Unperturbed Boundary Layer Research Articles

A shear stress parametrization for arbitrary wind farms in conventionally neutral boundary layers

In the context of large off-shore wind farms, power production is influenced greatly by the turbine array's interaction with the atmospheric boundary layer. One of the most influencing manifestations of such complex interaction is the increased level of shear stress observed within the farm. This leads to higher momentum fluxes that affect the wind speed at the turbine locations and in the cluster wake. At the wind farm entrance, an internal boundary layer (IBL) grows due to the change in effective roughness imposed by the wind turbines, and for large enough clusters, this can reach the unperturbed boundary layer height in what is referred to as the fully developed regime. Downwind, a second IBL starts growing, while the shear stress profile decays exponentially to its unperturbed state. In the present study, we propose a simple analytical model for the vertical profile of the horizontal shear stress components in the three regions identified above. The model builds upon the top-down model of Meneveau (J. Turbul., vol. 13, 2012, N7), and assumes that the flow develops in a conventionally neutral boundary layer. The proposed parametrization is verified successfully against large-eddy simulations, demonstrating its ability to capture the vertical profile of horizontal shear stress, and its evolution both inside and downwind of the wind farm. Our findings suggest that the developed model can prove extremely useful to enhance the physical grounds on which new classes of coupled wind farm engineering models are based, leading to a better estimation of meso-scale phenomena affecting the power production of large turbine arrays.

High-fidelity CFD modeling of pollutant dispersion from aircraft auxiliary power units (APUs) at a realistic airport and the effects on airport air quality

Many studies have investigated air-traffic impact on airport air quality through main-engine emissions, however very few have characterized the APU-related impact. As field-monitoring remains limited, our study used CFD simulations to provide a high-fidelity representation of 19 APU dispersion plumes in a realistic airport configuration. Results of three dominant wind configurations show that the global dispersion plume (from all APUs) was transported by incident winds. Depending on wind direction, pollutant trapping within a large downwash region was observed downstream of the terminal-building. Local differences were observed depending on source locations; emissions within the downwash region were pushed against the terminal-facade which promoted emission spillover on terminal-roof, while plumes within the unperturbed boundary layer were transported by incident winds. Quantitatively, APU pollutant concentrations dropped overall by 3–4 orders of magnitude around the terminal-building, while diluted concentrations by 5–6 orders of magnitude were monitored at the airport exit. Given source concentrations with an appropriate experimental apparatus, this model can serve as an airport air quality decision-making tool to finely characterize individual source impacts. Such information can help assist airport operation management (taxi to gate/runway, gate assignment, safe corridors for ground-handling personnel) so as to reduce/prevent the impact of pollutant hot spots depending on wind configurations.

Free-stream coherent structures in parallel compressible boundary-layer flows at subsonic and moderate supersonic Mach numbers

As a first step towards the description of coherent structures in compressible shear flows, we present an asymptotic description of nonlinear travelling-wave solutions of the Navier–Stokes equations in the compressible asymptotic suction boundary layer (ASBL). We consider free-stream Mach numbers $M_\infty$ in the subsonic and moderate supersonic regime so that $0\leqslant M_\infty \leqslant 2$ . We extend the large-Reynolds-number asymptotic theory of Deguchi & Hall (J. Fluid Mech., vol. 752, 2014, pp. 602–625) describing ‘free-stream’ coherent structures in incompressible ASBL flow to describe a nonlinear interaction in a thin layer situated just below the free stream. Crucially, the nonlinear interaction equations for the velocity field in this layer are identical to those obtained in the incompressible problem, and thus the asymptotic analysis supporting free-stream coherent structures in compressible ASBL is easily deduced from its incompressible counterpart. The nonlinear interaction produces streaky disturbances to both the velocity and temperature fields, which can grow exponentially towards the wall. We complete the description of the growth of the velocity and thermal streaks throughout the flow by solving the compressible boundary-region equations numerically. We show that the velocity and thermal streaks obtain their maximum amplitude in the unperturbed boundary layer. Increasing the free-stream Mach number enhances the thermal streaks and suppresses the velocity streaks, whereas varying the Prandtl number suppresses the velocity streaks, and can either enhance or suppress the thermal streaks depending on whether the flow is in the subsonic or moderate supersonic regime. Such nonlinear equilibrium states have been implicated in shear transition in incompressible flows; therefore, our results indicate that a similar mechanism may also be present in compressible flows.

Velocity Field behind a Plate Installed in the Inner Region of a Turbulent Boundary Layer

The authors have presented results of an experimental investigation into the velocity field in a turbulent boundary layer behind a thin (0.00045 m) three-dimensional plate. The chord of the plate (streamwise length) was equal to 0.55δ (δ is the boundary-layer thickness), and its width, to 1.0δ. The plate was installed at a zero angle of attack at the center of a water channel at a distance of 0.09δ from the surface. Velocity-field measurements have been performed by the Particle Image Velocimetry method at the Reynolds number Reh = 7750 calculated from the channel half-width and the velocity at the center of the channel. It has been shown that the average velocity increased in a logarithmic region of the boundary layer at a distance of its three thicknesses behind the plate. Longitudinal-velocity pulsations decreased in the buffer region of the boundary layer, but grew in the logarithmic region. Vertical pulsations only decreased to a distance of 0.8δ behind the plate, but downstream they were higher than in an unperturbed boundary layer. The high resolution of the velocity field (50·10–6 m) has made it possible to determine shear stresses on the wall from the velocity gradient in a laminar sublayer. Shear stresses on the surface behind the plate decreased in the interval where a growth in the average velocity in the logarithmic region was noted. Maximum reduction in the shear stresses occurred at a distance of 1.8δ and amounted to ~33%. The influence of edge effects was manifested in the less intense reduction on shear stresses in the shorter interval behind the plate.

Acoustic excitation of Tollmien–Schlichting waves due to localised surface roughness

Experiments on the receptivity of two-dimensional boundary layers to acoustic disturbances from two-dimensional roughness strips were performed in a low-turbulence wind tunnel on a at plate model. The freestream was subjected to a plane acoustic wave so that a Stokes Layer (SL) was created on the plate, thus generating a Tollmien-Schlichting (T-S) wave through the receptivity process. An improved technique to measure the T-S component is described based on a retracting two-dimensional roughness, which allowed for phase-locked measurements at the acoustic wave frequency to be made. This improved technique enables both protuberances and cavities to be explored in the range 30�m < jhj < 750�m (equivalent to 0:025 < jhj=��B < 0:630 in relative roughness height to the local unperturbed Blasius boundary layer displacement thickness). These depths are designed to cover both the predicted linear and non-linear response of the T-S excitation. Experimentally, cavities had not previously been explored. Results show that a linear regime is identifiable for both positive and negative roughness heights up to � 150 �m (jhj=��B � 0:126). The departure from the linear behaviour is, however, dependent on the geometry of the surface imperfection. For cavities of signi�cant depth, the non-linear behaviour is found to be milder than in the case of protuberances - this is attributed to the flow physics in the near field of the surface features. Nonetheless, results for positive heights agree well with previous theoretical work which predicted a linear disturbance response for small-height perturbations.

Experimental observation of hairpin auto-generation events in a turbulent boundary layer

Time-resolved tomographic particle image velocimetry experiments show that new hairpin vortices are generated within a fully developed and unperturbed turbulent boundary layer. The measurements are taken at a Reynolds number based on the momentum thickness of 2038, and cover the near-wall region below $y^{+}=140$, where $y^{+}$ is the wall-normal distance in wall units. Instantaneous visualizations of the flow reveal near-wall low-speed streaks with associated quasi-streamwise vortices, retrograde inverted arch vortices, hairpin vortices and hairpin packets. The hairpin heads are observed as close to the wall as $y^{+}=30$. Examples of hairpin packet evolution reveal the development of new hairpin vortices, which are created upstream and close to the wall in a manner consistent with the auto-generation model (Zhou et al., J. Fluid Mech., vol. 387, 1999, pp. 353–396). The development of the new hairpin appears to be initiated by an approaching sweep event, which perturbs the shear layer associated with the initial packet. The shear layer rolls up, thereby forming the new hairpin head. The head subsequently connects to existing streamwise vortices and develops into a hairpin. The time scale associated with the hairpin auto-generation is 20–30 wall units of time. This demonstrates that hairpins can be created over short distances within a developed turbulent boundary layer, implying that they are not simply remnants of the laminar-to-turbulent transition process far upstream.

Realistic boundary conditions for the simulation of atmospheric boundary layer flows using an improved k–ε model

Atmospheric flow simulations in engineering practice – such as simulations of pollutant dispersion, wind load on buildings, wind climate of urban areas – are fairly sensitive to the inlet boundary conditions. The objective of the present paper is to introduce suitable profiles for velocity and turbulent quantities, which do not only fit the measured vertical distributions, but also guarantee the overall consistency of the turbulence model. If the latter aspect is not verified, the inlet profiles deteriorate rapidly within the computational domain, leading to unrealistic wind profiles in the area of interest.Considering that, in general, the atmospheric boundary layer profiles might not satisfy the equations describing an unperturbed atmospheric boundary layer, turbulence models need to be corrected to guarantee the overall consistency of the approach. Former studies have addressed such a problem via the introduction of source terms in the transport equations of kinetic energy and turbulent dissipation rate, to guarantee consistency between the turbulence model and inlet profiles. In the present study, the formulation is further extended to improve the numerical stability of the approach as well as the realistic character of the produced profiles.

Free-stream coherent structures in growing boundary layers: a link to near-wall streaks

In a recent paper, Deguchi &amp; Hall (J. Fluid Mech., vol. 752, 2014a, pp. 602–625) described a new kind of exact coherent structure which sits at the edge of an asymptotic suction boundary layer at high values of the Reynolds number $Re$. At a distance $\ln Re$ from the wall, the structure is driven by the fully nonlinear interaction of tiny rolls, waves and streaks convected downstream at almost the free-stream speed. The interaction problem satisfies the unit-Reynolds-number three-dimensional Navier–Stokes equations and is localized in a layer of the same depth as the unperturbed boundary layer. Here, we show that the interaction problem is generic to any boundary layer that approaches its free-stream form through an exponentially small correction. It is shown that away from the layer where it is generated the induced roll–streak flow is dominated by non-parallel effects which now play a major role in the streamwise evolution of the structure. The similarity with the parallel boundary layer case is restricted only to the layer where it is generated. It is shown that non-parallel effects cause the structure to persist only over intervals of finite length in any growing boundary layer and lead to a flow structure reminiscent of turbulent boundary layer simulations. The results found shed light on a possible mechanism to couple near-wall streaks with coherent structures located towards the edge of a turbulent boundary layer. Some discussion of how the mechanism adapts to a three-dimensional base flow is given.

A robust method to estimate the variation of the vortex shedding frequency with the location of a single spanwise tripwire for circular cylinders in subcritical flow

For circular cylinders fitted with a single spanwise tripwire, this paper develops a mathematical estimation method to predict the variation of the vortex shedding frequency (in the form of Strouhal number (St)) with the tripwire location (θ) for a given Reynolds number (ReD) and tripwire size (d). The basis of this method comes from the experimentally-determined data of vortex shedding frequency through Constant Temperature Anemometry (CTA) measurements. During the course of these measurements, the Reynolds number is changed from ReD=5000 to 30,000, the tripwire size is varied in diameter from 2.9% to 5.9% of the cylinder diameter and the tripwire location on the cylinder surface is changed from θ=0° to 180° with respect to the forward stagnation point of the cylinder.The estimation method proposed in this study requires only the wire diameter (d), the cylinder diameter (D) and the Reynolds number (ReD) as the input variables. In the first step, the ratio of the wire size to the unperturbed boundary layer thickness is determined at a selected circumferential location on the cylinder. This non-dimensional parameter is, then, used to predict the critical wire angles, and the minimum and maximum values of St according to an experimentally determined linear functional relationship. In the second step, the similarity of the St–θ curves at different wire sizes and Reynolds numbers permits the transformation of the St–θ data to a new modified domain (called St⁎–θ⁎), which yields a universally valid quantitative relationship for any wire size and Reynolds number considered. Using this modified functional relationship in conjunction with the predicted critical wire angles and Strouhal number boundaries, the St–θ curves are constructed. Estimated St values using this method show a reasonably good agreement with the experimental data acquired in the current study.

Free-stream coherent structures in parallel boundary-layer flows

AbstractOur concern in this paper is with high-Reynolds-number nonlinear equilibrium solutions of the Navier–Stokes equations for boundary-layer flows. Here we consider the asymptotic suction boundary layer (ASBL) which we take as a prototype parallel boundary layer. Solutions of the equations of motion are obtained using a homotopy continuation from two known types of solutions for plane Couette flow. At high Reynolds numbers, it is shown that the first type of solution takes the form of a vortex–wave interaction (VWI) state, see Hall &amp; Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666), and is located in the main part of the boundary layer. On the other hand, here the second type is found to support an equilibrium solution of the unit-Reynolds-number Navier–Stokes equations in a layer located a distance of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}O(\ln \mathit{Re})$ from the wall. Here $\mathit{Re}$ is the Reynolds number based on the free-stream speed and the unperturbed boundary-layer thickness. The streaky field produced by the interaction grows exponentially below the layer and takes its maximum size within the unperturbed boundary layer. The results suggest the possibility of two distinct types of streaky coherent structures existing, possibly simultaneously, in disturbed boundary layers.

Large-scale spanwise periodicity in a turbulent boundary layer induced by highly ordered and directional surface roughness

The effect of converging–diverging riblet-type surface roughness (riblets arranged in a ‘herringbone’ pattern) are investigated experimentally in a zero pressure gradient turbulent boundary layer. For this initial parametric investigation three different parameters of the surface roughness are analysed in detail; the converging–diverging riblet yaw angle α, the streamwise fetch or development length over the rough surface Fx and the viscous-scaled riblet height h+. It is observed that this highly directional surface roughness pattern induces a large-scale spanwise periodicity onto the boundary layer, resulting in a pronounced spanwise modification of the boundary layer thickness. Hot-wire measurements reveal that above the diverging region, the local mean velocity increases while the turbulent intensity decreases, resulting in a thinner overall boundary layer thickness in these locations. The opposite situation occurs over the converging region, where the local mean velocity is decreased and the turbulent intensity increases, producing a locally thicker boundary layer. Increasing the converging–diverging angle or the viscous-scaled riblet height results in stronger spanwise perturbations. For the strongest convergent–divergent angle, the spanwise variation of the boundary layer thickness between the diverging and converging region is almost a factor of two. Such a large variation is remarkable considering that the riblet height is only 1% of the unperturbed boundary layer thickness. Increasing the fetch seems to cause the perturbations to grow further from the surface, while the overall strength of the induced high and low speed regions remain relatively unaltered. Further analysis of the pre-multiplied energy spectra suggests that the surface roughness has modified or redistributed the largest scale energetic structures.

Experimental characterization of transition region in rotating-disk boundary layer

The three-dimensional boundary layer due to a disk rotating in otherwise still fluid is well known for its sudden transition from a laminar to a turbulent regime, the location of which closely coincides with the onset of local absolute instability. The present experimental investigation focuses on the region around transition and analyses in detail the features that lead from the unperturbed boundary layer to a fully turbulent flow. Mean velocity profiles and high-resolution spectra are obtained by constant-temperature hot-wire anemometry. By carefully analysing these measurements, regions in the flow are identified that correspond to linear, weakly nonlinear, or turbulent dynamics. The frequency that dominates the flow prior to transition is explained in terms of spatial growth rates, derived from the exact linear dispersion relation. In the weakly nonlinear region, up to six clearly identifiable harmonic peaks are found. High-resolution spectra reveal the existence of discrete frequency components that are deemed to correspond to fluctuations stationary with respect to the disk surface. These discrete components are only found in the weakly nonlinear region. By systematically acquiring low- and high-resolution spectra over a range of narrowly spaced radial and axial positions, it is shown that while the transition from laminar to turbulent regimes occurs sharply at some distance from the disk surface, a complex weakly nonlinear region of considerable radial extent continues to prevail close to the disk surface.

Control of flow past a circular cylinder via a spanwise surface wire: effect of the wire scale

Flow phenomena induced by a single spanwise wire on the surface of a circular cylinder are investigated via a cinema technique of particle image velocimetry (PIV). The primary aim of this investigation is to assess the effect of the wire scale. To this end, consideration is given to wires with different diameters that are 0.5, 1.2, and 2.9% of the cylinder diameter. The Reynolds number has a subcritical value of 10,000. Compared to the thickness of the unperturbed boundary layer developing around the cylinder between 5° and 75° from the forward stagnation point, the former two wires have smaller scales and the latter has a larger scale. Two angular locations of the wire, defined with respect to the forward stagnation point of the cylinder, are found to be critical. When the wire is located at these critical angles, either the most significant extension or the contraction of the time-mean separation bubble occurs in the near wake. These critical angles depend on the wire scale: the smaller the wire, the larger the critical angle. The small-scale and large-scale wires that have diameters of 1.2 and 2.9% of the cylinder diameter induce bistable shear-layer oscillations between different separation modes when placed at their respective critical angles corresponding to maximum extension of the near-wake bubble. These oscillations have irregular time intervals that are much longer than the time scale associated with the classical Karman instability. Moreover, the large-scale wire can either significantly attenuate or intensify the Karman mode of vortex shedding at the critical states; in contrast, the small-scale wires do not notably alter the strength of the Karman instability.

Effects of a geometrical surface disturbance on flow past a circular cylinder: a large-scale spanwise wire

Flow control induced by a single wire that is attached on the outer surface and parallel to the span of a stationary circular cylinder is investigated experimentally. The Reynolds number has a value of 10 000 and the wire diameter is nearly two orders of magnitude smaller than the cylinder diameter, while being larger than the thickness of the unperturbed boundary layer forming around the cylinder. A technique of high-image-density particle image velocimetry is used to characterize mean and unsteady structures of the separating shear layer and the near wake. Only one of the shear layers is directly perturbed by the surface wire. This disturbance, however, has important global consequences over the entire near wake, provided that the wire is located within a certain range of angular positions with respect to the approach flow. Over this range, there are two angles that can be defined as critical on the basis of the streamwise extent of the near-wake structure. In a simplified sense, these critical angles are associated with significant extension and contraction of the near wake, relative to the wake in the absence of the effect of a surface disturbance. The critical angle of the wire that yields the most significant extension of the near wake is also found to lead to bistable oscillations of the separating shear layer at irregular time intervals, much longer than the time scale associated with the classical Kármán vortex shedding. The foregoing two critical states of extension and contraction of the near wake are, respectively, linked to attenuation or enhancement of the Kármán instability. Moreover, the onset of the shear-layer instability, Reynolds stress, Strouhal number and the transverse extent of shear-layer flapping are all shown to depend on the angular position of the wire within the defined range of angles.

Sound generation by turbulent boundary-layer flow over small steps

The aeroacoustics of low-Mach-number boundary-layer flow over backward and forward facing steps is studied using large-eddy simulation and Lighthill's theory. The Reynolds number based on the step height and free-stream velocity ranges from 21000 to 328 as the step height is varied from 53% to 0.83% of the unperturbed boundary layer thickness at the step. For the largest step size, statistics of wall pressure fluctuations such as the root mean square values and frequency spectral density yield favourable comparisons with available experimental measurements. A low-frequency Green's function for the step geometry, valid for an acoustically compact step height, is employed to evaluate the volume integral in the solution to Lighthill's equation. Consistent with the result of previous theoretical studies, the steps act primarily as a dipole source aligned in the streamwise direction. The sound from the forward step is shown to be significantly louder than that from the backward step and the underlying reason is analysed in terms of source strength and distribution relative to the Green's function. The forward step generates stronger sources in regions closer to the step corner, which is heavily weighted by the Green's function. A detailed analysis of flow field and Green's function weighted sources reveals that the backward step generates sound mainly through a diffraction mechanism, while the forward step generates sound through a combination of diffraction and turbulence modification by the step. As the step height decreases, the difference in noise level between forward and backward steps is much reduced as turbulence modification becomes less significant.

Effects of micro-ramps on a shock wave/turbulent boundary layer interaction

Stereoscopic particle image velocimetry is used to investigate the effects of micro-ramp sub-boundary layer vortex generators, on an incident shock wave/boundary layer interaction at Mach 1.84. Single- and double-row arrangements of micro-ramps are considered. The micro-ramps have a height of 20% of the unperturbed boundary layer thickness and the measurement planes are located 0.1 and 0.6 boundary layer thicknesses from the wall. The micro-ramps generate packets of individual vortex pairs downstream of their vertices, which produce counter-rotating longitudinal streamwise vortex pairs in a time-averaged view. These structures induce a pronounced spanwise variation of the flow properties, namely the mixing across the boundary layer interface. The probability of reversed-flow occurrence is decreased by 20 and 30% for the single- and double-row configurations, respectively. Both configurations of micro-ramps stabilize the shock motion by reducing the length of its motion by about 20% in the lower measurement plane. The results are summarized by a conceptual model describing the boundary layer’s and interaction’s flow pattern under the effect of the micro-ramps.

Stability of the laminar boundary layer flow encountering a row of roughness elements: Biglobal stability approach and DNS

The stability of the laminar boundary layer developing on a flat plate in the presence of a periodic row of roughness elements is investigated. A Direct Numerical Simulation is performed to compute the steady flow downstream of the roughness elements, which contains a pair of two counter-rotating streamwise vortices per element, which can be considered as a “pre-streaky” structure. The linear stability of this base flow is analyzed by means of the so-called “biglobal” stability approach. Three-dimensional eigenmodes are found, which are shown to be the continuation of the Tollmien–Schlichting waves present in the case of an unperturbed boundary layer. Moreover, a stabilizing effect due to the roughness-induced vortices is found. A Direct Numerical Simulation of the interaction between a two-dimensional Tollmien–Schlichting wave and the roughness array is also performed. The computed perturbation traveling downstream of the roughness elements is shown to be a linear combination of the biglobal eigenmodes.

On the flow structure within a turbulent spot

A computational technique is presented for determining the fully three-dimensional viscid unsteady perturbation to a non-developing laminar boundary layer flow. The results reveal the strongly three-dimensional nature of the flow within a turbulent spot and its associated calmed region. Separation of the flow is found to occur along the demarcation line between the spot and the calmed region. This separation line advances downstream at the spot trailing edge velocity which is approximately half that of the freestream. In interpreting the results it was found convenient to consider the flow as seen by an observer travelling at the spot trailing edge velocity. From this viewpoint the unperturbed laminar boundary layer would consist of two fluid streams. A low momentum stream close to the wall which is travelling slower than the observer and hence approaches from downstream and a high momentum stream which is travelling more rapidly and hence approaches from upstream. The results show that once the flow is perturbed, the low momentum stream approaching the observer from downstream is deflected away from the surface close to the separation line and rolls up into a vortex at the rear of the spot. This vortex grows in both the streamwise and spanwise directions as more fluid is added from the low momentum stream. The high momentum stream drops towards the surface as it approaches the observer from upstream to fill the space vacated by the diverted low momentum stream. This results in the formation of the calmed region. The skin friction is increased within this region and hence some of the fluid from the high momentum stream is slowed to a velocity below that of the observer and hence moves back upstream. However, most of the high momentum stream continues towards the separation line where it is deflected away from the surface as it is entrained into the vortex. The vortex is therefore fed by both the low and the high momentum stream resulting in the high local transient shear rates typical of turbulent eddies.

Modification of Turbulent Boundary Layer Flow by Local Wall Vibration

In this study, the modification of turbulent boundary layer flow by local wall vibration is investigated. The wall is locally vibrated using a wall deformation actuator, which moves up and down at the frequencies of 100Hz and 50Hz. Simultaneous measurements of the streamwise velocities in the spanwise direction are performed at several wall-normal and streamwise locations using an in-house multi-channel hot wire anemometer and a spanwise hot-wire-probe rake. The mean velocity is reduced in most places due to the wall vibration and its reduced amount becomes small as flow goes downstream. Interestingly, the mean velocity is found to increase very near the wall and near the actuator. This is due to the motion induced by the streamwise vortices which are generated by the downward motion of the actuator. In case of the streamwise velocity fluctuations, their magnitude increases as compared to the unperturbed turbulent boundary layer, and the increased amount becomes small as the flow moves downstream. The modified flow field at the forcing frequency of 50Hz is not much different from that of 100Hz, except the reduced amount of modification.

Measurements of the mean heat transfer in a shock wave-turbulent boundary layer interaction

Using thin-film resistance technology characterized by a fast response time and a high sensitivity to heat transfer, a method is developed to measure mean Stanton number in a supersonic blowdown facility under near-adiabatic conditions. The successful application of thin-film gauges required corrections for the changes in total temperature with time and for departures from one-dimensional heat conduction in the gauge itself. This method was then demonstrated in a shock wave-turbulent boundary layer interaction generated by a 16° compression corner in a Mach 2.84 flow. The results show a strong increase in Reynolds analogy factor across the shock, and it appears to level off at a value of 2.15, which is approximately 1.75 times the usually quoted value for an unperturbed boundary layer flow.