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Current Research of Dr. Scott Morris

Dr. Morris conducts his research in the Hessert Laboratory for Aerospace Research.

Air-analog Fluid Structure Interactions and Acoustics for Underwater Applications

The causes of radiated acoustic noise are related to direct hydroacoustic scattering and structural vibration. Vibrating surfaces can be excited either by direct mechanical coupling, hydrodynamic pressure fluctuations, or acoustic pressures. The resulting physics can only be perfectly simulated using underwater experiments. However, it would be prohibitively expensive to obtain anechoic acoustic data for a wide range of geometries and parameters in underwater facilities. In the present experiments, air-analog experiments are used to study fluid loaded, flexible walled struc tural sound generation. As noted, true dynamic similarity can not be achieved in air-analog struc tural acoustics. However, the air experiments offer a distinct advantage in that various physical phenomena such as flexural waves, membrane waves, mass loading, etc. can be investigated inde pendently. Specifically, three material configurations are proposed that will partition these differ ent sound mechanisms. This provides a distinct advantage for analytical modeling in which the radiated sound is considered a superposition of these effects.

Turbulence and Acoustics in Trailing Edge Flows

The study of the airframe noise produced by the vortex shedding behind the trailing edge of a wing is a problem of interest in submarine and aircraft applications. Particle image velocimetry (PIV) is being used to study the flow field downstream of an asymmetric airfoil. A method of phase averaging the data to the nearly periodic vortex shedding has been developed using a Kar-hunen-Lueve decomposition of the wake velocity. This method will also be used to phase average unsteady surface pressure measurements taken simultaneously with the PIV data.

The goal of this project is to correlate the flow field characteristics measured using the PIV sys tem to far field acoustic measurements taken with a phased microphone array in the anechoic wind tunnel.

Turbulence and Acoustics in Marine Propulsion Flows

The present research involves the experimental measurement of the velocity field downstream of a ten bladed propeller. Previous efforts have examined the interaction between upstream turbu lence, downstream stators, and the propeller at a single downstream location. The present mea surements investigate the evolution of the wake with various advance ratios and ingested turbulence levels. These data will provide a data base for the development and validation of com putational modeling of turbulence and acoustics

Turbulence in the Near Surface Region of the Atmospheric Boundary Layer

Engineering design that includes very large Reynolds number remains a significant challenge for theoretical an computational methods. Because laboratory Reynolds number are typically limited to under 20,000, very little is known about the flow physics of high Reynolds number wall flows, particularly in the near wall region. A recently developed facility in western Utah utilizes the atmospheric boundary layer in near laboratory conditions. The surface is nearly flat for over 50km north of the test site, with a local surface roughness of order 2mm. The measurements take place over a 2 week period each summer. The data acquisition equipment is taken to the test site and setup each evening. North winds typically set in at dusk resulting in ideal flow conditions. Typi cally up to 30 people from 4 or more universities participate in the event.

Development of a Microfabricated Sonic Anemometer

Recent advancements in silicon etching techniques have led to electronic transducers which have physical characteristics far superior to the piezoelectric crystals; see Figure 1. The current research involves the development and assembly of a micro-fabricated ultrasonic anemometer prototype. A schematic of the initial probe design is shown in Figure 2. The device shown will have less than 1/30 the size of current devices, with over 60 times the temporal resolution. These improvements in instrumentation will lead to enhanced understanding and modeling capability of fluid flow in both laboratory and atmospheric turbulent flows.

Active Control of Tip clearance Flows in Rotating Machinery

The past several decades have seen a substantial amount of research in turbomachinery related areas, particularly with regards to the documentation and understanding of the fluid mechanics involved. This includes both high speed applications, such as jet propulsion, as well as low speed applications, such as axial fans and blowers. One important aspect of these flows involves the region near the tip of the rotating element. As much as 30% of the losses in a turbomachine can be attributed to the tip clearance flow. The goal of this research project is to explore methods of active flow control to increase the overall efficiency of a machine. Current methodologies include the destruction of the tip vortex using blade mounted plasma actuators. Research is currently being conducted on a two-dimensional airfoil-endwall setup to look at the vortex formation with regard to a number of important parameters. Next, a linear cascade will be outfitted with an active control system. With this setup, the reduction or removal of the tip clearance vortex will be further analyzed.

Vorticity Correlations in Turbulent Flows

This project concerns the measurement of the multi-point spatio-temporal correlation function of vorticity in turbulent shear flows. The study of vorticity provides a unique perspective of turbu lent flows with advantages in both theoretical and applied problems. All real flow fields contain vorticity, and regions within the flow that are dynamically significant are almost always vortical. As a result, a significant amount of effort has been devoted to the theoretical understanding of vorticity, its transport equation, and the relationship of vorticity to other variables of interest. For example, acoustic source terms, Reynolds stresses, fluid pressure, and regions of intense mixing can be expressed in terms of the magnitude and spatial coherence of vorticity. Formulations in terms of vorticity are often the preferred, and sometimes the only way to link theoretical and applied research problems in fluid mechanics. In spite of the stated importance, the dynamics of vorticity in real flows is poorly understood because of the difficulty of experimental measure ments. The proposed experiments will be the first to measure multi-point vorticity correlation functions in turbulent flows.

The experiments involve three classes of the canonical turbulent shear flows: a two stream shear layer, a turbulent boundary layer, and the wakes of cylinders. These flows all contain complex vorticity dynamics, and are of direct relevance to a number of important applications. The experi ments will be repeated for each of the geometries in order to seek common characteristics and dis tinctive features of the vorticity fields. Recent evidence presented in this proposal indicates that inhomogeneous flows often contain large scale structure in the vorticity field that leads to aniso tropic effects at nearly all scales of motion. It is also suggested that a universal form of the corre lation and spectral functions of vorticity may exist in anisotropic turbulence. If discovered, this could lead to a number of new modeling strategies for the application areas defined.

Acoustics of Fans with Asymmetric Duct Geometry

The radiated sound field of a fan and duct is of interest in numerous applications. Asymmetric bends in the duct lead to unsteady loading of the fan blades, and the potential for significantly increased sound production. The present study involves the measurement of velocity, unsteady surface pressure, and radiated sound in a simple fan-duct system. The measurements took place in the Anechoic Flow Facility (AFF) at the Naval Surface Warfare Center - Carderock Division. Experimental data were acquired in summer 2003, and data processing is now underway.