scholarly journals Geometry Design of Coaxial Rigid Rotor in High-Speed Forward Flight

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Bo Wang ◽  
Xin Yuan ◽  
Qi-jun Zhao ◽  
Zheng Zhu
Keyword(s):  
High Speed ◽  
Reverse Flow ◽  
Geometrical Parameters ◽  
Rigid Rotor ◽  
Forward Flight ◽  
Geometry Design ◽  
Coaxial Rotor ◽  
Flow Field Characteristics ◽  
Speed Level ◽  
Blade Tip

The aerodynamic performance analysis and blade planform design of a coaxial rigid rotor in forward flight were carried out utilizing CFD solver CLORNS. Firstly, the forward flow field characteristics of the coaxial rotor were analyzed. Shock-induced separation occurs at the advancing side blade tip and severe reverse flow occurs at the retreating side blade root. Then, the influence of geometrical parameters of the coaxial rigid rotor on forward performance was investigated. Results show that swept-back tip could reduce the advancing side compressibility drag and elliptic shape of blade planform could optimize the airload distribution at high advance ratio flights. A kind of blade planform combining swept-back tapered tip and nonlinear chord distribution was optimized to improve the rotor efficiency for a given high-speed level flight based on geometric parameter studies. The optimized coaxial rotor increases lift-to-drag ratio by 30% under the design conditions.

Interactional Aerodynamic Analysis of an Asymmetric Lift-Offset Compound Helicopter in Forward Flight

2021 ◽  
Author(s):  
Jan-Arun Faust ◽  
Yong Su Jung ◽  
James Baeder ◽  
André Bauknecht ◽  
Jürgen Rauleder
Keyword(s):  
High Speed ◽  
Stokes Equations ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Particle Image Velocimetry Data ◽  
Operating Conditions ◽  
Test Case ◽  
Forward Flight ◽  
Compound Helicopter ◽  
Thrust And Torque

Recently, an asymmetric lift-offset compound helicopter has been conceptualized at the University of Maryland with the objective of improving the overall performance of a medium-lift utility helicopter. The investigated form of lift-compounding incorporates an additional stubbed wing attached to the fuselage on the retreating side. This design alleviates rotor lift requirements and generates a roll moment that enables increased thrust potential on the advancing side in high-speed forward flight. In this study, a numerical model was developed based on the corresponding experimental test case. Three-dimensional unsteady Reynolds-averaged Navier–Stokes equations were solved on overset grids with computational fluid dynamics–computational structural dynamics (CFD–CSD) coupling using the in-house CPU–GPU heterogeneous Mercury CFD framework. Simulations were performed at high-speed, high-thrust operating conditions and showed satisfactory agreement with the experimental measurements in terms of the cyclic control angles, rotor thrust, and torque values. CFD results indicated that for an advance ratio of 0.5 with a collective pitch of 10.6°, a vehicle lift-to-equivalent-drag ratio improvement of 47% was attainable using 11% wing-lift offset. The CFD-computed flow fields provide insights into the origin of a reverse flow entry vortex that was observed in particle image velocimetry data, and they characterize the wing–rotor interactional aerodynamics.

Blade Tip Carving Effects on the Aero-Thermal Performance of a Transonic Turbine

2013 ◽  
Author(s):  
C. De Maesschalck ◽  
S. Lavagnoli ◽  
G. Paniagua
Keyword(s):  
High Speed ◽  
Thermal Stresses ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Geometrical Parameters ◽  
Complex Flow ◽  
Turbine Rotor Blade ◽  
Blade Tip ◽  
Transonic Turbine

Tip leakage flows in unshrouded high speed turbines cause large aerodynamic penalties, induce significant thermal loads and give rise to intense thermal stresses onto the blade tip and casing endwalls. In the pursuit of superior engine reliability and efficiency, the turbine blade tip design is of paramount importance and still poses an exceptional challenge to turbine designers. The ever-increasing rotational speeds and pressure loadings tend to accelerate the tip flow velocities beyond the transonic regime. Overtip supersonic flows are characterized by complex flow patterns, which determine the heat transfer signature. Hence, the physics of the overtip flow structures and the influence of the geometrical parameters on the overtip flow require further understanding to develop innovative tip designs. Conventional blade tip shapes are not adequate for such high speed flows and hence, potential for enhanced performances lays in appropriate tip shaping. The present research aims to quantify the prospective gain offered by a fully contoured blade tip shape against conventional geometries such as a flat and squealer tip. A detailed numerical study was conducted on a modern transonic turbine rotor blade (Reynolds number is 5.5 × 105, relative exit Mach number is 0.9) by means of three-dimensional Reynolds-Averaged Navier-Stokes calculations. The novel contoured tip geometry was designed based on a 2D tip shape optimization in which only the upper 2% of the blade span was modified. This study yields a deeper insight into the application of blade tip carving in high speed turbines and provides guidelines for future tip designs with enhanced aerothermal performances.

Blade Tip Carving Effects on the Aerothermal Performance of a Transonic Turbine

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
C. De Maesschalck ◽  
S. Lavagnoli ◽  
G. Paniagua
Keyword(s):  
High Speed ◽  
Thermal Stresses ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Geometrical Parameters ◽  
Complex Flow ◽  
Leakage Flows ◽  
Blade Tip ◽  
Exit Mach Number

Tip leakage flows in unshrouded high speed turbines cause large aerodynamic penalties, induce significant thermal loads and give rise to intense thermal stresses onto the blade tip and casing endwalls. In the pursuit of superior engine reliability and efficiency, the turbine blade tip design is of paramount importance and still poses an exceptional challenge to turbine designers. The ever-increasing rotational speeds and pressure loadings tend to accelerate the tip flow velocities beyond the transonic regime. Overtip supersonic flows are characterized by complex flow patterns, which determine the heat transfer signature. Hence, the physics of the overtip flow structures and the influence of the geometrical parameters require further understanding to develop innovative tip designs. Conventional blade tip shapes are not adequate for such high speed flows and hence, potential for enhanced performances lays in appropriate tip shaping. The present research aims to quantify the prospective gain offered by a fully contoured blade tip shape against conventional geometries such as a flat and squealer tip. A detailed numerical study was conducted on a modern rotor blade (Reynolds number of 5.5 × 105 and a relative exit Mach number of 0.9) by means of three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) calculations. Two novel contoured tip geometries were designed based on a two-dimensional (2D) tip shape optimization in which only the upper 2% of the blade span was modified. This study yields a deeper insight into the application of blade tip carving in high speed turbines and provides guidelines for future tip designs with enhanced aerothermal performances.

scholarly journals Wind Tunnel Studies on Hover and Forward Flight Performances of a Coaxial Rigid Rotor

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 205
Author(s):  
Chang Wang ◽  
Minqi Huang ◽  
Xianmin Peng ◽  
Guichuan Zhang ◽  
Min Tang ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Tilt Angle ◽  
Lift Coefficient ◽  
Rotor System ◽  
Rigid Rotor ◽  
Forward Flight ◽  
Coaxial Rotor ◽  
Advance Ratio ◽  
Hover Flight ◽  
Development Center

The aerodynamic performance of a reduced-scale coaxial rigid rotor system in hover and steady forward flights was experimentally investigated to gain insights into the effect of interference between upper and lower rotors and the influences of the advance ratio, shaft tilt angle and lift offset. The rotor system featured by 2 m-diameter, four-bladed upper and lower hingeless rotors and was installed in a coaxial rotor test rig. Experiments were conducted in the Φ3.2 m wind tunnel at China Aerodynamics Research and Development Center (CARDC). The rotor system was tested in hover states at collective pitches ranging from 0° to 13° and it was also tested in forward flights at advance ratios up to 0.6, with specific focus on the shaft tilt angle and lift offset sweeps. To ensure that the coaxial rotor was operating in a similar manner to that of the real flight, the torque difference was trimmed to zero in hover flight, whilst the constant lift coefficient was maintained in forward flight. An isolated single-rotor configuration test was also conducted with the same pitch angle setting in the coaxial rotor. The hover test results demonstrate that the figure of merit (FM) value of the lower rotor is lower than that of the upper rotor, and both are lower than that of the isolated single rotor. Moreover, the coaxial rotor configuration can contribute to better hover efficiency under the same blade loading coefficient (CT/σ). In forward flight, the effective lift-to-drag (L/De) ratio of the coaxial rigid rotor does not monotonously change as the advance ratio increases. Increases in the required power and drag in the case with a high advance ratio of 0.6 leads to the decreasing L/De ratio of the rotor. Meanwhile, the L/De ratio of the rotor is relatively high when the rotor shaft is tilted backward. The increasing lift offset tends to result in reduced required rotor power and an increase in the rotor drag. When the effect of the reduced rotor power is greater than that of the increased rotor drag, the L/De ratio increases as the lift offset increases. The L/De ratio can benefit significantly from lift offset at a high advance ratio, but it is much less influenced by lift offset at a low advance ratio. The forward performance efficiency of the upper rotor is poorer than that of the lower rotor, which is significantly different from the case in the hover flight.

scholarly journals Impulsive Loading Noise of a Lift-Offset Coaxial Rotor in High-Speed Forward Flight

AIAA Journal ◽  
2020 ◽  
Vol 58 (2) ◽  
pp. 687-701 ◽  
Author(s):  
Zhongqi Jia ◽  
Seongkyu Lee
Keyword(s):  
High Speed ◽  
Impulsive Loading ◽  
Forward Flight ◽  
Coaxial Rotor

Aeromechanics Analyses of a Modern Lift-Offset Coaxial Rotor in High-Speed Forward Flight

2020 ◽  
Author(s):  
Young-Min Kwon ◽  
Jae-Sang Park ◽  
Seong-Yong Wie ◽  
Hee Jung Kang ◽  
Do-Hyung Kim
Keyword(s):  
High Speed ◽  
Forward Flight ◽  
Coaxial Rotor

Compound Helicopter: Insight and Optimization

2015 ◽  
Vol 60 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Omri Rand ◽  
Vladimir Khromov
Keyword(s):  
High Speed ◽  
Pareto Frontier ◽  
Optimization Process ◽  
Design Parameters ◽  
Forward Flight ◽  
Rotor Systems ◽  
Coaxial Rotor ◽  
Trade Offs ◽  
Compound Helicopter ◽  
Free Wake

The paper presents an insight into the complex task of design and optimizing a compound helicopter configuration. It introduces the “drag versus power chart” (DP chart) as a tool for separating the rotors, thrusters, wings, and fuselage contributions and understanding their optimal combination in a generic compound configuration. The analysis shows the dependency of the optimal configuration on the efficiencies of the rotors, the thrusters, and the wings, and a way to carefully examine the effect of many design parameters. As such, the analysis may be applied to various configurations including single and coaxial rotor systems. Among other conclusions, it is shown when and why a thruster is absolutely essential for high speed and clarifies the role of the wing in such cases. The paper also supplies a unique optimization process, which is based on a comprehensive and detailed nonlinear free-wake analysis of a compound configuration that includes a thruster and fixed wings. The optimization process is twofold: First, for a global search, a variety of randomly selected configurations are analyzed to determine an initial hover-forward flight Pareto frontier. Then, various types of local analyses are carried out to improve the above frontier. Such successive frontier refinements lead to an improved, detailed, and continuous frontier that may be exploited for a variety of missions. The configurations on the resulting Pareto frontier show design trade-offs between configurations that are more efficient in hover and those that are more efficient in high-speed forward flight.

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