Download or read book Numerical Study of Hypersonic Boundary Layer Receptivity Characteristics Due to Freestream Pulse Waves written by Xiaojun Tang and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A finite difference method is used to do direct numerical simulation (DNS) of hypersonic unsteady flowfield under the action of freestream pulse wave. The response of the hypersonic flowfield to freestream pulse wave is studied, and the generation and evolution characteristics of the boundary layer disturbance waves are discussed. The effects of the pulse wave types on the disturbance mode in the boundary layer are investigated. Results show that the freestream disturbance waves significantly change the shock standoff distance, the distribution of flowfield parameters and the thermodynamic state of boundary layer. In the nose area, the main disturbance modes in the boundary layer are distributed near the fundamental mode. With the evolution of disturbance along with streamwise, the main disturbance modes are transformed from the dominant state of the fundamental mode to the collective leadership state of the second order and the third order harmonic frequency. The intensity of bow shock has significant effects on both the fundamental mode and the harmonic modes in each order. The strong shear structure of boundary layer under different types of freestream pulse waves reveals different stability characteristics. The effects of different types of freestream pulse waves are significant on the distribution and evolution of disturbance modes. The narrowing of frequency band and the decreasing of main disturbance mode clusters exist in the boundary layer both for fast acoustic wave, slow acoustic wave and entropy wave.

Download or read book Numerical Study of Hypersonic Boundary Layer Receptivity and Stability with Freestream Hotspot Perturbations written by Yuet Huang and published by . This book was released on 2016 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents a numerical simulation study of linear hypersonic boundary-layer receptivity and stability over blunt compression cones with freestream hotspot perturbations. This study is conducted for freestream disturbances with broad, continuous frequency spectra over cones that have nose radii of 1, 0.5 and 0.1 mm under freestream conditions of Mach 6, 10 and 15. The simulations are carried out using the high-order shock-fitting finite-difference scheme developed by Zhong (1998), the results of which are shown to agree well with linear stability theory (LST) and experiments. The general receptivity mechanism is then studied by the simulation-LST comparisons under two parametric effects: nose bluntness and freestream Mach number. Among the new findings of the current study, the mechanisms of the receptivity process are found to be mainly caused by the fast acoustic waves that are generated behind the bow shock from the hotspot/shock interaction in the nose region. It is these fast acoustic waves that substantially enter the boundary layer and generate mode F through the synchronization of fast acoustic waves and mode F in the upstream part of the cone. Subsequently, the synchronization of modes F and S generates mode S, or the second mode, which eventually grows into a dominant level at the downstream part of the cone. Additionally, we have obtained the receptivity coefficients of mode S along the Branch-I neutral stability curve using a method that combines LST predicted N-factors and simulated disturbance amplitudes. These receptivity coefficients agree well with those obtained from the theoretical modal decomposition method. In addition to obtaining the general receptivity mechanism and receptivity coefficients, we have also studied the parametric effects of nose bluntness and freestream Mach number on boundary-layer receptivity and stability over cones. Specifically, our results have shown that nose bluntness reduces the boundary-layer receptivity to freestream entropy perturbations and stabilizes the perturbed boundary layer over a cone. The boundary layer is more receptive to freestream entropy perturbations at higher freestream Mach numbers, while the perturbed boundary layer is stabilized at higher freestream Mach numbers. The current receptivity and stability study has not only shed new light on the receptivity mechanism to freestream entropy spots over blunt cones, but also advanced the understanding of nose bluntness and freestream Mach number effects on the receptivity and stability over blunt cones. Furthermore, the currently-obtained broad, continuous spectra of unstable-second-mode receptivity coefficients could potentially provide the initial amplitudes for future amplitude-based transition predicting methods.

Download or read book Numerical Study of Freestream Waves Receptivity and Nonlinear Breakdown in Hypersonic Boundary Layer written by Jia Lei and published by . This book was released on 2013 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: Laminar-turbulent transition prediction in hypersonic boundary layer remains one of the most challenging topics in the design of hypervelocity vehicle. It requires thorough understanding of the physical mechanisms underlay freestream wave receptivity and nonlinear breakdown process. Freestream wave receptivity concerns the evolution of freestream disturbance passing through the shock and exciting the boundary layer normal modes that eventually become unstable. Nonlinear breakdown focuses on the study of the relevant mechanisms in the secondary instability region that leads to laminar-turbulent transition. These two topics have been extensively studied separately for decades. Significant progress has been made in terms of understanding how the instability waves form and develop in the early region as well as what are the viable paths from breakdown to turbulent. However, the linkage between receptivity and breakdown is still not well understood. The nature transition process commonly observed in hypersonic boundary layer consists of the following ingredients: freestream wave receptivity, linear growth, secondary instability and breakdown to turbulent. The transition location highly depends on the freestream wave disturbance profile. In order to attain a better understanding of the natural transition process, it is necessary to conduct a complete simulation from freestream wave receptivity all the way to nonlinear breakdown. This kind of simulation is considered beyond the capability of current computer power. The objective of current research is to devise a new three-step approach to simulate the flow from receptivity process to breakdown. In order to achieve the goal, direct numerical simulations (DNS) are performed over various freestream conditions and cone geometries to investigate the hypersonic boundary layer stability, freestream wave receptivity and nonlinear breakdown. In the study of nose bluntness effect on hypersonic boundary layer stability, three cone models with different nose radii are investigated by linear stability theory (LST). It is found that, if only considering the second-mode instabilities, the onset of instability is always delayed as the nose bluntness increases. In the effort to simulate the entire process from freestream wave receptivity to nonlinear breakdown, a new approach is applied to break the simulation into three steps: meanflow calculation, linear receptivity simulation and nonlinear breakdown simulation. Extensive case studies demonstrate that it is feasible to simulate the flow from receptivity to breakdown using our new simulation approach. From the breakdown simulations, it is found that the breakdown is the result of fundamental resonance that occurs between the two-dimensional second-mode wave and their three-dimensional modes. In the secondary instability growth region, the two-dimensional and three-dimensional modes need to attain the same amplitude level for the breakdown to take place.

Download or read book Advances in Some Hypersonic Vehicles Technologies written by Ramesh K. Agarwal and published by BoD – Books on Demand. This book was released on 2018-03-14 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book describes the recent progress in some hypersonic technologies such as the aerodynamic modeling and numerical simulations of rarefied flows, boundary layer receptivity, coupled aerodynamics, and heat transfer problems, including fluid-thermal-structure interactions and launcher aerodynamic design as well as other miscellaneous topics, such as porous ceramic composite phase change control system and vehicle profile, following LQR design. Both the researchers and the students should find the material useful in their work.

Download or read book Direct Numerical Simulation and Experimental Validation of Hypersonic Boundary layer Receptivity and Instability written by Xiaolin Zhong and published by . This book was released on 2007 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research project is to compare our numerical simulation solutions with available experimental or theoretical results on hypersonic boundary layer receptivity and stability; and to conduct extensive DNS studies on the flow mechanisms of hypersonic boundary layer receptivity and stability. During the three-year period, we have conducted extensive DNS studies on the receptivity of hypersonic boundary layer flows over a sharp wedge, a flat plate, a blunt cone, and the FRESH aeroshell. DNS studies are compared with Stetson's 1984 stability experiment on Mach 7.99 flow over a blunt cone, and Maslov's leading-edge receptivity experiment on Mach 5.92 flow over a flat plate. Our numerical studies have been validated to be of high accuracy and led to further understanding of hypersonic boundary layer receptivity mechanism. Such understanding can lead to better tools for the prediction and control of high-speed boundary layer transition.

Download or read book Direct Numerical Simulation of 3 D Hypersonic Boundary Layer Receptivity to Freestream Disturbances written by Xiaolin Zhong and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hypersonic Boundary Layer Receptivity to Acoustic Disturbances Over Cones written by Kursat Kara and published by . This book was released on 2008 with total page 334 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book DNS Studies of Transitional Hypersonic Reacting Flows Over 3 D Hypersonic Vehicles written by Xiaolin Zhong and published by . This book was released on 2003 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Receptivity of Straight Blunt Cones to Broadband Freestream Pulse Disturbances for Transition Prediction in Hypersonic Flow written by Simon He and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Traditional stability analysis for hypersonic flows has focused on the development and relative amplification of a dominant disturbance mode, namely Mack's second mode. However, conventional $e^N$ method transition estimates based purely on the relative amplification of the second mode ignore the receptivity mechanisms which govern the response of a flow to different environmental disturbances. These receptivity mechanisms are now known to play a much more significant role in the laminar-to-turbulent transition of hypersonic flows, and numerous theoretical, computational, and experimental studies have been made to characterize them. Computational studies in particular are useful due to the large amount of high precision data they can generate with a relatively low cost, while experimental receptivity studies face difficulties due to the high noise environments present in conventional hypersonic windtunnels, as well as the general expense of hypersonic experiments. While computational receptivity studies have been prominent in the literature, most of these prior studies have focused on discrete frequency disturbances and have neglected to consider the more continuous and broadband disturbance spectra that can be found in experiments and in flight. This work aims to expand the prior body of receptivity research by studying the response to broadband disturbances that are more reflective of realistic environmental forcing. This process involves simulating the receptivity to axisymmetric disturbances as well as some preliminary investigations of the receptivity to 3-D pulse disturbances which excite azimuthal wave modes. The axisymmetric receptivity coefficients are also used to explore further applications of the amplitude method for transition prediction. This work uses perfect gas linear stability theory (LST) and direct numerical simulation (DNS) to simulate the Mach 10 flow over 9.525 mm (Case B), 5.080 mm (Case I), and 1 mm (Case S) nose radius axisymmetric straight cones with 7-degree half-angles. Case B and Case I utilized approximately the same freestream conditions, while the unit Reynolds number for Case S is 60\% lower. The 2-D receptivity of Case B and Case I are studied using finite spherical and planar pulse disturbances in the freestream. These include freestream fast acoustic, slow acoustic, temperature, and vorticity disturbances in order to generate receptivity coefficient spectra for a wide variety of possible freestream noise sources. LST analysis predicted significant second mode growth for both Case B and Case I, with mode F being unstable for Case B and mode S being unstable for Case I. Case I was found to be more destabilizing to the second mode, as expected from the reduced nose radius. These LST results are used to validate the unsteady DNS, and to extract receptivity coefficients for the dominant second mode disturbance. The sharpest Case S is also studied using both axisymmetric planar acoustic pulses as well as azimuthally varying, 3-D acoustic pulse disturbances. Unsteady DNS for Case B and Case I show that all of the disturbances excite second mode growth and generally follow the amplification profile predicted by LST. The results for the blunter Case B show much stronger freestream noise effects than for Case I, while Case I seems to be more sensitive to extremely low frequency boundary layer modes associated with upstream disturbances originating in the entropy layer. Additionally, the blunter Case B is observed to have a much stronger supersonic mode, which is qualitiatively observed in acoustic radiation from the boundary layer disturbance wavepacket. This is attributed to the destabilized discrete mode F in Case B which is more capable than the discrete mode S of slowing and becoming supersonic relative to the meanflow. DNS and LST data are used to extract second mode receptivity coefficients and phase spectra for Case B and Case I for application to an iterative transition prediction method. The receptivity coefficients are decomposed from the total surface disturbance by renormalizing the unsteady DNS data with the LST-derived amplifcation rate. Most pulse cases saw the same spectral receptivity coefficient behavior, with peak amplitudes being at the most amplified downstream frequencies. However, the planar fast acoustic pulse in both Case I and Case B was found to excite a much more broadband disturbance profile associated with continuous mode instabilities. This likely necessitates more advanced modal decomposition methods, like the bi-orthogonal decomposition, to cleanly resolve the modes of interest. Additionally, Case I was found to be much more receptive to the temperature and vorticity pulses than Case B while the acoustic responses were fairly similar. This may be due to stronger low frequency upstream forcing that was found in Case I that is associated with entropy layer modes, and indicates differing receptivity mechanisms between the two nose bluntnesses. The receptivity cofficients for Case B and Case I are applied to a simplified 2-D implementation of Mack's amplitude method in an attempt to better approximate the transition location for those cases. Unlike the conventional $e^N$ method, the amplitude method directly estimates disturbance amplitudes in the boundary layer. This requires the use of receptivity data and freestream noise profiles along with other correlations for threshold breakdown amplitudes. The correlations for freestream noise and breakdown amplitude are taken from Marineau(AIAA Journal, 2017). While some improvement is seen over the base accuracy of standard $e^N$ method predictions, the estimated transition locations using the receptivity data from this study are found to still be significantly overpredicted. The Case I results, however, match much more closely with experimental measurements likely due to the stronger second mode. The disagreement with experiment and Marineau's results can be attributed to imprecise correlations of freestream noise and oversimplifications of the original amplitude method relations. True flight conditions will inevitably contain oblique disturbances, whether through local geometry or from the nature of freestream noise. Therefore, while the 2-D second mode disturbance has found to dominate in a large selection of hypersonic flows, consideration of 3-D disturbances is necessary to complete our view of the transition process. To accomplish this a preliminary analysis of both planar 2-D and 3-D azimuthally varying pulse simulations were also run on the small bluntness (1 mm nose radius) Case S. LST analysis of this new case shows an upstream shift in the destabilized second mode positions, as well as higher destabilized frequencies that match expectations for the smaller nose radius. While the peak growthrates were highest for Case S the reduced freestream unit Reynolds number compared to Case B and Case I led to a weaker overall amplification of the second mode in the streamwise direction, as measured by peak N-factor. Freestream fast and slow acoustic pulses were modelled using gaussian distributions in both the streamwise and azimuthal directions. Results for the 2-D pulses demonstrate strong similarities to prior results for Case B and Case I, with the planar fast acoustic pulse inducing strong broadband continuous mode variation while the slow acoustic pulse induced only second mode disturbances. The 3-D azimuthally varying pulses followed a similar pattern, as downstream excitations were primarily isolated to low wavenumber modes in the slow acoustic case. The 3-D fast acoustic pulse is found to also excite a wide range of disturbance frequencies, though excited frequency bands outside of the second mode are generally confined to lower wavenumbers. Disturbances at the second mode frequencies, however, saw little to no decay at higher wavenumbers compared to the 3-D slow acoustic case. This indicates that fast acoustic disturbances are highly capable of exciting both a broad range of disturbance wavenumbers as well as a broad range of disturbance frequencies.

Download or read book Laminar Turbulent Transition in a Hypersonic Boundary Layer Receptivity and Instability Pre History written by and published by . This book was released on 1997 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report results from a contract tasking Moscow Inst. of Physics and Technology as follows: The contractor will perform research in accordance with contractor's proposal entitled, 'Laminar-Turbulent Transition in an Hypersonic Boundary Layer.' This report addresses the initial phase of hypersonic boundary-layer transition comprising excitation of unstable normal modes and their downstream evolution from receptivity regions to the instability growth onset (instability pre-history problem). It is shown that this phase is more complicated than in subsonic and moderate supersonic cases due to the following features of the disturbance field: (1) the first and second modes are synchronized with acoustic waves near the body nose region; (2) further downstream the first mode is synchronized with entropy/vorticity waves; (3) near the instability growth onset the first mode is synchronized with the second mode. Disturbance behavior in the synchronism regions (2) and (3) are studied using the multiple-mode method, which accounts for interaction between modes of discrete and continuous spectrum due to nonparallel effects of the mean flow. It is shown that vorticity/entropy waves are partially swallowed by the boundary layer and effectively generate the first mode due to Synchronism (2). This mechanism can compete with the leading edge receptivity to the freestream acoustic waves in cases of 'quiet' freestream conditions and conical body configurations. The inter-mode exchange rule coupling input and output characteristics of the first and second modes crossing the branch point vicinity was established. Combination of the receptivity estimates related to Synchronism (2) and the inter-mode exchange rule related to Synchronism; (3) allows the evaluation of instability initial amplitudes required for the PSE calculations of the transition onset point.

Download or read book Numerical Simulation of Hypersonic Boundary Layer Receptivity Transient Growth and Transition With Surface Roughness written by and published by . This book was released on 2009 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research is to conduct DNS studies of hypersonic boundary layer receptivity, transient growth and transition with surface roughness. The main approach is to use DNS as a research tool to study the boundary layer receptivity and transient-growth mechanisms in hypersonic flows, including the development of numerical algorithms and parallel computer codes of higher order numerical methods for the simulation of hypersonic flows with surface roughness of finite heights. During the three-year period, we have conducted DNS studies on the hypersonic boundary layer flows over flat plates and blunt cones. A new high-order cut-cell method has been developed for the numerical simulation of hypersonic boundary layer transition with finite height surface roughness. The method has been applied to the numerical simulations of two-dimensional hypersonic flows over a flat plate. Furthermore, the stabilization effect of the surface porous coating over a flat plate is extensively studied by series of numerical simulations. We also collaborate with Prof. Tumin in the University of Arizona to compare numerical and theoretical results on receptivity of a Mach 5.92 flow over a flat plate to wall blowing-suction, and to analyze the nonparallel flow effect.

Download or read book Comments on Hypersonic Boundary layer Transition written by Kenneth F. Stetson and published by . This book was released on 1990 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a survey paper on the subject of hypersonic boundary-layer transition. Part 1 discusses boundary-layer stability theory, hypersonic boundary-layer stability experiments, and a comparison between theory and experiment. Part 2 contains comments on how many configuration and flow parameters influence transition. Part 3 discusses some additional general aspects of transition. Part 4 discusses problems of predicting transition and comments on three prediction methods. Part 5 contains some general guidelines for prediction methodology. Keywords: Boundary layer transition, Boundary layer stability, Hypersonic boundary layers.

Download or read book Receptivity of Hypersonic Non Gradient Boundary Layer to Wall Disturbances written by and published by . This book was released on 1999 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Theoretical analysis of hypersonic boundary-layer receptivity to wall disturbances is conducted using a combination of asymptotic and numerical methods. Excitation of the second-mode waves by distributed and local forcing on the flat plate surface is studied under adiabatic and cooled wall conditions. Analysis addresses receptivity to wall vibrations, periodic suction-blowing through a hole or slot, and temperature disturbances. A strong excitation occurs in local regions where forcing is in resonance with normal waves. It is revealed that the receptivity function tends to infinity as the resonance point tends to the branch point of discrete spectrum that is typical for the cooled wall case. Asymptotic analysis resolves this singularity and provides maximal receptivity levels in the branch-point vicinity. Analytical results are integrated into the computational module providing fast estimates of receptivity levels for different types and shapes of wall forcing. Numerical results indicate extremely high receptivity to vibrations and suction-blowing near the lower neutral branch. Critical amplitudes of local and distributed vibrations are estimated for bypass of the linear stability phase. The theoretical model can be used to predict initial amplitudes of unstable waves in active (ascending) flights accompanied by skin vibrations.

Download or read book Numerical Study of Hypersonic Boundary Layer Transition on a Blunt Body written by Heath B. Johnson and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Viscous Hypersonic Flow written by William H. Dorrance and published by Courier Dover Publications. This book was released on 2017-05-22 with total page 353 pages. Available in PDF, EPUB and Kindle. Book excerpt: Designed for advanced undergraduate and graduate courses in modern boundary-layer theory, this frequently cited work offers a self-contained treatment of theories for treating laminar and turbulent boundary layers of reacting gas mixtures. 1962 edition.

Download or read book Documentation of Two and Three dimensional Hypersonic Shock Wave turbulent Boundary Layer Interaction Flows written by Marvin I. Kussoy and published by . This book was released on 1989 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Direct Numerical Simulations of Hypersonic Boundary Layer Receptivity Using Compact Convex and Combined Schemes written by Kenshi Yamashita and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: