William C. Schneck

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.

Flow Control Over a Circular Cylinder Using Pulsed Dielectric Barrier Discharge Actuators

Immersed bodies such as struts, vanes, and instrumentation probes in gas turbine flow systems will, except at the lowest of flow velocities, shed separated wakes. These wakes can have both upstream and downstream effects on the surrounding flow. In most applications, surrounding components are designed to be in the presence of a quasi-steady or at least nonvariant flow field. The presence of unsteady wakes has both aerodynamic and structural consequences. Active flow control of wake generation can therefore be very valuable. One means to implement active flow control is by the use of plasma actuation. Plasma actuation is the use of strong electric fields to generate ionized gas that can be actuated and controlled using the electric fields. The controlling device can be based on AC, DC, or pulsed-DC actuation. The present research was conducted using pulsed-DC from a capacitive discharge power supply. The study demonstrates the applicability of, specifically, pulsed-DC plasma flow control of the flow on a circular cylinder at high Reynolds numbers. The circular cylinder was selected because its flow characteristics are related to gas turbine flowpath phenomena, and are well characterized. Further, the associated pressure gradients are some of the most severe encountered in fluid applications. The development of effective plasma actuators at high Reynolds numbers under the influence of severe pressure gradients is a necessary step toward developing useful actuators for gas turbine applications beyond laboratory use. The reported experiments were run at Reynolds numbers varying from 50,000 to 97,000, and utilizing various pulse frequencies. Further the observed performance differences with varying electric field strengths are discussed for these Reynolds numbers. The results show that flow behaviors at high Reynolds numbers can be influenced by these types of actuators. The actuators were able to demonstrate a reduction in both wake width and momentum deficit.

An electric field model developed for multi-physics plasma-fluid simulation for atmospheric dielectric barrier discharge actuators

Summary form only given. Immersed bodies such as struts and vanes in gas turbine flow systems will, except at the lowest of flow velocities, shed separated wakes. One means to mitigate this is through active flow control by the use of pulsed DC plasma actuation. A two-dimensional, plasma-fluid model and code, multi-PHysics Analysis of Fluid-plasma Numerical Integration algoRithm (PHAFNIR), that couples electrodynamics, plasma reaction kinetics, and fluid mechanics has been developed and validated extensively to experiment. Further, numerical verification has also been performed on this code.

Optical measurement of plasma-fluid interactions in dielectric barrier discharges in low reynolds flows

Summary form only given. Atmospheric plasmas created using dielectric barrier discharge (DBD) actuators have a wide variety of applications in flow control within gas turbines, struts, airfoils, inlets, and a variety of flow conditions. Though, the research presented here centers on flow control using a DBD actuator, atmospheric DBD plasmas have additional applications in other industries.

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.

Engine test for wavelength-multiplexed fiber Bragg grating temperature sensor

A temperature sensor link based on wavelength-multiplexed fiber Bragg grating (FBG) was designed and fabricated for distributed temperature measurement in a jet engine nozzle under field conditions. Eight FBGs with different Bragg wavelengths ranging from 1520 nm to 1560 nm were fabricated along one single-mode fiber which was packaged inside a stainless steel tube. The reflected signal from the sensor link was simultaneously collected by an optical sensing interrogator and converted into temperature information. The steel tube was embedded in a steel flange assembly attached to a jet engine. Three engine cycles were performed from 55% (idle) to 80% of the engine’s full power to test the sensor response under high temperature, vibration and strong exhaust flow conditions. Test results show good survivability of the sensor, and the temperature around the nozzle was measured up to 290 °C. The system has a temperature measurement range from 20 °C to 600 ° and the response time is less than 1 second.