Local Heat Transfer Measurements on a Rotating Flat Blade Model with a Single Film Hole

An experimental study was performed to measure the heat transfer coefficient distributions on a flat blade model under rotating operating conditions. A steady-state thermochromic liquid crystal technique was employed to measure the surface temperature, and all the signals from the rotating reference frame were collected by the telemetering instrument via a wireless connection. Both air and CO2 were used as coolant. Results show that the rotational effect has a significant influence on the heat transfer coefficient distributions. The profiles of hg/h0, which is the ratio of heat transfer coefficient with film cooling to that without film cooling, deflect towards the high-radius locations on both the pressure surface and suction surface as the rotation number (Rt) increases, and the deflective tendency is more evident on the suction surface. The variations in mainstream Reynolds number (ReD) and blowing ratio (M) present different distributions of hg/h0 on the pressure and suction surfaces, respectively. Furthermore, the coolant used for CO2 injection is prone to result in lower heat transfer coefficients.Peer reviewe

Experimental study and analytical modeling of the channel length influence on the electrical characteristics of small-molecule thin-film transistors

Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current-voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length (L = 2.5 mu m and 5 mu m) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7 x 10(-3) cm(2) V-1 s(-1) and 1 x 10(-3) cm(2) V-1 s(-1) were obtained for TFTs with channel lengths of L = 2.5 mu m and L = 5 mu m, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices (L = 2.5 mu m and 5 mu m). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices.Peer ReviewedPostprint (author's final draft

The Effect of Stainless Steel 304 Surface Roughness on Ice Adhesion Shear Strength of Accreted Impact Ice

Aircraft in-flight icing is problematic due to the ad-verse effect on vehicle performance. It occurs when supercooled water droplets (SCWD) present in clouds, under the appropriate environmental conditions, col-lide with the aircraft surface resulting in accretion of ice (i.e., impact icing). Impact ice can range from clear/glaze to rime or a combination of the two (i.e., mixed) with the type determined by the air temperature (0 to -20C), liquid water content (LWC, 0.3-0.6 g/cu.m), and droplet size [median volumetric diameter (MVD) of 15-40 m] present during accretion.1 These impact icing events generally occur at temperatures ranging from 0 to -20C. Below -20C, ice crystals dominate the environment and typically do not adhere to the aircraft surface. A main difference between an impact icing occurrence and a slow growth icing (i.e., freezer ice) one is the speed of the icing event. Besides environmental conditions, ice adhesion strength (IAS) to a metallic substrate depends upon surface roughness. It is known that increasing surface roughness and decreasing temperature lead to in-creases in IAS

Simulation of the Aerodynamic Interaction between Rotor and Ground Obstacle Using Vortex Method

The mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and generates high compensatory workload for pilots, degradation of the handling qualities, and performance, and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method, and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a “Large” and a “Wee” rotor near the ground and obstacle, and compared with the earlier experiments carried out at the University of Glasgow. The results show that predicted rotor induced inflow and flow field compare reasonably well with the experiments. Furthermore, at certain conditions, the tip vortices are pushed up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover, contrary to without the obstacle case, peak and thickness of the radial outwash near the obstacle are smaller due to the barrier effect of the obstacle, and an upwash is observed. In addition, as the rotor closes to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the upwash near the obstacle is faster, indicating a stronger interaction between the rotor wake and the obstacle. In addition, contrary to the case without the obstacle, the fluctuations of the rotor thrust, and rolling and pitching moments are obviously strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the obstacle is small

Unsteady Aerodynamic Interaction Between Rotor and Ground Obstacle

The mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and generates high compensatory workload for pilots, degradation of the handling qualities and performance, and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method, and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a “Large” and a “Wee” rotor near the ground and obstacle, and compared with the earlier experiments carried out at the University of Glasgow. The results show that the predicted rotor induced inflow and flow field compare reasonably well with the experiments. Furthermore, at certain conditions the tip vortices are pushed up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover, contrary to without the obstacle case, the peak and thickness of the radial outwash near the obstacle is smaller due to the barrier effect of the obstacle, and an up-wash is observed. Additionally, as the rotor closes to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the up-wash near the obstacle is faster, indicating a stronger interaction between the rotor wake and the obstacle. Also, contrary to the case without the obstacle, the fluctuations of the rotor thrust, rolling and pitching moments are obviously strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the obstacle is small

Magnetohydrodynamic Three-Dimensional Flow and Heat Transfer over a Stretching Surface in a Viscoelastic Fluid

In this paper, the problem of steady laminar three-dimensional magnetohydrodynamic (MHD) boundary layer flow and heat transfer over a stretching surface in a viscoelastic fluid is investigated. The equations which govern the flow are coupled nonlinear ordinary differential equations, which are solved numerically using a finite-difference scheme known as the Keller-box method. Various physical governing parameters such as the magnetic parameter M, the material or viscoelastic parameter K and the Prandtl number Pr are considered and the effects of these parameters are investigated. It is found that the material parameter K and the magnetic parameter M present opposite effects on the fluid flow and heat transfer characteristics. The numerical results obtained for the skin friction coefficient and the local Nusselt number are presented in tables. The features and profiles of the flow and heat transfer characteristics are illustrated in the forms of graphs

Sedimentation in the Upper Reaches of Lake Ouachita

Lake Ouachita in west-central Arkansas is the largest man-made reservoir in the state. The lake was created by the U.S. Army Corps of Engineers (USACE) in 1953 for the purposes of hydropower, flood control, and recreation. Although Lake Ouachita is widely known for its high water clarity near Blakely Dam, little is known about the volume and ultimate fate of sediments that enter the lake from two primary tributaries: the North and South Forks of the Ouachita River. This project utilized a dual-frequency echo sounding system in combination with geographic information system and statistical analysis to calculate an average post-impoundment sediment thickness of approximately 0.78 m present throughout the study area, with a maximum sediment thickness of 2.93 meters. The total volume of post-impoundment sediment in place was calculated as 2,750,000 m and the average linear sediment accumulation rate was determined to be 1.3 cm y-1. Variations within the project area show widespread sediment focusing with statistically significant variations in sediment thickness between littoral and deeper zones, as well as between the lotic-transitional and lacustrine zone