A BRIEF REVIEW ON VARIOUS NOISE REDUCTION TECHNIQUES EMANATING FROM WINGS OF AN AIRCRAFT

— One of the challenges and a point of need in the aviation industry is the problem of high level of noise emanation. There are various sources of noise emanating from aircraft which are the noises from engine and airframe including the wings. Noise from the wing is an important phenomenon to be put into consideration as it contributes significantly to the noise emanating from aircraft especially during take-off and landing. Airfoil noise emission emanate on the wing section of an aircraft due to the interaction of the airfoil turbulent boundary layer with the sharp leading edge. Noise reduction then becomes a thing of concern for many engineers and researchers who took it upon their shoulder the responsibility of coming up with design that can help reduce noise emanating from aircrafts to mitigate the noise. Due to this, many researchers have focused on reducing the noise emanating from the aircraft through various means and approaches which include theoretical, computational, and experimental analysis. In a means of compiling and making available a brief review of such work, for easy and quick access necessitate the need of this work. This paper focused on giving a summary and review of different work done by past and current researchers in the field. The review was based on selected current papers on the cutting-edge technology towards enhancing aerodynamic performance of the wing of aircraft and reduction of noise emanating from it. Although fruitful results have been achieved in the aerodynamic noise control, but only little work has been done to summarize the main findings and progresses in this area. This work focused on review of work carried out by many researchers in this area which involves various techniques and attempts ranging from leading edge serration, trailing edge serration, active flow actuation, flexible wing using theoretical, computational, and experimental approach etc. Additionally, some suggestions were made towards further study and improv

A Novel Method for Blunting the Leading Edge of Waverider with Specified Curvature

An ideal waverider has an infinite sharp leading edge, which causes difficulty for manufacture and aerothermal protection. Therefore, the leading edge of the waverider must be blunted. For this purpose, a parametric method for blunting the leading edge of the waverider is proposed here, which can fulfill the goals of setting a leading-edge blunt radius, achieving geometric continuity, and realizing the parametric design. First is the blunting procedure of the proposed method incorporating the construction of two-dimensional blunt curves and the integration of these curves on a three-dimensional waverider configuration. Second, waveriders blunted with different geometric continuities are built with corresponding computing grids generated. Numerical methods are then introduced and validated by the benchmark cases. Finally, results from these blunted configurations are presented and compared in terms of their geometric and flow characteristics. It shows that the proposed method has a better performance in the head region of the waverider and is thereby more suitable for the practical design.

Numerical study on aerodynamic performance of waverider with a new bluntness method

Abastrct The waverider is deemed the most promising configuration for hypersonic vehicle with its high lift-to-drag ratio at design conditions. However, considering the serious aero-heating protection, the sharp leading edge must be blunted. The existing traditional bluntness methods including the following two types: “reducing material method” and “adding material method”. Compared to the initial waverider, the volume will be smaller or larger using the traditional methods. With the fixed blunted radius, the volume and aerodynamic performance is determined. In this paper, a new bluntness method which is named “mixing material method” is developed. In this new method, a new parameter is introduced based on the traditional two bluntness methods. Under fixed blunted radius, the volume and aerodynamic performance can be changed within a wide range by adjusting the parameter. When the parameter is 0 and 1, the novel blunted method degenerated into the “reducing material method” and “adding material method” respectively. The influence of new parameter on the aerodynamic characteristics and volume are studied by numerical simulation. Results show that the volume, lift and lift-to-drag ratio increases with the increase of the parameter under the fixed blunt radius, but simultaneously, the drag will also increase. Therefore, considering the different requirements of the air-breathing hypersonic aircrafts for the balance of thrust and drag, lift and weight, a suitable bluntness parameter can be selected to achieve a balance. This research can provide reference for hypersonic waverider vehicle design.

Experimental investigations on the sharp leading-edge separation over a flat plate at zero incidence using particle image velocimetry

Leading-edge separated flow field over a sharp flat plate is experimentally investigated in Reynolds numbers ranging from 6.2 × 103 to 4.1 × 104, using particle image velocimetry (PIV) and its statistics. It was observed that the average reattachment length is nearly independent of Reynolds number and the small secondary bubble observed near the leading edge was found to shrink with increasing Reynolds number. The wall-normal profiles of the statistical values of kinematic quantities such as the velocity components and their fluctuations scaled well with average reattachment length lR and freestream velocity U∞. Their magnitudes compare well with previous investigations even though the current triangular shaped sharp leading edge is different from previous flat-faced or semi-circular ones. The shear layer was observed to exhibit 2 different linear growth rates over 2 distinct regions. Instantaneous PIV realizations demonstrate unsteady nature of the separation bubble, whose origins in the upstream portion of the bubble are analysed. Bimodal nature of the probability density function (PDF) of fluctuating streamwise velocity at around x/lR = 0.08–0.15 indicates successive generation and passage of vortices in the region, which subsequently interact and evolve into multiscale turbulent field exhibiting nearly Gaussian PDF. Shedding of vortices with wide range of scales are apparent in most of the instantaneous realizations. Proper Orthogonal Decomposition (POD) of the velocity fluctuation magnitude field revealed that the flow structures of the dominant modes and their relative energies are independent of Reynolds number. In each of the dominant modes (first 3 modes), the length scales corresponding to the large scale structures and their spacing are the same for all Reynolds numbers, suggesting that their Strouhal number (observed to be ~ 0.09–0.2 at Reynolds number of 6.2 × 103) of unsteadiness should also be independent of Reynolds number. A single large structure- comparable in size to lR—was apparent well before reattachment in a few instantaneous realizations, as compared to multiple small-scale structures visible in most realizations; at Reynolds number of 6.2 × 103, realizations with such large-scale structures occurred approximately after every 20–30 realizations, corresponding to non-dimensional frequency of 0.4–0.6, which is identified to be the “regular shedding”. It was possible to reconstruct the large-scale structure during the instances from just the first 3 POD modes, indicating that the Strouhal number of regular shedding too is independent of Reynolds number. Graphic abstract

Wave drag on asymmetric bodies

An asymmetric body with a sharp leading edge and a rounded trailing edge produces a smaller wave disturbance moving forwards than backwards, and this is reflected in the wave drag coefficient. This experimental fact is not captured by Michell’s theory for wave drag (Michell Lond. Edinb. Dubl. Phil. Mag. J. Sci., vol. 45 (272), 1898, pp. 106–123). In this study, we use a tow-tank experiment to investigate the effects of asymmetry on wave drag, and show that these effects can be replicated by modifying Michell’s theory to include the growth of a symmetry-breaking boundary layer. We show that asymmetry can have either a positive or a negative effect on drag, depending on the depth of motion and the Froude number.