Anthony M. Ferrar

Active Control of Flow in Serpentine Inlets for Blended Wing-Body Aircraft

The Blended Wing-Body commercial aircraft concept promises performance improvements in noise, emissions, and fuel consumption. Highly integrated airframepropulsion systems featuring embedded engines offer further improvements. Embedded engine systems are envisioned which require Boundary Layer Ingesting (BLI) serpentine inlets to provide the needed airflow to the engine. Due to the ingestion of a large boundary layer as well as the geometry of the serpentine inlet, significant flow distortions are developed that will affect engine performance and the stability of the fan. A bleed flow control system was tested that utilized no more than 2% of the total inlet flow. Two bleed slots were employed, one near the entrance of the BLI inlet and one near its aft exit. The bleed system successfully reduced inlet distortions by as much as 30%, implying improvements in stall margin and engine performance.

Improved Prediction Method for the Design of High-Resolution Total Pressure Distortion Screens

In ground test applications for simulated embedded engine systems, it is often necessary to forego direct-connect inlet/engine configurations and simulate inlet produced distortion profiles. Classically, this has been accomplished through the use of wire-mesh screens layered over a thick supporting grid. Other traditional approaches of distortion generation rely on active controls and/or empirical loss models for various geometries (such as airfoils, cylinders, and screens). These widely tabulated loss models limit the design of such device elements to those available in the literature. The freedom provided by advanced manufacturing methods would significantly expand the design space for such an application, giving rise to complex geometries that are not commercially available or feasible to manufacture. Therefore, an accurate distortion model relating total pressure losses to any geometry is necessary for a true design optimization of the distortion generator. This paper presents such a model by relating total pressure losses to various system interactions in classical fluid dynamic relationships. The total pressure loss models are formulated for incompressible and compressible flow conditions, where the total pressure across the screen is manipulated by either a mass exchange or adjusting the drag characteristics of the screen. This model is fully derived for the case of incompressible flow with drag, and validated against experimental data collected from a low-speed wind tunnel test. The accurate prediction of the reduced-order model with the low-speed results gives rise to a higher fidelity “continuous” screen in which every cell is tailored for a specific total pressure value.

Application of Additive Manufacturing to Rapidly Produce High-Resolution Total Pressure Distortion Screens

Detailed, accurate knowledge of interactions between embedded engines and inlet/ airframe-generated nonuniform flow profiles is essential for the successful design of robust integrated engine systems. In the absence of direct-connect experimentation, flow distortion patterns must be simulated by generating the nonuniformities with flow conditioning devices. Traditionally, wire screens installed on a supporting grid have been used to induce regions of steady total pressure distortions, utilizing sections of constant-porosity wire meshes assembled to form a complete screen. The design of wire screens that accurately reproduce steady total pressure distortions representing inlet-engine interactions is challenging because modern fluids and structures modeling approaches cannot be efficiently applied, resulting in numerous construction and testing iterations. Additive manufacturing methods (“rapid prototyping”) can be used to quickly and accurately produce distortion screens for testing of integrated inlet-engine systems. Rapid prototyping methods enable the production of unique screen geometries that are otherwise very difficult, impractical, or even impossible. A screen design method compatible with additive manufacturing methods that utilizes a hexagonal-element flow control grid composed of airfoil cross-sections is presented. Advantages of this new design and screen production method include improved aerodynamic and flow control features, a more durable structure, and greater design flexibility resulting in a more accurate reproduction of the desired distortion profile. Results of the design and fabrication of a prototype screen are presented.

Optical emission spectroscopy measurements of quiescent atmospheric plasmas created via dielectric barrier discharge actuators

Generating an atmospheric plasma as a form of flow control is a relatively novel technique for controlling boundary layer losses, reducing drag, and increasing overall airflow efficiency of immersed bodies in fluids. One method for achieving flow control through the use of atmospheric plasma is via a pulsed-dc dielectric barrier plasma actuator. The goal of this work is to measure and calculate the plasma temperature and electron density of the atmospheric plasma generated via a pulsed-dc actuator and using optical emission spectroscopy (OES) in quiescent air conditions. Through the course of this research, a method to measure and characterize dielectric barrier discharge plasmas was developed and used to quantify them through an experimental test stand, Spectroscopic Shadowgraphic Atmospheric Plasma Experiment (SeSAmE). Through testing of the plasma actuators with optical measurement techniques such as spectrometry and shadowgraphy, the necessary data is obtained and used in calculating plasma parameters such as electron temperature and electron density and values consistent with those expected in the literature. The spectra were analyzed using the relative line method and an absolute intensity transition method to compute electron temperatures and number densities, mainly through use of the N2 second positive set of transitions. Electron temperatures are found to be on the order of 0.25eV with number densities on the order of 1.1x1017 /m3. These data are also used to compare with a, first principles, multi-physics code coupling a fluid model, a chemistry model, and an electrostatics model.

Optical emission spectroscopy measurements of atmospheric plasmas in cross flow created via dielectric barrier discharge actuators

Generating an atmospheric plasma as a form of flow control is a relatively novel technique for controlling boundary layer losses, reducing drag, and increasing overall airflow efficiency of immersed bodies in fluids. A method for achieving flow control is through the use of a pulsed-dc dielectric barrier (DBD) plasma actuator.

Examining Sample Rate, Sample Time, and Test Replication for Reducing Uncertainty in Steady Timewise Experiments

This paper presents the ways that sample rate, sample time, and number of test replications can affect the random uncertainty in a measurement. Typical steady timewise experiments seek the average values of measured variables. Even in this case, sample rate and sample time can affect the signal standard deviations and yield different random uncertainty estimates. In addition, many random error sources vary slowly relative to the test time and take on a single value. Test replications can convert systematic uncertainties to random uncertainties by allowing their values to change from test to test. The goal is to record individual tests at a sample rate and time that capture the short timescale error sources, and to replicate tests on the scale of long timescale error sources. This paper presents how to leverage these effects to reduce the overall uncertainty of a measured result without increasing the cost of the experiment. This article is available in the ASME Digital Collection at http://dx.doi.org/10.1...