Low Aspect Ratio Rectangular Wing Research Articles

Examination and Prediction of the Lift Components of Low Aspect Ratio Rectangular Flat Plate Wings

An investigation of the lift components present over low aspect ratio rectangular wings is presented. Wing aspect ratios ranging from 0.5 to 3 are examined using published experimental results and analytic analysis methods. The methods are based on the fundamental decomposition of Polhamus; that is, lift is attributed to a potential flow lift component coupled with a vortical lift component stemming from the leading and side edges of the flat plate wing. The analysis suggests a low sensitivity to Reynolds numbers spanning three orders of magnitude and brings into doubt the realization of a leading edge vortex lift component for wings with unswept leading edges under steady state conditions. The analytic prediction method of Purvis is shown to provide close accord with all experimental data sets when lift contributions caused by a leading edge vortex are excluded.

Contribution of spanwise and cross-span vortices to the lift generation of low-aspect-ratio wings: Insights from force partitioning

This study reports on the vortex-induced lift production mechanisms in low Reynolds number flows over low aspect-ratio rectangular wings. We use a rigorous force partitioning method which allows for the estimation of the pressure-induced aerodynamic loads due to distinct flow features or vortex structures in the flow around the wing. The specific focus of this work is on distinguishing the effect of spanwise and cross-span oriented vortex structures on pressure-induced lift production. We quantify the lift induced on the wing by these different vortices, and also estimate their influence within different regions of the flow-field around the wing and in the wake. By varying the aspect-ratio and angle-of-attack of the wing, we show that for most cases, the spanwise oriented vorticity contributes less to the total lift than cross-span oriented vortices. Furthermore, the spanwise vorticity in the near wake is capable of producing net negative lift on the wing and this is explained by separating and quantifying the influence of vortex cores and regions of strain in the wake. The results demonstrate the utility of the force partitioning method for dissecting the flow physics of vortex dominated flows.

Numerical Investigation on Evolution of Tip Vortices Generated by Low-Aspect Ratio Rectangular Wings at High Angle of Attack

The onset and evolution of tip vortices generated by the vertical tip of a straight half wing, with a NACA 0012 airfoil section, were studied at a Reynolds number of 1 × 105 by a steady-state calculation at high angles of attack, namely, 10°, 18°, and 42°, where the maximum lift, deep stall, and second peak of the lift coefficient occur, respectively, with three different aspect ratios: 2, 3, and 4. It was found that the counter-rotating vortex wrap initiated within the short wake period at higher angles than the deep stall and affected the contraction of the core trail, as well as resulting in the calculated swirl velocity component exhibiting a significant deviation from the conventional model fit. It was noted that the swirl strength of tip vortices increased continuously, even up to the deep stall phase, where the lift started to decrease immediately after the first peak. Wake contraction was found to follow an exponential decay in the earlier wake region. Compared to both the infinite wing and the elliptical wing, the finite square wing seems to have an offset in the lift coefficient, which could represent the tip loss.

CFD Analysis of Low Aspect Ratio Rectangular Wings in Very Low Reynolds Number

CFD Analysis of Low Aspect Ratio Rectangular Wings in Very Low Reynolds Number

Experimental investigation of rotor/lifting surface interactions

Experiments were conducted to study the aerodynamic interactions between a rotor and a fixed lifting surface. A low aspect ratio rectangular wing was positioned at different locations in a rotor flowfield to simulate the aerodynamic environment encountered by the wings of tilt-rotors or the empennage of helicopters. Steady and unsteady pressure measurements were made on the wing at various chordwise and spanwise stations for different combinations of rotor thrust and advance ratio. Flow visualization was performed using the wide-field shadowgraph method, which helped to identify the locations of the rotor wake relative to the rotor and wing. The results have shown that the lifting surface operates in a highly unsteady three-dimensional flow environment with regions of partial or complete flow separation. In addition, large unsteady loads were induced on the wing by the rotor and its wake.

Sonic boom predictions using a solution-adaptive full-potential code

The TranAir full-potential code, which utilizes a solution-adaptive, unstructured Cartesian grid, was used to compute near-field pressure signatures of three generic geometries: (1) a cone-cylinder; (2) a low aspect ratio rectangular wing; and (3) a delta-wing/body. Pressure signatures computed by TranAir are extrapolated to near- and midfield distances using a quasilinear extrapolation technique. Results are compared with wind-tunnel data and, where possible, with extrapolated wind-tunnel data and Whitham-method results. In general, extrapolated TranAir data is in good agreement with experimental and Whitham-method pressure signatures, but peak pressures are slightly underpredicted. It is felt that data computed too close to the model caused some of the discrepancies. The flowfield grid structure was also found to be an important issue in obtaining accurate off-body data. Results were encouraging enough to proceed with the application of TranAir to conceptual configurations in support of the NASA high speed research program (HSRP).

48 油点追跡による表面摩擦力の推定

An approximate skin friction estimation method by tracking oil dot movement under the effect of skin friction is proposed. The method uses the correlation between oil dot velocity and skin friction obtained by measurements for flat plate laminar boundary layer in a wind tunnel. The correlation is divided into two zones. Linear correlations at early stage of oil dot streak developments are observed. But, the correlation factors are much differ among oil dots. If oil dots streaks develop enough after a long period, the correlations converge into a certain band. Present method uses the later correlation to estimate skin friction values. Skin friction values on a very low aspect ratio rectangular wing having NACA 4412 wing section are estimated. The results show approximate skin friction values on bodies can be easily estimated by the present method.

A Fundamental Study on Hull to Rudder Interaction

It is well known that there exists the hydrodynamic interaction between ship's hull and rudder which may have a remarkable effect on ship maneuvering. By many experimental investigations of lateral force acting on a ship during maneuver, it is found that the hydrodynamic force which is induced on the main hull of a ship by steering its rudder comes up to about 30% of rudder force. At present, however, the effect of presence of main hull on the rudder force is not yet made clear. The main aim of this paper is to deal with the latter problem.Assuming that the hull and the rudder can be replaced by a low aspect ratio rectangular wing and its flap which is separated from the wing, the integral equations based on nonlinear lifting surface theory are derived, and the results of numerical calculation are compared with the experimental data. The calculation values of normal force acting on rudder and main hull agree fairly well with the experimental ones. Furthermore, by comparing tine hydrodynamic forces of rudder and main hull obtained in hull-rudder system with those obtained when rudder and main hull exist independently, the authors discuss the hull to rudder interaction.Consequently, it is shown that additional hydrodynamic force due to steering is induced on the main hull, but on the contrary, the rudder effectiveness is reduced compared with that in open water.

Numerical Results for the Longitudinal Stability Derivatives and Stability Loci of a Low Aspect Ratio Rectangular Wing in Supersonic Flow

The longitudinal stability derivatives and stability loci for a single-degree-of-freedom, pitching oscillation of a rectangular wing having an effective aspect ratio less than unity have been calculated from the results of a previous, analytical investigation. The results extend those previously available for a rectangular wing of effective aspect ratio greater than unity.