Tandem Airfoil Configuration Research Articles

Large-eddy simulation of vortex interaction in pitching-fixed tandem airfoils

In this study, the interaction of vortices generated from an oscillating airfoil with a hindfoil placed downstream of the oscillating forefoil at low-Reynolds-number flow was investigated numerically. The forefoil entered a deep dynamic stall induced by large-amplitude pitching oscillation. The dynamic stall process is characterized by unsteady separation and the formation of a strong clockwise vortex. A wall-resolved large-eddy simulation approach was applied to compute the flowfield. The numerical measurements were performed for an incompressible flow at a Reynolds number of Re = 30 000 based on chord length with a pitching reduced frequency of K= 0.5, and amplitude of A = 14.1° over Selig–Donovan 7003 airfoils. A single-airfoil case was validated against numerical and experimental measurements. In the present study, we investigated the flowfield and aerodynamic coefficients resulting from the deep dynamic stall of the pitching forefoil and the vortex interaction in tandem-airfoil configuration related to micro-air vehicle applications by employing large-eddy simulation approach. Large-eddy simulation was also compared to two-dimensional unsteady Reynolds-averaged Navier–Stokes simulation to determine the accuracy and validity of the low-fidelity approach in prediction of deep dynamic stall and vortex interaction at low-Reynolds-number flow.

On the use of leading-edge serrations for noise control in a tandem airfoil configuration

Passive noise control for a tandem NACA 65-710 airfoil configuration is experimentally investigated by applying leading-edge serrations on the rear airfoil. With a sliding side-plate mechanism that allows the rear airfoil to move in the vertical direction relative to the front airfoil, the position of maximum turbulence interaction noise is first identified from the far-field noise measurements. Subsequently, detailed static surface pressure distribution and unsteady surface pressure fluctuations are acquired to shed more light on the physical phenomenon and underlying noise-reduction mechanism of the leading-edge serrations. The far-field noise measurements confirm that a notable turbulence interaction noise reduction can be achieved from 600 Hz < f < 3000 Hz, agreeing well with the previous literature on the effectiveness of the leading-edge serrations. The near-field hydrodynamic analyses obtained using remote-sensing techniques of the fluctuating pressure fields over the airfoil show that a significant reduction in the surface pressure fluctuation levels up to 20 dB/Hz can be observed at the serrated-tip plane of the rear serrated airfoil close to the leading-edge regions, over the range of frequencies investigated. Although reduction can also be observed on the serrated-root plane, the magnitude is much less significant. The present results suggest that the modification of the unsteady loading on the rear airfoil by the leading-edge serrations plays a crucial role in the reduction of turbulence interaction noise in the tandem airfoil configuration, which may find practical application for noise reduction in aerodynamic systems involving rows of airfoils, such as contra-rotating open rotors and outlet guide vanes.

Characterization of Tandem Airfoil Configurations of Axial Compressors

Abstract The objective of the current study is to investigate the effects of geometric parameters on the fluid flow patterns, diffusion factor, load-split, and off-design performance of the tandem configuration under subsonic, rectilinear, cascade flow. A 2-D computational model using finite volume formulation has been developed and validated against available experimental data. The obtained data is presented in a format involving loss parameter and loading and will help the designer to have sufficient number of combinations within the useful range of application. It is observed that general performance behavior of tandem cascade is similar to a single airfoil data. Load shifting from the front airfoil to the rear airfoil is noted at positive axial overlaps and higher camber ratios. An optimum gap ratio of around 2 is observed for the range of configurations investigated. Contrary to the previous literature, the present study indicates higher loading of the front airfoil for the best overall loading-to-loss ratio of the tandem configuration.

Prediction of Lift Coefficient for Tandem Wing Configuration or Multiple-Lifting-Surface System Using Prandtl’s Lifting-Line Theory

In tandem airfoil configuration or multiple-lifting-surface layouts, due to the flow interaction among their lifting surfaces, the aerodynamic characteristics can be affected by each other. In accordance with Prandtl’s classical lifting-line theory, a method to calculate the section lift coefficient for the tandem wing configuration or multiple-lifting-surface system is presented. In that method, the form of Fourier sine series is used to express the variation of the section circulation which changes continuously along the wingspan. The accuracy of the numerical solutions obtained by the method has been validated by the data obtained from computational fluid dynamics and tunnel experiment. By varying the design parameters, such as the gap, the stagger, the incidence angle, the wingspan, the taper ratio as well as the aspect ratio, a series of tandem wing configurations are tested to analyze the lift coefficient and the induced drag of each lifting surface. From the results, it can be seen that the bigger negative gap and stagger can produce better lift characteristic for tandem wing configuration. Besides, it will also be beneficial for the lift characteristic when the incidence angle and the wingspan of fore wing are appropriately declined or if the incidence angle and the wingspan of hind wing are appropriately increased.

Numerical investigation of the effect of stagger on the aerodynamic characteristics of a Busemann biplane

Busemann biplanes and its modified versions are recently being reinvestigated for possible low boom supersonic transport. The Busemann biplane offers a very favorable drag reduction at design supersonic Mach numbers due to wave cancellation effect. However, at the off design speeds its performance deteriorates and the wave cancellation effect offer no favorable drag reductions. Another problem associated with the Busemann biplane is the chocking of the flow due to inability of the biplane to engulf the normal starting shock wave in front of the biplane. This paper attempts to address the chocking problem through the numerical simulation of Busemann biplane with staggered airfoil configurations. Lift and drag characteristics of a Busemann biplane with staggered tandem airfoil configurations are investigated at various Mach numbers between 0.5 and 2.5 using Computational Fluid Dynamics. The stagger increases the throat area thus reduces the flow chocking characteristics of the Busemann biplane without effecting the wave cancellation much. The results suggest that a significant reduction in wave drag can be realized even at off-design conditions, especially at low Mach numbers through staggering of the Busemann biplanes.

Recovery of Energy from Leading- and Trailing-Edge Vortices in Tandem-Airfoil Configurations

Recovery of Energy from Leading- and Trailing-Edge Vortices in Tandem-Airfoil Configurations

3D Numerical Investigation of Tandem Airfoils for a Core Compressor Rotor

The tandem airfoil has potential to do more work as a compressor blade than a single airfoil without incurring higher losses. The goal of this work is to evaluate the fluid mechanics of a tandem rotor in the rear stages of a core compressor. As such, the results are constrained to shock-free fully turbulent flow with thick endwall boundary layers at the inlet. A high hub-to-tip ratio 3D blade geometry was developed based on the best-case tandem airfoil configuration from a previous 2D study. The 3D tandem rotor was simulated in isolation, in order to scrutinize the fluid mechanisms of the rotor, which had not been previously well documented. A geometrically similar single blade rotor was also simulated under the same conditions for a baseline comparison. The tandem rotor was found to outperform its single blade counterpart by attaining a higher work coefficient, polytropic efficiency, and numerical stall margin. An examination of the tandem rotor fluid mechanics revealed that the forward blade acts in a similar manner to a conventional rotor. The aft blade is strongly dependent on the flow it receives from the forward blade, and tends to be more three-dimensional and nonuniform than the forward blade.