L. de Luca

Boundary layer diagnostics by means of an infrared scanning radiometer

A computerized infrared (IR) scanning radiometer is employed to characterize the boundary layer development over a model wing, having a Göttingen 797 cross-section, by measuring the temperature distribution over its heated surface. The Reynolds analogy is used to relate heat transfer measurements to skin friction. The results show that IR thermography is capable of rapidly detecting location and extent of transition and separation regions of the boundary layer over the whole surface of the tested model wing. Thus, the IR technique appears to be a suitable and effective diagnostic tool for aerodynamic research in wind tunnels.

Azimuthal instability in an impinging jet: adiabatic wall temperature distribution

The present work has been aimed at gaining some new insights into instability phenomena arising when an air jet impinges on a flat plate under certain conditions. At a critical Mach number, depending on the impingement distance, the jet loses its circumferential appearance with the formation of evenly equidistant azimuthal structures, whose number and location depend on the nozzle geometry and on the flow conditions. The instability is investigated in terms of pressure and adiabatic wall temperature; the latter is measured by means of an infrared scanning radiometer. Entrainment effects are found to play a key role in the priming and evolution of the instability.

Experimental analysis of surface flow on a delta wing by infrared thermography

IR thermography has been employed for heat transfer measurements and surface flow visualizations on a 65-deg delta wing model.

Goertler instability of a hypersonic boundary layer

The Goertler instability of a hypersonic boundary layer and its influence on the wall heat transfer are experimentally analyzed. Measurements, made in a wind tunnel by means of a computerized infrared (IR) imaging system, refer to the flow over two-dimensional concave walls. Wall temperature maps (that are interpreted as surface flow visualizations) and spanwise heat transfer fluctuations are presented. Measured vortices wavelengths are correlated to non-dimensional parameters and compared with numerical predictions from the literature.

Görtler-type vortices in hypersonic flows: the ramp problem

Abstract This paper deals with the wall heat flux measurements in the presence of thermal striations that can occur in the reattaching flow after a Mach 7.1 shock wave-boundary layer interaction on a 15° flap. Two different experimental techniques were used: thin skin with thermocouples and thin film with infrared thermography. Special care was taken to correct the lateral conduction effects. They can be important because of the small wavelengths of the spanwise striations. The influence of the Reynolds number was assessed by varying the unit Reynolds number and the length of the flat plate while keeping the same leading edge geometry. The effect of a sinusoidal perturbation at the leading edge also was studied. Finally, Navier Stokes laminar computations were performed to obtain the proper level of the laminar heat flux and to analyze the effect of the leading edge thickness. The calculations confirm the strong influence of the leading edge on the interaction phenomena.

FLOW VISUALIZATION AND HEAT TRANSFER MEASUREMENT IN A HYPERSONIC WIND TUNNEL

Abstract Current state of the art of numerical codes does not allow the aerodynamic and thermal design of hypersonic vehicles, as well as of space shuttles, by means of computer simulations only. The need arises for proper wind tunnel testing and detailed heat flux measurements. In this article significant results referring to flow visualizations and heal transfer measurements performed with an infrared (IR) scanning radiometer in a blow-down hypersonic wind tunnel on simple and double ellipsoidal models art discussed. Comparisons of IR data with oil film flow visualizations, thermocouple measurements and computational predictions are made.

Lower incidence of macrovascular complications in patients on insulin glargine versus those on basal human insulins: A population-based cohort study in Italy

BACKGROUND AND AIM The aim of this study was to compare the use of insulin glargine and intermediate/long-acting human insulin (HI) in relation to the incidence of complications in diabetic patients. METHODS AND RESULTS A population-based cohort study was conducted using administrative data from four local health authorities in the Abruzzo Region (900,000 inhabitants). Diabetic patients without macrovascular diseases and treated with either intermediate/long-acting HI or glargine were followed for 3-years; the incidence of diabetic (macrovascular, microvascular and metabolic) complications was ascertained by hospital discharge claims and estimated using Cox proportional hazard models. Propensity score (PS) matching was also used to adjust for significant differences in the baseline characteristics between the two groups. RESULTS Overall, 1921 diabetic patients were included: 744 intermediate/long-acting HI and 1177 glargine users. During the 3-year follow-up, 209 (28.1%) incident events of any diabetic complication occurred in the intermediate/long-acting HI and 159 (13.5%) in the glargine group. After adjustment for covariates, glargine users had an HR (95% CI) of 0.57 (0.44-0.74) for any diabetic complication and HRs of 0.61 (0.44-0.84), 0.58 (0.33-1.04) and 0.35 (0.18-0.70) for macrovascular, microvascular and metabolic complications, respectively, compared to intermediate/long-acting HI users. PS analyses supported these findings. CONCLUSIONS The use of glargine is associated with a lower risk of macrovascular complications compared with traditional basal insulins. However, limitations inherent to the study design including the short length of observation and the lack of data on metabolic control or diabetes duration, do not allow us to consider this association as a proof of causality.

Water Spray Flow Characteristics Under Synthetic Jet Driven By a Piezoelectric Actuator

Particle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA) have been applied to investigate the droplets size and velocity distribution of a water spray, under the control of a piezo-element driven synthetic jet (SJ). Tests were carried out under atmospheric conditions within a chamber test rig equipped with optical accesses at two injection pressures, namely 5 and 10 MPa, exploring the variation of the main spray parameters caused by the synthetic jet perturbations. The SJ orifice has been placed at 45° with respect to the water spray axis; the nozzle body has been moved on its own axis and three different nozzle quotes were tested. PIV measurements have been averaged on 300 trials whereas about 105 samples have been acquired for the PDA tests. For each operative condition, the influence region of the SJ device on the spray has been computed through a T-Test algorithm. The synthetic jet locally interacts with the spray, energizing the region downstream the impact. The effect of the actuator decreases at higher injection pressures and moving the impact region upwards. Droplets coalescence can be detected along the synthetic jet axis, while no significant variations are observed along a direction orthogonal to it.

Flash Evaporation Phenomena in Actively Cooled Wing Leading Edge of Re-entry Vehicles

An innovative “active” cooling system of a wing leading edge of a hypersonic re-entry vehicle making use of water is studied. In particular, a steady model is developed to analyze the critical discharge of the cooling water into a very low pressure ambient simulating the outlet conditions of both the re-entry and wind tunnel environments. Due to the strongly subcooled operating conditions of the fluid, the model predicts no-flashing within the duct connecting the outlet (hot) manifold to the vacuum ambient. For a fixed water mass flow rate, the pressure within the outlet manifold is determined, giving that flow rate in connection with the proper head losses. The exit section (critical) pressure is determined as well. These findings are confirmed by unsteady numerical simulations of the system start-up.

Goertler Vortices in Hypersonic Flow Detected by IR Thermography

Abstrnef Heat transfer measurements performed by means of an Infrared Scanning Radiometer in a blowdown hypersonic wind tunnel are discussed In particular, the formation of Goertler-type vortices in the reattaching flow region over the flap following a flat plate is investigated, as well as its influence on the wall hezt transfer distribution Tests are carried out within the European Community Hermes space program to develop the first european space shuttle.