The Effect of Distributed Surface Roughness on Laminar Flow

Doenhoff, Albert E Von; Braslow, Albert L

doi:10.1016/b978-1-4832-1323-1.50005-1

Cited by 109 publications

(51 citation statements)

References 3 publications

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“…The implication is that at high Rek's transition occurs as the result of an instability of the distorted, reversed flow in the roughness element's wake that requires some finite distance to develop. Other key findings of the early transition correlation work are that Rekcrit scales roughly as (k/d) 2 / 5 meaning that transition 54 occurs for progressively lower Rek,crit values as the roughness diameter is increased (von Doenhoff and Braslow 1961;Tani 1969) and that elements in spanwise arrays behave as isolated elements when their spacing is three times their diameter or larger (von Doenhoff and Braslow 1961).…”

Section: Review Of Experiments On Isolated Surface Roughness Effectsmentioning

confidence: 99%

“…The historical literature on the effects of 3-D surface roughness in boundary layers is extensive but most of this work concerns roughness-induced breakdown that occurs at high roughness-based Reynolds numbers and does not directly address instability mechanisms (see reviews by Dryden 1959;Smith and Clutter 1959;Tani 1961;von Doenhoff andBraslow 1961 andTani 1969). More modern experiments on subcritical surface roughness by Reshotko and Leventhal (1981), Kendall (1981) and others sought evidence that roughness leads to accelerated transition by destabilizing steady boundary-layer profiles to Tollmien-Schlichting waves but were unsuccessful.…”

Section: Spatial Transient Growth In Glasius Boundary Layers: Theory mentioning

confidence: 99%

“…By "more critical" it is meant that that as Rekcrit is exceeded the transition location moves forward very rapidly but that below Rekcrit, an isolated 3D element has little or no effect on transition (Dryden 1959;Smith and Clutter 1959;Tani 1961;von Doenhoff and Braslow 1961;Tani 1969;Sedney 1973). This is quite different than the behavior of boundary layers with 2D roughness that tend to show transition gradually moving forward with increasing Rek.…”

Section: Review Of Experiments On Isolated Surface Roughness Effectsmentioning

confidence: 99%

“…Prior to the development of transient growth theory the role of isolated and distributed 3D roughness has not been as well understood on a theoretical basis because the stationary, spanwise varying disturbances created by 3D roughness are not unstable within the context of a normal-mode stability analysis (Reshotko 2001). Typically, transition in the wake of isolated 3D roughness elements is predicted using correlations based on a critical roughness-based Reynolds number, Rekcrit, established in the 1950's (Dryden 1959;Smith and Clutter 1959;Tani 1961;von Doenhoff and Braslow 1961;Tani 1969;Sedney 1973). Within the context of the correlation approach, if a roughness element exceeds Rek,crt transition is expected to occur at or just aft of the roughness element but if the critical value is not exceeded then no effect is expected.…”

Section: Unsteady Disturbances and Bypass Transitionmentioning

confidence: 99%

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Experiments in Transient Growth and Roughness-Induced Bypass Transition

White¹

2005

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SummaryThe work reported here is a series of wind-tunnel experiments that establishes the basic behavior of roughness-induced disturbances that undergo transient algebraic growth in a laminar boundary layer. The experiments explore three aspects of these disturbances' behavior: their fundamental response to various configurations of surface roughness, their receptivity, and their behavior when the surface roughness amplitude is large. The experiments consist of hotwire measurements of the steady and unsteady disturbances created by isolated 3D roughness elements, spanwise arrays of 3D elements and patches of random, distributed roughness. Spanwise roughness arrays are used most extensively as these are found to produce disturbances best-suited for comparison with theoretical predictions.The results establish that surface roughness does create disturbances that undergo transient growth and that it does so in a manner consistent with the physical picture known as Landahl's lift-up mechanism. The observed growth is qualitatively similar to what is predicted by optimal-disturbance theory. However, theoretical predictions tend to overestimate the length over which disturbances grow and are thought to overestimate the total amount of transient growth.The difference between what is predicted by optimal disturbance theories and what is observed in the experiments is linked to receptivity. Receptivity is found to play two roles in the transient growth phenomenon: it determines initial disturbance amplitude and also distributes energy among the modes of the continuous disturbance spectrum. This second effect is associated with the initial-value-problem formulation of the transient growth problem and explains why some disturbances grow and decay in a manner very similar to what is predicted by optimal-disturbance theory while others only decay and others undergo a significant decay and then a weak phase of transient growth. Regardless of whether certain disturbances undergo transient growth or not, all of the roughness-induced disturbances studied in this experiment have energies that scale approximately as the square of roughness-based Reynolds number across a wide range of Reynolds numbers. At high values of the roughness-based Reynolds number (above approximately 250) transition occurs just aft of the arrays of 3D roughness elements. This transition does not appear to be connected with transient growth. Rather, it occurs because the element's wakes are unstable to a high-frequency Kelvin-Helmoholtz type instability mechanism. Transient growth of steady disturbances only occurs if this rapid transition connected with the unsteady disturbances does not occur.

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Section: Review Of Experiments On Isolated Surface Roughness Effectsmentioning

confidence: 99%

Section: Spatial Transient Growth In Glasius Boundary Layers: Theory mentioning

confidence: 99%

Section: Review Of Experiments On Isolated Surface Roughness Effectsmentioning

confidence: 99%

Section: Unsteady Disturbances and Bypass Transitionmentioning

confidence: 99%

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Experiments in Transient Growth and Roughness-Induced Bypass Transition

White¹

2005

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“…Therefore the instability features had to be related to model roughness rather than to fixed features of the freestream flow generated by nonuniformities of the screens or other effects. Juillen & Arnal (1990) find that for isolated roughness elements the von Doenhoff & Braslow (1961) correlation that describes the limit for bypass transition is correct.…”

Section: Receptivitymentioning

confidence: 99%

Control of Transition in Swept-Wing Boundary Layers Using MEMS Devices as Distributed Roughness

Saric¹

1997

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REPORT DOCUMENTATION PAGEForm Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSOR/MONITOR'S ACRONYM(S) DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution is unlimited SPONSOR/MONITOR'S REPORT NUMBER(S)13. SUPPLEMENTARY NOTES 06414. ABSTRACT ~~ " Active flow control using MEMS-based microactuators holds tremendous promise for achieving laminar flow control and drag reduction for a wide class of aircraft. In order to achieve effective control it is necessary to have a complete understanding of the fundamental instability processes that apply to a particular boundary layer and to develop a sensor and actuator system that is capable of providing an appropriate control input to that boundary layer. In the present work, crossflow-dominated swept-wing boundary layers are the primary interest These boundary layers are known to undergo a highly nonlinear transition process that involves, in low-disturbance environments stationary waves of longitudinal vorticity. These stationary waves have to potential to be controlled or suppressed by an appropriate surface roughness configurations that could be provided by MEMS-based actuators. The work performed here consists of a parallel experimental and hardware development efforts. The breakdown phase of the crossflow instability is investigated in the experiments in an effort to determine an appropnate control input. A MEMS-based roughness actuator system is developed to provide controlled roughness inputs The results of the experimental phase conclusively demonstrate that the destabilization of a high-frequency secondary instability is responsible or breakdown The MEMS development effort did not produce a useful control device because of certain shortcomings in the present state of MEMS fabrication quality control and overall system integration. SUBJECT TERMS AbstractActive flow control using MEMS-based microactuators holds tremendous promise for achieving laminar flow control and drag reduction for a wide class of aircraft. In order to achieve effective control it is necessary to have a complete understanding of the fundamental instability processes that apply to a particular boundary layer and to develop a sensor and actuator system that is capable of providing an appropriate control input to that boundary layer. In the present work, crossflow-dominated swept-wing boundary layers are the primary interest. These boundary layers are known to undergo a highly nonlinear transition process that involves, in low-disturbance environments, stationary waves of longitudinal vorticity. ...

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Numerical and experimental studies on laminar flow control

Arnal

1999

Int. J. Numer. Meth. Fluids

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The Effect of Distributed Surface Roughness on Laminar Flow

Cited by 109 publications

References 3 publications

Experiments in Transient Growth and Roughness-Induced Bypass Transition

Experiments in Transient Growth and Roughness-Induced Bypass Transition

Control of Transition in Swept-Wing Boundary Layers Using MEMS Devices as Distributed Roughness

Numerical and experimental studies on laminar flow control

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