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Book Direct Numerical Simulation and Experimental Validation of Hypersonic Boundary layer Receptivity and Instability

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.

Book Attenuation of Hypersonic Second Mode Instability with Discrete Surface Roughness on Straight Blunt Cones

Download or read book Attenuation of Hypersonic Second Mode Instability with Discrete Surface Roughness on Straight Blunt Cones written by Christopher Haley and published by . This book was released on 2021 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hypersonic boundary layer research has studied surface features, such as isolated or distributed roughness, extensively for turbulence tripping. However, there are reports of a counterintuitive phenomenon within the literature whereby surface roughness can delay the onset of laminar-turbulent transition. The reports did not attract widespread attention, leaving the phenomenon's underlying mechanism uninvestigated for several decades. A renewed interest in boundary layer control strategies motivated Fong and Zhong in 2012 to conduct an extensive numerical study on what has been termed the ``roughness effect''. The research found that roughness elements immersed within the boundary layer and placed at the synchronization location for a particular unstable frequency can attenuate higher unstable frequencies while amplifying lower unstable frequencies. Thus, providing a passive means to delay laminar-turbulent transition with discrete surface roughness. However, these previous numerical investigations are limited to a flat plate geometry, 2-D spanwise roughness, limited in the scope of their freestream Mach number, and focus exclusively on Mack's second mode instability. In order to advance our knowledge of the roughness effect, the objectives of this dissertation are fourfold: (1) To investigate the roughness effect on a straight blunt cone geometry, (2) To investigate the long-term downstream consequences of the roughness effect, (3) Provide experimental evidence of second mode attenuation in a flow with a growing boundary layer containing a range of unstable frequencies, and the consequences of off-design flow conditions, and (4) To investigate the appearance of the supersonic mode in a low-enthalpy warm wall flow of the current study. A combined approach of direct numerical simulation, body-fitted surface roughness, and linear stability theory are used to numerically investigate the roughness effect. Four cases are computed as part of the research objective. Case C.1 is a Mach 8 flow computed for the design of a passive transition-delaying roughness configuration, along with studying the roughness effect on a straight blunt cone. Case C.1-Ext is a longer cone simulation of C.1 and is computed to investigate the long-term downstream response of the roughness effect. C.2 is similar to C.1 except for a smaller nose radius and is computed for experimental validation. The last case, C.3, is a Mach 5 flow and is computed to study the roughness effect on a straight blunt cone in off-design flow conditions and for experimental validation. The first objective to investigate the roughness effect on a straight blunt cone advances the research from a flat plate to more realistic test article geometries. Much of the experimental work done in hypersonic boundary layer stability research is done on straight cones due to the axisymmetric flows in hypersonic wind tunnels. The investigation found that the roughness effect behaves like a flat plate where unstable frequencies higher than the synchronization frequency are attenuated, and lower frequencies are amplified. The investigation also found that some flow features around the roughness elements, such as separation zones, are either smaller in size or absent in conical flow fields. The investigation also confirmed that the second mode's attenuation is a result of the element's proximity to the synchronization location and not due to its proximity with the branch I/II neutral points. The long-term downstream effect of second mode attenuation is also investigated for a single roughness and roughness array. The numerical investigation found that the range of targeted frequencies is attenuated as expected, especially for the roughness array, which proves to be effective at attenuating unstable frequencies over a longer distance. However, the amplitudes of frequencies below the targeted range grow many times higher than they would have otherwise on a cone with no roughness. The passive transition-delaying control strategy, rather than dissipating the disturbance energy, acts to transfer the energy to lower unstable frequencies, guaranteeing eventual turbulent transition. The result demonstrates that roughness must be applied to the entire cone to have an effective control strategy. The experimental results in this dissertation come from a joint numerical and experimental investigation of transition-delaying roughness with Dr. Katya Casper at Sandia National Laboratories. A numerical simulation is undertaken to design a surface roughness array that would attenuate Mack's second mode instability and maintain laminar flow over a Mach 8 hypersonic blunt cone. Multiple experimental runs at the Mach 8 condition with different Reynolds numbers are performed, as well as an off-design Mach 5 condition. The roughness array successfully delays transition in the Mach 8 case as intended but does not delay transition in the Mach 5 case. For validation and further analysis, numerical cases C.2 and C.3 are computed using the Mach 8 and Mach 5 experimental flow conditions. Stability analysis of case C.2 shows that the roughness array is adequately designed to attenuate the second mode. Analysis of case C.3 reveals the Mach 5 boundary layer is dominated by Mack's first mode instability and is not attenuated by the array. This investigation of multiple flow conditions combined with experimental results helps validate the numerical code and provides empirical evidence for the roughness effect. While investigating transition delaying surface roughness, acoustic-like waves are observed emanating from the boundary layer of case C.1-Ext. The acoustic-like wave emissions are qualitatively similar to those attributed to the supersonic mode. However, the supersonic mode responsible for such emissions is often found in high-enthalpy flows with highly cooled walls, making its appearance in a flow with relatively low freestream enthalpy and a warm wall unexpected. Stability analysis on the steady-state solution reveals an unstable mode S with a subsonic phase velocity and a stable mode F whose mode F- branch takes on a supersonic phase velocity. The stable supersonic mode F is thought to be responsible for the acoustic-like wave emissions. Unsteady simulations are carried out using blowing-suction actuators at two different surface locations. Analysis of the temporal data and spectral data reveals constructive/destructive interference occurring between a primary and a satellite wave packet in the vicinity of the acoustic-like wave emissions, which has a damping effect on individual frequency growth. Based on this study's results, it is concluded that a supersonic discrete mode is not limited to high-enthalpy, cold wall flows and that it does appear in low-enthalpy, warm wall flows; however, the mode is stable.

Book Numerical Study of Freestream Waves Receptivity and Nonlinear Breakdown in Hypersonic Boundary Layer

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.

Book Direct Numerical Simulation of Gortler Instability in Hypersonic Boundary Layers

Download or read book Direct Numerical Simulation of Gortler Instability in Hypersonic Boundary Layers written by Chong W. Whang and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Numerical Simulation of Hypersonic Boundary Layer Receptivity Transient Growth and Transition With Surface Roughness

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.

Book Numerical Study of Hypersonic Boundary Layer Receptivity and Stability with Freestream Hotspot Perturbations

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.

Book Hypersonic Shock Wave Turbulent Boundahb

Download or read book Hypersonic Shock Wave Turbulent Boundahb written by KNIGHT and published by IOP ebooks. This book was released on 2023-06-29 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive exposition of hypersonic turbulent boundary layers including the fundamental mathematical theory, structure of equilibrium boundary layers, and extensive surveys of Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and experiments.

Book Direct Numerical Simulation and Linear Analysis of Stability of Nonequilibrium Hypersonic Boundary Layers

Download or read book Direct Numerical Simulation and Linear Analysis of Stability of Nonequilibrium Hypersonic Boundary Layers written by and published by . This book was released on 1998 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this research project is to develop new advanced numerical methods and to perform direct numerical simulation (DNS) studies of transient hypersonic reacting flows over full 3-D maneuvering vehicles. The DNS tools and supporting theoretical approaches are used to gain new fundamental understanding of transition phenomena of 3-D chemically-reacting hypersonic boundary layers. Our research accomplishments in the report period can be classified into three areas. First, we have developed and validated new efficient and high-order accurate numerical methods for the DNS of 3-D hypersonic reacting boundary layers. The new methods include high-order semi-implicit Runge-Kutta schemes and new upwind high-order finite-difference shock-fitting schemes. These new methods were developed in order to overcome the difficulties associated with the DNS of hypersonic reacting flows with shock waves. Second, we have conducted extensive studies on the stability and receptivity phenomena of hypersonic boundary layers over blunt leading edges and elliptical cross-section blunt cones both by direct numerical simulation and by linear stability analyses. Third, the effects of using Burnett equations for rarefied hypersonic flow computations were investigated.

Book Effects of Thermochemical Nonequilibrium on Hypersonic Boundary Layer Instability in the Presence of Surface Ablation Or Isolated Two Dimensional Roughness

Download or read book Effects of Thermochemical Nonequilibrium on Hypersonic Boundary Layer Instability in the Presence of Surface Ablation Or Isolated Two Dimensional Roughness written by Clifton Mortensen and published by . This book was released on 2015 with total page 251 pages. Available in PDF, EPUB and Kindle. Book excerpt: The current understanding of the effects of thermochemical nonequilibrium on hypersonic boundary-layer instability still contains uncertainties, and there has been little research into the effects of surface ablation, or two-dimensional roughness, on hypersonic boundary-layer instability. The objective of this work is to study the effects of thermochemical nonequilibrium on hypersonic boundary-layer instability. More specifically, two separate nonequilibrium flow configurations are studied: 1) flows with graphite surface ablation, and 2) flows with isolated two-dimensional surface roughness. These two flow types are studied numerically and theoretically, using direct numerical simulation and linear stability theory, respectively. To study surface ablation, a new high-order shock-fitting method with thermochemical nonequilibrium and finite-rate chemistry boundary conditions for graphite ablation is developed and validated. The method is suitable for direct numerical simulation of boundary-layer transition in a hypersonic real-gas flow with graphite ablation. The new method is validated by comparison with three computational data sets and one set of experimental data. Also, a thermochemical nonequilibrium linear stability theory solver with a gas phase model that includes multiple carbon species, as well as a linearized surface graphite ablation model, is developed and validated. It is validated with previously published linear stability analysis and direct numerical simulation results. A high-order method for discretizing the linear stability equations is used which can easily include high-order boundary conditions. The developed codes are then used to study hypersonic boundary-layer instability for a 7 deg half angle blunt cone at Mach 15.99 and the Reentry F experiment at 100~kft. Multiple simulations are run with the same geometry and freestream conditions to help separate real gas, blowing, and carbon species effects on hypersonic boundary-layer instability. For the case at Mach 15.99, a directly simulated 525~kHz second-mode wave was found to be significantly unstable for the real-gas simulation, while in the ideal-gas simulations, no significant flow instability is seen. An N factor comparison also shows that real-gas effects significantly destabilize the flow when compared to an ideal gas. Blowing is destabilizing for the real gas simulation and has a negligible effect for the ideal gas simulation due to the different locations of instability onset. Notably, carbon species resulting from ablation are shown to slightly stabilize the flow for both cases. For the Reentry F flow conditions, inclusion of the ablating nose cone was shown to increase the region of second mode growth near the nose cone. Away from the nose cone, the second mode was relatively unaffected. Experimental and numerical results have shown that two-dimensional surface roughness can stabilize a hypersonic boundary layer dominated by second-mode instability. It is sought to understand how this physical phenomenon extends from an airflow under a perfect gas assumption to that of a flow in thermochemical nonequilibrium. To these ends, a new high-order shock-fitting method that includes thermochemical nonequilibrium and a cut-cell method, to handle complex geometries unsuitable for structured body-fitted grids, is presented. The new method is designed specifically for direct numerical simulation of hypersonic boundary-layer transition in a hypersonic real-gas flow with arbitrary shaped surface roughness. The new method is validated and shown to perform comparably to a high-order method with a body-fitted grid. For a Mach 10 flow over a flat plate, a two-dimensional roughness element was found to stabilize the second mode when placed downstream of the synchronization location. This result is consistent with previous results for perfect-gas flows. For a Mach 15 flow over a flat plate, a two-dimensional surface roughness element stabilizes the second-mode instability more effectively in a thermochemical nonequilibrium flow, than in a corresponding perfect gas flow.

Book Hypersonic Boundary Layer Stability Experiments in a Quiet Wind Tunnel with Bluntness Effects

Download or read book Hypersonic Boundary Layer Stability Experiments in a Quiet Wind Tunnel with Bluntness Effects written by Jason Thomas Lachowicz and published by . This book was released on 1996 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Numerical Study of Hypersonic Boundary Layer Receptivity Characteristics Due to Freestream Pulse Waves

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.