The nanoscale thermal anemometry probe (NSTAP) has been widely used to measure turbulence levels in high Reynolds number flows. Here, we report that the probe measurements are geometrically sensitive to its particular orientation in the flow under certain conditions. The geometric sensitivity appears as an amplification of the turbulence signal but has no effect on the mean. Data are taken using an NSTAP in multiple configurations and compared to data from previous studies and a conventional hot-wire. Results suggest that geometric sensitivity is caused by a difference between the mean and dynamic calibrations of the NSTAP.

When acquiring quantitative data using cameras, calibration is required to establish the mapping relation between the image space and physical space. Calibration targets with known dimensions are often used, with the most popular being physical targets. In setups where physical access is a challenge, using physical targets may not be possible, and so we develop an adaptive non-intrusive calibration target capable of conducting volumetric calibrations in free space. The calibration target is formed by two intersecting laser beams traversed in the test domain. A novel algorithm is presented for accurately finding the beam intersections, even at small crossing angles. The error sources are assessed along with their scaling behavior with respect to key parameters. The performance of the calibration method is evaluated by using it to examine a test object with known dimensions.

The 3D velocity and scalar concentration fields from a laidback fan-shaped film cooling hole are measured using Magnetic Resonance Velocimetry (MRV) and Magnetic Resonance Concentration (MRC). The velocity and scalar concentration fields of the same geometry are also obtained using Large Eddy Simulation (LES). The geometry under consideration features a single film cooling hole with a 30° inclination angle and 7° forward and lateral expansion angles. The results are compared to an existing adiabatic effectiveness experiment using infrared imaging of an identical geometry (Schroeder and Thole, 2014). Flow separation is observed inside the hole in the LES and MRV. The separated region in the LES is symmetrically located, but it is offset to a lateral side in the MRV which slightly skews the scalar concentration field to one side. Comparisons of the LES with the MRV and MRC experiments show good agreement in the velocity and scalar concentration field elsewhere throughout the 3D domain. Despite some disagreement in the adiabatic effectiveness values with the IR experiment immediately after injection, there is good agreement downstream of injection between the IR experiment and the LES and MRC. Differences in the concentration field can be attributed to differences in the in–hole velocity field. The results suggest that the mean position of the region of separation inside the hole is geometrically sensitive.

Herein, we describe the design and testing of a stereoscopic PIV system uniquely adapted for the high pressure environment of the Princeton Superpipe. The Superpipe is a recirculating pipe facility that utilizes compressed air as the working fluid to attain very high Reynolds numbers. Commercial piping is used as the pressure vessel to hold pressure up to 220 bars, and a test pipe is enclosed inside with a development length of 200 diameters that ensures a fully-developed condition at the test section. The highest achievable Reynolds number (based on the bulk velocity and the pipe diameter) is 35×106, corresponding to a maximum friction Reynolds number of 5×105. The unprecedented range of Reynolds number has enabled a number of new insights in the behavior of high Reynolds number wall-bounded turbulence (Zagarola and Smits, 1998; Hultmark et al., 2013). However, past measurements in the Superpipe have been primarily restricted to single-component, one- or two-point statistics of fully-developed pipe flows. The present work aims to expand the capability of the Superpipe to study turbulent coherent structures and multi-point statistics by means of a new stereoscopic PIV system. The high pressure environment and the confined space inside the pressure vessel pose challenges to both imaging and seeding, the solutions to which will be discussed.

Pipe flow responds to strong perturbations in ways that are fundamentally different from the response exhibited by boundary layers undergoing a similar perturbation, primarily because of the confinement offered by the pipe wall, and the need to satisfy continuity. We review such differences by examining previous literature, with a particular focus on the response of pipe flow to three different kinds of disturbances: the abrupt change in surface condition from rough to smooth, the obstruction due to presence of a single square bar roughness elements of different sizes, and the flow downstream of a streamlined body-of-revolution placed on the centerline of the pipe. In each case, the initial response is strongly influenced by the pipe geometry, but far downstream all three flows display a common feature, which is the very slow, second-order recovery that can be explained using a model based on the Reynolds stress equations. Some future directions for research are also given.

Magnetic resonance concentration (MRC) was introduced by Benson et al. (Exp Fluids 49:43–55, 2010) to obtain three-dimensional, time-averaged concentration fields in complex turbulent flows without the need for optical access using magnetic resonance imaging. It has since been applied to a wide variety of flows including jet engine film cooling configurations, mixing layers, and urban dispersion cases. However, the measurement uncertainty is currently limited to about 5% of the injected concentration, irrespective of the local concentration. This work presents an advanced MRC technique to greatly reduce the uncertainty at low concentration. Best practices for conducting MRC experiments are described to establish a baseline methodology. These include the choice of scan settings and fluids, calibration procedure, mixing experiment details, and method for computing concentration fields from scan data. An advanced technique is developed to reduce the uncertainty at low concentration by combining data from multiple experiments at increasing molarity of injected fluid, using Fourier-space averaging to reduce noise, and by minimizing fluid property differences using a low flip angle to reduce the maximum injected molarity without degrading the signal-to-noise ratio. The method is flexible and can be optimized to meet the uncertainty requirements of specific applications. Experiments are performed on the turbulent mixing downstream of an isolated, rectangular building as a test case. The advanced technique is validated against the baseline method and maps of spatially dependent experimental uncertainty are presented. Less than 1% uncertainty based on a 95% confidence interval is achieved near the plume boundaries. Results from the new technique reveal dilute but non-zero concentration regions near the wall which could not be resolved using the baseline method.

Diffuser holes are used extensively for film cooling because they dramatically improve film-cooling effectiveness relative to bound holes, but there is concern that the drawbacks of a compound angle (CA) may reduce the beneficial effects. This work Magnetic Resonance Velocimetry (MRV) to obtain the 3D, component mean velocity field for a shaped hole with a pitch angle of 30 degrees, blowing ratio of unity, and compound angles of 10 and 20 degrees. The data are compared to a previous MRV measurement of an identical hole with zero skew angle. in the 0 and 20 degree cases, a separation bubble is observed in the downstream wall of the diffuser. Streamtubes emanating,from the diffuser exit show the asymmetry of the flow as the jet is accelerated to align with the mainstream flow. Streamtube analysis shows evidence of competing effects of CA on film cooling performance: a wider streamtube footprint may increase courage while a decrease in streamtube thickness may make courage more susceptible to turbulent mixing. Analysis of the jet trajectory, defined as the streamtube centroid, shows that the realignment of the jet fluid with the freestream direction occurs in pie region of the diffuser exit. Although significant qualitative changes in film cooling performance are not expected, some ingestion of mainstream flow may occur due to vortices present in the diffuser below the plane of the blade surface.

Measurement techniques such as Magnetic Resonance Velocimety (MRV) and Magnetic Resonance Concentration (MRC) are useful for obtaining 3D time-averaged flow quantities in complex turbulent flows, but cannot measure turbulent correlations or near-wall data. In this work, we use highly resolved Large Eddy Simulations (LES) to complement the experiments and bypass those limitations. Coupling LES and magnetic resonance experimental techniques is especially advantageous in complex non-homogeneous flows because the 3D data allow for extensive validation, creating confidence that the simulation results portray a physically realistic flow. As such we can treat the simulation as data, which "enrich" the original MRI mean flow results. This approach is demonstrated using a cylindrical and inclined jet in crossflow with three distinct velocity ratios, r=1, r=1.5, and r=2. The numerical mesh is highly refined in order for the subgrid scale models to have negligible contribution, and a systematic, iterative procedure is described to set inlet conditions. The validation of the mean flow data shows excellent agreement between simulation and experiments, which creates confidence that the LES data can be used to enrich the experiments with near-wall results and turbulent statistics. We also discuss some mean flow features and how they vary with velocity ratio, including wall concentration, the counter rotating vortex pair, and the in-hole velocity.