Numerical study of the flow establishment time in hypersonic shock tunnels
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Lee, J. Y.↗
Engineering topics
Lee, J. Y.
Publications and source records attributed to Lee, J. Y..
Maximum orbit plane change with heat-transfer-rate considerations
Two aerodynamic maneuvers are considered for maximizing the plane change of a circular orbit: gliding flight with a maximum thrust segment to regain lost energy (aeroglide) and constant altitude cruise with the thrust being used to cancel the drag and maintain a high energy level (aerocruise). In both cases, the stagnation heating rate is limited. For aeroglide, the controls are the angle of attack, the bank angle, the time at which the burn begins, and the length of the burn. For aerocruise, the maneuver is divided into three segments: descent, cruise, and ascent. During descent the thrust is zero, and the controls are the angle of attack and the bank angle. During cruise, the only control is the assumed-constant angle of attack. During ascent, a maximum thrust segment is used to restore lost energy, and the controls are the angle of attack and bank angle. The optimization problems are solved with a nonlinear programming code known as GRG2. Numerical results for the Maneuverable Re-entry Research Vehicle with a heating-rate limit of 100 Btu/ft(2)-s show that aerocruise gives a maximum plane change of 2 deg, which is only 1 deg larger than that of aeroglide. On the other hand, even though aerocruise requires two thrust levels, the cruise characteristics of constant altitude, velocity, thrust, and angle of attack are easy to control.
Lee, J. Y.↗
The integrated optic RF spectrum analyzer
The results of measurements made on a fully integrated optic RF spectrum analyzer (IOSA) are reported. The performance of the device acousto-optic bandwidth, single-tone RF resolution, two-tone RF resolution, single-tone dynamic range, two-tone dynamic range, and single-tone RF response are presented. The device parameters that control device performance are analyzed. These results demonstrate the viability of the IOSA for real time spectrum analysis of pulsed and CW RF signals. Improvements of RF bandwidth resolution can be obtained by the use of larger collimated optical beams which requires larger optical lens elements, and hence, larger crystals.
Pedinoff, M. E.↗
Cryostatic influence of Formvar coatings on sizing of the stabilizer in superconductive NbTi-Cu - Conductor bundle effects
In continuation of single-conductor studies, quench onset data of quasi-steady operation are reported for a Formvar-coated composite (Nb48Ti/Cu) in bundle geometry (conductor thickness about 0.2 cm, approximately square cross section). Overall thermal conductances of the heater simulation technique applied are of the order 0.1 W/(sq cm-K), comparable to single-specimen results, around 4 K and below the lambda transition in agreement with model predictions. Considerable deterioration, however, occurs below 3 K and down to the lambda temperature during operation in near-saturated He I. Consequences for magnets of intermediate energy density are discussed with emphasis on the modifications necessitated by coatings.
Caspi, S.↗
Cryogenic-coolant He-4-superconductor interaction
The thermodynamic and thermal interaction between a type 2 composite alloy and cryo-coolant He4 was studied with emphasis on post quench phenomena of formvar coated conductors. The latter were investigated using a heater simulation technique. Overall heat transfer coefficients were evaluated for the quench onset point. Heat flux densities were determined for phenomena of thermal switching between a peak and a recovery value. The study covered near saturated liquid, pressurized He4, both above and below the lambda transition, and above and below the thermodynamic critical pressure. In addition, friction coefficients for relative motion between formvar insulated conductors were determined.
Caspi, S.↗
Cryostatic influence of formvar coatings on sizing of the stabilizer in composite NbTi-Cu superconductors
Often undesirable low energy densities are associated with extreme safety measures (e.g. cryostatic stability) in large superconducting magnets. Therefore, a medium-sized, formvar-coated composite NbTi alloy, Cu-stabilized, has been studied (48 filaments, approximately square cross section about 1/5 cm thickness). Thermal quench behavior (caused by heating) was investigated in various fluid states of He4, including pressurized and superfluid He4. The data obtained support existence of a particular coating thickness ('limiting' thickness) with the property that thermal boundary conditions of uncoated superconductors at a quench are not deteriorated.
Caspi, S.↗