Rotor Blade Span Research Articles

Flow mechanism of affecting an axial flow compressor performance and stability with cross-blade slot casing treatments

The objective of this study is to evaluate the effect of cross-blade slot casing treatment on the stability and performance of an axial flow compressor rotor. The experimental and unsteady calculated results both show that cross-blade slot casing treatment can generate about 22% stall margin improvement, and the compressor peak efficiency is reduced by about 13%. The detailed flow-field analyses indicate that the sucked and injected flow caused by the slots of cross-blade slot casing treatment can restrain the rotor tip passage blockage, which is made by the low energy tip clearance leakage vortex. When cross-blade slot casing treatment is applied, not only the rotor wheel flange work becomes lower in most of the rotor blade span, but also the flow loss in the blade tip passage becomes fairly large due to the strong interaction between the mainstream and the injected flows made by the slots. As a result, the compressor total pressure ratio and efficiency for cross-blade slot casing treatment are reduced obviously. Three kinds of new cross-blade slot casing treatment were designed according to the previous successful experience and investigated in this paper. The numerical results show that the new three cross-blade slot casing treatments both generate about 54% stall margin improvement at the cost of minor peak efficiency. For one new cross-blade slot casing treatment (CSCT2), the compressor peak efficiency is reduced by about 0.3%. The low energy TLV, which is present for cross-blade slot casing treatment, is removed by the strong sucked flow made by CSCT2. Moreover, the interaction between the mainstream and the injected flows caused by CSCT2 becomes weak obviously, and the corresponding flow loss is reduced greatly. Hence, the compressor stability and performance with CSCT2 are higher than those with cross-blade slot casing treatment.

Development of an Aeroelastic Flap to Increase the Aerodynamic Efficiency of a Wind Turbine’s Rotor Blade

Horizontal-axis wind turbines are sophisticated technical constructions that require modern design methods for further improvement and higher economic output. Thorough understanding of the whole turbine and its components is indispensable for this aim. The technological development in the last decades indicates the progress in this area and shows the potential of optimizations due to the improvement of rotor blade aerodynamics by additional aerodynamic devices. In this project the effect of an aeroelastic flap mounted on the trailing edge of a rotor blade on energy yield was investigated. For this purpose a flexible flap of fiberglass reinforced plastic for the profile at 70% of the rotor blade span has been designed for the trailing edge and analyzed using a 2-way fluid-structure-interaction simulation. In the first step the simulation is reduced to a two-dimensional investigation using the cross-section at 70% diameter of the rotor blade. Compared to an unmodified profile, the aeroelastic flap increases the lift-to-drag-ratio of the profile in an angle of attack range between 3.5° to 9.5°. The aeroelastic flap has a positive effect on the glide ratio, similar to a non-elastic, static flap.

High Altitude Cycloidal Wind Turbine System Design

As a novel high altitude wind power system, this paper describes a cycloidal wind turbine mounted on a tethered balloon or parafoil. The rotor system was designed conceptually and the performance was estimated. The rotor blade span length is 10 meters and its diameter is 10 meters. When the rotor operates at 1,500 meters above ground, it produces 4.6 times more energy by the balloon tethered model. The parafoil tethered rotor power generation becomes 4.1 times at the same condition, which is a little smaller comparing with the balloon tethered model. The reason is its energy consumption at low wind speed condition to produce supplementary lifting force through mode conversion.

Embedded absorbers for helicopter rotor lag damping

Radial and chordwise damped vibration absorbers embedded in the rotor blade are compared for rotor lag damping augmentation. Results show that the radial absorber is more effective in transferring damping to the rotor blade lag mode. The chordwise absorber needs to be at a more outboard location and have a larger mass to introduce levels of lag damping comparable to that introduced by the radial absorber. The 1/rev amplitude of a chordwise absorber at the blade tip, per degree of blade lead-lag motion in forward flight, is of the order of 35% of the blade chord, and such a stroke might be difficult to accommodate. The 1/rev amplitude of a radial absorber at 70% span (having significantly lower mass than the chordwise absorber and producing comparable lag damping) is of the order of 4% of the rotor blade span. The static displacement of the radial absorber under centrifugal load needs to be limited using a frequency-dependent (high static stiffness, low dynamic stiffness) or nonlinear spring. The chordwise absorber can also undergo a large static displacement under the chordwise component of the centrifugal load if there is an offset from the feather axis, and this would again have to be limited using a strategy such as a frequency-dependent spring. Significant advantages of the radial absorber are—higher lag damping, lower absorber mass, space for absorber mass travel, and no chordwise travel of blade center of gravity reducing susceptibility to aeroelastic instability and dynamic pitch-link loads.

논문 : 헬리콥터 비행 시뮬레이션을 위한 로터운동방정식 유도

헬리콥터 비행 시뮬레이션을 위한 로터 운동방정식을 implicit formulation 형태로 유도하였다. 좌표계 사이의 상대운동을 고려한 일반화된 벡터 kinematics 를 유도하고 이를 적용하여 브레이드 임의 위치 에서 관성속도 및 관성가속도를 구하였다. 유도된 속도 및 가속도 벡터를 이용하여 플래핑, 리드래그 및 토오크 방정식 등을 implicit form으로 유도하였다. 브레이드 스팬에 따른 공간 적분 방법을 살펴보고, 다양한 힌지형상 및 힌지배열 순서에 관계없이 응용영역을 확장할 수 있음을 밝혔다. DAE(Differential Algebraic Equation) 형태를 갖는 본 연구의 결과식을 이용하여 동특성 계산을 위한 시간적분법을 검토하였다. The implicit formulation of rotor dynamics for helicopter flight simulation has been derived and and presented. The generalized vector kinematics regarding the relative motion between coordinates were expressed as a unified matrix operation and applied to get the inertial velocities and accelerations at arbitaty rotor blade span position. Based on these results the rotor aeromechanic equations for flapping dynamics, lead-lag dynamics and torque dynamics were formulated as an implicit form. Spatial integration methods of rotor dynamic equations along blade span and the expanded applicability of the present implicit formulations for arbitrary hings geometry and hinge sequences have been investigated. Time integration methods for present DAE(Differential Algebraic Equation) to calculate dynamic response calculation are recommenaded as future works.

Computation of Broadband Noise Radiated by a Ducted Fan

— Acoustic pressure amplitude Am! a — Speed of sound B — Number of rotor blades b — Rotor blade span C — Blade load constant — Spherical coordinates for free-field radiation D,,# — Cylindrical coordinates of a source on the rotor d,$, y1 y — Blade load, and its azimuthal Fourier transform F,F f — Frequency G — Green’s function I — Sound intensity — Integral on a point source ! — Bessel function of first kind and of order m Jm — Total, transverse, and axial wave-numbers K,kt,kz L — Duct length l — Radial turbulence length scale — Spinning mode (m azimuthal, radial) m,! ! — Axial Mach number in the annular duct in front Max of the rotor — Tip rotational Mach number Mtip — Mach number of the uniform flow in the duct Mz N — Rotor angular rotation speed (either in rpm or in Hz) n — Number of point sources along the blade span in non-compact calculations — Sound pressure in the duct and in the far field, p,P respectively q — Exponent of decrease of the blade pressure fluctuations at high frequency R — Duct radius — Cylindrical coordinates of a point in the duct r,%,x1 x S — Blade surface area — Reception time, emission time t,& — Rotation speed of a point source on a blade Urot W — Sound power — Dirac function ' — Mean fluid density (0 — Fan hub-to-tip ratio ) — -th root of *m! ! Jm ! 0 — Rotor angular rotation speed ( ) + + ! 2,N — Angular frequency ( ) ! 2,f ! aK

Variations in Upstream Vane Loading With Changes in Back Pressure in a Transonic Compressor

Dynamic loading of an inlet guide vane (IGV) in a transonic compressor is characterized by unsteady IGV surface pressures. These pressure data were acquired for two spanwise locations at a 105 percent speed operating condition, which produces supersonic relative Mach numbers over the majority of the rotor blade span. The back pressure of the compressor was varied to determine the effects from such changes. Strong bow shock interaction was evident in both experimental and computational results. Variations in the back pressure have significant influence on the magnitude and phase of the upstream pressure fluctuations. The largest unsteady surface pressure magnitude, 40 kPa, was obtained for the near-stall mass flow condition at 75 percent span and 95 percent chord. Radial variation effects caused by the spanwise variation in relative Mach number were measured. Comparisons to a two-dimensional nonlinear unsteady blade/vane Navier–Stokes analysis show good agreement for the 50 percent span results in terms of IGV unsteady surface pressure. The results of the study indicate that significant nonlinear bow shock influences exist on the IGV trailing edge due to the downstream rotor shock system. [S0889-504X(00)00303-2]

Optimizing tuning masses for helicopter rotor blade vibration reduction and comparison with test data

This article describes the development and validation of an optimization procedure to systematically place tuning masses along a rotor blade span to minimize vibratory loads. The masses and their corresponding locations are the design variables that are manipulated to reduce harmonics of hub shear for a four-bladed rotor system without adding a large mass penalty. The procedure incorporates a comprehensive helicopter analysis to calculate the airloads. Predicting changes in airloads due to changes in design variables is an important feature of this research. The procedure was applied to a one-sixth, Mach-scaled rotor blade model to place three masses and then again to place six masses. In both cases the added mass was able to achieve significant reductions in the hub shear. In addition, the procedure was applied to place a single mass of fixed value on a blade model to reduce the hub shear for three flight conditions. The analytical results were compared to experimental data from a wind-tunnel test performed in the Langley transonic dynamics tunnel (TDT). The correlation of the mass location was good and the trend of the mass location with respect to flight speed was predicted fairly well. However, it was noted that the analysis was not entirely successful at predicting the absolute magnitudes of the fixed-system loads.