Helicopter Model Rotor‐Blade Vortex Interaction Impulsive Noise: Scalability and Parametric Variations

Splettstoesser, W. R.; Schultz, Klaus J.; Boxwell, D. A.; Schmitz, Fredric H.

doi:10.4050/jahs.32.1.3

Cited by 42 publications

(15 citation statements)

References 1 publication

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“…3,14) interaction. These interactions are classified into four general categories (Type "α", "β", "γ " and "δ") based on the variation of the trace Mach number along the interaction path (i.e.…”

Section: Classification By Trace Mach Numbermentioning

confidence: 99%

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Radiation and Directionality Characteristics of Helicopter Blade-Vortex Interaction Noise

Schmitz¹,

Sim²

2003

j am helicopter soc

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The geometric factors that govern the radiation of helicopter blade-vortex interaction (BVI) noise are explored using simplified aerodynamics and wake modeling. Formulation of the BVI problem is restricted to a constant strength, epicycloid tip-vortex system that is initially confined to a plane parallel to the tip-path-plane at a fixed distance below the rotor. The resulting equations, when solved, illustrate the connection between the trace Mach number profile of each interaction and the phased summation of acoustic sources for each individual BVI. Areas of peak acoustic radiation are identified on a radiation sphere surrounding the helicopter as a function of advance ratio and hover tip Mach number for a two-bladed rotor. BVI noise radiation patterns show that the peak noise of each distinct BVI is very directional and is primarily a function of the advance ratio of the helicopter. The directivity of the peak level of each interaction changes in a continuous manner as advance ratio is increased-first radiating predominantly in the direction of the flight path near the plane of the rotor for oblique BVI, and then increasing in level and radiating more downward to the advancing side of the rotor for near parallel BVI. When the miss-distances of the tip-vortices are allowed to vary, the closeness of the younger shed vortices associated with oblique BVI tend to make the intensity levels of the oblique and near parallel interactions similar for many operating conditions. For flight along constant angles of descent at varying advance ratios, the direction of peak helicopter BVI becomes discontinuous with advance ratio-suddenly switching when different BVI become dominant. Nomenclature

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Section: Classification By Trace Mach Numbermentioning

confidence: 99%

“…14). The controlling parameters are the advance ratio and the hover tip Mach number of the rotor (Ref.…”

Section: Trace Mach Numbermentioning

confidence: 99%

Radiation and Directionality Characteristics of Helicopter Blade-Vortex Interaction Noise

Schmitz¹,

Sim²

2003

j am helicopter soc

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“…Both the advance ratio, µ and the backward shaft tilt, α s (which is synonymous to the tip-path-plane angle in the absence of rotor cyclic flapping) are varied, and such variation in wind tunnel conditions can be used to represent variations in flight trajectory or descent glide path for a flight vehicle in descent (Ref. 28). Figure 2 shows variation in peak BVI Sound Pressure Level (BVISPL) as a function of µ and α s , where dark regions denote flight conditions of the greatest noise and light regions the least noise.…”

Section: Model Rotor In Wind Tunnel Trim Conditionsmentioning

confidence: 99%

Analysis of Helicopter Blade-Vortex Interaction Noise with Flight Path or Attitude Modification

Munsky¹,

Gandhi²

2005

j am helicopter soc

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This study examines the effects of flight-path modification and attitude modification through the introduction of an X-force on helicopter blade-vortex interaction (BVI) noise in low-speed descent.A free-wake analysis is used in conjunction with a rotor aeroelastic model, to accurately determine the positions of the vortices relative to the blades and the unsteady impulsive BVI loading. The aeroacoustic code WOPWOP is used to calculate the resulting BVI noise. The results in the present study indicate that while regimes of high BVI noise show general qualitative correlation to regimes of zero inflow from simple momentum theory based analyses, the maximum noise levels are actually seen at different advance ratio and rotor disk tilt combinations from those at which momentum theory predicted zero mean inflow. As the rotor shaft angle is varied (corresponding to change in descent rate) different advancing side BVI events become dominant, even as others recede in importance. Thus, small to moderate changes in shaft angle have little effect in reducing the total BVI noise. It is also seen that as different BVI events become dominant, the directionality of the total radiated noise changes. An X-force in the drag direction tilts the rotor disk forward, convects the vortices lower relative to the baseline. In contrast, a propulsive X-force convects the vertices upward relative to the baseline. For a high-noise baseline condition, with one or more parallel vortices in the rotor plane either a propulsive or drag X-force does not, in equal measure, reduce noise. This is again related to different interactions dominating for different levels of X-force; these changes depend on the flight path. Thus, while a drag force was found to reduce BVI noise for a 0.1875 advance ratio moderate glide path, a propulsive force was found to be beneficial for the same advance ratio and a steeper glide path. This makes exploiting the X-force control concept more challenging. Even so, reductions of more than 10 dB in peak BVI noise levels certainly appear to be possible using X-force levels of the order of about 5% of the vehicle weight.

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“…When BVI noise occurs, it can dominate the radiated noise field and adversely affect community acceptance of rotorcraft (Refs. [1][2][3][4]. In addition to BVI noise, rotor broadband noise has also been shown to be significant and even dominate the radiated noise field for certain operating conditions, such as shallow climb (Refs.…”

Section: Introductionmentioning

confidence: 99%

“…HART II is a comprehensive experimental program conducted with a 40% Mach scaled model of a BO-105 main rotor in the Duits-Nederlandse Windtunnel (DNW) in the Netherlands. The objective of the test was to obtain extensive 3-C PIV measurements of the rotor wake over both the advancing and retreating sides of the rotor disk, along with acoustic directivity measurements, unsteady blade surface pressure measurements, and blade deformation measurements in order to (1) to investigate the physics of BVI, broadband noise and vibration reduction concepts with the HHC technology, (2) to develop an analytical prediction capability for rotor BVI and broadband noise, and (3) to generate a comprehensive experimental database for code validation.…”

Section: Introductionmentioning

confidence: 99%

Rotor Wake Vortex Definition-Evaluation of 3-C PIV Results of the HART-II Study

Burley¹,

Brooks²,

Rozier

et al. 2006

International Journal of Aeroacoustics

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An evaluation is made of extensive three-component (3-C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a centerof-vorticity criterion and a vorticity "disk" integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction. SYMBOLS C rotor blade chord, 0.121 m C T rotor thrust coefficient, thrust/ρπR 2 (ΩR) 2 CV center of vorticity in (x,y) plane, m DNW German-Dutch Wind tunnel DLR German Aerospace Center HART HHC Aeroacoustic Rotor Test HHC Higher Harmonic Control k grid point indices j indices for instantaneous image LDV Laser Doppler Velocimetry LLS Laser Light Sheet n number associated with analytical velocity profile, Eq. 5 R rotor radius, 2 m vortex core radius, m core radius associated with Rankine vortex, m shape factor for vortex velocity profile u,v,w velocity components for x,y,z coordinates, m/s rotor hover tip speed, RΩ (218 m/s) 'spin' velocity at r C , m/s (x,y,z) TUN windtunnel coordinate system: (x TUN positive downstream, y TUN positive starboard, z TUN positive up). x,y,z PIV image frame coordinates, m, Fig. 4. α rotor shaft angle with respect to z TUN axis, deg δ vortex wander parameter, m circulation within , m/s 2 σ standard deviation of parameters derived from instantaneous images Ω rotor rotation frequency, rad/s vorticity normal to (x, y) plane, s −1 Ψ blade azimuth angle (0 0 aft), deg.

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Helicopter Model Rotor‐Blade Vortex Interaction Impulsive Noise: Scalability and Parametric Variations

Cited by 42 publications

References 1 publication

Radiation and Directionality Characteristics of Helicopter Blade-Vortex Interaction Noise

Radiation and Directionality Characteristics of Helicopter Blade-Vortex Interaction Noise

Analysis of Helicopter Blade-Vortex Interaction Noise with Flight Path or Attitude Modification

Rotor Wake Vortex Definition-Evaluation of 3-C PIV Results of the HART-II Study

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