Scale-Adaptive Simulations of flow in clean transonic cavities with and without doors are presented in this paper. Results were also compared with DetachedEddy Simulations for cavities with length-to-depth ratios of 5 and 7. The Mach and Reynolds numbers (based on the cavity length) were 0.85 and 6.5 × 10 6 respectively, and the grid sizes were 5.0 million for the clean cavity with doors-off and 5.5 million for the clean cavity with doors-on. Instantaneous Mach number contours showed that the shear layer broke down for both the doors on and doors off cases and that the flows had a high level of unsteadiness inside them. Numerical schlieren contours made it possible to visualise the propagation of pressure waves in and around these cavities. The two L/D ratios of cavities were seen to have similar acoustic signatures reaching maximum sound levels of 170dB. Spectral analyses for the cavities without doors revealed that by changing the length-to-depth ratio from 5 to 7, the dominant acoustic modes at the front and rear of the cavities were shifted from the second and third modes to the first and second modes respectively. Proper Orthogonal Decomposition was used to reduce the data storage using modes constructed from flowfield snapshots taken at regular intervals. Cumulative energy plots of the constructed modes showed that Detached-Eddy Simulations were able to capture 10% more energy for Pressure and Density variables for the same number of modes.
Purpose -The design of main rotor blade tips is of interest to helicopter manufacturers since the tip details affect the aerodynamic performance and acoustics of the rotor. The aim of this paper is the numerical simulation the flow around hovering helicopter blades with different tip designs.Design/methodology/approach -In this paper, CFD is used to simulate the flow around hovering helicopter blades with different tip designs. For each type of blade tip a parametric study on the shape is also conducted. For comparison, calculations were performed at the same rotor thrust. The collective pitch of the blades and the coning angle of the rotor were determined by an iterative trimming process. The aeroacoustic characteristics of the rotors were obtained using the Ffowcs Williams -Hawkings equation.Findings -Analysis of the distributed blade loads shows that the tip geometry has a significant influence on aerodynamics and aeroacoustics especially for stations where blade loading is high.Originality/value -The results are useful for design new blades with high performance and low acoustic emission. INTRODUCTIONResearch into helicopter blade tips is important for helicopter manufacturers. Past and recent papers demonstrate the constant interest of researchers in this problem. The results show potential to increase the aerodynamic efficiency of the rotor and to reduce its acoustics (aero-acoustic noise). Brocklehurst and Barakos (2012) present a recent review of works dedicated to different aspects of blade tip design. In (Yen, 1994) swept-tapered blade tips were compared with swept, tapered and rectangular versions. In high speed flight the swept-tapered tip reduced the pitch link loads and the blade vibration. Trailing vortex measurements in hover have also been reported in (Martin and Leishman, 2002) for various tip shapes including rectangular, tapered, swept, and a sub-wing tips. One of the primary differences noted was the dependence of wake geometry on the tip shape. The tapered tip reduced the initial swirl velocity, increased the radial convection and decreased the axial convection. The quiet Helicopter demonstrator is discussed in (Allongue et al., 1999). The blade tip shape has a parabolic leading edge and is highly tapered, and therefore has low volume. This tip has some benefits in hover efficiency and noise performance but use on heavier, faster helicopters may be limited by advancing side compressibility effects and retreating side blade stall. According to (Brocklehurst and Barakos, 2012) three families of blade tips (Figure 1) have so far received attention: parabolic, swept and BERP tips. Further improvements and a reduction of the blade noise can be achieved by modifying the rest of the blade plan form. This was attempted with the "ERATO" (Beaumier and Delrieux, 2003) and "Blue Edge" (Rauch et al., 2011) designs. On the ERATO rotor, the blade curves forward and the main sweep-back starts inboard. The aim of this blade design is to reduce blade-vortex interaction (BVI) noise. Anhedral has been...
Abstract. This research aims to investigate a virtual blade model and assess rotor influence on helicopter fuselage aerodynamics. The rotor disk is discretized in the azimuthal direction, and a time-varied pressure jump is applied in regions occupied by the blades. To obtain the pressure jump, an actuator disk is employed using uniform and non-uniform blade load distribution, based on momentum theory.
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