Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer

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Total Pages : 115 pages
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Book Synopsis Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer by : Dale Evan Berg

Download or read book Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer written by Dale Evan Berg and published by . This book was released on 1977 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface roughness and its adjustment to the new surface conditions was examined. Both mean and fluctuating flow properties were acquired for smooth-to-rough and rough-to-smooth surface configurations. (Author).

Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer

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Book Synopsis Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer by :

Download or read book Surface Roughness Effects on the Hypersonic Turbulent Boundary Layer written by and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation of the response of a hypersonic turbulent boundary layer to a step change in surface roughness has been performed. The boundary layer on a flat nozzle wall of a Mach 6 wind tunnel was subjected to abrupt changes in surface roughness and its adjustment to the new surface conditions was examined. Both mean and fluctuating flow properties were acquired for smooth-to-rough and rough-to-smooth surface configurations. The boundary layer was found to respond gradually and to attain new equilibrium profiles, for both the mean and the fluctuating properties, some 10 to 25 delta downstream of the step change. Mean flow self-similarity was the first to establish itself, followed by the mass flux fluctuations, followed in turn by the total temperature fluctuations. Use of a modified Van Driest transformation resulted in good correlations of smooth and rough wall data in the form of the incompressible law of the wall. This is true even in the nonequilibrium vicinity of the step for small roughness heights. The present data are found to correlate well with previously published roughness effect data from low and high speed flows when the roughnesses are characterized by an equivalent sand grain roughness height.

Boundary Layer Transition and Surface Roughness Effects in Hypersonic Flow

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Book Synopsis Boundary Layer Transition and Surface Roughness Effects in Hypersonic Flow by :

Download or read book Boundary Layer Transition and Surface Roughness Effects in Hypersonic Flow written by and published by . This book was released on 1981 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental studies are being conducted to examine the stagnation region heating in transitional flow over blunt nose tips; and the effects of surface roughness on the heat transfer and skin friction to hypersonic re-entry vehicles. Measurements have been made of the distribution of heat transfer and skin friction over sharp and blunted cones to a range of incidences for surface roughness of 0, 10 and 15 mils. These studies have been conducted at a local Mach number of 11.7 and Reynolds numbers based on model length of 30 x million, giving roughness Reynolds numbers from transitional to fully rough over the models. New calorimeter and thin film instrumentation was developed expressly for the rough wall heating measurements. The measurements indicated that while the roughness-induced augmentations in heat transfer and skin friction were less than would be predicted using theories based on low speed data for low R sub k's, close to the nose tip significantly larger augmentation factors were observed. The current studies suggest that significant compressibility effects may be present in hypersonic turbulent boundary layers over rough walls. The models and highly detailed heat transfer and pressure instrumentation have been completed for the stagnation point heating studies. A new and novel throat valve has been developed to eliminate the frangible mylar diaphragm which can cause particles and disturbances during flow establishment in the shock tunnel. The experimental studies are now in progress.

A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers

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ISBN 13 :
Total Pages : 219 pages
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Book Synopsis A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers by : Kahei Danny Fong

Download or read book A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers written by Kahei Danny Fong and published by . This book was released on 2017 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: The current understanding and research efforts on surface roughness effects in hypersonic boundary-layer flows focus, almost exclusively, on how roughness elements trip a hypersonic boundary layer to turbulence. However, there were a few reports in the literature suggesting that roughness elements in hypersonic boundary-layer flows could sometimes suppress the transition process and delay the formation of turbulent flow. These reports were not common and had not attracted much attention from the research community. Furthermore, the mechanisms of how the delay and stabilization happened were unknown. A recent study by Duan et al. showed that when 2-D roughness elements were placed downstream of the so-called synchronization point, the unstable second-mode wave in a hypersonic boundary layer was damped. Since the second-mode wave is typically the most dangerous and dominant unstable mode in a hypersonic boundary layer for sharp geometries at a zero angle of attack, this result has pointed to an explanation on how roughness elements delay transition in a hypersonic boundary layer. Such an understanding can potentially have significant practical applications for the development of passive flow control techniques to suppress hypersonic boundary-layer transition, for the purpose of aero-heating reduction. Nevertheless, the previous study was preliminary because only one particular flow condition with one fixed roughness parameter was considered. The study also lacked an examination on the mechanism of the damping effect of the second mode by roughness. Hence, the objective of the current research is to conduct an extensive investigation of the effects of 2-D roughness elements on the growth of instability waves in a hypersonic boundary layer. The goal is to provide a full physical picture of how and when 2-D roughness elements stabilize a hypersonic boundary layer. Rigorous parametric studies using numerical simulation, linear stability theory (LST), and parabolized stability equation (PSE) are performed to ensure the fidelity of the data and to study the relevant flow physics. All results unanimously confirm the conclusion that the relative location of the synchronization point with respect to the roughness element determines the roughness effect on the second mode. Namely, a roughness placed upstream of the synchronization point amplifies the unstable waves while placing a roughness downstream of the synchronization point damps the second-mode waves. The parametric study also shows that a tall roughness element within the local boundary-layer thickness results in a stronger damping effect, while the effect of the roughness width is relatively insignificant compared with the other roughness parameters. On the other hand, the fact that both LST and PSE successfully predict the damping effect only by analyzing the meanflow suggests the mechanism of the damping is by the meanflow alteration due to the existence of roughness elements, rather than new mode generation. In addition to studying the unstable waves, the drag force and heating with and without roughness have been investigated by comparing the numerical simulation data with experimental correlations. It is shown that the increase in drag force generated by the Mach wave around a roughness element in a hypersonic boundary layer is insignificant compared to the reduction of drag force by suppressing turbulent flow. The study also shows that, for a cold wall flow which is the case for practical flight applications, the Stanton number decreases as roughness elements smooth out the temperature gradient in the wall-normal direction. Based on the knowledge of roughness elements damping the second mode gained from the current study, a novel passive transition control method using judiciously placed roughness elements has been developed, and patented, during the course of this research. The main idea of the control method is that, with a given geometry and flow condition, it is possible to find the most unstable second-mode frequency that can lead to transition. And by doing a theoretical analysis such as LST, the synchronization location for the most unstable frequency can be found. Roughness elements are then strategically placed downstream of the synchronization point to damp out this dangerous second-mode wave, thus stabilizing the boundary layer and suppressing the transition process. This method is later experimentally validated in Purdue's Mach 6 quiet wind tunnel. Overall, this research has not only provided details of when and how 2-D roughness stabilizes a hypersonic boundary layer, it also has led to a successful application of numerical simulation data to the development of a new roughness-based transition delay method, which could potentially have significant contributions to the design of future generation hypersonic vehicles.

Experiments on the Hypersonic Turbulent Shockwave/boundary Layer Interaction and the Effects of Surface Roughness

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Book Synopsis Experiments on the Hypersonic Turbulent Shockwave/boundary Layer Interaction and the Effects of Surface Roughness by : S. A. Prince

Download or read book Experiments on the Hypersonic Turbulent Shockwave/boundary Layer Interaction and the Effects of Surface Roughness written by S. A. Prince and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Effects of Unit Reynolds Number, Nose Bluntness, and Roughness on Boundary Layer Transition

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ISBN 13 :
Total Pages : 166 pages
Book Rating : 4.3/5 (91 download)

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Book Synopsis Effects of Unit Reynolds Number, Nose Bluntness, and Roughness on Boundary Layer Transition by : J. Leith Potter

Download or read book Effects of Unit Reynolds Number, Nose Bluntness, and Roughness on Boundary Layer Transition written by J. Leith Potter and published by . This book was released on 1960 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Condtions encountered in the high Mach number flow regime are show to profoundly affect the longitudinal extent of the boundary layer from beginning to end of transition, the distribution of fluctuation energy in the laminar layer, and effectiveness of surface roughness in promoting transition. A critical layer of intense local energy fluctuations was found at all Mach numbers studied. The existence of such a critical layer is predicted by stability theory. Hot-wire surveys of the laminar, transitional, and turbulent boundary layers are presented to illustrate the critical layer in laminar flow and subsequent development into the transition process. The relation between boundary layer transition on flat plates and cones in supersonic flow is explored and a process for correcting data to account for leading edge bluntness is devised. On the basis of a comparison of data corrected for the effects of leading edge geometry, it is shown that the Reynolds umber of transition on a cone is three times that on a vanishingly thin flate plate. Close agreement between data from various wind tunnels is demonstrated. Study of the effect of finite leading edges yields significant illustrations of the influence of unit Reynolds number on boundary layer transition. A correlation of the effects of surface roughness on transition is achieved. This treatment includes two- and three-dimensional roughness in both subsonic and supersonic streams. At this time only zero pressure gradients have been studied. The entire range of movement of transition from its position with no roughness up to its reaching the roughness element is describable by the procedure give. Examples of application of the correlation results show excellent agreement with experimental data from a variety of sources. Implications concerning tripping hypersonic boundary layers are discussed.

Boundary Layer Transition at Supersonic Speeds

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Total Pages : 108 pages
Book Rating : 4.3/5 (91 download)

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Book Synopsis Boundary Layer Transition at Supersonic Speeds by : E. R. Van Driest

Download or read book Boundary Layer Transition at Supersonic Speeds written by E. R. Van Driest and published by . This book was released on 1961 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments carried out in the 12-inch supersonic wind tunnel to investigate the effect of three dimensional roughness elements (spheres) on boundary-layer transition on a 10-degree (apex angle) cone without heat transfer are described. The local Mach number for these tests was 2.71. The data show clearly that the minimum (effective) size of trip required to bring transition to its lowest Reynolds number varies power of the distance from the apex of the cone to the trip. Use of available data at other Mach numbers indicates that the Mach number influence for effective tripping is taken into account by a simple expression. Some remarks concerning the roughness variation for transition on a blunt body are made. Finally, a general criterion is introduced which gives insight to the transition phenomenon and anticipates effects of external and internal disturbances, Mach number transfer.

The Influence of Surface Roughness on Supersonic High Reynolds Number Turbulent Boundary Layer Flow

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ISBN 13 : 9781423562139
Total Pages : 362 pages
Book Rating : 4.5/5 (621 download)

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Book Synopsis The Influence of Surface Roughness on Supersonic High Reynolds Number Turbulent Boundary Layer Flow by : Robert M. Latin

Download or read book The Influence of Surface Roughness on Supersonic High Reynolds Number Turbulent Boundary Layer Flow written by Robert M. Latin and published by . This book was released on 1998-03-01 with total page 362 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive study of rough-wall high speed (M=2.9) high Reynolds number (Re/m = 1.9. 10 to the 7th power) turbulent boundary layer flow was performed consisting of experimental, analytical, and numerical methods. Six wall topologies consisting of a smooth and five rough surfaces (two and three dimensional machined roughness plates; and 80, 36, and 20 grit sand-grain roughened plates) were studied. A confocal laser scan microscope was used to measure the topography of the sand grain roughnesses. The experimental measurement techniques included a convention Pitot pressure probe, laser Doppler velocimetry, hot wire anemometry; color schlieren and laser sheet Mie scattering images. Mean measurements included velocity, Mach number, density, and mass flux. Turbulent measurements included velocity and mass flux turbulence intensities, kinematic Reynolds shear stress, compressible Reynolds shear stress in two planes, and the traverse apparent mass flux. Kinematic turbulent flow statistical properties were found to scale by local mean quantities and displayed a weak dependence on surface roughness. Turbulent flow statistical properties with the explicit appearance of density did not scale by local mean quantities, and had a strong linear dependence on roughness. Surface roughness also had a significant effect on the flow structure size, angles, and energy spectra. A theoretical analysis was performed and a new integral method for the estimation of skin friction was developed. The skin friction estimates were within 4% of compressible semi-empirical relations. A numerical study was performed which used a parabolized Navier Stokes solver with two algebraic turbulence models and the Rotta model for surface roughness. A new method for the estimation of momentum loss improved the numerical flow predictability.

An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds

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Book Synopsis An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds by : Felix W. Fenter

Download or read book An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds written by Felix W. Fenter and published by . This book was released on 1958 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Effects of Surface Roughness on Boundary Layer Transition in a Hypersonic Flow

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Book Synopsis Effects of Surface Roughness on Boundary Layer Transition in a Hypersonic Flow by : Oliver Taylor

Download or read book Effects of Surface Roughness on Boundary Layer Transition in a Hypersonic Flow written by Oliver Taylor and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds

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ISBN 13 :
Total Pages : 63 pages
Book Rating : 4.:/5 (227 download)

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Book Synopsis An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds by : Felix W. Fenter

Download or read book An Experimental Investigation of the Effects of Several Types of Surface Roughness on Turbulent Boundary Layer Characteristics at Supersonic Speeds written by Felix W. Fenter and published by . This book was released on 1953 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: A theory is described which can be used to predict accurately the skin friction drag of surfaces with uniform grain-type roughness. The roughness does not necessarily have to extend to the leading edge of the surface for an accurate calculation to be made. Uniform surface roughness composed of spherical beads does not affect the boundary layer in a manner significantly different from grain-type roughness, provided that the grains and the spheres are bonded to the surface in a similar manner. Consequently, the theory accurately predicts the effects of spherical roughness elements on skin friction under these conditions. The effect of a given type of roughness on turbulent boundary layer characteristics is strongly dependent upon the density of distribution of the roughness elements. The effect of maximum density V-grooves on turbulent boundary layer characteristics is dependent upon the sweepback angle. The effect of increasing sweepback is to reduce the skin friction drag. (Author).

Roughness Effects on Boundary-layer Transition for Blunt-leading-edge Plates at Mach 6

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ISBN 13 :
Total Pages : 52 pages
Book Rating : 4.:/5 (31 download)

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Book Synopsis Roughness Effects on Boundary-layer Transition for Blunt-leading-edge Plates at Mach 6 by : Paul F. Holloway

Download or read book Roughness Effects on Boundary-layer Transition for Blunt-leading-edge Plates at Mach 6 written by Paul F. Holloway and published by . This book was released on 1966 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Turbulent Boundary Layer Heat Transfer

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ISBN 13 :
Total Pages : 46 pages
Book Rating : 4.:/5 (227 download)

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Book Synopsis Turbulent Boundary Layer Heat Transfer by : Michael L. Finson

Download or read book Turbulent Boundary Layer Heat Transfer written by Michael L. Finson and published by . This book was released on 1981 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Reynolds stress model for turbulent boundary layers is used to study surface roughness effects on skin friction and heat transfer. The issues of primary interest are the influence of roughness character (element shape and spacing) and the nature of roughness effects at high Mach numbers. Computations based on the model compare satisfactorily with measurements from experiments involving variations in roughness character, in low speed and modestly supersonic conditions. The more limited data base at hypersonic Mach numbers is also examined with reasonable success, although no quantitative explanation is offered for the reduction of heat transfer with increasing roughness observed by Holden at Me = 9.4. The present calculations indicate that the mean velocity is approximately uniform over much of the height range below the tops of the elements, y less than or equal to k. With this constant 'roughness velocity, ' it is simple to estimate the form drag on the elements. This roughness velocity has been investigated by systematically exercising the present model over ranges of potential parameters. The roughness velocity is found to be primarily a function of the projected element frontal area per unit surface area, thus providing a new and simple method for predicting roughness character effects. The model further suggests that increased boundary layer temperatures should be generated by roughness at high edge Mach numbers, which would tend to reduce skin friction and heat transfer, perhaps below smooth wall levels. (Author).

Study of Turbulent Boundary Layers Over Rough Surfaces, with Emphasis on the Effects of Roughness Character and Mach Number

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ISBN 13 :
Total Pages : 73 pages
Book Rating : 4.:/5 (227 download)

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Book Synopsis Study of Turbulent Boundary Layers Over Rough Surfaces, with Emphasis on the Effects of Roughness Character and Mach Number by : M. L. Finson

Download or read book Study of Turbulent Boundary Layers Over Rough Surfaces, with Emphasis on the Effects of Roughness Character and Mach Number written by M. L. Finson and published by . This book was released on 1982 with total page 73 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Reynolds stress model for turbulent boundary layers on rough walls is used to investigate the effects of roughness character and compressibility. The flow around roughness elements is treated as form drag. A method is presented for deriving the required roughness shape and spacing from profilometer surface measurements. Calculations based on the model compare satisfactorily with low speed data on roughness character and hypersonic measurements with grit roughness. The computer model is exercised systematically over a wide range of parameters to derive a practical scaling law for the equivalent roughness. In contrast to previous correlations, for most roughness element shapes the effective roughness is not predicted to show a pronounced maximum as the element spacing decreases. The effect of roughness tends to be reduced with increasing edge mach number, primarily due to decreasing density in the vicinity of the roughness elements. It is further shown that the required roughness Reynolds number for fully rough behavior increases with increasing Mach number, explaining the small roughness effects observed in some hypersonic tests. (Author).

Roughness, Bluntness, and Angle of Attack Effects on Hypersonic Boundary Layer Transition

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ISBN 13 :
Total Pages : 55 pages
Book Rating : 4.:/5 (227 download)

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Book Synopsis Roughness, Bluntness, and Angle of Attack Effects on Hypersonic Boundary Layer Transition by : H. T. Nagamatsu

Download or read book Roughness, Bluntness, and Angle of Attack Effects on Hypersonic Boundary Layer Transition written by H. T. Nagamatsu and published by . This book was released on 1964 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: An investigation was conducted in a hypersonic shock tunnel to study the laminar boundary layer transition on a highly cooled 10-degree cone of 4-foot length over the Mach number range of 8.5 to 10.5 with a stagnation temperature of 1400K. The effects on transition of tip surface roughness, tip bluntness, and =2-degree angle of attack were investigated. With fast response thin film surface heat transfer gauges, it was possible to detect the passage of turbulent bursts that appeared at the beginning of transition. It was found that the surface roughness greatly promoted transition in the proper Reynolds number range. The Reynolds number for the beginning and end of transition at the 8.5 Mach number location were 3,800,000 to 9,600,000 and 2,200,000 to 4,200,000 for the smooth sharp tip and rough sharp tip, respectively. The local skin friction data agreed with the heat transfer data through Reynolds analogy. The tip bluntness data showed a strong delay in the beginning of transition for a cone base to tip diameter ratio of 20, approximately a 35% increase in Reynolds number over that of the smooth sharp tip case. The angle of attack data indicated the cross flow to have a strong influence on transition by promoting it on the sheltered side of the cone and delaying it on the windward side. (Author).

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

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ISBN 13 :
Total Pages : 194 pages
Book Rating : 4.:/5 (129 download)

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Book Synopsis Attenuation of Hypersonic Second Mode Instability with Discrete Surface Roughness on Straight Blunt Cones by : Christopher Haley

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.

Effect of Distributed Three-dimensional Roughness and Surface Cooling on Boundary-layer Transition and Lateral Spread of Turbulence at Supersonic Speeds

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Total Pages : 48 pages
Book Rating : 4.:/5 (317 download)

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Book Synopsis Effect of Distributed Three-dimensional Roughness and Surface Cooling on Boundary-layer Transition and Lateral Spread of Turbulence at Supersonic Speeds by : Albert L. Braslow

Download or read book Effect of Distributed Three-dimensional Roughness and Surface Cooling on Boundary-layer Transition and Lateral Spread of Turbulence at Supersonic Speeds written by Albert L. Braslow and published by . This book was released on 1959 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: