Showing papers by "Othon K. Rediniotis published in 2005"

A New Class of Synthetic Jet Actuators—Part II: Application to Flow Separation Control

Abstract: We present the application of the new synthetic jet actuator (SJA) to flow separation control over a NACA 0015 wing. The actuator is compact enough to fit in the interior of the wing that has a chord of 0.375 m. The wing was tested in the Texas A&M University Aerospace Engineering 3 ftX4 ft wind tunnel. An experimental investigation into the effects of the synthetic jet actuator on the performance of the wing is described. Emphasis is placed on the capabilities of the actuator to control the separation of the flow over the wing at high angles of attack. The results include force balance measurements, on surface and off surface flow visualization, surface pressure measurements, and wake surveys. All of the reported tests were performed at a free-stream velocity of 35 m/s, corresponding to a Reynolds number of 8.96×10 5 . The angle of attack was varied from -2.0 deg to 29.0 deg.

A New Class of Synthetic Jet Actuators—Part I: Design, Fabrication and Bench Top Characterization

Abstract: Although the potential of synthetic jets as flow separation control actuators has been demonstrated in the existing literature, there is a large gap between the synthetic jet actuators (SJA) used in laboratory demonstrations and the SJAs needed in realistic, full-scale applications, in terms of compactness, weight, efficiency, control authority and power density. In most cases, the SJAs used in demonstrations are either too large or too weak for realistic applications. In this work, we present the development of a new class of high-power synthetic jet actuators for realistic flow control applications. The operating principle of the actuator is the same as that of crankshaft driven piston engines, which makes a significant part of the technology necessary for the actuator development available off-the-shelf. The design of the actuator is modular and scalable. Several building block units can be stacked in series to create the actuator of the desired size. Moreover, active exit slot reconfiguration, in the form of variable exit slot width, decouples the actuator frequency from the actuator jet momentum coefficient and allows the user to set the two independently (within limits). We present the design, fabrication and bench top characterization of the actuator. Several versions of the actuator were designed, built and tested, leading up to the development of a six-piston compact actuator that has a maximum power consumption of 1200 W (1.6 hp) and can produce (for the tested conditions) peak exit velocities as high as 124 m/s.

Unsteady Calibration of Fast-Response Pressure Probes, Part 1: Theoretical Studies

Abstract: Recent advances in miniaturization of pressure transducers, including microelectromechanical systems technology, have provided miniature, high-bandwidth pressure transducers and transducer arrays well suited for fast-response, multihole probes. The miniature size of these arrays enables a design in which the transducers are embedded in, or close to, the probe tip while maintaining a tip diameter of 1‐2 mm. Although the frequency response of such a probe is excellent, there are several unresolved issues pertaining to fluid inertia-related unsteady aerodynamic effects on probe calibration. As a result of these effects, when the probe is used in a dynamically changing flowfield a quasi-steady probe calibration can no longer be used to resolve the instantaneous velocity vector. We present theoretical analysis of these effects and formulate methods of calibrating multihole, fast-response probes for use in unsteady flows in order to accurately resolve the instantaneous velocity vector. The main objective of the theoretical analysis is to study and quantify the dependence of the probe measured pressures on the magnitude of the flow inertial effects in terms of properly formulated nondimensional parameters, as well as allow a direct comparison of theory and experiment. Among the contributions of this work, it was particularly interesting to find that proper definition of the nondimensional, flow-angle-dependent pressure coefficients renders them insensitive to unsteady effects. This has the significant ramification that the steady calibration of these coefficients can be also used in unsteady flowfields for the calculation of the flow angles. Calculation of the velocity magnitude, however, requires quantification of and correction for the fluid inertial effects.

Calibration and Data-Reduction Algorithms for Nonconventional Multihole Pressure Probes

Abstract: The development of calibration and data-reduction algorithms for nonconventional multihole pressure probes is presented. The algorithms that have been developed in the past for conventional five- and seven-hole probes are not optimal for probes with port arrangements (on the probe tip) that are nonconventional. Conventional algorithms utilize the axisymmetry of the port distribution pattern to define the nondimensional pressure coefficients. These coefficients are typically defined specifically for these patterns, but fail to represent correctly different patterns of port arrangements, such as patterns without axisymmetry or regularity. The algorithms introduced can handle any pattern of port arrangement, from axisymmetric and regular to random. Moreover, they eliminate the need to separate the measurement domain of a probe to low-angle and high-angle regimes, typical in conventional five-and seven-hole-probe algorithms that require two different sets of pressure coefficient definitions and procedures. Additionally, the algorithms have been formulated such that they facilitate redundancy implementations, especially in applications where such redundancy is important, such as air-data systems. The developed algorithms are applied to a nonconventional probe, a nearly omnidirectional 18-hole probe, and demonstrate very high flow-measurement accuracy

Unsteady calibration of fast-response pressure probes, Part 3: Air-jet experiments

Abstract: A facility was developed that produces a known and repeatable oscillating air jet used to test the unsteady probe calibration techniques developed in Parts 1 and 2 for fast-response, multihole pressure probes. Its characteristics. in the steady and unsteady operation modes were studied. The facility can produce flow velocities up to Mach 0.3 with oscillation frequencies up to 1500 Hz and oscillation amplitudes of up to ±20%. A hemispherical-tip, fast-response five-hole probe was developed and tested in this facility. The unsteady flowfield was measured via hot-wire anemometry, to document the instantaneous unsteady flow velocity, and a specially designed fast-response static-pressure probe in order to measure the jet's instantaneous unsteady static pressure

Unsteady Calibration of Fast-Response Pressure Probes, Part 2: Water-Tunnel Experiments

Abstract: This part of our work presents the development of a water-tunnel setup to experimentally determine the instantaneous pressure distribution over a sphere in unsteady flow, the unsteady pressure coefficient, and to provide validation of the unsteady probe calibration techniques discussed in Part 1 To generate an unsteady flowfield with significant inertial effects, a water-tunnel setup was developed where flow unsteadiness was generated by oscillating a spherical probe with a diameter of 508 mm at frequencies up to 4 Hz The steady and unsteady pressure coefficients were experimentally determined

Morphing Wing: A Demonstration of Aero Servo Elastic Distributed Sensing and Control

Abstract: This paper details efforts made in the design, analysis, and control of a novel morphing wing for NASA utilizing cuttingedge intelligent material technology. The theoretical modeling of the aerodynamic characteristics of a morph-able wing has been achieved by applying Prandtl-Glauert’s Lifting Line Theory. Using this Vortice-Lattice method in accordance with the computing language FORTRAN the drag, lift, and pitching moments of the morphing wing were calculated. The functional behavior that explains the aerodynamic response to the three twisting sections was studied. Relationships between motor outputs and achieved twist angles were derived from measurements; these relationships were then validated via sensor feedback systems.