations of a contra-rotating fan.
Impact of Sweep on Part Speed Performance of an Axial Compressor Rotor With Circumferential Casing Grooves
Authors: Goswami Shraman , Govardhan M.
Published: January 2020

High performance and increased operating range of an axial compressor is obtained by employing three-dimensional design features, such as sweep, as well as shroud casing treatments, such as circumferential casing grooves. A number of different rotor blades with different amounts of sweeps and different sweep starting spans are studied at design speed. Different swept rotors, including zero sweep, are derived from Rotor37 rotor geometry. In the current study the best performing rotor with sweep is analyzed at part speed. The analyses were done for baseline rotor, devoid of any sweep, and with and without circumferential casing grooves. A detailed flow field investigation and performance comparison is presented to understand the changes in flow field at part speed. It is found that that at 100% design speed, stall margin improvement is achived by both sweep and casing grooves, but at 90% speed improvement in stall margin due to sacing groove is very minimal over and above the gain due to sweep. It is also noticed that due to reduced shock loss efficiency is higher at 90% speed than at 100% speed.
Local-Correlation Based Zero-Equation Transition Model for Turbomachinery
Authors: Sandhu Jatinder Pal Singh
Published: January 2020

In this paper, we present a new local-correlation based zero-equation transition model. The new model, which is derived from the local-correlation based one-equation gamma transition model (Menter, F. R., Smirnov, P. E., Liu, T., and Avancha, R., A One-Equation Local Correlation-Based Transition Model, Flow, Turbulence and Combustion, vol. 95, 2015, pp. 583619.), does not require any additional equation to be solved, by defining a new variable, which captures the turbulent kinetic energy and intermittency collectively. The new model only adds three more source terms to the existing transport equation of turbulent kinetic energy. Hence the new model is straightforward to implement in already existing RANS solvers and reduces the computational memory requirement as compared to the other transition models. The transition prediction capability of the new model is tested and compared against the one-equation gamma transition model, especially for turbomachinery applications, where bypass transition is the primary transition mechanism, using a standard flat plate test case, and S809 airfoil. Preliminary results show that the new zero-equation transition model produces satisfactory results in terms of transition-location prediction.
Dynamic Behavior and Off-Design Performance Analysis of Solar Driven ORC Using Scroll Expanders
Authors: Zhang Ying , Narasimhan Arun Kumar , Bai Mengjie , Zhao Li , Deng Shuai , Goswami D. Yogi
Published: January 2020

Solar driven ORC system is a possible solution for small-scale power generation. A scroll expander is considered due to its better suitability among other positive displacement expanders for small-scale power outputs. This work conducted a test of an ORC system with an expansion valve by varying the working fluid mass flow rate in two scenarios. A dynamic system-level model of ORC was developed and validated with experimental data. The validated model was used to predict the ORC performance considering off-design conditions of expander and solar insolation. The experimental data showed that pressures and temperatures exhibited the same trend as that of the working fluid mass flow rate, of which the evaporation pressure was the most sensitive to this variation. The simulation results are in good agreement with the experimental results. Results from the dynamic model showed that the ORC power output was underestimated by up to 54.7%, when off-design performance of expander was not considered. Considering the expander off-design performance and solar insolation, a highest thermal efficiency of 7.6% and an expander isentropic efficiency of 80.6% were achieved.
Computational Study of Mist Assisted Film Cooling on a Flat Plate
Authors: Rao Pabbi Setty Mallikarjuna , Prasad B. V. S. S. S.
Published: January 2020

Previous investigation [1, 2] proposed that an introduction of water droplets into the film cooling air significantly improves the effectiveness of gas turbine blade. In order to allow comparison with experimental data, all the previous studies were confined to laboratory conditions. However, under typical gas turbine operating conditions temperature difference between the main stream flow (1561 K) and the coolant air (644 K) is approximately 917 K. The aim of this study is to numerically investigate the performance of mist assisted film cooling under the typical operating conditions of the gas turbine. Results showed the value of mist assisted film cooling effectiveness are greater than pure air cooling. Trajectories of droplets show that the water droplets vaporize faster. Typical percentage enhancement of the mist assisted film cooling effectiveness is 16% when the cooling air contains 6% mist with droplet diameter of one micron.
Experimental Investigation of Active Control of Cracked Rotor-Bearing System Equipped With Magnetic Bearing
Authors: Sarmah Nilakshi , Tiwari Rajiv
Published: January 2020

The present work investigates the online vibration control of a cracked rotor-bearing system incorporated with AMB. A fatigue crack, which exhibits the opening and closure behavior of cracked faces while rotation, is introduced artificially in the shaft to understand the dynamic behavior of a cracked rotor system. For this, three-point bending tests were performed to obtain edge transverse crack in the shaft. An eight-pole electromagnetic actuator was used to apply control forces directly on to the shaft in the radial direction. The radial force was used to assist vibration suppression in the rotor. In order to achieve active control to mechanical vibration and other disturbances, a simple PID control strategy is used. Closed loop tests are conducted on the d-SPACE DS1202 platform using the differential driving mode of the PID controller to suppress the vibration of a shaft containing a transverse crack integrated with an AMB supported on two conventional bearings. The comparison of the dynamic behavior of the laboratory test rig with and without active magnetic bearing (AMB) with the numerically simulated data is analyzed. The vibration suppression is found to be achieved satisfactorily in the presence of the unbalance force, bow force, crack force, and with other forces on the rotor-bearing system.
Effect of Tip Gap Variation on the Performance of the Transonic Fan Stage With Tandem Stator
Authors: Ananthakrishnan K. , Das Shyama Prasad , Prasad B. V. S. S. S.
Published: January 2020

The main goal of modern axial compressor development is to increase the power to weight ratio with higher efficiency. In the present investigation, highly loaded single stage axial compressor with tandem stator vanes is used. Tandem vanes help in attaining the compact compressor stage along with high pressure loading. It is designed for a stage pressure ratio of 2, mass flow rate of 9.02 kg/s operating at 30800 rpm resulting in transonic flow field. The aerodynamic performance of this compressor detoriates due to the tip leakage and secondary flows. Steady-state numerical investigation is carried out to study the flow structures near the tip region of transonic rotor and how different tip gaps influence the overall performance of the compressor. Further the effects of tip leakage flow variation on the performance of tandem vanes are also highlighted. Transonic fan stage with baseline tip gap of 0.5mm is analyzed along with different tip clearance values ranging from 0 % to 3 % of axial chord. Three-dimensional viscous Reynolds Averaged Navier Stokes (RANS) equations are solved using SST k-ω turbulence model. Computational domain discretized with high quality hexahedral elements (Y+ < 2) in AUTOGRID, Numeca. The numerical procedure is verified against the experimental results of Rotor37 transonic rotor test case. Tip leakage losses contribute a substantial amount to the total loss of stage. Overall performance and the stall characteristics for the compressor stage has been evaluated for different tip gap variations.. Further, the topological properties are exploited to visualize the critical points and separation lines on rotor and tandem vanes. Increase in rotor total pressure loss coefficient is observed with increasing tip gap. In contrary, overall total pressure loss coefficient improves for smaller tip gap values and then detoriates. It is observed optimum tip gap height lies close to the 1.125mm, 2% of baseline design value.
Numerical Study of Part Clearance and Free Stream Turbulence on High End-Wall LP Turbine Nozzle Annular Cascade
Authors: Bhavsar Hardikkumar , Mistry Chetan S.
Published: January 2020

The performance of the gas turbine engines can be improved using variable area nozzle turbine (VANT) in the off-design condition by actively controlling the mass flow rate for various applications of engine. However, VANT demands part clearances to be provided near both the hub and tip of the vane for its mechanical movement. This clearance induces leakage flow and formation of the leakage vortex which interacts with the secondary flow in the vane passage. In this paper, the numerical study is performed on high endwall angle vane geometry of 2nd stage LPT from Pratt and Whitney E3 engine using commercially available CFD tool ANSYS CFX. The effect of free stream turbulence at 0.5%, 5% and 10% is studied along with the change of incidence angle from −10 to +10 on the annular cascade nozzle flow field. The static entropy contour, vorticity contour and total pressure loss coefficient are used to analyzed the flow. The free stream turbulence affects the structure of the vortices within the flow passage. However, no significant change on total pressure loss coefficient is present as turbulence intensity is changed from 0.5% to 5%, but total pressure loss coefficient increases as turbulence intensity is changed to 10%.
Comparative Study of Force Prediction Techniques Using Multi Component Accelerometer Force Balance for High Enthalpy Ground Testing
Authors: Kamal Abhishek , Das Gagan Chandra , Kulkarni Vinayak , Sahoo Niranjan
Published: January 2020

Large wave drag and high surface heating are the major concerns of hypersonic flows. Hence, development of force measurement technique or prediction of force has always remained a promising research topic in this field. Present studies also deal with force prediction techniques and force balance calibration methodology for ground testing in an impulse test facility. A blunt double cone model is fabricated along with a three component accelerometer force balance. Impulse hammer hits are made on different locations of this test model. In these calibration experiments, the applied impulse and acceleration responses from three accelerometers are recorded. These calibration tests are repeated multiple times to apply hammer hits of different magnitude. All the input and corresponding output singles are then processed first to arrive at the impulse response function or correlation between input and outputs. Then the force recovery techniques are applied to recover the axial and normal forces generated during application of one of the calibration forces. The experimentally recovered force signals from different techniques are compared and then the accuracy of these predictions is estimated using different error estimation techniques. Such studies are found essential not only in defining the most accurate force prediction technique but also in understanding the time required for prediction by a particular technique. Additionally, such studies essentially helps to improve a force prediction algorithm.
Experimental Analysis of Biogas Combustion With Different Foam Materials in a Porous Media Burner
Authors: Devi Sangjukta , Sahoo Niranjan , Muthukumar P.
Published: January 2020

The existing biogas Conventional Burners (CBs) are less energy efficient and are designed for rich fuel combustion. Porous Media Burner (PMB), working on the principle of combustion in porous media offer several advantages including high thermal efficiency, low emissions, high power intensity, etc. In this work, a study on the effect of porous material on the thermal behaviour of a biogas operated PMB is presented. A state-of-the-art PMB working in the thermal load range of 5 to 10 kW has been developed, which can be used for both industrial and domestic purposes. It is a two section burner composed of a combustion zone and a preheat zone. Keeping the material of the preheat zone unchanged (Al2O3 ceramic), the burner is tested with two different materials in the combustion zone (SiC and ZrO2 foams). Experimental investigation has been done to analyze the stability criteria and study the temperature distribution in the PMB. This includes the identification of the stable operating limits (flashback and blow off) and measurement of temperature profiles in axial and radial direction. These assessments confirm that SiC is a better choice over ZrO2 for lean biogas combustion in PMB.
Performance Improvement of a Combined Power and Cooling Cycle for Low Temperature Heat Sources Using Internal Heat Recovery and Scroll Expander
Authors: Leveni Martina , Narasimhan Arun Kumar , Almatrafi Eydhah , Goswami D. Yogi
Published: January 2020

Low temperature heat sources inherently result in lower cycle efficiencies, which can be improved by means of combined power and cooling generation. In order to produce power and cooling, appropriate thermodynamic cycles and working fluids must be used. Goswami cycle is a combined cycle that produces power and refrigeration by using ammonia-water mixture for low temperature heat sources. In the present study, a scroll expander is modeled specifically for the cycle operating conditions and a theoretical investigation is conducted to determine the cycle performance. A scroll expander design suitable for the operating conditions improves the power output and thereby overall thermal efficiency. The scroll expander efficiency varied between 0.05 and 0.61 for the pressure ratio between 2.2 and 8.6, with a maximum efficiency of 0.697 achieved at a pressure ratio of about 4.4. An internal heat recovery from the rectifier is proposed along with a flow split in the strong solution and analyzed for overall cycle energy efficiency improvement. Internal heat recovery from the rectifier increased the first law effective efficiency and the effective exergy efficiency by 7.9% and 7.8%, respectively, over the basic configuration.
RANS Based Iso-Thermal CFD Analysis of the Flow Field Created by a Radial Swirler in a Conical Nozzle
Authors: Rana Rampada , Kumar Sonu , Muthuveerappan Nagalingam
Published: January 2020

Improvement of specific fuel consumption and specific thrust of gas turbine engines have necessitated to have better combustion performances requirements in terms of combustion efficiency, flame stability, better ignition characteristics, lower emissions etc. Injector designs play a very pivotal role to meet the above requirements. In this paper steady state flow field studies have been carried out in a conical nozzle fitted with single swirler which is the fundamental part of a typical injector. The aspects of the flow field both inside and outside the injector have been captured by using RANS based calculations of commercial software Ansys Fluent. The computational domain extends from 500mm in the upstream direction and the exit flow of the nozzle is allowed to meet on to a domain of length more than 2000mm. The downstream domain is so chosen that the impact of the wall on to the evaluation of the flow field is found to be negligible resembling the flow field studies in open atmosphere. Realizable k-ε turbulent model and standard wall function were used with wall y+ extended from 30 onwards. The study shows a distinct feature of maximum flow velocity at the exit of the injector lip apart from the presence of regular re-circulation bubble at the exit of the injector.
Experimental Investigations on Meridional and Circumferential Stresses of Bellows due to Internal Pressure
Authors: Pagar Nitin D. , Gawande S. H.
Published: January 2020

Bellows Expansion joints are mostly linked with the piping connections of turbines, heat exchangers, process equipment’s etc. Its primary function is to absorb expansion and contraction in pipelines on which it is fixed and fulfill its functioning through peculiar springy shaped convolutions. At design stage, it is very difficult to guess fatigue life cycles due to evolved stresses in convolutions. When it is subjected to purely axial load, stress generation per convolution acting along longitudinal line is same; however the behavior is different under very small angular rotation and axial shift due to misalignments in structural mountings. To understand it, preliminary investigations on axial case is necessary and also to identify the location of various stresses in convoluted section. This work aims to determine the meridional and circumferential stresses on the convoluted shape when it is subjected to an axi-symmetric internal pressure loading. Experimentation is carried out to determine the maximum stresses and verified it with the help of numerical simulation and analytically. 10 convolution bellows is used for the experiments. It is observed that the meridional stresses are highly dominating the circumferential stresses along the same longitudinal line. Meridional membrane stresses and meridional bending stresses due to pressure are evaluated on two different locations, one on perfectly meridional line and another at the top surface of convolution along the same longitudinal line. The stresses found higher on the top surface of convolutions. Meridional membrane and bending stresses due to deflection are higher than the meridional membrane and bending stresses due to pressure. Evaluation of the maximum stresses is very helpful for the designers to develop the fatigue analysis model and exact prediction of the cycle life of the bellows.
NSF rolls out huge makeover of science statistics
Authors: Mervis Jeffrey
Published: January 2020

Agency wants its biennial
Indicators
to be more timely in tracking global trends.
A type Ia supernova at the heart of superluminous transient SN 2006gy
Authors: Jerkstrand Anders , Maeda Keiichi , Kawabata Koji S.
Published: January 2020

Modeling a superluminous supernova

Superluminous supernovae can be up to 100 times brighter than normal supernovae, but there is no consensus on how such bright transients are produced. Jerkstrand
et al.
identified emission lines of iron in the spectrum of a superluminous supernova that appeared more than a year after the explosion. The authors explored models of several possible mechanisms, finding that only one is consistent with all the observations: a normal Type Ia supernova that interacts with a dense shell of circumstellar material. The shell must have been ejected by the progenitor star less than a century before the explosion, perhaps owing to interaction with a binary partner.

Science
, this issue p.
415
Visualizing H
2
O molecules reacting at TiO
2
active sites with transmission electron microscopy
Authors: Yuan Wentao , Zhu Beien , Li Xiao-Yan , Hansen Thomas W. , Ou Yang , Fang Ke , Yang Hangsheng , Zhang Ze , Wagner Jakob B. , Gao Yi , Wang Yong
Published: January 2020

Imaging reactive surface water

Recent developments in transmission electron microscopy (TEM) have enabled imaging of single atoms, but adsorbed gas molecules have proven more challenging because of a lack of sufficient image contrast. Yuan
et al.
adsorbed water and carbon monoxide (CO) on a reconstructed nanocrystalline anatase titanium dioxide (TiO
2
) surface that has protruding TiO
3
ridges every four unit cells, which provide regions of distinct contrast. Water adsorption on this surface during environmental TEM experiments led to the formation of twinned protrusions. These structures developed dynamic contrast as the water reacted with coexposed CO to form hydrogen and carbon dioxide.

Science
, this issue p.
428
A common hub for sleep and motor control in the substantia nigra
Authors: Liu Danqian , Li Weifu , Ma Chenyan , Zheng Weitong , Yao Yuanyuan , Tso Chak Foon , Zhong Peng , Chen Xi , Song Jun Ho , Choi Woochul , Paik Se-Bum , Han Hua , Dan Yang
Published: January 2020

Interneurons control brain arousal states

The underlying circuit mechanisms coordinating brain arousal and motor activity are poorly understood. Liu
et al.
found that glutamic acid decarboxylase 2 (GAD2)–expressing, but not parvalbumin-expressing, interneurons in a part of the brain known as the substantia nigra promote sleep (see the Perspective by Wisden and Franks). Parvalbuminergic neurons fire at higher rates in states of high motor activity, and their activation increases movement termination consistent with the function of the substantia nigra in suppressing unwanted movements during action selection. By contrast, GAD2 neurons are preferentially active in states of low motor activity. In addition to motor suppression, their activation powerfully enhances the transition from quiet wakefulness to sleep, which differ mainly in the arousal level rather than motor behavior. GAD2 interneurons thus provide general suppression of both motor activity and brain arousal to promote states of quiescence.

Science
, this issue p.
440
; see also p.
366
Rational construction of a scalable heterostructured nanorod megalibrary
Authors: Steimle Benjamin C. , Fenton Julie L. , Schaak Raymond E.
Published: January 2020

Heterostructured nanorod libraries

The synthesis of nanostructures with well-defined interfaces between different materials can enable applications in areas such as catalysis and solar energy harvesting. Nanomaterials containing several different materials are usually synthesized through top-down approaches, such as surface growth or templating techniques, which usually produce small quantities of particles. Steimle
et al.
performed up to seven cation-exchange reactions (with ions such as Zn
2+
and Co
2+
) on solution-synthesized copper sulfide nanorods. In principle, more than 65,000 different variations of materials and their interfaces can be made, depending on the order and extent of cation exchange.

Science
, this issue p.
418
A two-way molecular dialogue between embryo and endosperm is required for seed development
Authors: Doll N. M. , Royek S. , Fujita S. , Okuda S. , Chamot S. , Stintzi A. , Widiez T. , Hothorn M. , Schaller A. , Geldner N. , Ingram G.
Published: January 2020

Filling in the gaps

In a plant seed, the embryo lies dormant surrounded by nutritive endosperm while awaiting suitable conditions to germinate. A hydrophobic cuticle around the embryo protects it from catastrophic water loss during the early days of growth. Doll
et al.
identified a back-and-forth signaling pathway that ensures an intact cuticle. The precursor of a signaling peptide is made in the embryo and transferred to the endosperm, where it is processed into an active form. The activated peptide diffuses back into the embryo to activate receptor-like kinases that drive cuticle development. Serve and return continues until all leaks in the cuticle are filled in and the peptide can no longer cross the barrier.

Science
, this issue p.
431
Can phase separation buffer cellular noise?
Authors: Riback Joshua A. , Brangwynne Clifford P.
Published: January 2020

By suppressing concentration fluctuations, condensation may stabilize cellular processes
Support cells in the brain promote longevity
Authors: Miklas Jason Wayne , Brunet Anne
Published: January 2020

Glial cells in the brain use neuropeptides to communicate stress responses and longevity
Drop the chalk
Authors: Thorp H. Holden
Published: January 2020

A diverse scientific workforce; policy-makers who recognize the importance of science; a voting public that understands the scientific process (and even some facts about the ancient universe and climate change, too)—this has been the mantra of the scientific community, but these words don't match actions. Look no further than the way science is still taught at universities—it's no wonder that there is a struggle to recruit students to science. That is costing society a generation of researchers, educators, a population that better grasps science, and maybe more.
Diagnostic Mycology: Xtreme Challenges
Authors: Wickes Brian L. , Romanelli Anna M.
Published: January 2020

Developing any diagnostic assay that receives United States Food and Drug Administration (FDA) approval can be a slow and difficult process. FDA-approved assays for fungal diagnosis are generally few in number and are focused mainly on diagnosing candidiasis, which is caused by several species of
Candida
, in addition to a limited number of systemic mycotic agents. While all microbial diagnostic assays face challenges before they are FDA approved and reach the market, there are a number of challenges to fungal diagnostic assay development that have been difficult hurdles to overcome.