P C Klimas

Bio: P C Klimas is an academic researcher. The author has contributed to research in topics: Wind tunnel & Airfoil. The author has an hindex of 1, co-authored 1 publications receiving 617 citations.

Aerodynamic characteristics of seven symmetrical airfoil sections through 180-degree angle of attack for use in aerodynamic analysis of vertical axis wind turbines

Abstract: When work began on the Darrieus vertical axis wind turbine (VAWT) program at Sandia National Laboratories, it was recognized that there was a paucity of symmetrical airfoil data needed to describe the aerodynamics of turbine blades. Curved-bladed Darrieus turbines operate at local Reynolds numbers (Re) and angles of attack (..cap alpha..) seldom encountered in aeronautical applications. This report describes (1) a wind tunnel test series conducted at moderate values of Re in which 0 less than or equal to ..cap alpha.. less than or equal to 180/sup 0/ force and moment data were obtained for four symmetrical blade-candidate airfoil sections (NACA-0009, -0012, -0012H, and -0015), and (2) how an airfoil property synthesizer code can be used to extend the measured properties to arbitrary values of Re (10/sup 4/ less than or equal to Re less than or equal to 10/sup 7/) and to certain other section profiles (NACA-0018, -0021, -0025).

Flexible flapping airfoil propulsion at low Reynolds numbers

Abstract: Water tunnel experiments on a flexible airfoil plunging with constant amplitude have been carried out for Reynolds numbers of 0 to 27000. Peaks in thrust coefficient at intermediate values of airfoil stiffness were observed at both zero and non-zero Reynolds numbers, indicating that a degree of flexibility is beneficial at low Reynolds numbers. Time-averaged velocity fields and momentum flux data revealed a broader, higher-velocity jet in cases of optimum airfoil stiffness. Stronger vortices, separated by a larger lateral distance, characterised the corresponding instantaneous velocity fields. The flexibility causes the airfoil to pitch passively; the phase angle of the pitch was found to lead the plunge. Pitch amplitude and trailing-edge amplitude were found to be single-valued functions of pitch phase angle. The shape characteristics of the airfoil could therefore be described by the pitch phase angle only. Thrust coefficient was found to be a function of only two parameters: Strouhal number and pitch phase angle. For each Strouhal number, a peak in thrust coefficient was observed at a particular value of the pitch phase angle. The optimum pitch phase angle was found to tend to a limit of 105±5 degrees at very large Strouhal numbers. A significant thrust benefit was observed over very stiff airfoils when the optimum flexibility is utilized.

Modeling and Testing of a Novel Aeroelastic Flutter Energy Harvester

Abstract: This paper proposes a novel piezoelectric energy harvesting device driven by aeroelastic flutter vibrations of a simple pin connected flap and beam. The system is subject to a modal convergence flutter response above a critical wind speed and then oscillates in a limit cycle at higher wind speeds. A linearized analytical model of the device is derived to include the effects of the three-way coupling between the structural, unsteady aerodynamic, and electrical aspects of the system. A stability analysis of this model is presented to determine the frequency and wind speed at the onset of the flutter instability, which dictates the cut-in conditions for energy harvesting. In order to estimate the electrical output of the energy harvester, the amplitude and frequency of the flutter limit cycle are also investigated. The limit cycle behavior is simulated in the time domain with a semi-empirical nonlinear model that accounts for the effects of the dynamic stall over the flap at large deflections. Wind tunnel test results are presented to determine the empirical aerodynamic model coefficients and to characterize the power output and flutter frequency of the energy harvester as functions of incident wind speed.

Modeling, Control, and Flight Testing of a Small Ducted-Fan Aircraft

Abstract: Small ducted fan autonomous vehicles have potential for several applications, especially for mi ssions in urban environments. This paper discusses the use of dynamic inversion with neural network adaptation to provide an adaptive controller for the GTSpy, a small ducted fan autonomous vehicle based on the Micro Autonomous Systems’ Helispy. This app roach allows utilization of the entire low speed flight envelope with a relatively poorly understood vehicle. A simulator model is constructed from a force and moment analysis of the vehicle, allowing for a validation of the controller in preparation for flight testing. Data from flight testing of the system is provided. Nomenclature B A A 2 1 ˆ , ˆ , ˆ = linearized vehicle dynamics a