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23 pages, 14288 KiB

Open AccessArticle

The Influence of Rotor Overlapping Azimuth on Compound Coaxial Helicopter Performance Based on Unsteady CFD Simulation

by Liang Li, Chenglong Zhou, Ming Chen, Fang Wang and Anan Xu

Appl. Sci. 2023, 13(2), 820; https://doi.org/10.3390/app13020820 - 6 Jan 2023

Cited by 2 | Viewed by 1455

Abstract

In this paper, a computational fluid dynamics simulation method is developed to study the influence of the rotor overlapping azimuth on the aerodynamic performance of compound coaxial helicopter. The simulation method is verified by comparing the numerical simulation results with the wind tunnel experiment data of the NASA coaxial rotor. Two overlapping azimuths of the upper and lower blades are considered, and the aerodynamic performance of the isolated rotor and the compound coaxial helicopter in hover and forward are analyzed respectively. State 1 means the upper and lower blades overlap at azimuth

0 / 180 °

90 / 270 °

, state 2 means the upper and lower blades overlap at azimuth

45 / 225 °

135 / 315 °

. It is found that the performance of isolated rotors is not affected by rotor overlapping azimuth in hover, but the total thrust fluctuation amplitude of isolated rotors in state 2 is 76.3% smaller than that in state 1 in forward. In the hovering flight of compound coaxial helicopter, compared with state 1, the fluctuation amplitude of the lift of the wing in state 2 is 42.7% smaller; the lift fluctuation amplitude of the flat tail in state 2 is 52.4% smaller. In the forward flight of compound coaxial helicopter, compared with state 1, the total thrust fluctuation amplitude in state 2 is 83.5% smaller; the fluctuation amplitude of the lift of the wing in state 2 is 61.2% smaller. It can be concluded that the compound coaxial helicopter working in state 2 has better aerodynamic performance than the compound coaxial helicopter working in state 1; changing the rotor overlapping azimuth of the upper and lower rotors has a high engineering application value, which can increase aerodynamic stability and reduce lift fluctuations. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Aerospace Engineering)

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15 pages, 4844 KiB

Open AccessArticle

Influence of Wake Sweeping Frequency on the Unsteady Flow Characteristics of an Integrated Aggressive Interturbine Duct

by Zhijun Lei, Shuang Sun, Gang Li, Hongrui Liu, Xiaoqing Ouyang, Yanfeng Zhang, Xingen Lu, Gang Xu and Junqiang Zhu

Appl. Sci. 2022, 12(22), 11751; https://doi.org/10.3390/app122211751 - 18 Nov 2022

Cited by 1 | Viewed by 1071

Abstract

A dynamic simulation was launched to research the influence of high-pressure turbine (HPT) rotor wake passing frequency on the flow mechanism in an integrated aggressive interturbine duct (AITD). Sweeping rods were adopted to replace the HPT rotors to decouple the influence of its wake from those of other secondary flows. The diameter of the rods (d/s, nondimensionalized by the pitch (s) of the integrated struts at midspan) was 0.10, and their reduced frequency (f) ranged from 0.49 to 1.61. The k–ω SST turbulence model and γ–θ transition model were adopted for the turbulence closure. A 6.3-million-node structured grid was used to meet the grid dependency. Along with increasing f, the intensified circumferential motion of the wake (1) enhances the wake vortex stretching and exhaustion near the hub; (2) promotes the radial inclination of wakes and elongates and narrows the wake vortex band, resulting in increased spacing between the adjacent wake vortices and the weakened vortex interaction. In the high-f cases, the enhanced turbulence intensity in the interval between the adjacent wakes could suppress the separation bubble on LPT-GV in advance, but the elongated and narrowed wake vortices resulted in a substantial reduction in the radial extent and duration of their suppression on the separation bubble. Therefore, the influence of f on the integrated AITD and its parts was bidirectional, and adjusting the sweeping frequency to balance its positive and negative effects could minimize the total loss in the integrated AITD. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Aerospace Engineering)

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12 pages, 4271 KiB

Open AccessArticle

Effects of Cowl Lip Angle on Starting Performances for a Mixed-Compression Two-Dimensional Axisymmetric Hypersonic Inlet

by Yunfan Zhou, Shangcheng Xu and Yi Wang

Appl. Sci. 2022, 12(14), 7127; https://doi.org/10.3390/app12147127 - 14 Jul 2022

Cited by 5 | Viewed by 1688

Abstract

The third quasi-uniform B-spline was adopted to design the cowl profiles with various cowl lip angles. Starting performances were simulated by the numerical method and the results showed that the starting processes for different cowls can be classified into two types. In the first type, the inlet starts when the opened large-scale separation zone is swallowed; in the second type, the opened separation zone enters the internal contraction region to form a closed separation zone, which is then swallowed to enable the start. In addition, inlets with small and large cowl lip angles exhibit the first and second types of the starting process, respectively. Moreover, there is an optimal cowl lip angle to achieve the best starting performance. For the inlet investigated herein, the starting Mach number is the lowest when the cowl lip angle is 9°. In addition, as the internal contraction ratio increases, the optimal cowl lip angle gradually decreases and the starting performance deteriorates. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics in Aerospace Engineering)

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