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The active control of the leading-edge (LE) separation on the suction surface of a stalled airfoil (NACA 0012) at a Reynolds number of 106 based on the chord length is investigated through a computational study. The actuator is a steady or unsteady jet located on the suction surface of the airfoil. Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations are solved on hybrid meshes with the Spalart-Allmaras turbulence model. Simulations are used to characterize the effects of the steady and unsteady actuation on the separated flows for a large range of angle of attack (0 <α < 28 deg). Parametric studies are carried out in the actuator design-space to investigate the control effectiveness and robustness. An optimal actuator position, angle, and frequency for the stalled angle of attack α = 19 deg are found. A significant increase of the lift coefficient is obtained (+84% with respect to the uncontrolled reference flow), and the stall is delayed from angle of attack of 18 deg to more than 25 deg. The physical nonlinear coupling between the actuator position, velocity angle, and frequency is investigated. The critical influence of the actuator location relative to the separation location is emphasized. [ABSTRACT FROM AUTHOR]

A systematic study of the effect of the Reynolds number on the fluid dynamics and turbulence statistics of pulsed jets impinging on a flat surface is presented. It has been suggested that the influence of the Reynolds number may be somewhat different for a jet subjected to pulsation when compared to an equivalent steady jet. A comparative study of both steady and pulsating jets is presented for a Reynolds number range from Re = 4,730 to Re = 10,000. All the other factors that affect the flowfield are kept constant, which are H/d = 3, St = 0.25, and d = 30.5 mm. It was found that for the range of the Reynolds numbers tested, pulsation results in a shortening of the jet core, the centerline axial velocity component declines more rapidly, and higher values of the radial velocity component for r/d > 0.75 are observed. As the Reynolds number increases, the jet spreads more rapidly, the turbulent kinetic energy and nondimensionai turbulent fluctuations decrease, and the flowfield near the impinging surface changes drastically, which is evident with the development of a turbulent momentum exchange interaction away from the wall for r/d > 1.5. [ABSTRACT FROM AUTHOR]

Abstract: Drag enhancement is reported for turbulent pipe flow of aqueous electrolyte solutions. No electroviscous effect was obtained with laminar flow. Nor was any unusual pressure drop observed for laminar or turbulent flow of non-electrolyte aqueous solutions such as sugar. An electroviscous theory was advanced that predicted the drag enhancement for a 1/1 electrolyte solution. The theory depended on consideration of Debye length. [Copyright &y& Elsevier]

Abstract: Pressure drop data are reported for two phase air–water flow through a vertical to horizontal 90° elbow bend set in 0.026m i.d. pipe. The pressure drop in the vertical inlet tangent showed some significant differences to that found for straight vertical pipe. This was caused by the elbow bend partially choking the inflow resulting in a build-up of pressure and liquid in the vertical inlet riser and differences in the structure of the flow regimes when compared to the straight vertical pipe. The horizontal outlet tangent by contrast gave data in general agreement with literature even to exhibiting a drag reduction region at low liquid rates and gas velocities between 1 and 2ms−1. The elbow bend pressure drop was best correlated in terms of l e/d determined using the actual pressure loss in the inlet vertical riser. The data showed a general increase with fluid rates that tapered off at high fluid rates and exhibited a negative pressure region at low rates. The latter was attributed to the flow being smoothly accommodated by the bend when it passed from slug flow in the riser to smooth stratified flow in the outlet tangent. A general correlation was presented for the elbow bend pressure drop in terms of total Reynolds numbers. A modified Lockhart–Martinelli model gave prediction of the data. [Copyright &y& Elsevier]

Abstract: A wide range of experimental results carried out in low enthalpy facilities is used to sustain simple correlations predicting heat transfer rates on an attachment line in hypersonic flow. It is observed that for long swept cylinders a nearly asymptotic state can be reached for which transition Reynolds number does not change substantially quite far from the apex of the cylinder. Intermittency based on measured heat fluxes was used to describe the laminar–turbulent process. Prediction of turbulent heat transfer rates is established using a reference temperature method that provides quick and relatively accurate estimates for a wide range of Mach number and temperature ratio. [Copyright &y& Elsevier]