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Understanding, modeling and control of the high-speed wall-bounded transition and turbulence not only receive wide academic interests but also are vitally important for high-speed vehicle design and energy saving because transition and turbulence can induce significant surface drag and heat transfer. The high-speed flows share some fundamental similarities with the incompressible counterparts according to Morkovin’s hypothesis, but there are also significant distinctions resulting from multi-physics coupling with thermodynamics, shocks, high-enthalpy effects, and so on. In this paper, the recent advancements on the physics and modeling of high-speed wall-bounded transitional and turbulent flows are reviewed; most parts are covered by turbulence studies. For integrity of the physical process, we first briefly review the high-speed flow transition, with the main focus on aerodynamic heating mechanisms and passive control strategies for transition delay. Afterward, we summarize recent encouraging findings on turbulent mean flow scaling laws for streamwise velocity and temperature, based on which a series of unique wall models are constructed to improve the simulation accuracy. As one of the foundations for turbulence modeling, the research survey on turbulent structures is also included, with particular focus on the scaling and modeling of energy-containing motions in the logarithmic region of boundary layers. Besides, we review a variety of linear models for predicting wall-bounded turbulence, which have achieved a great success over the last two decades, though turbulence is generally believed to be highly nonlinear. In the end, we conclude the review and outline future works. [ABSTRACT FROM AUTHOR]

With continuous expansion of flight speed and altitude domains, the high-temperature gas effects, especially the thermochemical non-equilibrium (TCNE) effects in hypersonic high-enthalpy boundary layers invalidated the calorically perfect gas (CPG) assumption. They can also largely influence the flow transition process. In recent years, the emergence of unstable supersonic modes in the downstream region of the second mode has been conerned. The so-called supersonic mode refers to the mode with a relative Mach number greater than one at the boundary layer edge, that is, a sound wave that propagates faster than that in the far field. Linear parabolized stability equations (PSE) theory was used to study the critical wall temperature of the supersonic mode under the condition of sharp wedge winding with Mach number 20 and half top angle of 6°. It is found that the lower the wall temperature, the more prone to unstable supersonic mode appeared. Furthermore, the supersonic mode situation and disturbance development form under different Mach number conditions in the flow of the plate boundary layer were explored. It is found that the Mach number continues to increase, the earlier the se-cond mode appears, the maximum growth rate of the second mode decreases, and the peak value of N decreases. At a speci-fic altitude of 30 km, when the Mach number exceeds a certain critical value, the disturbance growth rate and the development form of the supersonic mode are significantly different.

To improve the drag reduction performance of underwater vehicles, a skin composed of a porous compliant wall and micro floating raft elements is proposed. A two-dimensional stability model of boundary-layer flow over the compliant skin is established, and the effect of structural parameters on the flow stability is investigated. It is found that enlarging the spacing l attenuates the Tollmien-Schlichting Instability (TSI) mode but promotes the occurrence of the Compliance-Induced Flow Instability (CIFI) mode, while the permeability coefficient a presents an opposite effect on the instability modes. Moreover, the CIFI mode is stabilised by increasing the stiffness ratio β, damping ratio γ and intermediate mass m, within limits. The skin proposed in this paper with specific parameters can better reduce the arising of TSI and CIFI modes in boundary-layer flow compared with the corresponding rigid and compliant walls, leading to a favourable performance for delaying boundary-layer transition. [ABSTRACT FROM AUTHOR]

Abstract The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities. In this work, the oblique-mode breakdown, as one of the most available transition mechanisms, is studied using the nonlinear parabolized stability equations (NPSE) with consideration of the thermal-chemical non-equilibrium effects. The flow over a blunt cone is computed at a free-stream Mach-number of 15. The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture. It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient. In comparison to the CPG flow, the TCNE effects destabilize the second mode and push upstream the N factor envelope. The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves.

Analysis of screen‐level and land‐surface temperature forecasts are known to have long‐standing warm nighttime, and cold daytime, temperature biases in regional models. During a record‐breaking spring and subsequent summer in 2020, over 100 radiosondes were launched at the Met Office Cardington site under clear skies on ten morning and one evening transitions. We compare observations with operational Met Office UKV forecasts and a standalone land‐surface model (JULES). Wind profiles show the UKV nocturnal jet was too high, suggesting too much mixing in the modelled boundary layer. The simulated nighttime surface inversion was too weak and the profile too cold immediately above the inversion. The radiosondes were in addition to comprehensive long‐term observations. The evapotranspiration was too large on a seasonal timescale for both the UKV and JULES. For spring and summer, UKV mean screen temperature errors were −0.2 ± 1.3∘C during daytime and 1.3 ± 1.9∘C at night. The soil temperature diurnal range was too large in both the UKV (by 3.9°C) and JULES (2.9°C), suggesting the surface is too highly coupled to the soil in the simulations. For the spring experimental days, UKV mean maximum screen temperature error was −0.8 ± 0.4∘C. The buoyancy‐flux crossover times in the morning were slightly too early in the UKV (18 min on average) yet much earlier in JULES (52 min). Observations show the diagnosed boundary layer lifts too early in the UKV with onset of convection occurring on average 67 min too early. The UKV develops summertime boundary layers that are too deep by early afternoon. There was a time lag between the observed screen‐skin temperature and buoyancy‐flux crossovers in the morning that was not captured by the simulations. The evening buoyancy‐flux crossovers in JULES agreed well with the observations, but the UKV crossovers were on average 55 min too early. [ABSTRACT FROM AUTHOR]

The effect of sharp forward-facing steps on boundary-layer transition is systematically investigated in this work in combination with the influence of variations in Mach number, Reynolds number and streamwise pressure gradient. Experiments have been conducted in a quasi-two-dimensional flow at Mach numbers up to 0.77 and chord Reynolds numbers up to 13 million in the Cryogenic Ludwieg-Tube Göttingen. The adopted experimental set-up allows an independent variation of the aforementioned parameters and enables a decoupling of their respective effects on the boundary-layer transition, which has been measured accurately and non-intrusively by means of a temperature-sensitive paint. The functional relations determined between a non-dimensional transition parameter and the non-dimensional step parameters allow the step effect on transition to be isolated from the influence of variations in Mach number, Reynolds number and pressure gradient. Criteria for acceptable heights of forwardfacing steps on natural laminar flow surfaces for the examined test conditions are derived from the present functional relations. The measured transition locations are also correlated with the results of linear, local stability analysis for the smooth configuration, enabling the estimation of the step-induced increment of the amplification factor eN of Tollmien-Schlichting waves, which can be incorporated in the eN transition prediction method. [ABSTRACT FROM AUTHOR]

The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities. In this work, the oblique-mode breakdown, as one of the most available transition mechanisms, is studied using the nonlinear parabolized stability equations (NPSE) with consideration of the thermal-chemical non-equilibrium effects. The flow over a blunt cone is computed at a free-stream Mach-number of 15. The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture. It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient. In comparison to the CPG flow, the TCNE effects destabilize the second mode and push upstream the N factor envelope. The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves. [ABSTRACT FROM AUTHOR]

The wavy wall surface has been reported to be effective in suppressing the growth of second mode instability waves in hypersonic boundary layer, while the allocation of wavy wall relative to the synchronization point requires further study. Upon this work experimental investigation of hypersonic boundary layer instability with wavy wall located downstream of synchronization point based on 7° half-angle sharp cone at zero angle of attack was carried out in a hypersonic noisy wind tunnel. The evolution of instability waves with wavy wall surface is measured using both surface-mounted pressure fluctuation sensors and focused laser differential interferometer (FLDI). The results reveal that the growth of instability waves has been enhanced significantly when the wavy wall region is allocated downstream of the synchronization point when the wavy wall height is slightly smaller than the local boundary layer thickness. Additionally, second mode instability waves are observed at both crests and troughs within the wavy wall region based on the FLDI measurement and moreover, the high-frequency instability waves measured in the separation bubbles of troughs are speculated to be the transmission of second mode instability waves from the shear layer, rather than the local generation of second mode instability. [ABSTRACT FROM AUTHOR]

Results of a computational study are discussed which investigate roughness-induced and geometry-induced (confinement) effects on the steady-state velocity components in 3-D boundary-layer flow over the rotor disc in a rotor–stator flow configuration. It is found that, for the rotor–stator flow investigated, the roughness-induced effects are very similar to geometry-induced effects, both in nature and magnitude. The overall aim was to compare these two types of effects with corresponding roughness-induced effects in the von Kármán boundary-layer flow over a disc spinning freely in an unrestricted fluid environment. The research was conducted in the context of a programme investigating surface roughness as a means of laminar flow control for the development of new passive drag-reduction techniques. The goal was to establish whether it was possible unequivocally to distinguish between roughness-induced and geometry-induced effects on the boundary-layer flow above the rotor disc. The results obtained suggest that, for the type of system discussed here, it must be expected to be difficult to distinguish between these effects in experiments. The similarities regarding the nature and magnitude of results obtained from comparing predictions for three different computational modelling approaches indicate the required sensitivity of measurement technologies aiming to resolve the investigated effects in experimental studies.

A measuring method to detect wall flow topologies by active infrared thermography was developed. Quadcopter rotor blades were studied in typical hover and forward flight conditions, while using a high-power infrared laser to heat the blade surface. By this, the distance between heat source and measuring object could be significantly increased compared to conventional heat sources. The resulting images show little blurring at high signal-to-noise ratios. In steady-state flow conditions, wall flow topologies could be detected reliably and show good agreement with performed oil-film interferometry measurements. Wind tunnel experiments at forward flight conditions were conducted and indicate unsteady shifts of the transition location.

Knowledge about laminar−turbulent transition on operating multi megawatt wind turbine (WT) blades needs sophisticated equipment like hot films or microphone arrays. Contrarily, thermographic pictures can easily be taken from the ground, and temperature differences indicate different states of the boundary layer. Accuracy, however, is still an open question, so that an aerodynamic glove, known from experimental research on airplanes, was used to classify the boundary-layer state of a 2 megawatt WT blade operating in the northern part of Schleswig-Holstein, Germany. State-of-the-art equipment for measuring static surface pressure was used for monitoring lift distribution. To distinguish the laminar and turbulent parts of the boundary layer (suction side only), 48 microphones were applied together with ground-based thermographic cameras from two teams. Additionally, an optical camera mounted on the hub was used to survey vibrations. During start-up (SU) (from 0 to 9 rpm), extended but irregularly shaped regions of a laminar-boundary layer were observed that had the same extension measured both with microphones and thermography. When an approximately constant rotor rotation (9 rpm corresponding to approximately 6 m/s wind speed) was achieved, flow transition was visible at the expected position of 40% chord length on the rotor blade, which was fouled with dense turbulent wedges, and an almost complete turbulent state on the glove was detected. In all observations, quantitative determination of flow-transition positions from thermography and microphones agreed well within their accuracy of less than 1%.

A single, simple correlating equation between the discharge coefficient of critical-flow Venturi nozzles (CFVNs) having an ISO 9300 toroidal throat and their Reynolds number is proposed in the Reynolds number range from 2.1×10 4 to 3.2×10 7 . The equation covers the whole Reynolds number range from laminar to turbulent boundary-layer regimes and can thus be used instead of the two correlating equations defined in ISO 9300 : 2005. The deviation of the discharge coefficients of well-made CFVNs is expected to be less than ±0.2% throughout the Reynolds number range. Tolerances for the diffuser length, inlet curvature and inlet diameter are also proposed. It is shown that the widely-accepted theories that estimate the core flow distribution result in significant error when the inlet curvature is small and that removing the third term in Hall׳s equation results in very good agreement with the experimental data regardless of the magnitude of the inlet curvature. The use of CFVNs with the inlet curvature of 1.0 D is discussed in order to reduce the uncertainty owing to undefined boundary-layer transition Reynolds number. A possibility is shown that such a CFVN may not have an apparent boundary-layer transition in the investigated Reynolds number range from 1.5×10 4 to 2.0×10 6 . [ABSTRACT FROM AUTHOR]

Nocturnal low-level jets (LLJs) are maxima in the wind profile, which often form above the stable nocturnal boundary layer. Over the Sahara, the world's largest source of mineral dust, this phenomenon is of particular importance to the emission and transport of desert aerosol. We present the first ever detailed large-eddy simulations of dust-generating LLJs. Using sensitivity studies with the UK Met Office large-eddy model (LEM), two key controls of the nocturnal LLJ are investigated: surface roughness and the Coriolis force. Functional relationships derived from the LEM results help to identify optimal latitude-roughness configurations for a maximum LLJ enhancement. Ideal conditions are found in regions between 20 and 27°N with roughness lengths >0.0001 m providing long oscillation periods and large jet amplitudes. Typical LLJ enhancements reach up to 3.5 m s−1 for geostrophic winds of 10 m s−1. The findings are largely consistent with results from a theoretical LLJ model applied for comparison. The results demonstrate the importance of latitude and roughness in creating regional patterns of LLJ influence. Combining the functional relationships with high-resolution roughness data over northern Africa gives good agreement with the location of morning dust uplift in satellite observations. It is shown that shear-induced mixing plays an important role for the LLJ evolution and surface gustiness. With decreasing latitude the LLJ oscillation period is longer and, thus, shear-induced mixing is weaker, allowing a more stable nocturnal stratification to develop. This causes a later and more abrupt LLJ breakdown in the morning with stronger gusts, which can compensate for the slower LLJ evolution that leads to a weaker jet maximum. The findings presented here can serve as the first step towards a parametrization to improve the representation of the effects of nocturnal LLJs on dust emission in coarser-resolution models. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of the angle-of-attack (AOA) on the windward boundary-layer stability over a blunt cone with a nose radius of 5 mm. We consider a free-stream Mach number of 6 and a unit Reynolds number of 4.0 × 107 m−1 and conduct both wind-tunnel experiments and stability analyses for AOAs ranging from 2°–10° at intervals of 2°. The results suggest that, as the AOA increases, the pressure gradient across the spanwise range becomes more pronounced, and the windward-side boundary layer becomes thinner. Using bi-global stability analysis, two unstable three-dimensional modes (varicose and sinuous) are identified in the windward boundary layer at various AOAs. The most unstable mode is the varicose V1 mode, in which the amplitude peak is initially close to the windward centerline and gradually shifts to the centerline downstream. Hence, the primary unstable disturbance exhibits a “V-like” distribution along the streamwise direction, which is likely to cause the V-shaped transition front observed in the wind-tunnel experiments. The eN method based on bi-global analysis is used to predict the transition location along the centerline on the windward region of the cone. The results indicate that, as the AOA increases, the transition location shifts forward, in line with our experimental results. Moreover, linear stability theory accurately predicts the eigenfunction and growth rate of the V1 mode obtained from bi-global analysis. This indicates that linear stability theory can be used to predict transitions in the windward boundary layer of a blunt cone at large AOAs under the conditions studied in this paper. [ABSTRACT FROM AUTHOR]

A series of experiments were carried out to investigate unsteady behavior of the flow field as well as the boundary layer of an airfoil oscillating in plunging-type motion in a subsonic wind tunnel. The measurements involved surface-mounted hot films complimented with surface pressure. In addition, wind tunnel wall pressure distribution was acquired to furnish a baseline for the wall interference corrections. The airfoil is the section of a 660-kW wind turbine blade. The experiments were conducted at a Reynolds number of 0.42 million, and over two reduced frequencies of k = 0.06 and 0.085, at prestall, nearstall, and poststall regions. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. The plunging displacements were transformed into the equivalent angle of attack. The surface hot-film measurements provided information about the boundary-layer events. The boundary-layer transition occurred via a laminar separation bubble. Variations of the surface pressure coefficients and aerodynamic loads with the equivalent angle of attack showed strong sensitivity to the reduced frequency and the mean angles of attack. The wall pressure distribution was affected by the model oscillation especially the region underneath the model. [ABSTRACT FROM AUTHOR]

The effect of hull dynamics on the hydrodynamic performance of a single scull is investigated via a combination of field trials and tank tests. The location of laminar-turbulent transition in unsteady flow is explored via several series of hot-film measurements on the bow of a full-scale single scull in unsteady flow in both towing tank and field-trial conditions. Results demonstrate that the measured real-world viscous-flow behaviour can be successfully reproduced in the tank using an oscillating sub-carriage to reproduce the surging motion measured in the field trials. It can be seen that there is a strong link between turbulence and acceleration; results show that the link is relatively insensitive to mean velocity, but that small changes in acceleration time-histories can have a marked effect, as can the presence of small waves.The impact of the location of laminar turbulent transition is investigated by way of a series of resistance tests, both with free transition and with transition forced by turbulence stimulation at two different locations. Results indicate that an aft movement of 200 mm of the location of transition can reduce resistance by almost 0.5 per cent. Unsteady tests using the oscillating sub-carriage indicate that unsteady effects add around 3 per cent to the total mean resistance with free transition. [ABSTRACT FROM PUBLISHER]

This paper presents analyses of particle image velocimetry measurements from a boundary layer on a flat plate subject to grid-generated free-stream turbulence. The pre-transition region and early stages of breakdown to turbulent spots are explored by means of quadrant analysis and quadrant hole analysis. By isolating the contributors to the Reynolds shear stresses, it is possible to identify coherent structures within the flow that are responsible for the production of TKE. It is found that so called ‘ejection’ events are the most significant form of disturbance, exhibiting the largest amplitude behaviour with increased negative spanwise vorticity. Sweep events become increasingly large close to the wall with increased Reynolds number and intermittency. [ABSTRACT FROM AUTHOR]

Transitional boundary layer flows on a flat plate, subjected to different freestream turbulence intensities, have been investigated experimentally in details. The inlet freestream turbulence levels were varied from 1.5 to 4.4 per cent using different circular bar grids of various sizes installed upstream in a proper distance from the plate leading edge. A single hot-wire probe was used for the measurements of instantaneous flow velocities within the boundary layer. Longitudinal and vertical movements of the hot-wire probe were performed by a two-component traversing device, which was itself controlled by a computerized system. Experiments were conducted in an open circuit wind tunnel of suction type. For each level of freestream turbulence, boundary-layer surveys of the mean longitudinal velocity and root mean square of the velocity fluctuations were obtained at several streamwise locations. Experimental results were used to determine the variations of streamwise skin-friction coefficient and the boundary-layer shape factor versus the local Reynolds number. Evaluation of the final results showed that increasing the freestream turbulence intensity causes the transitional region to shrink and to shift up-stream. Current experimental results together with reliable data presented by other researchers led to propose a new correlation capable of predicting the onset of transition for a wide range of freestream turbulence intensities. [ABSTRACT FROM AUTHOR]

The challenges in understanding hypersonic flight are discussed and critical hypersonic aerothermodynamics issues are reviewed. The ability of current analytical methods, numerical methods, ground testing capabilities, and flight testing approaches to predict hypersonic flow are evaluated. The areas where aerothermodynamic shortcomings restrict our ability to design and analyze hypersonic vehicles are discussed, and prospects for future capabilities are reviewed. Considerable work still needs to be done before our understanding of hypersonic flow will allow for the accurate prediction of vehicle flight characteristics throughout the flight envelope from launch to orbital insertion. [ABSTRACT FROM AUTHOR]

In this paper an efficient split-type Finite-Difference (FD) scheme with high modal resolution – most important for the streamwise convection terms that cause wave transport and interaction – is derived for a mixed Fourier-spectral/FD method that is designed for the spatial direct numerical simulation (DNS) of boundary-layer transition and turbulence. Using a relatively simple but thorough and instructive modal analysis we discuss some principal trouble sources of the related FD discretization. The new scheme is based on a 6th-order compact FD discretization in streamwise and wall-normal direction and the classical 4th-order Runge–Kutta time-integration scheme with symmetrical final corrector step. Exemplary results of a fundamental-(K-) type breakdown simulation of a strongly decelerated Falkner–Skan boundary layer (Hartree parameter βH = − 0.18) using 70 mega grid points in space are presented up to the early turbulent regime (ReΘ,turb ≈ 820). The adverse pressure gradient gives rise to local separation zones during the breakdown stage and intensifies final breakdown by strong amplification of (background) disturbances thus enabling rapid transition at moderate Reynolds number. The appearance and dynamics of small-scale vortical structures in early turbulence basically similar to the large-scale structures at transition can be observed corroborating Kachanov's hypothesis on the importance of the K-regime of breakdown for coherent structures in turbulence. [ABSTRACT FROM AUTHOR]

A review is made in this paper of the three-dimensional nature of instability leading to transition in a two-dimensional flow on a flat plate (Blasius boundary layer) or between parallel plates (plane Poiseuille flow), with additional reference to the flow on a concave wall. Instability and transition in a three-dimensional boundary layer are then reviewed, with particular attention to the flow due to a rotating disk and the flow perturbed by a three-dimensional roughness element on a flat plate. The growth of a turbulent spot is discussed as a phenomenon exhibiting a similar feature of instability. Only the flow of an incompressible fluid is considered. [ABSTRACT FROM AUTHOR]

Slotted, natural-laminar-flow (SNLF) airfoils are a novel aerodynamic concept that enable significant performance improvements over conventional, single-element NLF airfoils. The S207, SNLF airfoil has been designed using requirements derived from a transonic, truss-braced wing commercial aircraft configuration. The airfoil is designed for a cruise Reynolds number of 13.2 × 10 6 and it exhibits a drag divergence Mach number exceeding 0.71. At these conditions, low drag is predicted to occur between lift coefficients of 0.40 and 0.79. The S207 airfoil exhibits a range-based figure of merit nearly triple that of a turbulent airfoil representative of modern commercial transport aircraft. Slotted configurations also have benefits for low-speed, high-lift conditions representative of approach. The S207 airfoil exhibits a low-speed, maximum lift coefficient in excess of 2.1, and is limited by compressibility effects around the leading edge. Incorporation of this airfoil onto a transonic, truss-braced wing configuration shows strong potential for meeting mid- and far-term goals for reducing aircraft fuel/energy consumption. [ABSTRACT FROM AUTHOR]

The inevitable boundary-layer transition and severe heating argumentation of Hypersonic Inflatable Aerodynamic Decelerator (HIAD) pose challenge for survivability of a Thermal Protection System (TPS). In the current study, the effects of sphere-cone angle on hypersonic heating and boundary-layer transition of stacked tori HIADs with 60°, 65° and 70° sphere-cone are demonstrated minutely by solving compressible Navier-Stokes equations with k-ω-γ transition model. Transition and heating augmentation triggered on the leeward where the shape deformation causes crossflows and local flow separations are sensitive to the cone angle. Smaller cone angle withstands severer heating flux. The study reveals that the first-mode disturbance and crossflow instability are dominators to the transition. Whereas the contribution of second-mode disturbance could be negligible. Larger cone angle postpones transition onsets as a result of weaker crossflow and more limited affected region of the first-mode disturbance. The 70° sphere-cone model, whose crossflow is lower than the critical value is only determined by the first mode, and thus has a quite smaller transition zone as compared to the other two models. [ABSTRACT FROM AUTHOR]

Knowledge about laminar–turbulent transition on operating multi megawatt wind turbine (WT) blades needs sophisticated equipment like hot films or microphone arrays. Contrarily, thermographic pictures can easily be taken from the ground, and temperature differences indicate different states of the boundary layer. Accuracy, however, is still an open question, so that an aerodynamic glove, known from experimental research on airplanes, was used to classify the boundary-layer state of a 2 megawatt WT blade operating in the northern part of Schleswig-Holstein, Germany. State-of-the-art equipment for measuring static surface pressure was used for monitoring lift distribution. To distinguish the laminar and turbulent parts of the boundary layer (suction side only), 48 microphones were applied together with ground-based thermographic cameras from two teams. Additionally, an optical camera mounted on the hub was used to survey vibrations. During start-up (SU) (from 0 to 9 rpm), extended but irregularly shaped regions of a laminar-boundary layer were observed that had the same extension measured both with microphones and thermography. When an approximately constant rotor rotation (9 rpm corresponding to approximately 6 m/s wind speed) was achieved, flow transition was visible at the expected position of 40% chord length on the rotor blade, which was fouled with dense turbulent wedges, and an almost complete turbulent state on the glove was detected. In all observations, quantitative determination of flow-transition positions from thermography and microphones agreed well within their accuracy of less than 1%. [ABSTRACT FROM AUTHOR]