aerodynamics of helicopter. ppt

This material gives a basic aerodynamics related to rotor craft systems. This is a basic theory behind the helicopter blades. How the relative wing is affecting during hover, transnational flight, vertical flight. The theory also gives idea about the ground effect on rotor blades at different conditions.

2006

The airflow through the main rotor blade system of a helicopter is still not exceedingly well understood owing to its obscurity in aerodynamics. It is prognosticated that helicopter wakes can be significantly greater than those formed by a fixed wing aircraft of the same weight. Nuisance incidents such as brownout & noises are engendered from rotor wake. Study through flow visualization plays a key role in understanding the airflow distinctiveness and vortex interaction of a helicopter rotor blade. Inspecting and scrutinizing the effects of wake vortices during operation is a great challenge and imperative in designing effective rotor system. This study aimed at finding a suitable method to visualize the main rotor airflow pattern of a remote controlled subscale helicopter and seek for the vortex flow at the blade tip. The experimental qualitative data is correlated with quantitative data to perform meticulous study on the airflow behaviour & characteristics along with its distinctiveness generated by the main rotor in various flight conditions. Simulation is also performed in similar conditions to bequeath with comparability between the flow visualization results. Several dissimilar flow patterns were identified throughout the blade span. At the centre of the main rotor hub, the presence of turbulent flow was perceived. This is because of the low energy of air pooled in this region. Conversely, an apparent straight streamline pattern in the middle portion of the rotor blade was noticed as the air in this section encompassed high kinetic energy.

2018

This book provides an introduction to helicopters through the fundamental theories and methods of rotor aerodynamics and flight mechanics. The arguments have been structured in order to provide the reader with the physical aspects of problems, the basic mathematical tools involved, the presentation of theories with solved numerical examples or ready to be implemented on the computer. Therefore, the understanding of both the rotary-wing principles of flight and the magnitude of parameters and variables involved is achieved through a clear and step by step practical presentation. The topics include rotor aerodynamics and elements of rotor dynamics, helicopter flight performance, helicopter stability and control. This text may be used as a reference for students in aerospace engineering, and, moreover, the material is useful for both practicing engineers and professionals in helicopter technology.

The orthogonal blade-vortex interaction has been simulated using unsteady Reynolds-averaged Navier-Stokes equations with turbulence closure equations. The cases investigated are relative to an interaction between a lifting blade at a high angle of attack and an orthogonal vortex that travels either head-on or at 45 deg to the leading edge. The numerical simulations have been performed at a Reynolds number of Re ˆ 1:85 10 5 and a vortex Reynolds number of Re v ˆ 10 5. The impact parameter is equal to 8, which places the interaction in the weak vortex regime. The initial axial velocity of the vortex is zero, but as the vortex travels a self-induced velocity causes the vortex to move axially well before the impact on the blade. The analysis is carried out on the vortex dynamics and on the blade aerodynamics. The data investigated include the behavior of the pressure field as the vortex advances, the distribution of vorticity, the interaction of the vortex with the blade and the wake, the flow separation at the blade surface, and the path lines of the flow. A comparison between the case of straight and oblique blade-vortex interaction indicates that the blade-vortex interaction pressure peak is less severe in the latter case. A comparison is also made for the corresponding aerodynamic force coefficients (lift and drag and normal force). Nomenclature A = vortex axial flow parameter C D = drag coefficient C L = lift coefficient C n = normal force coefficient C n o = steady-state C n C p = pressure coefficient, p p 1 †=U 2 =2 c = blade chord I = impact parameter L = lift force p = pressure r = radial vector R = blade radius Re = Reynolds number Re v = vortex Reynolds number, U r c= T = rotor thrust t = thickness of the blade section U r = relative velocity U s = vortex self-induced velocity U tip = tip speed U v = convection velocity of vortex U 1 = flight speed w = downwash velocity of a rotor w o = swirl velocity at the vortex core x, y, z = Cartesian coordinate system = angle of attack = vortex circulation = lift-curve slope factor = blade's advance ratio, U 1 =U tip = fluid viscosity o = vortex core = rotor speed ! = vorticity vector

Journal of Aeronautics and Space Technologies, 2018

This study presents the outcomes of a series of computational fluid dynamics analyses conducted to obtain unsteady solutions of the flowfields around single rotor helicopter configurations. We use a methodology to obtain the time dependent solutions of the 3D, compressible Navier Stokes equations adapted for a rotating frame of reference. In order to carry out the simulations, the developed mathematical model is solved on hybrid meshes to optimally benefit the advantages of both the structured and the unstructured grids. For the entire flowfield calculations, one-equation Spalart-Allmaras turbulence model is employed. To decrease the computational time and memory requirements, parallel processing with distributed memory is utilized. We validate the developed model and the simulation methodology by comparing the results with the published experimental data. In the following phase of the study, the unsteady calculations of the flowfields around single, two bladed helicopter rotor configurations are conducted for hover and forward flight cases. As the forward flight speed increases, development of the dissymmetry of lift on advancing and retreating blades has been observed for six advance ratios. These time-accurate computations help to analyze the adverse effect of increasing forward flight speed in order especially to determine the never-exceed speed for single rotor helicopter configurations.

Journal of Aircraft, 1996

An overset grid thin-layer Navier-Stokes code has been extended to include dynamic motion of helicopter rotor blades through relative grid motion. The unsteady flowfield and airioads on an AH-IG rotor in forward flight were computed to verify the methodology and to demonstrate the method's potential usefulness towards comprehensive helicopter codes. In addition, the method uses the blade's first harmonics measured in the flight test to prescribe the blade motion. The solution was impulsively started and became periodic in less than three rotor revolutions. Detailed unsteady numerical flow visualization techniques were applied to the entire unsteady data set of five rotor revolutions and exhibited flowfield features such as blade vortex interaction and wake rollup. The unsteady blade loads and surface pressures compare well against those from flight measurements. Details of the method, a discussion of the resulting predicted flowfield, and requirements for future work are presented. Overall, given the proper blade dynamics, this method can compute the unsteady flowfleld of a general helicopter rotor in forward flight.

International Journal of Unmanned Systems Engineering, 2013

Marqués P, Maligno A, Dierks S, Penev V and

2018

Contents 2.5.2.2. Velocities induced by vortices, Biot-Savart's Law 2.5.3. Modelling rotor in hover and approach to calculation 2.5.4. Interference phenomenon due to blade tip vortex 2.5.5. Prescribed wake, Landgrebe's model in hovering flight Chapter 3 Rotor dynamics 3.1. Introduction 3.2. Fundamental axes and planes 3.3. The flapping motion of the blade 3.4. Flapping hinge offset and control moments 3.5. The rotor in forward flight and the blade flapping 3.6. The lagging motion of the blade 3.7. The cyclic feathering 3.8. Coupling of fundamental motions of the rotor blade 3.9. Calculation of centrifugal force along the blade Chapter 4 Rotor aerodynamics, forward flight 4.1. Introduction 4.2. Momentum Theory 4.3. Blade Element Theory 4.3.1. Parameters for determination of blade angle of attack 4.3.2. Blade element and local incidence 4.3.3. Aerodynamic forces acting on the rotor, closed form equations 4.3.3.1. Calculation of the thrust 4.3.3.2. Rotor coning and flapping coefficients 4.3.3.3. Calculation of the drag 4.3.3.4. Calculation of the torque 18 27 4.4. Reverse flow region 4.5. Forces and parameters related to tip path plane and to hub plane 4.5.1. Equations referred to the tip path plane 4.5.2. Equations referred to the hub plane 4.6. Helicopter in trim and rotor aerodynamics 4.7. Corrections of results of Blade Element Theory 4.8. Blade element theory limitations 4.9. Stall and compressibility phenomena 4.9.1. Swept blade tip and local Mach number Contents 9 4.10. Rotor wake models in forward flight 4.11. Computational aerodynamics, advanced methodologies, multidisciplinary approach Chapter 5 Helicopter trim analysis 5.1. Introduction 5.2. Systems of axes 5.3. General equations of motion of helicopter 5.4. Helicopter trim conditions 5.4.1. The general trim analysis 5.5. The rotor-fuselage system and the torque reaction 5.6. Simplified development of equilibrium (trim) 5.6.1. Trim equations in forward flight 5.6.2. The expression for power in forward level flight 5.7. Approximate and quick estimation of longitudinal equilibrium 5.8. General trim solution 5.9. Autorotation 5.9.1. Autorotation of a rotor 5.9.1.1. Aerodynamics of autorotation 5.9.1.2. Final phase of an autorotation 5.9.2. Limitations in autorotation and Height-Velocity Diagram