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A NACA 0012 wing tip was tested at Mach 0.75 and chord Reynolds number of 3 million at incidences from -4 to 7 deg in a transonic Ludwieg tube. The Mach and Reynolds numbers are representative of full-scale rotorcraft blades. Because of the short test time of 0.1 s and high impulse loads, a dynamic calibration was applied to a conventional sidewall force balance to compensate for stress waves propagating within the force balance and test article. Numerical simulations of the entire test section were accomplished to provide data for comparison. The compensated, experimental lift and drag data compared well with the numerical results. This suggests that dynamic calibration improved the experimental data. This comparison demonstrates the feasibility of using complex models for calibrating short-duration wind tunnels in concert with numerical simulation. [ABSTRACT FROM AUTHOR]

Experiments were performed to investigate a transonic, turbulent boundary layer over a bi-convex corner. The total turning angle η ranged from 10 deg to 17 deg. In subsonic expansion flows, the presence of a bi-convex corner results in a decrease in local peak Mach number M peak and the amplitude of peak surface pressure fluctuations ( σ p / p w ) max . There is a delay in transition from subsonic to transonic expansion flows. A dual expansion is observed in transonic expansion flows. Shock structure, boundary-layer separation and ( σ p / p w ) max were dependent on freestream Mach number M , first turning angle η 1 and η . The length of the first corner L 1 also plays an important role. An increase in L 1 results in less flow expansion, while a decrease in the amplitude of ( σ p / p w ) max is associated with a shorter L 1 . [ABSTRACT FROM AUTHOR]

Experiments were performed to investigate the flow of a transonic, turbulent boundary layer over regions of sharp and rounded convex surface curvature. The freestream Mach numbers were 0.64, 0.70, 0.83 and 0.89. Test models with three different radii of curvature from 13.7 to 41.7 times the upstream boundary-layer thickness were employed. The total turning angles were 13, 15 and 17°. The flow was found to be accelerated upstream of the curved region. The peak Mach number decreased with increasing radius of curvature for a given turning angle. In comparison with the sharp convex corner, a delay in the transition from subsonic to transonic expansion flows was observed. The shock structure, boundary-layer separation and peak fluctuating pressure were dependent on freestream Mach number, turning angle and radius of curvature. [ABSTRACT FROM AUTHOR]

This study assessed turbulence models for high-Reynolds-number transonic junction flows by comparing flow separation characteristics obtained from experiment and computational fluid dynamics. The test model used was a NACA 0012 wing of aspect ratio 2 at a Mach number of 0.76 and a Reynolds number of 6 ⋅ 106 with varying angles of attack. The computational fluid dynamics study involved an 18.8-million-cell structured grid of the wind-tunnel test section using the ANSYS Fluent 12.0 solver. The k-ω shear stress transport turbulence model was the main turbulence model employed. Experiments were conducted in a high-Reynolds-number transonic Ludwieg tunnel. The wing was simulated at different Mach numbers and inlet conditions to account for some of the experimental uncertainties. Porous walls eliminated shock reflection across the tunnel. Surface oil-flow visualization was used to indicate the interference flow patterns. The assessment shows that computational fluid dynamics overpredicts separation and therefore interference drag, likely due to deficiencies in the turbulence model. [ABSTRACT FROM AUTHOR]

Abstract: This study compares the energy dissipative characteristics of bolted t-stub connections using steel and shape memory alloy (SMA) fasteners. The initial phase of the study focused on the optimization of the SMA superelastic effect using two different heat treatment temperatures. The samples were then subjected to tensile testing to determine transformation stress, tensile strength, and fracture strain. In addition, low cycle fatigue tests were conducted to examine the energy dissipative characteristics of these superelastic SMAs heat treated at the two temperatures. The cycled samples were then tensile tested to determine the effect of fatigue cycling on transformation stress, tensile strength, and fracture strain. Results from the mechanical tests were analyzed to determine the preferred heat treatment temperature that resulted in the least residual strain and the largest energy dissipative characteristics. The second phase of the study involved t-stub connection testing using steel and SMA double-ended threaded rod fasteners. The optimum heat treatment determined in the first phase was used to develop the SMA fasteners for the t-stub connection tests. Experimental hysteresis results from the t-stub connection tests were used to compare the energy dissipation capacity of the connections with SMA and steel fasteners. [Copyright &y& Elsevier]