Fluid Mechanics Research Laboratory

The Fluid Mechanics Research Laboratory (FMRL) is a research facility with a diverse and dynamic research program. Among the primary strengths of FMRL are its unique, state-of-the-art testing and diagnostic facilities, not commonly available in university research centers. Research is supported by and conducted in close collaboration with industry, government agencies such as NASA and ONR, and researchers at other universities. One of the goals is to study fluid dynamics problems which are not only of fundamental importance but also have direct practical applications. Some of the programs currently under investigation include: unsteady separated flows, compressible turbulence, compressible mixing and enhancement, aeroacoustic behavior of supersonic jets and its dependence on jet geometry, optical diagnostics development for fluid flows, and thrust vectoring of supersonic jets using counterflow.

The objective of the work in the area of unsteady separated flows is to provide the knowledge and methodology needed for predicting unsteady loads on a wing undergoing rapid variations in angle of attack. This is important for the design of future aircraft emphasizing high maneuverability. The experimental program utilizes the whole field velocity measuring technique known as Particle Image Velocimetry (PIV) to obtain instantaneous vorticity field measurements. These measurements are then compared with those obtained from the numerical simulations of Navier-Stokes equations. The main experimental facilities used in these investigations are a 5m long water towing tank facility and a 20cm x 20cm transonic wind tunnel.

The aeroacoustic characteristics of supersonic jets and the associated problem of compressible mixing constitutes one of the major research endeavors at the FMRL. Flowfield behavior of supersonic jets, including the effect of parameters such as nozzle geometry, jet temperature and the presence of coflow, is being extensively studied. These experiments are conducted in the FMRL's High Speed Jet Facility. This is a blow down facility capable of producing an ideally expanded, primary supersonic jet stream over a Mach number range of 1 to 2.5 and over temperatures ranging from ambient to 1000 degrees F. Additionally, a co-flowing stream can also be produced with freestream Mach numbers from 0.3 to 1.5. The high speed facility is equipped with PIV instrumentation to provide detailed velocity and vorticity field data. The infrared radiation properties of supersonic jets are also investigated using an IR camera. These measurements are of considerable practical importance for the design of exhaust nozzles for supersonic aircraft. A newly designed six-component force balance, which allows for the direct measurement of the forces and moments produced by a jet has also been recently added to the high speed facility.

An effort is underway to provide a basic understanding of the various mechanisms involved in the generation of noise from supersonic jets. The objective of the work is to investigate the performance of active and passive noise suppression devices for supersonic jets with the final goal of proposing a silencer design applicable to high speed aircraft such as the High Speed Civil Transport (HSCT). The acoustic behavior of supersonic jets is primarily examined in the anechoic facility which has primary jet with temperatures up to 1000 degree F and jet exit Mach numbers up to 2.5. This unique anechoic facility is also capable of providing a coflowing stream (Mach 0.1 to 0.3) via an open jet (0.6m X 0.6m), close return subsonic wind tunnel.

Through the detailed characterization of supersonic jet properties, we not only gain insight into the flow physics governing such flowfields, but have also produced data which may serve as benchmark for computational fluid dynamics (CFD) code validation. The whole-field velocity and vorticity data obtained through the PIV technique are especially unique, in that reliable measurements of these primary flow properties are sparse in the existing database. To date, axisymmetric, rectangular and diamond shaped jets have been extensively studied. A novel approach, which employs counterflow to produce a countercurrent shear layer (a shear layer in which the primary and secondary freestreams flow in opposing directions), is being used to enhance mixing in compressible shear layers. It has been discovered that such shear layers have significantly higher mixing rates than conventional, coflowing shear layers. This result has important implications for the design of efficient propulsion systems. The effect of counterflow on combustion properties, especially combustion efficiencies and NOx emissions, is being examined in the combustion laboratory, one of the newer facilities at the FMRL. In addition to the conventional diagnostics, this laboratory is also equipped with PIV instrumentation and gas analyzers.

A relatively new fluidic control technique, which employs a secondary counterflow traveling in a direction opposite to the primary jet, is being explored as a means of providing thrust vector control of supersonic jets. The Counterflow Thrust Vectoring (CFTV) technique has been shown to produce continuous thrust vectoring of supersonic jets. In contrast to existing thrust vectoring schemes, CFTV is relatively simple and does not require complicated control hardware and software for implementation. The relative simplicity of this technique, its excellent dynamic characteristics and its robustness (it can be used with nozzles of various geometry), makes it a very powerful and efficient way to achieve pitch, yaw and roll control.

One of the notable contributions of this laboratory is the development of PIV and its application to supersonic flows. The PIV technique is currently being extended to provide the particle size distribution as well as size/velocity correlation. Efforts are also underway to extend the PIV capabilities to three dimensions, such that instantaneous, three-dimensional, velocity fields can be measured in a volume of the flowfield. Each test facility at FMRL is equipped with extensive state-of-the-art optical diagnostics. Some of the primary hardware includes 3 Nd: Yag pulsed lasers, 5W and 15WArgon-Ion cw lasers and several He:Neon lasers. Digital image processing facilities include two IBM RISC 6000 stations and several microcomputer based image processors. A new technique is also being developed to measure instantaneous density fields using laser speckle photography.

In addition to the combustion laboratory, the Short Take Off and Vertical Landing (STOVL) hover test facility and the FMRL shock tunnel facility have also been recently brought on-line. The hover test rig is used to measure jet induced aerodynamic phenomenon on STOVL models in and out of close ground proximity hover. The problems associated with near ground operations are poorly understood due to the unsteady nature of the flow field and its interaction with the aerodynamic surfaces. The facility is designed to operate at nozzle pressure ratios (P0/Pamb.) up to 8.0, and future plans include the addition of flow heaters to simulate temperature effects. The current investigation involves the measurement of unsteady pressures on the lower surfaces of the model, as well as the near field acoustics. The thrust of the study is to isolate the noise component associated with the fountain flow. The STOVL facility is also equipped with a large scale focusing schlieren system with a 3 ft x 3 ft field of view. The FMRL shock tunnel facility consists of a 6.5 foot high pressure driver, a 19.5 foot low pressure driven section, and a supersonic nozzle attachment. The facility is capable of producing supersonic jets at temperatures in excess of 2200Á F to better simulate real flight conditions. The primary focus of the facility is to study the flowfield properties, including density, viscosity, and stability behavior, in order to understand the role of high temperatures on screech tones.

The laboratory group consists of: Professors Anjaneyulu Krothapalli, Luiz Lourenco, George Buzyna, Chiang Shih, Leon Van Dommelen, Chris Tam, Farrukh Alvi, a number of full time staff members and numerous graduate and undergraduate students The laboratory is housed in a separate 5000 sq. ft. laboratory building with a fully equipped CNC machine shop for the fabrication of various experimental facilities. Faculty and students can obtain direct access to the supercomputer facilities at FSU.

The research in the FMRL is currently supported by the Airforce Office of Scientific Research, NASA Headquarters, NASA Ames Research Center, NASA Langely Research Center, the Office of Naval Research, General Electric Aircraft Engines, and McDonnell Douglas Aircraft.