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The aim of the current experimental program is to use PIV to measure turbulent statistics within a smooth surface boundary layer at Mach 7.4. It has been shown that the high shear present in a hypersonic boundary layer can lead to an error called peak locking, known to have a significant impact on first order statistics. To limit its effects, parti...
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... was shown to produce the most consistent peak locking between both datasets, as can be seen in Fig.2. This figure also gives a sense of the change in scale between each of the datasets and illustrates why the effect of peak locking on turbulent statistics is significantly reduced when spread over a greater number of pixels. ...
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Citations
... In-plane PIV resolution Laser sheet thickness Tracer Urban and Mungal [12]~1 mm Unknown 15 nm TiO 2 Weisgerber et al [15] 0.5 mm 250 µm 12 nm Aerosil R812 Goyne et al [16] 1.2 mm 800 µm 0.3 µm Al 2 O 3 Scarano and Oudheusden [13] 420 µm estimated 500 µm 27 nm TiO 2 Scheel [17] 1 mm estimated 200 µm 12 nm Aerosil R812 Wagner et al [18] 1.78 mm 1.4 mm 0.02 µm Evonik P25 TiO 2 Tuttle et al [19] 1.81 mm 0.5 mm 100 nm TiO 2 Kirik et al [20] and Peltier and Carter [21] 0.96 mm 1 mm 100 nm TiO 2 Williams and Smits [14] 480 µm 1 mm 100 nm TiO 2 Kirik et al [3] 1 mm 0.3 mm Graphite nanoflakes ...
... They used interrogation window deformations and multi-grid methods to improve the spatial resolution to 420 µm, resolving a wider range of spatial scales. Williams and Smits [14] applied PIV to measure turbulence within the boundary layer of a Mach 7.4 flow. The authors reached resolutions down to 480 µm and noted the presence of large density and velocity gradients, which reduced seeding uniformity and skewed the correlation peaks. ...
A methodology for the implementation of high-resolution, two-component, two-dimensional particle image velocimetry (PIV) in a high-speed, high-enthalpy flow is presented and demonstrated. The objective is to resolve the finer scales of combusting flows at high subsonic Mach numbers for accurate boundary conditions quantification for direct numerical simulations. A three-pronged approach consists of finding a near-optimum setup specific to the experiment, enhancing the raw signal with a novel filter for high-speed flows based on a logarithmic transform, and quantifying uncertainties. The methodology effectiveness is demonstrated with synthetic PIV, real PIV, and comparison with numerical simulations.
... The seeder can be pressurized up to 1.8 MPa without the use of a separate pressure vessel, which allows smoke to be injected directly into the stagnation chamber for evenly distributed global seeding of the test section. Mineral oil was sought because of its minimal health and safety hazards (Humble et al. 2006;Schreyer et al. 2011;Williams and Smits 2012) and because of the simplicity of smoke production. Using the effective particle diameter given by Beresh et al. (2019), particle concentrations of up to 36 particles per interrogation window were initially expected with this configuration, well within the guidelines put forth by Melling (1997). ...
... 107 Page 6 of 12 prior to entering the area of interest. This Stokes number closely aligns with that found in other high-speed shear layer studies (Williams and Smits 2012;Humble et al. 2006) and as such, the system performance was deemed adequate for the following experiments. ...
Experiments were performed within the Rutgers University Mach 3.4 supersonic wind tunnel to quantify the turbulent boundary layer in the test section, using stereoscopic particle image velocimetry (SPIV). Seeding of the tunnel was accomplished using atomized mineral oil, resulting in a Stokes number of 0.09. The Reynolds number based on momentum thickness and the friction-velocity Reynolds number were 64,000 and 4320, respectively, marking this as a high Reynolds number boundary layer. SPIV measurements were capable of resolving the mean velocity profile, along with turbulence quantities, permitting comparison against the known literature. Furthermore, the convection of vorticity concentrations representing hairpin vortices was observed within instantaneous vector fields. The resulting Reynolds stresses demonstrate that the boundary layer had typical values of anisotropy, while comparing well with data obtained within a slightly adverse pressure gradient. This was particularly noticeable from the trends in the Reynolds stresses, which exhibited higher-than-expected peak levels. These data provide a unique measurement of a supersonic turbulent boundary layer at Reynolds numbers not often encountered within existing data sets.
Graphic abstract
... 2.4. Particle image velocimetry Due to rapid developments in CCD cameras since the first application of PIV in hypersonic flows (Moraitis & Riethmuller 1988), this technique is now more commonly used in high-speed flows (Scarano 2005;Schrijer, Scarano & van Oudheusden 2006;Sahoo, Papageorge & Smits 2010;Schreyer, Sahoo & Smits 2011;Williams & Smits 2012;Avallone et al. 2014). The key issues include the selection of seeding particles, their dispersion in the flow and the analysis of particle image recordings (Scarano 2005). ...
The evolution of multi-mode instabilities in a hypersonic boundary layer and their effects on aerodynamic heating are investigated. Experiments are conducted in a Mach 6 wind tunnel using Rayleigh-scattering flow visualization, fast-response pressure sensors, fluorescent temperature-sensitive paint (TSP), and particle image velocimetry (PIV). Calculations are also performed based on both parabolized stability equations (PSE) and direct numerical simulations (DNS). It is found that second-mode dilatational waves, accompanied by high-frequency alternating fluid compression and expansion, produce intense aerodynamic heating in a small region that rapidly heats the fluid passing through it. As a result, the surface temperature rapidly increases and results in an overshoot over the nominal transitional value. When the dilatation waves decay downstream, the surface temperature decreases gradually until transition is completed. A theoretical analysis is provided to interpret the temperature distribution affected by the aerodynamic heating.
... Although particle image velocimetry (PIV) is becoming feasible to provide global measurements of the velocity fluctuations and Reynolds stresses, the application of PIV to hypersonic boundary layers with M ∞ significantly greater than 5 remains an emerging technology. [15][16][17] The current DNS of a spatially-developing turbulent boundary layer with a combination of higher freestream Mach number and colder wall temperature than previous studies thus extends the available database to a more extreme yet practical case. Such a case would also allow one to assess the effects of intrinsic compressibility and the validity of the Morkovin's Hypothesis under these conditions. ...
... Specifically, Sun et al (2012) studied the flow downstream of a micro ramp in a turbulent supersonic boundary layer using tomographic PIV. Applications in the hypersonic flow regime are not yet reported in literature, although Havermann et al (2002), Schrijer et al (2006) and Williams and Smits (2012) report experiments using planar PIV in hypersonic flow facilities. Schrijer et al (2006) applied planar PIV to study the flow at Mach 7 on a double compression ramp flow in the Hypersonic Test Facility Delft (HTFD). ...
The application of non-intrusive experimental techniques is a break-through in the comprehension of the physical mechanisms governing roughness-induced transition in hypersonic flows.
In this thesis, IR Thermography, Planar and Tomographic Particle Image Velocimetry are applied. They show a great potentiality in quantifying the most relevant flow features upstream and downstream of three-dimensional roughness elements. Particularly, non-intrusive measurements of the two-dimensional and three-dimensional velocity flow fields are reported and discussed.
... Specifically, Sun et al. (2012) studied the flow downstream of a micro ramp in a turbulent supersonic boundary layer using tomographic PIV. Applications in the hypersonic flow regime are not yet reported in the literature, although Havermann et al. (2002), Schrijer et al. (2006) and Williams and Smits (2012) report experiments using planar PIV in hypersonic flow facilities. Schrijer et al. (2006) applied PIV to study the flow at Mach 7 on a double compression ramp flow in the Hypersonic Test Facility Delft (HTFD). ...
The disturbance generated by roughness elements in a hypersonic laminar boundary layer is investigated, with attention to its three-dimensional properties. The transition of the boundary layer is inspected with tomographic particle image velocimetry that is applied for the first time at Mach 7.5 inside a short duration hypersonic wind tunnel. A low aspect ratio cylindrical roughness element is installed on a flat plate, and experiments are conducted downstream of the element describing the mean velocity field and the turbulent fluctuations. Details of the experimental procedure needed to realize these measurements are discussed, along with the fluid dynamic behaviour of the perturbed hypersonic boundary layer.
... Specifically, Sun et al. (2012) studied the flow downstream of a micro ramp in a turbulent supersonic boundary layer using tomographic PIV. Applications in the hypersonic flow regime are not yet reported in the literature, although Havermann et al. (2002), Schrijer et al. (2006) and Williams and Smits (2012) report experiments using planar PIV in hypersonic flow facilities. Schrijer et al. (2006) applied PIV to study the flow at Mach 7 on a double compression ramp flow in the Hypersonic Test Facility Delft (HTFD). ...
The disturbance generated by roughness elements in a hypersonic laminar boundary layer is investigated, with attention to its three-dimensional properties. The transition of the boundary layer is inspected with tomographic particle image velocimetry (Tomo-PIV) that is applied for the first time at Mach 7.5 inside a short duration hypersonic wind tunnel. A low aspect ratio cylindrical roughness element is installed on a flat plate and experiments are conducted downstream of the element describing the time-averaged velocity field. Details of the experimental procedure needed to realize these measurements are discussed, along with the fluid dynamic behaviour of the perturbed hypersonic boundary layer.
For the first time, a tomographic particle image velocimetry system with a 1 MHz sampling rate is used to investigate the evolution of three-dimensional instabilities in a Mach 6 flat plate boundary layer. The system is combined with three ultrafast cameras, one eight-channel ultrafast laser, and one 36-channel synchronization controller. PCB ® fast response pressure sensors are also applied to detect the instability evolution in the streamwise direction. Two near-wall volumes are investigated, the upstream one (volume 1) being in a laminar state and the downstream one (volume 2) containing evolving instabilities. For the laminar flow in volume 1, increasing the boundary layer thickness reduces distortion compared to the hypersonic Blasius solution; decreasing the streamwise location or increasing the angle of attack from 0 ○ to 2 ○ increases the distortion. For the disturbed flow in volume 2, the time-resolved evolution of a three-dimensional instability wave is captured in three snapshots, with its phase speed, wavelength, and frequency about 732 m/s, 49 mm, and 20 kHz. Because of the superposition effect of oblique waves, the instability travels like a chain of wavepackets in the streamwise direction, which is accompanied by an alternative distribution of high-speed and low-speed streaks in the spanwise direction. Published under license by AIP Publishing. https://doi.
Instability evolution in a transitional hypersonic boundary layer and its effects on aerodynamic heating are investigated over a 260 mm long flared cone. Experiments are conducted in a Mach 6 wind tunnel using Rayleigh-scattering flow visualization, fast-response pressure sensors, fluorescent temperature-sensitive paint (TSP) and particle image velocimetry (PIV). Calculations are also performed based on both the parabolized stability equations (PSE) and direct numerical simulations (DNS). Four unit Reynolds numbers are studied, 5.4, 7.6, 9.7 and . It is found that there exist two peaks of surface-temperature rise along the streamwise direction of the model. The first one (denoted as HS) is at the region where the second-mode instability reaches its maximum value. The second one (denoted as HT) is at the region where the transition is completed. Increasing the unit Reynolds number promotes the second-mode dissipation but increases the strength of local aerodynamic heating at HS. Furthermore, the heat generation rates induced by the dilatation and shear processes (respectively denoted as and ) were investigated. The former item includes both the pressure work and dilatational viscous dissipation . The aerodynamic heating in HS mainly arose from the high-frequency compression and expansion of fluid accompanying the second mode. The dilatation heating, especially , was more than five times its shear counterpart. In a limited region, the underestimated was also larger than . As the second-mode waves decay downstream, the low-frequency waves continue to grow, with the consequent shear-induced heating increasing. The latter brings about a second, weaker growth of surface-temperature HT. A theoretical analysis is provided to interpret the temperature distribution resulting from the aerodynamic heating.
