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Recurrence analysis of surface pressure characteristics over symmetrical aerofoil

CHAOS 2020年第1期30卷 013116-013116页

作者： Arunvinthan, S. Gopal, R. Chandrasekar, V. K. Pillai, S. Nadaraja SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India SASTRA Deemed Univ Sch Elect & Elect Engn Ctr Nonlinear Sci & Engn Thanjavur 613401 Tamilnadu India

We study the surface pressure data exhibiting the underlying dynamical behavior of the flow transition over the upper surface of the aerofoil by using recurrence quantification analysis (RQA). In this study, NACA 2415 aerofoil subjected to a turbulent inflow of TI = 8.46% at various angles of attack ranging from alpha = 0 degrees to 20 degrees with an increment of 5 degrees corresponding to Re = 2.0 x 10(5) is considered. We show that the values of recurrence quantification measures effectively distinguish the underlying dynamics of time series surface pressure data at each port, which proves RQA as an effective tool in accurately predicting the flow transitions. Published under license by AIP Publishing.

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Buoyancy driven flow and slippage constraints influences on Casson hybridity nanofluid of Yamada-Ota and Xue type via rotating cone

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AIN SHAMS ENGINEERING JOURNAL 2023年第4期14卷

作者： Pasha, Amjad Ali Rahman, Mustafa Mutiur Jamshed, Wasim Juhany, Khalid Ahmed Pillai, S. Nadaraja King Abdulaziz Univ Aerosp Engn Dept Jeddah 21589 Saudi Arabia King Abdullah Univ Sci & Technol Mech Engn Program Phys Sci & Engn Div Thuwal 23955 Saudi Arabia Capital Univ Sci & Technol CUST Dept Math Islamabad 44000 Pakistan SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

Analysis of the extended two-hybrid nanofluid models: The Casson fluid with the combination of the base fluid (Ethylene Glycol) and two different nanoparticles is described in detail by Yamada-Ota and Xue (CoFe2O4 and Mn-Zn Fe2O4). This fluid is considered to flow in a rotating cone system, where the tangen-tial vector (x-axis), azimuthal vector (y-axis) and normal vector are all part of the coordinate system (z-axis). The flow and thermal properties of the Casson hybrid nanofluid are controlled by the slipping boundary conditions (velocity and temperature components), the porous media, and buoyancy. To create a collection of ordinary differential equations (ODEs) from the initial mathematical specification, similar-ity transformations are used. Then, using a specialized method, namely the Galerkin finite element method (GFEM), these ODEs are solved numerically. Finally, this research has produced the graphical results of the velocity in the tangential and azimuthal directions, as well as thermal dispersal. Additionally, under the effect of relevant regulating parameters, the values of the tangential and azi-muthal skin friction coefficients, along with the dimensionless Nusselt number, are tabulated. The results showed that radiation raises the thermal field while the Darcy-Forchheimer parameter escalates the flow for the two-dimensional axes (x and y). The buoyancy ratio parameter also upsurges the frictional coef-ficient for both the x-and y-components. Additionally, the dimensionless Nusselt number is decreased by managing variables like radiation, porosity, and slipping boundary conditions (velocity and temperature).(c) 2022 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Ain Shams Uni-versity. This is an open access article under the CC BY-NC-ND license (http://***/licenses/ by-nc-nd/4.0/).

关键词： Hybrid nanofluid Porous medium Viscous dissipation Homogeneous heterogeneous reactions GFEM

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One-equation turbulence models applied to practical scramjet inlet

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INTERNATIONAL JOURNAL OF TURBO & JET-ENGINES 2021年第0期

作者： Pasha, Amjad A. Juhany, Khalid A. Pillai, Subramania N. King Abdulaziz Univ Aerosp Engn Dept Jeddah 21589 Saudi Arabia SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

Reynolds-averaged Navier-Stokes equations are used to simulate a practical scramjet inlet geometry using the shock-unsteadiness modified Spalart-Allmaras (SA) turbulence model. The geometry consists of fore-body ramps, expansion corners, and inlet ducts. The focus is to study the impingement of the cowl shock on the opposite wall boundary-layer. The resulting separation bubble can lead to blockage and inlet unstarts. The shock-unsteadiness correction is employed and is found to improve the computational fluid dynamics (CFD) prediction of flow separation in shock/boundary-layer interactions. The shock-unsteadiness parameter is calibrated against available experimental data of canonical flows, and the predicted flow-field is analyzed in detail. A large separation bubble size normalized to the upstream boundary-layer thickness of 4.6 is observed in the interaction region. Across the reattachment region in the interaction region, a peak value of wall pressure is observed. The inlet performance parameters are also calculated. The total pressure losses of 62% are observed across different shock waves, with an additional loss of 15% due to viscous boundary-layer effects.

关键词： CFD high-speed flows scramjet separation bubble shock wave turbulence models

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Dynamic mode decomposition analysis and aerodynamic characteristics prediction of circular cylinder with variously modified ridges

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International Journal of Numerical Methods for Heat and Fluid flow 2025年

作者： R, Rajesh E, Karthikvel S.B.M, Priya S, Nadaraja Pillai Turbulence and Flow Control Lab School of Mechanical Engineering SASTRA Deemed University Thanjavur India School of Electrical and Electronics Engineering SASTRA Deemed University Thanjavur India

Purpose: This study aims to explore the impact of surface modifications on a circular cylinder with ridges of diverse configurations. Dynamic mode decomposition (DMD) is used for flow field analysis and deep learning gated recurrent unit (GRU) framework is used to predict variations in surface pressure. Design/methodology/approach: The research entails wind tunnel testing of a cylinder with ridges of different diameters and angular position in a flow field of Re = 1.01 × 105 and the surface pressure is measured by a Scanivalve pressure scanner. DMD is used to scrutinize pressure field data, elucidating significant dynamic modes and their influence on aerodynamic characteristics. The GRU model is trained with an experimental surface pressure data set, 80% for training, 15% for testing and 5% for validation phase to predict the surface pressure distribution of the model. Findings: The study inferred that the ridge ratio and angular position of the ridge on a cylindrical surface significantly influence the drag coefficient (Cd), while the DMD reveals alterations in dynamic mode frequencies and amplitudes;In addition, the GRU model accurately predicts time-dependent aerodynamic characteristics, assessed through K-fold cross-validation, demonstrating superior predictive accuracy with minimal root mean squared error. Originality/value: This study uses DMD for flow field analysis and the GRU model to predict the surface pressure distribution, presenting a more efficient and time-saving alternative to conventional methodologies. © 2025, Emerald Publishing Limited.

关键词： Etching

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Gradient-Free Optimization in Thermoacoustics: Application to a Low-Order Model

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JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME 2022年第5期144卷 051004-051004页

作者： Reumschuessel, Johann Moritz von Saldern, Jakob G. R. Li, Yiqing Paschereit, Christian Oliver Orchini, Alessandro Tech Univ Berlin Chair Fluid Dynam D-10623 Berlin Germany Tech Univ Berlin Lab Flow Instabilities & Dynam D-10623 Berlin Germany Harbin Inst Technol Ctr Turbulence Control Shenzhen 518055 Peoples R China Tech Univ Berlin Inst Fluid Mech & Tech Acoust D-10623 Berlin Germany

Machine learning and automatized routines for parameter optimization have experienced a surge in development in the past years, mostly caused by the increasing availability of computing capacity. Gradient-free optimization can avoid cumbersome theoretical studies as input parameters are purely adapted based on output data. As no knowledge about the objective function is provided to the algorithms, this approach might reveal unconventional solutions to complex problems that were out of scope of classical solution strategies. In this study, the potential of these optimization methods on thermoacoustic problems is examined. The optimization algorithms are applied to a generic low-order thermoacoustic can-combustor model with several fuel injectors at different locations. We use three optimization algorithms - the well established downhill simplex method, the recently proposed explorative gradient method, and an evolutionary algorithm - to find optimal fuel distributions across the fuel lines while maintaining the amount of consumed fuel constant. The objective is to have minimal pulsation amplitudes. We compare the results and efficiency of the gradient-free algorithms. Additionally, we employ model-based linear stability analysis to calculate the growth rates of the dominant thermoacoustic modes. This allows us to highlight general and thermoacoustic-specific features of the optimization methods and results. The findings of this study show the potential of gradient-free optimization methods on combustor design for tackling thermoacoustic problems, and motivate further research in this direction.

关键词： Stability Fuel injectors Oscillations Optimization Fuels Optimization algorithms Flames Fluctuations (Physics) Acoustics Gradient methods Pressure Algorithms Evolutionary algorithms

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Numerical Analysis to Evaluate the Effect of Wall Temperature on Skin Friction and Stanton Number for Turbulent flows over a Flat Plate from Mach 2-8

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ARABIAN JOURNAL FOR SCIENCE AND ENGINEERING 2022年第7期47卷 8243-8256页

作者： Pasha, Amjad A. Reddy, D. Siva Krishna Abdulla, Mohammed Mahdi Pillai, S. Nadaraja Islam, Nazrul Juhany, Khalid A. Reddy, V. Mahendra Abdul Jameel, Abdul Gani King Abdulaziz Univ Aerosp Engn Dept Jeddah 21589 Saudi Arabia SRM Inst Sci & Technol Sch Mech Engn Chennai 603203 Tamil Nadu India SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India King Abdulaziz Univ Dept Mech Engn Jeddah 21589 Saudi Arabia Indian Inst Technol Kharagpur Dept Mech Engn Kharagpur 721302 W Bengal India King Fahd Univ Petr & Minerals Dept Chem Engn Dhahran 31261 Saudi Arabia King Fahd Univ Petr & Minerals Ctr Refining & Adv Chem Dhahran 31261 Saudi Arabia

The computational approaches of CFD are more powerful than the analytical solutions for high-speed compressible flows over a flat plate. A small number of expensive experimental data can be generated to aid high-speed vehicle design. However, CFD can be used to simulate a large variety of flows with different freestream and wall conditions in a cost-effective manner. The current work aims to numerically calculate the turbulent boundary layer flows over a flat plate at different Mach numbers in the range of 2-8 at different wall conditions and unit Reynolds numbers. The Reynolds-averaged Navier-Stokes method with k - omega turbulence model is applied to resolve the flow over the flat plate at zero angle of attack. The computed skin friction coefficient and Stanton number are compared with the available experimental data in the literature. The calculated results indicate some agreement with the experimental data. An increase in the Mach number and wall temperature decreases the skin friction and the Stanton number. A polynomial curve fit data estimation is proposed for skin friction under adiabatic wall conditions for Mach numbers in the range of 2-8. Numerical simulations over compression corner flows are also presented in the present work. The freestream Mach number influences the thickness of the subsonic layer in the undisturbed boundary layer on the flat plate in compression corner flows. The higher freestream Mach number results in a lower subsonic thickness near the wall, leading to a small separation bubble and lower peak heat transfer in shock/boundary-layer interaction flows.

关键词： Computational fluid dynamics (CFD) High-speed flows Reynolds-averaged Navier-Stokes (RANS) Turbulent boundary layer turbulence models Shock wave boundary-layer interaction

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Parametric Investigation on Single Cylinder Spark Ignition Engine Fueled Methanol Blends;Water-Based Micro Emulsions and Conventional Gasoline

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INTERNATIONAL JOURNAL OF HEAT AND TECHNOLOGY 2021年第3期39卷 919-924页

作者： Qadiri, Ufaith Pasha, Amjad Ali Rahman, Mustafa Mutiur Raheem, Mohammed Abdul Jameel, Abdul Gani Abdul Pillai, Subramania Nadaraja Malla Reddy Engn Coll Dept Mech Engn Medchal 500100 Telangana India King Abdulaziz Univ Dept Aerosp Engn Jeddah 21589 Saudi Arabia Univ Waterloo Dept Mech & Mechatron Engn Waterloo ON N2L 3G1 Canada King Fand Univ Petr & Minerals Dept Chem Engn Dhahran 31261 Saudi Arabia SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

In this contribution, the investigation conducted on alternative fuels includes methanol 20% blended with gasoline 80% and emulsion-based fuel with the composition of gasoline 80%, ethanol 15%, and H2O 5% are compared with 100% conventional gasoline fuel. These fueled single-cylinders spark ignition engine is studied for checking their performance and emission characteristics as per future emission norms. This work is performed on One-dimensional AVL Boost Simulation Software. The simulations predicted the performance and emission characteristics were far lesser than conventional 100% gasoline. These fuels meet the strict emission regulations of Euro VII. The main purpose of this investigation is to use alternative fuels to improve the performance and emission characteristics of the single- cylinder spark ignition engine and reduce the consumption of fossil fuel reserves. This investigation led to the conclusion that by using methanol 20% in 80% gasoline and micro-emulsion, fuel improves the power, BSFC (brake specific fuel consumption), thermal efficiency and combustion properties of the single-cylinder spark-ignition engine. The CO, HC and NOx emissions were also reduced for alternative fuel than 100% gasoline fuel. The novel water-based emulsion fuel showed the lowest value of NOx emissions as compared to blended 20% methanol with 80% gasoline and 100% gasoline fuel.

关键词： AVL boost alternative fuel combustion performance emissions

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Effect of thermal boundary condition on forced convection from circular cylinders

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NUMERICAL HEAT TRANSFER PART A-APPLICATIONS 2019年第6期76卷 420-437页

作者： Abdelhady, Mohamed Wood, David Univ Calgary Lab Turbulence Res Aerodynam & Flow Control LTRAC Mech & Mfg Engn Calgary AB T2L 1Y6 Canada

Researchers commonly assume that the effect of constant temperature and constant heat flux thermal boundary condition on forced convection from a circular cylinder is negligible. Such claim was assessed using Computational Fluid Dynamics for Reynolds number, Re, <= 3,000. The flow was directly solved without modeling for Re <= 300, and Large Eddy Simulation was used for Re = 1,000 and Re = 3,000. Constant property simulations were done for Prandtl number of 0.7. Fluid dynamics parameters: drag coefficient, Strouhal number, separation angle and recirculation length, were used to assess the accuracy of the simulations. The main parameter of interest, the Nusselt number, is higher locally for constant heat flux than constant temperature for 60 <= Re <= 3,000. In addition, the ratio of overall Nusselt number for constant heat flux to that for constant temperature increases for Re < 30 and is similar to 1.15 between 30 <= Re <= 3,000, showing that thermal boundary condition has significant effect on heat transfer from circular cylinder. Finally, the study developed empirical correlations relating overall Nusselt number to studied Reynolds number range.

关键词： Circular cylinders

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Evidence of extreme events in wind-induced normal stress of the columns of low- and medium-rise building structures

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EPL 2021年第1期136卷 10005-10005页

作者： Suresh, R. Gopal, R. Pillai, S. Nadaraja Chandrasekar, V. K. SASTRA Deemed Univ Ctr Nonlinear Sci & Engn Sch Elect & Elect Engn Dept Phys Thanjavur 613401 India SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India

We designed models for low- and medium-rise building structures with square and rectangular plans and tested the wind-induced normal stress of the building columns. We demonstrate the structures' normal stress response due to the wind load is non-Gaussian and shows evidence of extreme events, which are four to seven times larger than the mean standard deviation. We have estimated the probability distribution function to corroborate the long-tail nature of the extreme events, and randomness of the events is confirmed by plotting inter-event intervals and return maps. Further, the number of extreme events is calculated, which validates the exponentially decaying fit as a function of the number of standard deviations. Copyright (C) 2022 EPLA

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Aerodynamic Characteristics of Shark Scale-Based Vortex Generators upon Symmetrical Airfoil

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ENERGIES 2021年第7期14卷 1808-1808页

作者： Arunvinthan, S. Raatan, V. S. Nadaraja Pillai, S. Pasha, Amjad A. Rahman, M. M. A. Juhany, Khalid SASTRA Deemed Univ Sch Mech Engn Turbulence & Flow Control Lab Thanjavur 613401 Tamil Nadu India King Abdulaziz Univ Dept Aerosp Engn Jeddah 21589 Saudi Arabia King Abdullah Univ Sci & Technol Phys Sci & Engn Div Thuwal 23955 Saudi Arabia

A series of wind tunnel tests were carried out to determine the effect of shark scale-based vortex generators (SSVG) on a NACA 0015 symmetrical airfoil's aerodynamic characteristics. Three different sets of SSVG with varying geometrical parameters, such as chord length, amplitude, and wavelength, were designed and fabricated using 3D printing. The SSVG models were blended to the baseline NACA 0015 symmetrical airfoil. The wind tunnel experiments were performed over the test airfoil mounted with different sets of SSVG at various angles of attack, ranging from 0 degrees to 24 degrees in increments of 3 degrees, and operating in the range of Re = 2 x 10(5). The results revealed that the SSVG blended test airfoil reduced the drag and increased the maximum coefficient of lift (C-Lmax), thereby enhancing the overall aerodynamic performance. The SSVG offered noteworthy aerodynamic benefits by effectively altering the flow and causing significant spanwise variation in the flow properties. Additionally, attempts were made to identify the optimum chordwise location to blend the SSVG for effective use.

关键词： aerodynamic efficiency airfoils force balance shark scale vortex generators wind tunnel

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