Significant Side Forces Research Articles

Side Force on Bodies of Revolution: Role of Attached Flow

The flowfield past a body of revolution at large incidence may develop an asymmetric wake that induces a significant side force. It remains a challenging problem for both computational and experimental analyses, with massive separation and coexistence of steady and unsteady regions. A number of researchers have studied the complex separated flow on the lee side. This paper focuses on the role played by the attached flow on the windward side. Solutions obtained with unsteady Reynolds-averaged Navier–Stokes computation, shown to be in good agreement with experimental data, are used to investigate the contributions of the attached and separated regions of the flow to the forces acting on the body. A strongly unbalanced pressure distribution of the attached flow is responsible of most of the side force. A description of the crossflow structure is given to explain the large magnitude of the sectional side force, sometimes exceeding that of the normal force.

Electromagnetic Design and Dynamic Characteristics of Permanent Magnet Linear Oscillating Machines Considering Instantaneous Inductance According to Mover Position

Interior permanent magnet (IPM)-type linear oscillating actuators (LOAs) have a higher output power density than typical LOAs. Their mover consists of a permanent magnet (PM) and an iron core, however, this configuration generates significant side forces. The device can malfunction due to eccentricity in the electromagnetic behavior. Thus, here an electromagnetic design was developed to minimize this side force. In addition, dynamic analysis was performed considering the mechanical systems of LOAs. To perform a more accurate analysis, instantaneous inductance was considered according to the mover's position.

Pulsed Actuation Control of Flow Separation on a ROBIN Rotorcraft Fuselage

Separation control of the three-dimensional flow over the aft segment of a NASA Rotor-Body-Interaction (ROBIN) rotorcraft fuselage is investigated in wind-tunnel experiments using arrays of miniature combustion-based actuators. Successive pulsed actuation is effected by momentary jets each having a characteristic time scale that is an order of magnitude shorter than the convective time scale of the flow. The actuators are placed upstream of the transition ramp between the ROBIN’s fuselage and the tail boom. The jet-induced interactions with the massively separated crossflow over the ramp and their effects on the global aerodynamic forces and moments are investigated using high-resolution particle image velocimetry that is acquired phase-locked to the actuation waveform in conjunction with simultaneous force and moment measurements using an onboard load cell. The present investigations show that symmetric actuation about the model’s centerline can significantly mitigate separation, lead to a reduction in drag and lift, and alter the pitching moment. Asymmetric actuation, and consequently nonuniform attachment, can induce significant side forces as well as roll and yaw moments that may be exploited for steering and improved flight maneuverability.

Side force over slender body with rings at different location at subsonic speed

Investigations have been made adopting experiments and computations on an ogive-nosed slender body at different angles of attack and Reynolds number of 29,000 based on the model base diameter diameter. The results indicated an increase in the side force at large angles of attack, which is mainly due to the presence of asymmetric vortices in the leeward of the body. The inclusion of a rectangular cross-sectioned ring in the initial portion of the body reduced the side force at higher angles of attack. However, significant side force was experienced at lower angles of attack (30° < α < 40°). Use of a ring of 3% height was found to be suitable for reducing the side force at a higher angle of attack. From the results obtained it was observed that a ring if placed at a different axial location alters the flow field and changes the side force at higher angles of attack. Further studies indicated that placing of rings pair at an axial location of 3.5 and 4.5 times the base diameter reduced the side force to a very low value at all the angles of attack for the present shape of body and flow conditions.

Closed-Loop Flow Control of a Forebody at a High Incidence Angle

The flowfield around an axisymmetric forebody at a high angle of attack () produces a significant side force. This side force results from an asymmetric pressure distribution around the body due to an asymmetric vortex configuration. Numerical studies of open-loop control using mass blowing slots near the tip of the model have shown a proportional response of the side force over a range of momentum coefficient amplitudes. From the open-loop simulations, a prediction-error minimization method was employed to formulate a linear time-invariant model, which captured the dynamics of the side force response to different mass flow rates applied to either the port or starboard actuator. Based on the linear time-invariant model, a proportional–integral control law was developed for set-point tracking a prescribed side force. The development of the linear time-invariant model, and corresponding linear time-invariant feedback solution are presented to illustrate the model’s capabilities and limitations. The ability to track a set-point signal based on the linear time-invariant model and corresponding proportional–integral control law are shown. The results indicate that the bandwidth of the controller is limited to frequencies below the convective frequency due to the convective time delay. Finally, the linear time-invariant feedback solutions are compared to Navier–Stokes feedback simulations, which show very good agreement.

Interactions of a propeller with a stator-induced circumferentially varying flow

The interactions of a circumferentially varying stator cascade and a downstream fixed pitch propeller were investigated experimentally. The global performance of the components and the coupled system were systematically investigated through force and moment measurements on the propulsor model in a water tunnel. In addition, the wake of the cyclic stator cascade with and without the propeller was investigated downstream from a propulsor model using the Stereoscopic PIV technique. A cyclic distribution of the stators’ deflections resulted in non-axisymmetric distributions of the flow field downstream of the stator array. The stator distribution alone produced a significant side force that increased linearly with stator pitch amplitude. When a propeller was incorporated downstream from the cyclic cascade, the side force from the stator cascade was reduced, but a small normal force and pitching moment were created. The generation of these secondary forces and moments can be related to the redistribution of the tangential flow from the cyclic cascade into the axial direction by the retreating and advancing blade states of the fixed pitch propeller.

EXPERIMENTAL INVESTIGATION OF SLENDERNESS EFFECT ON SIDE FORCE OF SLENDER BODY

This study investigates side force of a slender body with slenderness from 4.4 to 8.0. The experimental results show that flow over a slender body experiences a significant side force at angle-of-attack (AOA) higher than 30°. The side force reaches its maximum at AOA ≈ 50°. The present study demonstrates that slenderness (L/D) produces obvious influence on sectional side force distribution at high AOA. To understand the mechanism, evolution of near-wall vortex structure is investigated via hot wire and surface pressure measurements. It was found that one strong vortex is situated close to body surface and the other weak vortex away from the body, inducing a significant side force. Because the weak vortex lifts off early, a new vortex forms in near-wall region. Formation and evolution of the new vortex is the major mechanism that causes local sectional side force distribution exhibiting a wavy form with an alternating sign along the body. Therefore, overall side force does not necessarily increase with increasing slenderness. Reducing overall side force by canceling the alternating vortex-induced forces over the body surface is found if the slenderness L/D > 6.8 at AOA > 40°.

SHAPE MEMORY ALLOY ACTUATED MICRO-FLOW EFFECTORS FOR VORTEX MANIPULATION

Smart structures are seen as an enabling technology for designing innovative control actuation systems for future missiles. In this study, the feasibility of employing shape memory alloy (SMA)-actuated micro-flow effectors to control the vortex shedding behaviour that produces side forces on slender body missiles is examined. Supersonic wind tunnel tests were performed on a slender finless missile equipped with static micro-flow effectors on a conical nose to determine suitable configurations that could generate significant side forces. Shape memory alloy actuators for the flow effector were developed using numerical techniques and validated experimentally. Matching the force-displacement characteristics of the SMA actuator to the micro-flow effector force-displacement requirement was accomplished by a compliant transmission mechanism. The dynamic performance of the micro-flow effector was assured with a two-step variable structure control law. Closed-loop test results showed that the control law was capable of providing effective displacement control up to 1.0 Hz.

Alleviation of side force on tangent-ogive forebodies using passive porosity

An experimental investigation to determine the effectiveness of porosity for alleviating side forces on forebodies was conducted in the NASA Langley Research Center 7 x 10 ft High-Speed Wind Tunnel. The study consisted of a comparison of experimental force, moment, and surface pressure results obtained on a fineness ratio 5.0 tangent-ogive porous forebody with 0.020 in. hole diameter and 22 percent porosity with results obtained on a solid forebody. The forebodies were tested with cylindrical afterbodies. The solid forebody was tested with transition grit to simulate fully turbulent conditions and without transition grit to simulate free transition conditions. The extent of porosity on the forebody was varied to determine the extent of porosity needed to alleviate side forces. Static longitudinal and lateral-directional stability and surface pressure data were obtained at Mach numbers of 0.2, 0.5, and 0.8. The angle of attack range was from 5 to 45 deg and roll angles from -90 to 180 deg. The solid forebody exhibited large asymmetries at moderate to high angles of attack causing large side forces and yawing moments. The porous forebody exhibited no significant side forces or yawing moments at any angle of attack tested.

Lateral aerodynamic interference between tanker and receiver in air-to-air refueling

Wind-tunnel data have been obtained from a tapered tanker wing and receiver aircraft model at varying vertical separation. The data are presented in derivative form and compared with theory using a flat vortex sheet model of the tanker wing wake to determine the induced angle-of-attack variation on the receiver wing, fin, and tailplane due to the tanker wing. Aerodynamic loads on the receiver are obtained by the vortex lattice method, with an allowance made for the vertical displacement of the tanker wake in the estimation of the fin side force. In the experiments, the lateral aerodynamic interference between tanker and receiver was determined by banking the tanker wing and displacing it sideways, and by yawing the receiver aircraft model. Data were obtained from open and closed test sections in order to assess the significant boundary interference effect and corrections estimated from the image vortex system of the tanker and receiver wings in the test section. In general, the theory compares favorably with the experimental data. The most significant terms are the rolling moments due to sideways and bank displacements. Significant side forces are produced due to sidewash on the fin from the tanker and receiver wings and, when displaced in yaw, the receiver experienced a loss in directional stability.

Proprotor Short-Haul Aircraft-STOL and VTOL

This Paper examines the characteristics of a series of aircraft for the short-haul market. The low disk-loading propeller/rotor is applied to a prdpeller-STOL (short takeoff and landing) transport, a fan jet-STOL transport, a tilt rotor-VTOL (vertical takeoff and landing) transport, and a fan jet-VTOL transport. The resulting aircraft concepts have an efficient low-speed, lift-propulsion system, and can operate with low noise and air pollution from metropolitan V/STOL airports. This paper concentrates on the first two STOL configurations. For low and medium disk-loading STOL aircraft, the gimbal propeller Has important operational advantages compared to the rigid propeller. At takeoff, longitudinal cyclic pitch can be used to produce an upward force to reduce tail download requirements. For takeoff and landing in severe crosswinds, significant side force can be produced by means of lateral cyclic pitch. In cruise, the gimbal propellers give a significantly better ride than rigid propellers. In the approach, longitudinal cyclic pitch can control glide-slope height precisely. A STOL transport with a cruise speed of 400-500 knots (wing loading near 75 psf) could use the deflected slip-stream concept and medium disk-loading (30 psf), folding propeller/rotors (Frontispiece). Propulsion-system power requirements in both the cruise and low-speed mode would be supplied by convertible fan-shaft engines. This Paper shows the power balance between a twin fan-jet cruise requirement of 475 kt and an engine-out critical maneuver requirement at 60 knots.