Tobias Ecker

Eddy Convection in Developing Heated Supersonic Jets

An experimental study of the spatial distribution of integral eddy speeds in heated, supersonic free jets is presented. The physics of such jets are of immediate interest to noise-reduction approaches for tactical aircraft jet noise. In these flows, the noise produced has a strong influence from eddy speeds, particularly for radiation in peak noise directions, due to Mach wave contributions. The measurements obtained using a time-resolved Doppler global velocimetry instrument experimentally indicate a key mechanism of the role of heating in jet noise reduction relative to the classical Lighthill U8 scaling. Measurements are presented in jets issuing from an axisymmetric biconic nozzle at two conditions: total temperatures of 1.6 and 2.0 times that of the ambient and both at approximately 106 diameter Reynolds number and pressure-matched exit conditions. For the higher total temperature case, the scaled streamwise eddy convective velocities within the shear layer were measurably reduced compared to the low...

Experimental Reynolds Stress Spectra in Hot Supersonic Round Jets

The motion and evolution of coherent structures in supersonic jet flows is directly related to the intense noise the flow generates. As a preliminary study to experimentally address these relationships, novel non-intrusive measurements using two-component laser Doppler velocimetry (LDV) have been conducted at exceptionally high data rates to lend insight into the statistical behavior of noise-generating flow structures. A new heated supersonic jet facility has been constructed to provide supersonic flow at total temperatures ratios up to 3. The new LDV used here allows for highly spatially and temporally resolved measurements of velocity in the hot supersonic jet under study. In the present work, the instrumentation is validated via comparison of LDV measurements along the centerline of a screeching cold jet with microphone and high-speed shadowgraph results. LDV results for the local appearance of screech tones and harmonics in the Reynolds stress spectra are presented for an over-expanded case (nozzle pressure ratio of 3.2) of a design Mach number 1.65 nozzle operated cold ( = 1). A preliminary study was then conducted in the nearnozzle shear layer, up to x/d = 4.0, at design nozzle pressure ratio (4.58) and total temperature ratio of 2.0. Results are presented for Reynolds stress time-delay correlations and power spectra at Red = 1.1M for this case. The stream-wise Reynolds normal stress spectra are compared with published spectral behavior reported by other researchers, indicating a similar spectral shape in the downstream stations as previously measured with LDV and hot wire anemometry for cold jets, but which differ in shape from density-based techniques. The results reveal spectral detail of an interesting transition region between the nozzle turbulent boundary layer and the jet shear layer in which flow time scales are exceptionally small and spectral signatures of large scale instabilities are superimposed on the incoming boundary layer turbulence. The results point toward the importance of very high frequency coherent phenomena in this region, particularly evident in the radial and shear stresses time-delay behavior.

Velocity Statistics and Spectra in Three-Stream Jets

Velocimetry measurements were obtained in three-stream jets at the NASA Glenn Research Center Nozzle Acoustics Test Rig using the time-resolved Doppler global velocimetry technique. These measurements afford exceptional frequency response, to 125 kHz bandwidth, in order to study the detailed dynamics of turbulence in developing shear flows. Mean stream-wise velocity is compared to measurements acquired using particle image velocimetry for validation. Detailed results for convective velocity distributions throughout an axisymmetric plume and the thick side of a plume with an offset third-stream duct are provided. The convective velocity results exhibit that, as expected, the eddy speeds are reduced on the thick side of the plume compared to the axisymmetric case. The results indicate that the time-resolved Doppler global velocimetry method holds promise for obtaining results valuable to the implementation and refinement of jet noise prediction methods being developed for three-stream jets.

A rapid response 64-channel photomultiplier tube camera for high-speed flow velocimetry

In this technical design note, the development of a rapid response photomultiplier tube camera, leveraging field-programmable gate arrays (FPGA) for high-speed flow velocimetry at up to 10 MHz is described. Technically relevant flows, for example, supersonic inlets and exhaust jets, have time scales on the order of microseconds, and their experimental study requires resolution of these timescales for fundamental insight. The inherent rapid response time attributes of a 64-channel photomultiplier array were coupled with two-stage amplifiers on each anode, and were acquired using a FPGA-based system. Application of FPGA allows high data acquisition rates with many channels as well as on-the-fly preprocessing techniques. Results are presented for optical velocimetry in supersonic free jet flows, demonstrating the value of the technique in the chosen application example for determining supersonic shear layer velocity correlation maps.

Spectral analysis of over-expanded cold jets via 3-component point Doppler velocimetry

Supersonic jet noise is a major health concern in military aviation which may be alleviated with physicsbased control strategies. In order to understand the physics of sound generation from supersonic free jets, highly resolved experimental investigation of the dominant unsteady flow features is necessary. In this study we present a single point Doppler Velocimeter (pDV) based on the Doppler Global Velocimetry principle used for spectral analysis of an over-expanded supersonic cold jet. Using discrete laser beams and high speed photomultiplier tubes allow resolution of the finest scales in the flow. Acousto-optic beam multiplexing enables three component measurement, producing velocity vectors at 100kHz mean rates over extended time windows. This information is used to generate spectral correlations as well as three dimensional mean velocity and turbulence statistics in the core of the supersonic jet (Md = 1.65). Measurements at different nozzle pressure ratios (NPR = 2.2−4.7) and along the streamwise direction (NPR = 3.2) in a cold jet are presented.

Early Development of Time-Resolved Volumetric Doppler Velocimetry for New Insights in Hot Supersonic Jet Noise

The early development of a novel implementation of Doppler-based flow velocimetry, termed the time-resolved volumetric Doppler velocimetry (TRVDV) technique, is discussed for the specific application of kinematics measurements related to flow-generated noise in hot supersonic jets. By combining new detector technologies with unique uses of advanced laser-based photonics, TRVDV promises to produce many hundreds of velocity vectors distributed throughout volumes of the flow at 100kHz repetition rates over long contiguous durations—information needed in real flows to quantitatively evaluate noise sources. Herein, we describe the instrument currently under development and present some single-point velocity statistics and signals from a two-point prototype instrument in a cold supersonic jet. Spectral analysis for the stream-wise normal stress has been done for the single-point data at the center of the jet near the exit plane via slot correlation, with results out to approximatlely 400kHz presented. Initial results for measuring two points spaced along the collection optics axis exhibit the key attribute required for obtaining volumetric results with the system, namely, sufficient scattering intensity with varying depth of focus. Future development of the instrumentation system for many point measurements are discussed in light of current results. It is planned that the mature TRVDV package will be portable such that the system may be shipped to larger facilities for aeroacoustics experiments with results at levels of detail never before obtained.

Augmenting convection-enhanced delivery through simultaneous co-delivery of fluids and laser energy with a fiberoptic microneedle device

This paper describes a new infusion catheter, based on our fiberoptic microneedle device (FMD), designed with the objective of photothermally augmenting the volumetric dispersal of infused therapeutics. We hypothesize that concurrent delivery of laser energy, causing mild localized photothermal heating (4-5 °C), will increase the spatial dispersal of infused chemotherapy over a long infusion period. Agarose brain phantoms, which mimic the brain’s mechanical and fluid conduction properties, were constructed from 0.6 wt% Agarose in aqueous solution. FMDs were fabricated by adhering a multimode fiberoptic to a silica capillary tube, such that their flat-polished tips co-terminated. Continuous wave 1064 nm light was delivered simultaneously with FD&C Blue #2 (5%) dye into phantoms. Preliminary experiments, where co-delivery was tested against fluid delivery alone (through symmetrical infusions into in vivo rodent models), were also conducted. In the Agarose phantoms, volumetric dispersal was demonstrated to increase by more than 3-fold over a four-hour infusion time frame for co-delivery relative to infusion-only controls. Both forward and backward (reflux) infusions were also observed to increase slightly. Increased volumetric dispersal was demonstrated with co-delivery in an in vivo rodent model. Photothermal augmentation of infusion was demonstrated to influence the directionality and increase the volume of dye dispersal in Agarose brain phantoms. With further development, FMDs may enable a greater distribution of chemotherapeutic agents during CED therapy of brain tumors.

Characterizing Thermal Augmentation of Convection-Enhanced Drug Delivery with the Fiberoptic Microneedle Device

ABSTRACT Convection-enhanced delivery (CED) is a promising technique leveraging pressure-driven flow to increase penetration of infused drugs into interstitial spaces. We have developed a fiberoptic microneedle device for inducing local sub-lethal hyperthermia to further improve CED drug distribution volumes, and this study seeks to quantitatively characterize this approach in agarose tissue phantoms. Infusions of dye were conducted in 0.6% (w/w) agarose tissue phantoms with isothermal conditions at 15 °C, 20 °C, 25 °C, and 30 °C. Infusion metrics were quantified using a custom shadowgraphy setup and image-processing algorithm. These data were used to build an empirical predictive temporal model of distribution volume as a function of phantom temperature. A second set of proof-of-concept experiments was conducted to evaluate a novel fiberoptic device capable of generating local photothermal heating during fluid infusion. The isothermal infusions showed a positive correlation between temperature and distribution volume, with the volume at 30 °C showing a 7-fold increase at 100 min over the 15 °C isothermal case. Infusions during photothermal heating (1064 nm at 500 mW) showed a similar effect with a 3.5-fold increase at 4 h over the control (0 mW). These results and analyses serve to provide insight into and characterization of heat-mediated enhancement of volumetric dispersal.

Improving convection-enhanced delivery through photothermal augmentation of fluid dispersal

Malignant tumors of the central nervous system are the third leading cause of cancer-related deaths in adolescents and adults between the ages of 15 and 34; in children, brain tumors are the leading cause of cancer death. Convection-enhanced delivery (CED) has emerged as a promising method for the transport of high concentrations of chemotherapeutic macromolecules to brain tumors. CED is a minimally-invasive surgical procedure wherein a stereotactically-guided small-caliber catheter is inserted into the brain parenchyma, to a tumor site, for low flowrate infusion of chemotherapy [1]. This direct-delivery method bypasses obstacles to systemic chemotherapy caused by the selective impermeability of the blood-brain barrier. Although preliminary studies were favorable, CED recently failed Phase III FDA trials because clinical goals for tumor regression were not met [2]. This was primarily attributed to insufficient diffuse delivery of the drug throughout tumor masses and their surrounding margins.Copyright

Modelling of Magnetic Targeting of Therapeutic Nanoparticles in a Two Phase Microvessel Flow

Magnetic particle targeting is a new approach in cancer drug administration which aims to reduce side effects, increase healing rate and reduce treatment time. For this purpose a therapeutic agent is equipped with a magnetizable membrane and administered intravenously. A rare earth magnet can then be used to target cancerous tissue in proximity of the blood vessel.Copyright