Florida Center for Advanced Aero-Propulsion

Better understanding of intake performance relies on having an accurate idea of the incoming flow conditions. Understanding the effects of inflow conditions is crucial to both the performance and safety of the aircraft. Recent testing at the Florida Center for Advanced Aero-Propulsion investigated flow development over the compression ramp of a Mach 3 intake. Various inflow conditions were tested using steps and vortex generators to better approximate realistic flight conditions. One qualitative technique used to understand the flow development is oil flow, in which the model is painted with oil before performing a test. During a test, the oil will move in the direction of the surface streamlines, potentially revealing unique features within the flow. The results shown are a pair of vortex generators generating a unique flow field over the surface of a compression ramp.

An experimental study involving Particle Image Velocimetry (PIV) and far-field microphone measurement was carried out to investigate the mixing characteristics of a low aspect ratio supersonic rectangular nozzle (design Mach number 1.44). Rectangular jets have unique flow characteristics that may make them superior to traditional circular nozzles. Rapid decay of the jet potential core, and enhanced mixing of the ambient fluid with the jet exhaust, can have a significant reduction in the jet noise produced. To determine the radiated sound field from the jet, acoustic measurements were taken in the anechoic chamber of the FCAAP Hot Jet facility, using nine microphones arranged in an arc around the nozzle exit. The experiments were conducted at the ideal operating condition and select conditions above and below ideal. Measurements were taken at both orientations of the rectangular nozzle: major and minor axis. The insulated walls of this Hot Jet facility minimize sound reflections and increase the accuracy of the acoustic measurements. Analysis of the acoustic data revealed a highly directional sound field. The overall sound pressure levels (OASPL) were lower in the major axis as compared to the minor axis. PIV measurements were taken in the FCAAP STOVL facility to reveal the flow pattern at the different operating conditions. PIV is an optical measurement technique that injects very small glycol-based water droplets into the jet stream. A high-speed camera acquires images of the flow field; and special processing software is used to reveal the flow structures present and determine the time-averaged velocity of the jet. Each operating condition produced a unique flow field pattern. At the ideal condition, there was an absence of shock cells and relatively minimal turbulence downstream. At non ideal conditions, shock cells were clearly visible, with increased turbulence downstream. The acoustic levels at the ideal condition were lower than that at the non-ideal conditions. Investigating the relationship between the flow field and the radiated sound field is crucial in helping researchers understand how rectangular nozzles, particularly those of low aspect ratio, can be integrated into the design of newer quieter aircraft, both in the subsonic and supersonic regime. 

The phenomenon of Fluid-Structure Interaction in high-speed flows is an important mystery that needs attention for the design of efficient next-generation high-speed flight vehicles. Here the fluid-structure interaction on a flexible panel is studied under the effect of a Mach 2 impinging shock wave boundary layer interaction. The panel has a cavity underneath which is left open to ambient pressure. The rectangular region enclosed by the dashed lines shows the location of the panel. The mean flow effects of the coupling between the fluid and the structure on the mean flow, flow dynamics, and structural dynamics are shown using 4 different experimental techniques, namely shadowgraph to visualize the interaction features along a plane normal to the flexible panel, surface oil flow to visualize the signature of the interaction over the panel surface and extract important quantitative information such as the separation bubble length, the location of the separation and reattachment on the panel and its overall structure. Unsteady pressure-sensitive paint measurements are shown to understand the pressure fluctuations within the flow as well as the oscillation of the separation line in response to the combined effect of the shock and panel oscillation. The digital image correlation technique shows the vibration of the panel in response to the flow-associated fluctuations, which involve the fluctuations of flow parameters within the boundary layer as well as due to shock wave boundary layer interaction.  For more details, refer to the published papers on this work.    These experiments were carried out at the Polysonic test facility at Florida Centre for Advanced Aero Propulsion (FCAAP) and are funded by FCAAP.    #shockwaveboundarylayerinteraction #fluidstructureinteraction #aerodynamics #gasdynamics #experimentaltesting #flowvisualization 

Got our paper published in Experiments in Fluids! Big shout out to YANG ZHANG and Lou Cattafesta for the significant contributions to the paper and the reviewers/editors of EXIF for helping us improve the quality of our manuscript. As an experimentalist, you quickly realize that sensors do not only respond to what they are intended to measure. In all aspects of test engineering there are external sources of noise that can be picked up by sensors that will contaminate their measurements. For example, I frequently use pressure sensors in wind tunnel testing and they measure the unsteady pressure fluctuations in the flow in addition to just about every other obscure source of noise you can think of, like the electromagnetic interference of the tunnel fan motor, the structural vibrations of the facility, and even the signature of the compressors running on the second floor of the building. Our paper provides a method to remove contamination (`denoise’) from sensor measurements in both the time and frequency domains with multiple independent measurements of the contaminating sources. This technique is very practical and has the ability to be implemented in many aspects of test engineering. Details can be found in the paper, check it out if you’re interested!

Ensuring the safe release of internally carried payloads, or stores, from an aircraft bay at supersonic speeds presents significant aerodynamic challenges. An integral component of an experimental store separation investigation is the characterization of aerodynamic forces and moments experienced by the store during release, as well as free flight. Here, shadowgraph visualization results from two different experiments are shown, where the aerodynamic loads during each phase of the trajectory were measured using a six-component force balance mounted internally within the store. These tests were performed at supersonic speeds using a rectangular cavity model as a representative aircraft bay. This work was done in the Polysonic Wind Tunnel (PSWT) at the Florida Center for Advanced Aero-Propulsion (FCAAP) with the support of the Air Force Research Laboratory (AFRL). Distribution A. Approved for public release; distribution unlimited. PA# AFRL-2023-3296. #FCAAP #AFRL #FSU #Experimental #Aerodynamics #Supersonic #WindTunnelTesting

Recently, experiments were conducted in the Florida State University Polysonic Wind Tunnel (PSWT) investigating the surface flowfield created by a shock wave impinging onto a slender cone at multiple supersonic Mach numbers. These experiments were conducted to advance our understanding of shock wave-boundary layer interactions (SBLI) over three-dimensional objects in an effort to apply fundamental flow physics to the design of real-world flight vehicles. The majority of previous research on SBLI was focused on flow over planar surfaces, creating a need for these experiments on a generic flight geometry. These experiments included shadowgraph imaging and surface oil flow visualization, both shown here, along with pressure sensitive paint measurements which will be published in future work.