Article
Mechanics
Xiao-Hua Fan, Gang Wang, Jing-Zhou Lin, Yan-Guang Yang, Zhi-Gong Tang
Summary: The experiment investigates the effects of expansion waves on incident shock-wave/boundary-layer interactions at Mach 4.96. The flow characteristics of the interaction zone are quantitatively analyzed under different intensities and positions of the incident shock wave and expansion waves. The expansion waves weaken the intensity of the shock waves encountered, thereby weakening the strength of the SWBLIs. The total wall pressure jump and interference length show a linear growth trend with increasing distance between the expansion waves and the interaction zone. However, the expansion waves have no impact on the initial pressure jump of the separation, consistent with the free-interaction theory. Finally, the scaling model proposed by Souverein et al. [A scaling analysis for turbulent shock-wave/boundary-layer interactions, J. Fluid Mech. 714, 505 (2013)] is modified using the measured pressure jump value, providing a better approximation for SWBLIs under the influence of expansion waves.
Article
Engineering, Aerospace
Davide Ninni, Francesco Bonelli, Gianpiero Colonna, Giuseppe Pascazio
Summary: The paper presents highly detailed two-dimensional numerical simulations of hypersonic nitrogen and air flows around a double wedge, focusing on the unsteady behavior and thermo-chemical non-equilibrium effects. The results show that the occurrence of unsteady periodic behavior depends on the flow conditions and is inhibited in the high enthalpy case. Furthermore, discrepancies between the results obtained with different thermo-physical models are observed in the case of high enthalpy flows.
Article
Mechanics
Ming-Zhi Tang, Gang Wang, Zhu-Xuan Xie, Wen-Feng Zhou, Yan-Chao Hu, Yan-Guang Yang
Summary: The aerothermodynamic characteristics in curved compression ramp flows with bistable states are studied, analyzing wall friction, pressure, and heat flux distributions. The study suggests that the occurrence of reversed-flow singularity is less likely in CCR flows, and the prediction of pressure peak of separation states can be confirmed by the minimum viscous dissipation theorem.
Article
Mechanics
Shibin Cao, Jiaao Hao, Igor Klioutchnikov, Herbert Olivier, Karl Alexander Heufer, Chih-Yung Wen
Summary: This study investigates the flow characteristics of hypersonic flows over compression ramps with different leading-edge radii using numerical simulations and global stability analysis. The results show that increasing the leading-edge radius can suppress flow separation, reduce aerodynamic heating, and stabilize the flow system.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Fluids & Plasmas
Stephan Priebe, M. Pino Martin
Summary: The study conducted DNS of a hypersonic shock wave/turbulent boundary layer interaction. The results showed consistent behavior with experimental observations. The shock wave interaction with the boundary layer was analyzed and compared with experimental data.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Mechanics
Youcheng Xi, Jie Ren, Liang Wang, Song Fu
Summary: This study obtained the characteristics of the leading attachment-line mode with sweep angle variations and successfully applied a bi-orthogonal eigenfunction system to address the receptivity problem of hypersonic flows. The analyses showed that global modes are most responsive to external forces and surface perturbations near the attachment line.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Anubhav Dwivedi, G. S. Sidharth, Mihailo R. Jovanovic
Summary: In this study, resolvent and weakly nonlinear analyses are combined with DNS to identify the mechanisms for oblique transition in a Mach 5 hypersonic flow over an adiabatic slender double wedge. It is demonstrated that the amplification of oblique waves comes from the streamline curvature of the separated shear layer. The weakly nonlinear analysis shows that the resolvent operator associated with linearization around the laminar base flow governs the evolution of steady reattachment streaks.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
L. Srinath, R. Sriram, P. Akhilesh, G. Jagadeesh
Summary: This study investigates the leading-edge separation induced by an impinging shock on a sharp flat plate using experiments and a theoretical model. The experiments validate the accuracy of the theoretical model and reveal that the flow field is no longer geometrically similar when the impingement location gets closer to the leading edge.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
A. Khraibut, S. L. Gai
Summary: This paper presents a numerical investigation on the effects of bluntness and incidence on the leading-edge separation in a laminar hypersonic flow. The results show that both bluntness and incidence have significant influences on the separation characteristics. A combined parameter is proposed and applied to plateau pressures in the separated region, differentiating the effects of small and large bluntness at different angles of incidence. The study also highlights the importance of the relationship between the two shear stress minima and the separation length.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Shibin Cao, Jiaao Hao, Igor Klioutchnikov, Herbert Olivier, Chih-Yung Wen
Summary: Direct numerical simulations are used to study hypersonic flow over a compression ramp, revealing the formation of streamwise heat flux streaks downstream of reattachment that exhibit low-frequency unsteadiness and are non-uniformly distributed in the spanwise direction. The unsteadiness of the heat flux streaks is coupled with a pulsation of the reattachment position, and global instabilities are found to be responsible for the flow unsteadiness.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Zhuxuan Xie, Zhixiang Xiao, Gang Wang, Yanguang Yang
Summary: The study found that Reynolds number can significantly affect the characteristics of shock wave/boundary layer interaction in expansion-compression corner flows. Different Reynolds numbers result in significant differences in separation and reattachment pressures, which also have important effects on turbulent changes.
Article
Engineering, Mechanical
Jin Lu, Hua Yang, Qinghu Zhang, Xin Wen, Zhouping Yin
Summary: An experimental investigation on flow separation of hypersonic laminar boundary layer flow over compression ramps with different angles is conducted. Particle image velocimetry is used to measure the detailed structures and to capture typical flow structures. Proper orthogonal decomposition analysis is performed to reveal the spatial structure of the flow field. The results show that flow separation occurs as the ramp angle increases and more coherent flow structures are present in the flow field.
JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME
(2022)
Article
Mechanics
Anurag Adityanarayan Ray, Ashoke De
Summary: This numerical investigation explores the effects of leading-edge bluntness on a double wedge with different aft-wedge angles under low enthalpy hypersonic free stream conditions. The study shows that even a small bluntness ratio can significantly alter the shock interaction pattern and increase the unsteadiness of the flow field. The cause of this unsteadiness is attributed to the increased shock-boundary layer interaction strength, leading to changes in the separation point and perturbations in the shear layer dynamics.
Article
Computer Science, Interdisciplinary Applications
D. Exposito, S. L. Gai, A. J. Neely
Summary: This paper discusses the relationship between wave-packets and discontinuities in the numerical solution of unsteady, supersonic triple-deck equations. It is found that large gradients at the corner compromise the stability of the algorithm. Two numerical methods have been developed to deal with these gradients: a time-splitting explicit method with a first-order approximation of the pressure derivative, and the Haar Wavelet Method. The results are analyzed in terms of the maximum pressure gradient and the second shear stress minimum.
JOURNAL OF COMPUTATIONAL PHYSICS
(2023)
Article
Engineering, Aerospace
Carson L. Running, Thomas J. Juliano
Summary: Measurements were conducted on a high-speed model using pressure-sensitive paint to capture unsteady shock-wave/boundary-layer interactions, with results indicating a significant effectiveness in providing insights into surface behavior. By calculating mean and fluctuating surface pressure, researchers were able to analyze the local characteristics of shock feet locations and frequency-dependent relationships, highlighting the importance of such measurements.
Correction
Engineering, Aerospace
Kunihiko Taira, Steven L. Brunton, Scott T. M. Dawson, Clarence W. Rowley, Tim Colonius, Beverley J. McKeon, Oliver T. Schmidt, Stanislav Gordeyev, Vassilios Theofilis, Lawrence S. Ukeiley
Article
Mechanics
J. S. Mueller, F. Lueckoff, P. Paredes, V. Theofilis, K. Oberleithner
JOURNAL OF FLUID MECHANICS
(2020)
Article
Mechanics
Kai Zhang, Shelby Hayostek, Michael Amitay, Wei He, Vassilios Theofilis, Kunihiko Taira
JOURNAL OF FLUID MECHANICS
(2020)
Article
Mechanics
Kai Zhang, Shelby Hayostek, Michael Amitay, Anton Burtsev, Vassilios Theofilis, Kunihiko Taira
JOURNAL OF FLUID MECHANICS
(2020)
Article
Mechanics
Saurabh S. Sawant, Deborah A. Levin, Vassilios Theofilis
Summary: The study focuses on the low-frequency molecular fluctuations within straight shocks and proposes a linear correlation between the shape of energy probability density functions and characteristic low frequencies of shocks. By deriving noncentral Chi-squared distributions of particle energies inside shocks and analyzing changes in most-probable-speed, the research aims to predict and estimate low-frequency oscillations in shocks for different Mach numbers and input temperatures. This model provides a physics-based approach to boundary conditions in the analysis of laminar-turbulent transition in high-speed flows, offering insights into receptivity and linear stability studies.
THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS
(2022)
Article
Mechanics
Helio Quintanilha, Pedro Paredes, Ardeshir Hanifi, Vassilis Theofilis
Summary: Non-modal linear stability analysis is conducted for hypersonic flow over an elliptic cone with an aspect ratio of two, showing increased significance of non-modal growth for laminar-turbulent transition with higher flight altitudes. The study reveals that transient growth is stronger at the tip of the cone and in azimuthal locations away from the major and minor axes, with linear optimal disturbances peaking in the crossflow region of the cone.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Saurabh S. Sawant, Deborah A. Levin, Vassilios Theofilis
Summary: Low-frequency molecular fluctuations in the translational nonequilibrium zone of one-dimensional strong shock waves are characterized for the first time within a kinetic collisional framework. The study reveals the bimodal nature of the probability density function in the shock region, suggesting the introduction of a novel two-bin model to describe the reduced-order dynamics of a large number of collision interactions of gas particles with strong correlation between perturbations and fluctuations in the normal stress.
Editorial Material
Mechanics
Vassilis Theofilis, Sergio Pirozzoli, Pino Martin
THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS
(2022)
Article
Mechanics
Angelos Klothakis, Helio Quintanilha, Saurabh S. Sawant, Eftychios Protopapadakis, Vassilis Theofilis, Deborah A. Levin
Summary: Linear stability analysis using DSMC method was performed on boundary layers of nitrogen, argon, and air, showing that perturbations in DSMC profiles are more damped than in the boundary layer.
THEORETICAL AND COMPUTATIONAL FLUID DYNAMICS
(2022)
Article
Mechanics
Saurabh S. Sawant, V Theofilis, D. A. Levin
Summary: This study investigates linear three-dimensional instability in shock layers and laminar separation bubbles induced by shock-wave/boundary-layer interactions in Mach 7 nitrogen flow over a double wedge. High-fidelity simulations using the direct simulation Monte Carlo method capture the evolution of flow features from the beginning of three-dimensionality to the early stages of nonlinear saturation.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Anton Burtsev, Wei He, Kai Zhang, Vassilios Theofilis, Kunihiko Taira, Michael Amitay
Summary: This paper investigates the linear modal instabilities of flow over untapered wings with aspect ratios AR = 4 and 8. Multiple unstable linear global modes have been identified and their dependence on geometric parameters has been examined. It is found that tip vortex effects dominate on the AR = 4 wing, while amplification of the leading mode is caused by wing tip recirculation on the AR = 8 wing. These findings are important for understanding flow stability and wake instability.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ozgur Tumuklu, Kyle M. Hanquist
Summary: This study investigates the spatial-temporal characteristics of laminar hypersonic flows at Mach 7.10 with different Reynolds numbers. The validity of the continuum assumption is tested by comparing previous kinetic and current continuum approaches. The impact of velocity slip and temperature jumps on flow and surface parameters is investigated. It is found that the flow field depends on spanwise effects and is fully 3D even at low pressure. High-fidelity numerical schlieren videos show strong spanwise oscillations in 3D configurations.
Article
Mechanics
Jean Helder Marques Ribeiro, Jacob Neal, Anton Burtsev, Michael Amitay, Vassilios Theofilis, Kunihiko Taira
Summary: This study investigates the influence of taper and sweep on the post-stall wake characteristics of aircraft wings using direct numerical simulations. The results show that tapered wings have smaller tip chord length, generating weaker tip vortices and attenuating inboard downwash. Tapered swept wings exhibit enhanced aerodynamic performance, with higher time-averaged lift and lift-to-drag ratio.
JOURNAL OF FLUID MECHANICS
(2023)
Proceedings Paper
Mechanics
Saurabh S. Sawant, Ozgur Tumuklu, Vassilis Theofilis, Deborah A. Levin
Summary: In this study, the self-excited spanwise homogeneous perturbations in a hypersonic flow system are investigated using the kinetic DSMC method. The growth rates of unstable modes, the wavelength, location, and characteristic frequencies of spanwise periodic flow structures in this interaction are assessed.
IUTAM LAMINAR-TURBULENT TRANSITION
(2022)
Article
Mechanics
Shahram Karami, Daniel Edgington-Mitchell, Vassilis Theofilis, Julio Soria
JOURNAL OF FLUID MECHANICS
(2020)