Rounded Leading-edge Research Articles

Heat/mass transfer augmentation in a leading-edge channel with extended ribs

Gas turbine blade leading-edge cooling is critical due to a high thermal load in the stagnation region. It requires a significant portion of total cooling air supplied to the turbine blade. In order to meet the durability requirement, various cooling schemes are applied. One of the most commonly found in the leading-edge cooling passage is a rib-turbulator design. In this study, a novel rib-turbulator design is investigated for flow and heat transfer characteristics using numerical and experimental methods. The test section was designed to simulate a realistic internal passage, as a triangular channel with a rounded leading-edge. The rib turbulators are installed in a staggered manner. Numerical analyses were performed using a commercial CFD tool, ANSYS CFX. Naphthalene sublimation method was adopted to measure local convective heat/mass transfer distributions. The main geometrical parameter of interest was the extension length of the rib-turbulators (l/e = 0.0, 1.0, 1.5) in the leading-edge region. Based on the parametric study, the optimized case was found, and its heat transfer performance was compared to the baseline (conventional) case. The Reynolds number varied from 20,000 to 40,000. The optimized case showed a 12.7% better heat transfer performance in the leading-edge region than the baseline case at the Reynolds number 30,000 case.

CFD Modelling of a Pump as Turbine (PAT) with Rounded Leading Edge Impellers for Micro Hydro Systems

A Pump as Turbine (PAT) is one of micro hydro system components that is used to substitute a commercially available turbine due to its wide availability and low acquisition cost. However, PAT have high hydraulic losses due to differences in pump-turbine operation and hydraulic design. The fluid flowing inside the PAT is subjected to hydraulic losses due to the longer flow passage and unmatched fluid flow within the wall boundaries. This paper presents the effect of rounding the impeller leading edges of the pump on turbine performance. A CFD model of a PAT was designed to simulate virtual performance for the analysis. The aim of this study is to observe the internal hydraulic performance resulting from the changes in the performance characteristics. Highest efficiency was recorded at 17.0 l/s, an increase of 0.18%. The simulation results reveal that there is an improvement in hydraulic performance at overflow operation. The velocity vector visualization shows that there is a reduction in wake and consequently less flow separation along impeller flow passages. However, adjusting the sensitive impeller inlet geometry will also alter the velocity inlet vector and consequently change the velocity triangles for the turbo machinery system.

Reversible airfoils for stopped rotors in high speed flight

This study starts with the design of a reversible airfoil rib for stopped-rotor applications, where the sharp trailing-edge morphs into the rounded leading-edge, and vice-versa. A NACA0012 airfoil is approximated in a piecewise linear manner and straight, rigid outer profile links used to define the airfoil contour. The end points of the profile links connect to control links, each set on a central actuation rod via an offset. Chordwise motion of the actuation rod moves the control and the profile links and reverses the airfoil. The paper describes the design methodology and evolution of the final design, based on which two reversible airfoil ribs were fabricated and used to assemble a finite span reversible rotor/wing demonstrator. The profile links were connected by Aluminum strips running in the spanwise direction which provided stiffness as well as support for a pre-tensioned elastomeric skin. An inter-rib connector with a curved-front nose piece supports the leading-edge. The model functioned well and was able to reverse smoothly back-and-forth, on application and reversal of a voltage to the motor. Navier–Stokes CFD simulations (using the TURNS code) show that the drag coefficient of the reversible airfoil (which had a 13% maximum thickness due to the thickness of the profile links) was comparable to that of the NACA0013 airfoil. The drag of a 16% thick elliptical airfoil was, on average, about twice as large, while that of a NACA0012 in reverse flow was 4–5 times as large, even prior to stall. The maximum lift coefficient of the reversible airfoil was lower than the elliptical airfoil, but higher than the NACA0012 in reverse flow operation.

Low Reynolds number aerodynamics of free-to-roll low aspect ratio wings

The aerodynamics of thin, flat-plate wings of various planforms (rectangular, elliptical and Zimmerman) have been studied in free-to-roll experiments in a wind tunnel. Non-zero trim angles at low angles of attack, self-induced roll oscillations with increasing angle of attack and even autorotation in some cases were observed. The rectangular wings with round leading-edge had non-zero trim angles at low incidences due to the asymmetric development of the three-dimensional separation bubble at these low Reynolds numbers. With increasing angle of attack, the bubble increases in length and once reattachment is lost, large amplitude roll oscillations develop. The Strouhal number of the roll oscillations is of the order of 10−2, which is in the same range as those expected for small aircraft experiencing atmospheric gusts. Velocity measurements revealed that variations in the strength of the vortices drove the rolling motion. At the mean roll angle, because of the time lag in the strength of the vortices, an asymmetric flow is generated, which results in a net rolling moment in the direction of the rolling motion.

204 簡易模型車両周りの流れ解析(OS2.流体の数値計算手法と数値シミュレーション(1),オーガナイズドセッション)

204 簡易模型車両周りの流れ解析(OS2.流体の数値計算手法と数値シミュレーション(1),オーガナイズドセッション)

前縁ミニフラップによる４５°デルタ翼のロール制御

The characteristics of rolling moment in a 45-deg delta wing with a leading-edge flap were studied to examine its effects in pre- and post-stall regimes, where conventional control surfaces are ineffective. A small flap with a height of 2mm was employed to control the flow, which was placed on the round leading-edge of the delta wing from 10 to 75% chord. Wind-tunnel experiments were carried out for static aerodynamic force measurements and flow visualization. In the pre-stall regime, it is observed that the single flap can produce about ±0.01 of rolling moment coefficient, which is sufficient for flight control. On the other hand, in the post-stall regime, its rolling moment characteristics are quite nonlinear and complex. The flap can basically reduce the unsteady moment by interfering with the development of a leading-edge vortex, or promoting the flow attachment to the wing surface.

Control of Leading-Edge Vortices with Suction

Abstract : Several control techniques have been applied in order to control leading-edge vortices at high angle of attack. The purpose of these control techniques is to influence the strength and structure of the vortices, to generate rolling moment, and to delay vortex breakdown. Since the vorticity of the leading-edge vortices originates from the separation point along the leading-edge, control of development of the shear layer has been chosen as a control strategy in several investigations: blowing and suction in the tangential direction along a rounded leading-edge.

Theoretical investigation of the aerodynamics of double membrane sailwing airfoil sections

The type of sailwing here investigated has a rigid leading-edge spar with a rib at each end, a wire trailing-edge, and membranes which are wrapped around this structure to form upper and lower wing-surfaces. There appears to have been no previous theoretical investigation of a sailwing of this type, although it is expected to have aerodynamic and structural advantages, including controllability by using internal pressure, and to have various applications (e.g. wind-driven generators). Previous theoretical investigations of sailwings have concerned wings with a zero-thickness single membrane. The paper presents a two-dimensional numerical analysis method for obtaining the aerodynamic characteristics of such double-membrane sailwings. Numerical examples are given which show that: i) the pressure distribution on a sailwing with a rounded leading-edge is completely different from that on a single-membrane sailwing. ii) A sailwing with a circular or oval leading-edge has sharp suction peaks in the pressure distribution that may impair performance. iii) A D-spar leading-edge sailwing shows a large improvement in respect of pressure peaks; this is in qualitative agreement with the performance improvement noted in earlier experiments elsewhere with this form of leading edge. See next Abstract.

A Note on Application of Transonic Linearization to an Airfoil with a Round Leading Edge

A Note on Application of Transonic Linearization to an Airfoil with a Round Leading Edge