▪ Abstract The recent progress in three-dimensional boundary-layer stability and transition is reviewed. material focuses on the crossflow instability that leads to swept wings rotating disks. Following a brief overview of mechanisms problem, summary important findings 1990s given.

Crossflow-dominated swept-wing boundary layers are known to undergo a highly nonlinear transition process. In low-disturbance environments, the primary instability of these flows consists mainly stationary streamwise vortices that modify mean velocity field and hence stability characteristics layer. The result is amplitude saturation dominant mode strong spanwise modulation unsteady modes. Breakdown not caused by but instead high-frequency secondary shear distorted flow. has been observed in...

Theoretical and direct numerical simulation models of transient algebraic growth in boundary layers have advanced significantly without an adequate, parallel experimental effort. Experiments that feature disturbances excited by high levels freestream turbulence or distributed surface roughness show behavior consistent with optimal-disturbance theories but cannot address the theories’ key predictions concerning decay at specific spanwise wavenumbers. The present experiment seeks to provide...

The role of surface roughness in boundary layers continues to be a topic significant interest, especially with regard how controlled might used delay laminar-to-turbulent transition. Although it may useful for control, large-amplitude itself lead In an effort understand the breakdown mechanics associated roughness, experiments are conducted investigate steady and unsteady disturbances generated by three-dimensional elements whose amplitudes close critical roughness-based Reynolds number Re k...

Recent experiments on transient disturbance growth in boundary layers indicate that disturbances generated by surface roughness undergo suboptimal growth. The implication is the receptivity mechanism governing distribution of energy among continuous spectrum damped Orr–Sommerfeld/Squire modes produces distributions are significantly different from theoretical optimum. Experiments presented here intended to investigate how amplitude and diameter cylindrical elements arranged a spanwise array...

Recent experiments on transient disturbances generated by three-dimensional roughness have used spanwise-periodic arrays of geometrically simple cylindrical elements. Connecting these laboratory to more realistic situations requires the study surfaces with distributed roughness. This is accomplished in this work numerically generating quasi-random rough and manufacturing using rapid-prototyping technology. Measurements that surface creates a Blasius boundary layer are obtained for three test...

Leading edge erosion and roughness accumulation is an issue observed with great variability by wind plant operators, but little understanding of the effect on turbine performance. In tunnels, airfoil models are typically tested standard grit trip tape to simulate effects in field operation, there a lack established relation between measurements tunnel test conditions. A research collaboration lab, academic, industry partners has sought establish method estimate blades that correlates...

No AccessTechnical NotesQuality-Informed Test Design for Wind Tunnel TestingDrew A. Curriston and Edward B. WhiteDrew CurristonUnited States Military Academy, West Point, New York 10997 WhiteUniversity of Texas at Dallas, 75080Published Online:31 Mar 2025https://doi.org/10.2514/1.C038081SectionsRead Now ToolsAdd to favoritesDownload citationTrack citations ShareShare onFacebookXLinked InRedditEmail About References [1] "Assessment Experimental Uncertainty with Application Testing," AIAA...

Quasi-random distributed roughness topologies were produced to transition the boundary layer over an axisymmetric tangent ogive nosecone in hypersonic flow. Surface was accomplished by applying a cylindrical 2D Fourier series triangulated surface of nosetip manner that resembles sand grit roughness. In total, one smooth tip and three rough tips with varying heights 3D-printed examine their effectiveness at transition. The models assessed Infrared (IR) Thermography Focused Laser Differential...

Receptivity of transient disturbances to surface roughness is a complicated phenomenon that governs both initial disturbance amplitudes and features the disturbances’ growth decay throughout boundary layer. The experiments described here use hotwire measurements in Blasius layer obtain detailed information on generated by spanwise-periodic array elements follows disturbances. results indicate energy associated with roughness-induced scales roughness-based Reynolds number, Rek, for values as...

Abstract The cross-flow instability that arises in swept-wing boundary layers has resisted attempts to describe the path from disturbance initiation transition. Following concerted research efforts, surface roughness and free-stream turbulence have been identified as leading providers of initial disturbances for growth. Although a significant body work examines role problem, data more relevant flight environment (turbulence intensities less than 0.07 %) are sparse. A series recent...

Calculations are performed to analyze the stability of steady roughness-induced transient growth unsteady fluctuations. The basic states consist an optimal model and a previously computed direct numerical simulation that fully resolves three-dimensional roughness element. It is shown sub-optimal produced by surface much more susceptible destabilization than perturbation predictions. factors contributing this behavior analyzed in detail. Scaling properties from experiments allow computation...

The Klebanoff-Saric Wind Tunnel is a low-speed, closed-return facility with lowdisturbance flow capabilities suitable for boundary-layer stability and transition studies. Previously known as the Arizona State University (ASU) Transition Facility or ASU Unsteady Tunnel, tunnel was relocated to Texas A&M in 2005. During its subsequent reconstruction, several component modifications were introduced, including more advanced acoustic treatments, pneumatic isolation, duct reshaping, motor-drive...

Wind farm operators observe power production decay over time, with the exact cause unknown and difficult to quantify. A likely explanation is blade surface roughness, as wind turbines are continuously subjected environmental hazards. Difficulty arises in understanding quantifying performance degradation. Historically, turbine airfoil families were designed for lift be insensitive roughness by simulating 2D trip strips. Despite this, still shown negatively affect performance. Experiments have...

A surface roughness model extending the Langtry-Menter transition has been implemented in a RANS framework. The model, originally proposed by Dassler, Kozulovic, and Fiala, introduces an additional scalar field amplification quantity. This value is explicitly set at rough wall boundaries using parameters local flow quantities. transport equation allows non-local effects of to be accounted for downstream sections. variable coupled with used modify criteria transition. Results from flat plate...

Surface roughness can affect boundary layer transition by acting as a receptivity mechanism for transient growth. While experiments have investigated growth of steady disturbances generated discrete elements, very few studied distributed surface roughness. Some work predicts ‘shielding’ effect, where smaller displaces the away from wall and lessens impact larger peaks. This describes an experiment specifically designed to study this effect. Three configurations (a deterministic patch,...

For transition to turbulence in crossflow-dominated swept-wing boundary layers, details of the strongly nonlinear nature stationary primary instability are well understood both experimentally and theoretically. It is particular action nonlinearities that makes possible a control scheme using subcritically spaced leading-edge surface roughness arrays. What desired means by which this can be generalized all cases transition. To end, two elements presented here: experimental examination process...

Many animals locate food, mates and territories by following plumes of attractive odors. There are clear differences in the structure this plume-tracking behavior depending on whether an animal is flying, swimming, walking or crawling. These could arise from different control rules used central nervous system during these modes locomotion one set interacting with environments while surface versus flying swimming. Flow speeds turbulence that characterize where insects track may alter odor...

Predicting the runback threshold for liquid drops in aerodynamic boundary layers is a challenging problem with numerous applications including aircraft icing simulations. The critical parameters that govern drop are investigated this experiment by using wind tunnel provides turbulent accelerated flow similar to flows near an unswept wing’s leading edge. experiments feature water on aluminum contact angle of 70±5deg. Results show significant water∕air interface unsteadiness precedes runback....

Over time it has been reported wind turbine power output can diminish below manufacturers promised levels. This is clearly undesirable from an operator standpoint, and also put pressure on companies to make up the difference. A likely explanation for discrepancy in contamination of leading edge due environmental conditions creating surfaces much coarser than intended. To examine effects airfoil roughness, a comprehensive study performed both experimentally computationally NACA 633 − 418...

Liquid drops adhere to solid surfaces due surface tension but can depin and run back along the wind or gravity forcing. This work develops a simple mechanistic model for depinning by combined high-Reynolds-number forcing tests that using water on roughened aluminum surface. On non-inclined surfaces, at constant critical Weber number, $W\!e_{\mathrm{crit}}=7.9$, present wettability conditions. inclined $W\!e_{\mathrm{crit}}$ decreases linearly with product of Bond number width-to-height...

Abstract : This work completes a series of detailed experiments boundary layers undergoing transition to turbulence with the major effort directed toward most important issue facing understanding fundamental causes transition, i.e., receptivity freestream disturbances. problem is reviewed in detail by Saric et al. (1994). The present concentrates on leading-edge and two-dimensional roughness. effects large-amplitude noise considered determining limits linear receptivity. Single-frequency...