Peter F. Lorber

Bio: Peter F. Lorber is an academic researcher. The author has contributed to research in topics: Rotor (electric) & Helicopter rotor. The author has an hindex of 6, co-authored 6 publications receiving 70 citations.

An unsteady helicopter rotor: Fuselage interaction analysis

Abstract: A computational method was developed to treat unsteady aerodynamic interactions between a helicopter rotor, wake, and fuselage and between the main and tail rotors. An existing lifting line prescribed wake rotor analysis and a source panel fuselage analysis were coupled and modified to predict unsteady fuselage surface pressures and airloads. A prescribed displacement technique is used to position the rotor wake about the fuselage. Either a rigid blade or an aeroelastic blade analysis may be used to establish rotor operating conditions. Sensitivity studies were performed to determine the influence of the wake fuselage geometry on the computation. Results are presented that describe the induced velocities, pressures, and airloads on the fuselage and on the rotor. The ability to treat arbitrary geometries is demonstrated using a simulated helicopter fuselage. The computational results are compared with fuselage surface pressure measurements at several locations. No experimental data was available to validate the primary product of the analysis: the vibratory airloads on the entire fuselage. A main rotor-tail rotor interaction analysis is also described, along with some hover and forward flight.

Aerodynamic and acoustic test of a United Technologies model scale rotor at DNW

Abstract: The UTC model scale rotors, the DNW wind tunnel, the AFDD rotary wing test stand, the UTRC and AFDD aerodynamic and acoustic data acquisition systems, and the scope of test matrices are discussed and an introduction to the test results is provided. It is pointed out that a comprehensive aero/acoustic database of several configurations of the UTC scaled model rotor has been created. The data is expected to improve understanding of rotor aerodynamics, acoustics, and dynamics, and lead to enhanced analytical methodology and design capabilities for the next generation of rotorcraft.

Directional elastomeric coupler

Abstract: An elastomeric coupler assembly having a helical elastomeric bearing movably supports an active slat relative to a main element. An inner elastomeric coupler assembly and an outer elastomeric coupler assembly support the slat therebetween. Centrifugal force operates to drive the slat to a first position and an actuator rod operates in tension to pull upon the inner elastomeric coupler assembly to drive the slat in opposition to the centrifugal force to a second position. The helical elastomeric bearing is layered such that it defines a section of a circular helix. The circular helix provides a coupling, which converts a linear input parallel to a virtual hinge axis into a rotary output to pitch the slat. In operation, centrifugal force operates to slide the slat outboard toward the blade tip such that the attached slat moves elastomerically along the helical arc of the helical elastomeric bearing to rotate the slat nose down. To retract the slat, the actuator operates to place the actuator rod under tension to pull upon the active member and retract the slat in opposition to centrifugal force.

An unsteady rotor/fuselage interaction method

Abstract: An analytical method has been developed to treat unsteady helicopter rotor, wake, and fuselage interaction aerodynamics. An existing lifting line/prescribed wake rotor analysis and a source panel fuselage analysis were modified to predict vibratory fuselage airloads. The analyses were coupled through the induced flow velocities of the rotor and wake on the fuselage and the fuselage on the rotor. A prescribed displacement technique was used to distort the rotor wake about the fuselage. Sensitivity studies were performed to determine the influence of wake and body geometry on the computed airloads. Predicted and measured mean and unsteady pressures on a cylindrical body in the wake of a two-bladed rotor were compared. Initial results show good qualitative agreement.

Separation Control for Rotorcraft

Abstract: : Active flow control can play a significant role in improving rotorcraft performance by delaying flow separation. Retreating blade stall (RBS) limits rotor capability to generate lift and transmits large pitching moments to the flight control system. This project developed compact, high-power flow control actuators for RBS and evaluated them using a combination of computation and a wind tunnel test on a full scale helicopter blade section. A set of electromechanical Directed Synthetic Jet (DSJ) actuator modules were designed, fabricated, and installed. The actuators produced the intended unsteady momentum coefficient of 0.1% at Mach 0.4 at 260 Hz. Flow control improved airfoil steady and dynamic stall characteristics, but the improvements were not as large as desired, especially for dynamic stall at higher Mach number. Additional computations of the coupled flow fields showed that moving the DSJ exit slot further aft could increase recovery of post-stall lift, but could not further increase unsteady peak lift or stall delay at momentum coefficients less than 0.5%. A 2nd generation DSJ actuator was designed and bench tested. By operating two slots, inboard and outboard of the piston, this actuator avoids back acoustic losses and can tolerate the centrifugal loads of a rotating blade.

Transient Separation Control Using Pulse-Combustion Actuation

Abstract: The transitory response of the flow over a stalled, two-dimensional (NACA 4415) airfoil to pulsed actuation on time scales that are an order of magnitude shorter than the characteristic convective time scale is investigated experimentally (Re = 570, 000). Actuation is effected by momentary [O(1 ms)] pulsed jets that are generated by a spanwise array of combustion-based actuators integrated into the center section of the airfoil. The flowfield in the cross-stream plane above the airfoil and in its near wake is computed from multiple high-resolution particle image velocity images that are obtained phase locked to the actuation waveform and allow for tracking of vorticity concentrations. The brief actuation pulse leads to a remarkably strong transitory change in the circulation about the entire airfoil that is manifested by a severing of the separated vorticity layer and the subsequent shedding of a large-scale clockwise vortex that forms the separated flow domain. The clockwise severed vorticity layer that follows behind this detached vortex has a distinct sharp streamwise edge that grows and rolls up as the layer is advected along the surface. It is shown that the shedding of the severed vortex and the accumulation of surface vorticity are accompanied by a transitory increase in the magnitude of the circulation about the airfoil that lasts 8—10 convective time scales. The attached vorticity layer ultimately lifts off the surface in a manner that is reminiscent of dynamic stall, and the flow separates again.

An unsteady helicopter rotor-fuselage aerodynamic interaction analysis

Abstract: A computational method has been developed to treat the unsteady aerodynamic interaction between a helicopter rotor, wake, and fuselage. Two existing codes, a lifting line-prescribed wake rotor analysis and a source panel fuselage analysis, were modified and coupled to allow prediction of unsteady fuselage pressures and airloads. A prescribed displacement technique was developed to position the rotor wake about the fuselage. Also coupled into the method were optional blade dynamics or rigid blade performance analyses to set the rotor operating conditions. Sensitivity studies were performed to determine the influence of the wake and fuselage geometry on the computational results. Solutions were computed for an ellipsoidal fuselage and a four bladed rotor at several advance ratios, using both the classical helix and the generalized distorted wake model. Results are presented that describe the induced velocities, pressures, and airloads on the fuselage and the induced velocities and bound circulation at the rotor. The ability to treat arbitrary geometries was demonstrated using a simulated helicopter fuselage. Initial computations were made to simulate the geometry of an experimental rotor-fuselage interaction study performed at the Georgia Institute of Technology.

Surface Pressure Measurements on a Body Subject to Vortex Wake Interaction

Abstract: Wind-tunnel experiments were conducted to examine the interaction effects between a rotor and an idealized airframe in forward flight. Mean and unsteady pressures were measured on the airframe suface for various flight speeds. Strong rotor-wake interactions with the airframe create large excursions in the mean pressure distribution. Extreme fluctuations in the unsteady component of pressure are also observed. The flowfield features that cause these effects are identified and discussed. It is essential that a comprehensive aerodynamic interaction code account for these features if accurate predictions of mean and unsteady airloads on the fuselage are to be obtained. b c Cp Cp' Cp» CT H/R P

Velocity measurements of airframe effects on a rotor in a low-speed forward flight

Abstract: Aerodynamic interactions between the rotor and the airframe of a rotorcraft can have severe effects and are difficult to predict analytically To attack this problem, the velocity field of a two-bladed rotor has been measured in a wind tunnel with and without an airframe model in proximity The periodic and time-averged velocity fields were measured using a laser velocimeter in planes both parallel to and above and below the rotor tip path plane at an advance ratio of 01 and a rotor tip Mach number of 029 The data were shown to be free of tunnel wall effects The effect of including the cylindrical airframe model were measured For the geometry studied, airframe influence on the rotor flowfield was mostly confined to the front half of the rotor disc Hub effects were noticeable, even with the minimal-sized hub used Strong vortex interaction effects were observed using strobed laser sheet flow visualization and measured using laser velocimetry