Dale M. Pitt

Effect of synthetic jet arrays on boundary layer control

An investigation into the interaction of a synthetic jet actuator array with a thick, turbulent boundary layer was conducted and the results are presented here. This paper documents an experimental effort that was directed towards improving the understanding of synthetic jet actuator arrays and the mechanism by which these actuators control flows at scales much larger than themselves. Of specific interest in the interaction of a synthetic jet flow and the boundary layer flow on a flat or curved wall where the axis of the synthetic jet is perpendicular to the direction of the oncoming flow. The investigation addressed, in broad terms, a typical control application involving internal flows. A synthesis of the results will provide guidance and direction in future actuator designs and implementation strategies, and feed design input to test plans for an extensive study of actuator control effects in a duct with variable pressure gradient and variable streamline curvature.

Overview of the SAMPSON smart inlet

The SAMPSON program will demonstrate the application of Smart Materials and Structures to large-scale aircraft and marine propulsion systems and show that smart materials can be used to significantly enhance vehicle performance, thereby enabling new missions and/or expanding current missions. Two demonstrations will be executed in relevant environments and at scales representations of actual vehicle components. The demonstrations will serve to directly address questions of scalability and technology readiness, thereby improving the opportunities and reducing the risk for transitioning the technology into applications. The aircraft application to be examined is the in-flight structural variation of a fighter engine inlet. Smart technologies will be utilized to actively deform the inlet into predetermined configurations to improve the performance of the inlet at all flight conditions. The inlet configurations to be investigated consists of capture area control, compression ramp generation, leading edge blunting, and porosity control. The operation and demonstration of this Smart Inlet is described in detail.

Thermal Acoustic Test and Analysis Model Updating and Correlation

Complex test articles that are exposed to combined loading conditions require a rigorous model updating, calibration, and test correlation process. The objective of model correlation process is to reduce uncertainty; such that, any difference between final predictions and test measurements can be attributed to deficiencies in simulating the physics and adapted tools, instead of model errors. Testing and analysis were conducted on a representative aircraft flap structure, subjected to realistic, severe in-service thermal and acoustic loads due to an engine exhaust environment. Test articles and finite element models were designed such that a large amount of data could be collected and used for correlation. The outer face of the skin was loaded both thermally and acousticly in a heated acoustic testing chamber. Several techniques were used to perform the correlation and model updating tasks to best match the test and analysis articlesThe methodology for correlating the FEM to the test data involved three different sets of data to fully update the model. The first set of data, gathered using thermocouples and infrared imaging, was used to update the thermal properties, conductivity and specific heat. A second set, collected using linear variable differential transducers (LVDTs), was needed to update the mixed thermal and structural property of thermal expansion. Lastly, a set obtained by using accelerometers and a laser vibrometer was necessary to update the structural property of mass, stiffness, and damping. Using ModelCenter, a model updating multi-input, multi-output optimization was performed to minimize the differences between the data and the finite element model. Three separate analyses, one for each data set, were used in the optimization process: a thermal analysis for the thermal properties, a nonlinear static analysis for expansion property, and a modal analysis for the dynamic properties. In each of these analyses, the optimization routine was given an appropriate set of input parameters, including both material and load variation, to allow for a well correlated solution. The end result was a model tuned to the right frequencies and with the correct modeshapes at elevated temperature.

Application and Demonstration of Nonlinear Reduced Order Modeling (NLROM) for Thermal/Acoustic Response

Dynamic response analysis tools used by the aerospace industry rely heavily on linear modal frequency response finite element methods. These linear methods are straight forward to use even in the analysis of a complex structural component that require a large number of degrees-of-freedom to model. However, this approach is not suitable for predicting the response of highly loaded thermal/acoustic aircraft structures that may respond in a nonlinear geometric manner. This type of problem requires a nonlinear transient analysis. The nonlinear analysis of a complex structural component is computationally prohibitive, especially for random acoustic response prediction which requires long duration time simulations for fatigue analysis. To overcome these computational deficiencies, nonlinear reduced order modeling (NLROM) methods have been developed. However, these methods need to be validated using realistic structural applications. This paper describes the results from a recent demonstration of the NLROM methods applied to the analysis of aircraft flap skin exposed to high thermal/acoustic loads.

Smart-actuated continuous moldline technology (CMT) mini wind tunnel test

The Smart Aircraft and Marine Propulsion System Demonstration (SAMPSON) Program will culminate in two separate demonstrations of the application of Smart Materials and Structures technology. One demonstration will be for an aircraft application and the other for marine vehicles. The aircraft portion of the program will examine the application of smart materials to aircraft engine inlets which will deform the inlet in-flight in order to regulate the airflow rate into the engine. Continuous Moldline Technology (CMT), a load-bearing reinforced elastomer, will enable the use of smart materials in this application. The capabilities of CMT to withstand high-pressure subsonic and supersonic flows were tested in a sub-scale mini wind- tunnel. The fixture, used as the wind-tunnel test section, was designed to withstand pressure up to 100 psi. The top and bottom walls were 1-inch thick aluminum and the side walls were 1-inch thick LEXAN. High-pressure flow was introduced from the Boeing St. Louis poly-sonic wind tunnel supply line. CMT walls, mounted conformal to the upper and lower surfaces, were deflected inward to obtain a converging-diverging nozzle. The CMT walls were instrumented for vibration and deflection response. Schlieren photography was used to establish shock wave motion. Static pressure taps, embedded within one of the LEXAN walls, monitored pressure variation in the mini-wind tunnel. High mass flow in the exit region. This test documented the response of CMT technology in the presence of high subsonic flow and provided data to be used in the design of the SAMPSON Smart Inlet.