Takehiro Himeno

Numerical Analysis for Propellant Management in Rocket Tanks

To track the three-dimensional behavior of liquid surfaces in storage tanks on orbit, a numerical scheme based on the level set method was developed. For the verification of the numerical methods, experimental data were acquired through the observation of the unsteady deformations of liquid surfaces in cylindrical containers under low-gravity conditions in a drop tower. Primary emphasis was placed on the dynamic behavior of the liquid surface and the displacement of the contact line on the solid wall. Based on the results, the boundary condition for surface tension was discussed and the model of wetting phenomena was adequately introduced into the computation. Compared with the experimental data, the corresponding numerical results showed good agreement. With the developed code, the flowfields at the draining process in the liquid oxygen (LO X ) tank for the upper-stage propulsion system of an H-IIA launch vehicle under low-gravity conditions were also investigated. It was found that the buoyancy induced by a slight acceleration was efficient to prevent dip growth and that the serviceable propellant in the launch-vehicle tank could thereby be increased in a realistic situation.

Numerical Analysis of Flow in a Transonic Compressor With a Single Circumferential Casing Groove: Influence of Groove Location and Depth on Flow Instability

The effect of circumferential single grooved casing treatment on the stability enhancement of NASA Rotor 37 has been examined with computational fluid dynamics analysis. Stall inception mechanism of Rotor 37 is presented first with principal focus on the tip leakage flow behavior, passage blockage, and the vortical flow structures. Detailed observation showed that the combined interaction of the stagnated flow of tip leakage vortex breakdown and the jetlike leakage flow from the midchord region leads to the blade tip-initiated stall inception. The result of numerical parametric study is then demonstrated to show the effect of varying the axial location and the depth of a circumferential single groove. The evaluation based on stall margin improvement showed a higher potential of deeper grooves in stability enhancement, and the optimal position for the groove to be located was indicated to exist near the leading edge of the blade.

Study on Atomization Process of Liquid Sheet Formed by Impinging Jets

Aiming at clarifying and quantifying atomization characteristics at impinging jet injector, numerical analysis, experimental observation and theoretical analysis were conducted. For computing atomization phenomena, a numerical method was developed. The method was verified through quantitative comparisons with corresponding experiment of pinch off. Then experimental and theoretical studies were performed on atomization of axisymmetric liquid sheet, which was produced by collision of two water jets in opposite direction, as well as numerical analysis. The numerical results of the atomization process through KelvinHelmholtz type of instability showed qualitative resemblance with experimental visualization and theoretical analysis. Finally, atomization characteristics at impinging jet injector were numerically analyzed. Liquid distributions from the injector face plate were quantified, and the dynamic behavior of the liquid sheet was found to affect strongly on liquid distributions at downstream.

Demonstration of Supercritical CO2 Closed Regenerative Brayton Cycle in a Bench Scale Experiment

Power generation with a supercritical CO2 closed regenerative Brayton cycle has been successfully demonstrated using a bench scale test facility. A set of a centrifugal compressor and a radial inflow turbine of finger top size is driven by a synchronous motor/generator controlled using a high-speed inverter. A 110 W power generating operation is achieved under the operational condition of rotational speed of 1.15kHz, CO2 flow rate of 1.1 kg/s, and respective thermodynamic states (7.5 MPa, 304.6 K) at compressor and (10.6 MPa, 533 K) at turbine inlet. Compressor work reduction owing to real gas effect is experimentally examined. Compressor to turbine work ratio in supercritical liquid like state is measured to be 28% relative to the case of ideal gas. Major loss of power output is identified as rotor windage. It is found the isentropic efficiency depends little on compressibility coefficient. Off design performance of gas turbine working in supercritical state is well predicted by a Meanline program. The CFD analysis on compressor internal flow indicates that the presence of backward flow around the tip region might create a locally depressurized region leading eventually to the onset of flow instability.Copyright

Atomization and Flow Characteristics of Liquid Sheet Produced by Jet Impingement

Aiming at elucidating the relationship between a liquid sheet atomization and the detailed flowfield inside the sheet produced by an impingement-type injector, numerical computation, experimental observation, and theoretical analysis were performed. A numerical methodwas developed to examine atomization phenomena. First, themethod was verified through quantitative comparisonwith a corresponding experiment of pinch off. Then, experimental and theoretical analyses were conducted on the atomization of an axisymmetric liquid sheet through Kelvin–Helmholtztype instability, which was produced by two opposing watexr jets. The numerical results showed qualitative resemblance to the corresponding experimental and theoretical analyses. Finally, it was clarified that a nonuniform injection velocity profile resulted in a velocity distribution with an inflection point inside the sheet. As a result, the sheet tended to be unstable and enhanced atomization.

Investigation of FC/GT Hybrid Core in Electrical Propulsion for Fan Aircraft

Distributed propulsion systems have been investigated by many researchers because the propulsion system can enhance the benefits of unconventional airframe concepts such as blended wing body (BWB) aircraft. The core-separated fan propulsion system mostly considered for use in the distributed propulsion is unique compared to conventional jet engines because the propulsion fans are separated and the driving power is delivered from the core engines placed apart from the propulsion fans. Several power sources might be used, but the most promising one to realize ultralow fuel emission aircraft is electrical. This paper presents the background and the potential for research activities for the core-separated fan propulsion systems. One referenced turboelectric propulsion system was evaluated for validation using a new analytical tool. The authors are emphasizing the configuration of electric fan propulsion system powered by a SOFC-GT core. Benefits and challenges of that core configuration are explained.

Impinging Atomization Enhanced by Microjet Injection - effect, mechanism and optimization -

Impinging atomization, which has been widely utilized in liquid rocket propulsion systems, is able to produce fine drops at a rated operation. In contrast, the atomization characteristics deteriorate under off design conditions when injection velocity comes to be slower. In the present study, for improving atomization characteristics at off design conditions, an effective technique is verified utilizing small amount of gas (microjet) injection. The microjet is supplied from a pressurized reservoir and is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effect, experimental visualizations, drop size measurements and corresponding numerical analyses are carried out. It is elucidated that Sauter Mean Diameter (SMD) becomes one-tenth of the original SMD by the microjet injection with the amount of only 1% of liquid mass flow rate. The dominant non-dimensional number is found to be the ratio of the dynamic pressure (microjet/liquid jet) at the impingement point. The optimized atomization efficiency is achieved when the dynamic pressure ratio is approximately two.

Consistent Theoretical Model of Mean Diameter and Size Distribution by Liquid Sheet Atomization

A consistent theoretical model is proposed and validated for calculating droplet diameters and size distributions. The model is derived based on the energy conservation law including the surface free energy and the Laplace pressure. Under several hypotheses, the law derives an equation indicating that atomization results from kinetic energy loss. Thus, once the amount of loss is determined, the droplet diameter is able to be calculated without the use of experimental parameters. When the effects of ambient gas are negligible, injection velocity profiles of liquid jets are the essential cause of the reduction of kinetic energy. The minimum Sauter mean diameter produced by liquid sheet atomization is inversely proportional to the injection Weber number when the injection velocity profiles are laminar or turbulent. A non-dimensional distribution function is also derived from the mean diameter model and Nukiyama-Tanasawa’s function. The new estimation methods are favorably validated by comparing with corresponding mean diameters and the size distributions, which are experimentally measured under atmospheric pressure.Copyright

Investigation of Microjet Injection for Reduction of Supersonic Jet Noise

Jet noise reduction is one of essential issues to realize environmentally-friendly and highly-efficient supersonic jet propulsion system. In the present study, experimental and numerical investigations were conducted in order to clarify the effect of microjet injection on supersonic jet noise. The experiments were focused on supersonic jet with Mach number up to 1.49, generated from a rectangular nozzle with high aspect ratio. The microjet injection angle was set to 90 degrees against the main jet axis. Far field measurements were conducted for the jet noise in the cases with and without microjet injection, and the noise reduction up to 7.5 dB was obtained. To study the mechanism of noise reduction, flow field visualization by schlieren technique and CFD analysis were conducted.Copyright

Experimental Study of Supersonic Jet Noise Reduction With Microjet Injection

Experimental study was conducted concerning active control of supersonic jet noise with a microjet injection technique. The microjets were injected into a rectangular main jet with Mach number up to 1.49. The nozzle lip of the main jet was equipped with 44 injection holes of the microjets, whose angles against the main jet were changed as 60 and 90 degrees. From far-field sound pressure data, a significant reduction of the jet noise by several dB was found in the cases with 60 and 90 degrees of injection angles. The microjet was found to affect all components of supersonic jet noise, namely, turbulent mixing noise, shock-associated broadband noise and screech tone noise. In the results of FFT analysis, the effect of the microjet was observed in the sound pressure level of the shock-associated broadband noise, the pressure level and frequency of the screech tone noise, and average level of the turbulent mixing noise. Schlieren visualization was also made for the jet flow, and the microjet was seen to change the shock structure and shear layer behavior of the supersonic jet.© 2009 ASME