Leading Edge Shape Research Articles

Effect of the freestream turbulence scale and the leading edge shape on boundary layer laminar-turbulent transition

The effect of the leading edge shape and the turbulence scale on laminar-turbulent transition in the flat-plate boundary layer due to grid turbulence is investigated. In the experiments, the turbulence scale was changed by a factor of three and the bluntness radius of the edge by a factor of four, all other factors being fixed. It is shown that on the plate with a sharp edge the fluctuation growth rate and the laminar-turbulent transition point depend nonmonotonically on the turbulence scale. On the blunt plate transition occurs considerably earlier than on the sharp plate.

스텔스 형상 공력특성에 관한 실험적 연구

An experimental study of the aerodynamic characteristics of a stealth configuration, the test techniques developed for the testing in the Low Speed Wind Tunnel of Agency for Defense Development(ADD-LSWT), and the lessons learned have been presented. The main objectives of this test are to determine the aerodynamic characteristics of a stealth configuration and to measure the flow field characteristics with a 5-hole pressure probe. The test results are discussed and the effect of the leading edge shape on the aerodynamic characteristics is also given. ⨀ᐍ܀㘱㔮㠹㬃G〵

앞전 형상에 따른 삼각 날개의 공력 특성

Flow visualization and aerodynamic characteristics of delta wings with two different leading edge geometries are investigated by PIV system and wind tunnel balance when the Reynolds number is about based on the freestream velocity and the root chord length. Delta wing models have 65-deg swept angle, and the leading edge shapes are divided into round- and sharp- type. The experimental results indicated that the leading-edge vortex strength and aerodynamic coefficient in the round leading edge are stronger and more, respectively than those in the sharp one. Therefore the flow interactions between vortices and the boundary layer are more desirable or more rapidly swirled in the round-type leading edge.

Emergence of Large-Scale Cell Morphology and Movement from Local Actin Filament Growth Dynamics

Variations in cell migration and morphology are consequences of changes in underlying cytoskeletal organization and dynamics. We investigated how these large-scale cellular events emerge as direct consequences of small-scale cytoskeletal molecular activities. Because the properties of the actin cytoskeleton can be modulated by actin-remodeling proteins, we quantitatively examined how one such family of proteins, enabled/vasodilator-stimulated phosphoprotein (Ena/VASP), affects the migration and morphology of epithelial fish keratocytes. Keratocytes generally migrate persistently while exhibiting a characteristic smooth-edged “canoe” shape, but may also exhibit less regular morphologies and less persistent movement. When we observed that the smooth-edged canoe keratocyte morphology correlated with enrichment of Ena/VASP at the leading edge, we mislocalized and overexpressed Ena/VASP proteins and found that this led to changes in the morphology and movement persistence of cells within a population. Thus, local changes in actin filament dynamics due to Ena/VASP activity directly caused changes in cell morphology, which is coupled to the motile behavior of keratocytes. We also characterized the range of natural cell-to-cell variation within a population by using measurable morphological and behavioral features—cell shape, leading-edge shape, filamentous actin (F-actin) distribution, cell speed, and directional persistence—that we have found to correlate with each other to describe a spectrum of coordinated phenotypes based on Ena/VASP enrichment at the leading edge. This spectrum stretched from smooth-edged, canoe-shaped keratocytes—which had VASP highly enriched at their leading edges and migrated fast with straight trajectories—to more irregular, rounder cells migrating slower with less directional persistence and low levels of VASP at their leading edges. We developed a mathematical model that accounts for these coordinated cell-shape and behavior phenotypes as large-scale consequences of kinetic contributions of VASP to actin filament growth and protection from capping at the leading edge. This work shows that the local effects of actin-remodeling proteins on cytoskeletal dynamics and organization can manifest as global modifications of the shape and behavior of migrating cells and that mathematical modeling can elucidate these large-scale cell behaviors from knowledge of detailed multiscale protein interactions.

Simulation of blunt leading edge aerothermodynamics in rarefied hypersonic flow

The steady-state aerodynamic characteristics of a new family of blunted leading edges immersed in a high-speed rarefied air flow are examined by using a Direct Simulation Monte Carlo (DSMC) Method. A very detailed description of the flow properties has been presented separately at the vicinity of the nose and adjacent to the afterbody surface of the leading edges by a numerical method that properly accounts for non-equilibrium effects that arise near the leading edges and that are especially important at high Mach number. Comparisons based on geometry are made between these new blunt configurations and round leading edge. Some significant differences between these leading edges are noted on the flowfield structure and on the aerodynamic surface quantities. It is found that the upstream effects have different influence on velocity, density, pressure and temperature along the stagnation streamline ahead of the leading edges. The analysis also shows that, despite the seeming advantages of the new blunt leading edge shapes, round leading edge still provides smaller stagnation point heating. Nevertheless, round leading edge provides larger total drag than the new blunt shapes under the range of condition investigated.

21403 三次元形状翼の前縁形状の違いがダイナミックリフトに及ぼす影響(流体工学(3))

21403 三次元形状翼の前縁形状の違いがダイナミックリフトに及ぼす影響(流体工学(3))

Aerodynamic performance and noise characteristics of a centrifugal compressor with modified vaned diffusers

Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressor with vaned diffusers are discussed by experiments and visualization techniques using a colored oil-film method. The focus of the research is concentrated on the leading edge shape of diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by more than ten decibels by using modified diffuser vanes which have 3-D tapered shapes on both pressure and suction surfaces of the leading edge. Furthermore, by adopting the proposed modified diffuser vanes, the secondary flow which is considered to be an obstruction of diffuser pressure recovery can be suppressed, and also the pressure decrease observed in the throat part of the diffuser flow passage is reducible. Thus, the proposed diffuser vanes show a favorable result for both noise and the aerodynamic performance of the centrifugal compressor, and offer a few basic guidelines for the diffuser vane design.

Automatic computational fluid dynamics-based procedure for the optimization of a centrifugal impeller

A typical centrifugal impeller characterized by a low flow coefficient and cylindrical blades is redesigned by means of an intelligent automatic search program. The procedure consists of a feasible sequential quadratic programming algorithm (Fletcher, R. Practical Methods of optimization, 2000 (Wiley)) coupled to a lazy learning (LL) interpolator 1 to speed-up the process. The program is able to handle geometric constraints to reduce the computational effort devoted to the analysis of non-physical configurations. The objective function evaluator is an in-house developed structured computational fluid dynamics (CFD) code. The LL approx-imator is called each time the stored database can provide a sufficiently accurate performance estimate for a given geometry, thus reducing the effective CFD computations. The impeller is represented by 25 geometric parameters describing the vane in the meridional and s-0 planes, the blade thickness, and the leading edge shape. The optimization is carried out on the impeller design point maximizing the polytropic efficiency with nearly constant flow coefficient and polytropic head. The optimization is accomplished by maintaining unaltered those geometrical parameters which have to be kept fixed in order to make the impeller fit the original stage. The optimization, carried out on a cluster of 16 PCs, is self-learning and leads to a geometry presenting an increased design point efficiency. The program is completely general and can be applied to any component which can be described by a finite number of geometrical parameters and computed by any numerical instrument to provide performance indices. The work presented in this paper was done under the METHOD EC funded project for the implementation of new technologies for optimization of centrifugal compressors.

Aerothermodynamic Performance Analysis of Hypersonic Flow on Power Law Leading Edges

A numerical study is reported on power-law-shaped leading edges situated in a rarefied hypersonic flow. The work is motivated by interest in investigating the flowfield properties of power-law-shaped leading edges as possible candidates for blunting geometries of hypersonic leading edges because power-law leading-edge shapes have both blunt (infinite body slope at the nose) and sharp (zero radius of curvature at the nose) characteristics. The sensitivity of the stagnation point heating, total drag, and shock wave standoff distance to shape variations of such leading edges is calculated by using the direct simulation Monte Carlo method. Comparisons based on equivalent stagnation point heating, equivalent total drag, and equivalent shock standoff distance are made between power law shapes and round leading edges. For the flow conditions considered, round leading edges provide lower drag and smaller shock standoff distance than power law leading edges for equivalent stagnation point heating. It was also found that power law shapes have smaller shock standoff distance and larger stagnation point heating than the round leading edges for equivalent total drag.

Leading edge noise from thick foils in turbulent flows

The prediction of dipole sound from the diffraction of turbulence by the leading edge of a rigid foil is made using acoustic analogies for homogeneous flows with and without mean shear. The Green’s function accounts for the foil thickness and leading edge shape. A comparison between the theory and published measurements suggests that the foil thickness exponentially attenuates the dipole sound pressure power spectrum by the product of the convection wavenumber and half the maximum section thickness. The ratio of the predicted dipole sound from the mean shear source to the source without mean shear is determined to be proportional to the ratio of the mean shear to the frequency of the sources.

Iterative Inverse Design Method Based on Streamline Equations

Aerodynamic characteristics are very sensitive to airfoil leading-edge geometry, and its accurate treatment is a limitation of many existing design methods. The objective of the present research is to develop an interactive inverse design method that is not only efficient but can also treat the leading-edge region accurately. In the formulation of the method, a small-perturbation geometric equation is deduced from the streamline momentum equations, the continuity equation, and the isentropic relations with the geometry similarity assumption of near streamlines to the airfoil surface. Moreover, the transonic correction is considered in the aforementioned equation with the assumption for the effects of waves reflected from the free surface (sonic line) because the method based on the surface flow values cannot take into account the transonic characteristics such as wave interference. The geometric perturbation normal to the airfoil surface is then calculated by solving this second-order initial value ordinary differential equation iteratively to obtain an airfoil design. Techniques such as airfoil smoothing, nonuniform relaxation, and the strained coordinate transfer are employed to accelerate convergence. The airfoil design cases demonstrate the remarkable efficiency and accuracy of the method not only for compressible flows but also for low-speed flows. Moreover, the method allows the leading-edge shape to be determined accurately and, thus, to overcome the deficiency of many of the related methods.

A Study on Aerodynamic Sound Generated from Plates (2nd Report, Effects of Chord-to-Sound Wave Length Ratio on Characteristics of Radiated Sound)

In order to investigate the characteristics of aerodynamic sound generated from plates which have various chord-to-thickness ratios (=2.0∼37.5) and four types of edge shapes consisting of the semi-circular and square, wind tunnel experiments are conducted. Moreover, the sound source distributions of the aerodynamic sound generated from the plates with the square edges are calculated by the 2-dimensional numerical analysis based on the Lighthill's equation with the incompressible flow data. In this study, some basic characteristics of the aerodynamic sound such as (i) the Peak Strouhal number St, (ii) the increase in Peak SPL with the wind velocity U, (iii) the radiation directivity and (iv) the practical critical condition of acoustically compact for chord-to-sound wave length ratio c/λ, are investigated. As a result, it is found that the St depends on the leading edge shape and that the Peak SPL isn't proportional to U6 under the condition that c/λ becomes greater than about 0.3 (≒1/π). Moreover, the Lighthill's sound source near the trailing-edge is the main contributor for the sound field independently of the edge shape. This result leads to a simple model which consists of the dipole source and the rigid plate for the acoustic analysis. We can also derive the same critical condition of c/λ from the sound calculation results of the previous model by the 2-dimensional boundary element method.

Dynamic Stall Alleviation Using a Deformable Leading Edge Concept-A Numerical Study

Dynamic stall calculations were carried out for an airfoil with a dynamically deformed leading-edge (DDLE) shape at a freestream Mach number of 0.3. The surface deformations were done about a baseline NACA 0012 airfoil, effectively increasing the airfoil leading-edge radius and thickness at high angles of attack. It was found that the DDLE airfoil had a slightly dynamic stall behavior compared to the baseline NACA 0012 airfoil. In particular, the lift, drag, and pitching-moment hysteresis loops were milder for the DDLE airfoil compared to the baseline airfoil. It was also found that a static shape that corresponds to the thickest deformed shape performed just as well as the DDLE shape, indicating that the shape itself, and not its time rate of change, was the reason for the improved performance. At higher Mach numbers around 0.4, the DDLE shape exhibited a strong dynamic stall triggered by a shock-induced separation, offsetting any benee t from the change in the shape of the airfoil. Additional work is needed on the development of DDLE shapes that will perform well at higher speeds.

Modification of the NACA 632-415 Leading Edge for Better Aerodynamic Performance

Double stall causes more than one power level when stall-regulated wind turbines operate in stall. This involves significant uncertainty on power production and loads. To avoid double stall, a new leading edge was designed for the NACA 632-415 airfoil, an airfoil that is often used in the tip region of wind turbines. A numerical optimization tool incorporating XFOIL was used with a special formulation for the airfoil leading edge shape. The EllipSys2D CFD code was used to analyze the modified airfoil. In theory and in wind tunnel tests, the modified airfoil showed smooth and stable stall characteristics with no tendency to double stall. Also, both theory and wind tunnel tests showed that the overall aerodynamic characteristics were similar to NACA 632-415 except for an increase in the lift-drag ratio below maximum lift and an increase in maximum lift. The wind tunnel tests showed that dynamic stall and aerodynamic damping characteristics for the modified airfoil and the NACA 632-415 airfoil were the same. The modified airfoil with leading edge roughness in general had better characteristics compared with the NACA 632-415 airfoil.

Numerical Study of the Effect of the Leading Edge Shape on Cavitation Around Inducer Blade Sections.

A numerical study of the cavitation behaviour of two-dimensional hydrofoils simulating a section of an inducer blade is presented. Two leading edge shapes were chosen to approach rocket engine inducer designs. They were tested with respect to the development of sheet cavitation. The numerical model of cavitating flows is based on the 3D code FINE/TURBOTM, developed by NUMECA International. The cavitation process is taken into account by using a single fluid model, which considers the liquid vapour mixture as a homogeneous fluid whose density varies with respect to the static pressure. Numerical results are compared with experimental ones, obtained in the CREMHyG large cavitation tunnel(1). Pressure distributions along the foil suction side and the tunnel walls were measured for different cavity lengths. Total pressure measurements along the foil suction side allow characterizing the effects of cavitation on the liquid flow. Influence of the leading edge shape on the cavitation behaviour and comparison between experiments and numerical predictions are discussed.

Unsteady Stall Control Using Dynamically Deforming Airfoils

Introduction An experiment documenting the compressible flow over a dynamically deforming airfoil is presented. This airfoil, which has a leading edge radius that can be dynamically changed, was tested at various defor- mation rates for fixed airfoils angle of attack. Selected leading-edge shapes were also tested during airfoil os- cillation. These tests show that for a range of Mach numbers observed on the retreating blades of heli- copter rotors the dynamic stall vortex can be avoided by the judicious variation of leading-edge curvature

Flow Visualization and Leakage Measurements of Stepped Labyrinth Seals: Part 2—Sloping Surfaces

An experimental investigation was conducted to determine the geometry–leakage relationship for advanced, stepped labyrinth seals. A unique, variable-geometry water test facility was constructed and used to acquire leakage resistance measurements for two-dimensional, planar models. Flow visualization techniques were also used to assist in identifying and understanding the turbulence generating flow patterns. It was found that contoured surfaces and restrictor tooth leading-edge shapes of proper dimensions can be incorporated into the cavity geometry to reduce seal leakage. Specifically, the combination of a sloping surface and a curved surface on the rotor within the labyrinth cavity gave significant improvement.

Numerical simulation of the flow about a swept wing with leading-edge ice accretions

The aerodynamic load characteristics and the performance degradation of moderate aspect ratio wings with simulated glaze leading-edge ice have been studied using a three-dimensional compressible Navier-Stokes solver. Correlation of predictions with experimental data for swept wings with and without leading-edge ice formation shows the ability of the present computational technique to predict accurately both the distributed surface pressures and integrated sectional loads. The leading-edge flow separation and reattachment on the wing surface caused by the leading-edge ice shape are also well captured, showing a vortex formation and the spanwise migration of the flow inside the separated flow region. The performance degradation of the wing as a result of the leading-edge ice formation is numerically well demonstrated.

Analysis of hypersonic shock-wave laminar boundary-layer interaction phenomena

In the present paper hypersonic viscous flows dominated by strong shock-wave laminar boundary-layer interactions over wing-flap and wing-fuselage junction configurations have been analyzed. The effects of the control surface deflection angle, leading edge shape and viscous interaction parameter on the flowfield have been evaluated. Scaling laws for the upstream influence, peak heating and aerodynamic coefficients have been established by means of numerical simulations and theoretical considerations.

Viscous interaction phenomena in hypersonic wedge flow

We deal with an experimental investigation carried out to study some aspects of shock/boundary-layer interaction in nominally two-dimensional hypersonic wedge flow, i.e., over flat plate/rump configurations. These flow conditions are two dimensional only geometrically because some spanwise periodic variations of the heat flux over the ramp in the reattaching flow region are observed. The measurements, basically made by means of a computerized infrared (IR) imaging system, have been performed in a blowdown wind tunnel at Mach number equal to 7.14 and unit Reynolds number ranging from 7.6 x 10 6 to 24 X 10 6 /m. The influence of the leading-edge shape (bluntness and geometry), flat plate length, and ramp angle on the separation region, average heat transfer at reattachment, and wavelength of the heat transfer variations has been analyzed. IR results are compared to other experimental data as well as to semiempirical correlations for the heat flux peak.