Volume 30, Issue 2

This updated, PART C REVIEW, covers the dangerous global spread of JS-stealth, drone technology [1–91], canard-free, stealth, new agile drones and the highly debated, $480 billion F-35 International Program as reported on March 13, 2013 to the U.S. Congress [92]. Due to serious design issues, spiraling high costs and years in delays, alternatives are analyzed here, depicted and proposed, mainly from the propulsion-design point of view. These include fleets of low-cost, stealth, jet-steered-drones mixed with non-stealthy, low-cost, ready-to-be-delivered, U.S. or European or Russian fighter aircraft. Can a few F-35s win against large fleets of stealth agile drones? To understand the dangers and critical issues involved, the author’s own, past classified information is partly disclosed, while resorting to images in Figs. 2(a) and 2(b) taken from his book [2] and from Wikipedia , the “Free Encyclopedia”, in all other images.

As a new concept propulsion system, the pulse detonation engine has received extensive concerns from all over the world in the past few years. With oxidizer on board, it operates as a rocket engine which is known as pulse detonation rocket engine. In this study, a rocket model powered by a single-tube pulse detonation rocket engine was fabricated to demonstrate and validate whether or not it could operate stably and reliably independently. The single-tube pulse detonation rocket prototype consisted of a wireless control unit, three tanks for oxidizer, fuel and purge gas, various valves and a detonation tube. With compact design, the pulse detonation rocket prototype had an outer diameter of 260 mm and a length of 2200 mm. Oxygen, liquid aviation kerosene and nitrogen were utilized as oxidizer, fuel and purge gas, respectively. Operation tests were carried out to obtain proper operating conditions for the pulse detonation rocket prototype first, and then sliding test was conducted. It was concluded that the pulse detonation rocket prototype could operate stably and reliably. The generated thrust was estimated and compared with theoretical value.

A study is conducted to evolve an effective design concept to improve mixing in a combustor chamber to reduce the amount of intake air. The geometry used is that of a gas turbine combustor model. For simplicity, both the jets have been considered as air jets and effect of heat release and chemical reaction has not been modeled. Various contraction shapes and blockage have been investigated by placing them downstream at different locations with respect to inlet to obtain better mixing. A commercial CFD code ‘Fluent 6.3’ which is based on finite volume method has been used to solve the flow in the combustor model. Validation is done with the experimental data available in literature using standard k - ω turbulence model. The study has shown that contraction and blockage at optimum location enhances the mixing process. Further, the effect of swirl in the jets has also investigated.

The performance of centrifugal pumps during transient operating periods has been obtained increasing concern recently. In this paper, the transient behavior of a prototype centrifugal pump during rapid startup period is studied experimentally and theoretically. The variations of the rotational speed, flow rate, and head during the startup period are recorded in the experiment. The non-dimensional flow rate and head are used to analyze the transient behavior. Then, the additional theoretical head during the startup is calculated quantitatively by means of the generalized equation of turbomachinery. The research result shows that there exists clear transient effect during the rapid startup period, and the quasi-steady analysis is unable to accurately assess the transient flow.

Gas turbine diagnostic algorithms widely use fault simulation schemes, in which measurement errors are usually given by theoretical random number distributions, like the Gaussian probability density function. The scatter of simulated noise is determined on the basis of known information on maximum errors for every sensor type. Such simulation differs from real diagnosis because instead of measurements themselves the diagnostic algorithms work with their deviations from an engine baseline. In addition to simulated measurement inaccuracy, the deviations computed for real data have other error components. In this way, simulated and real deviation errors differ by amplitude and distribution. As a result, simulation-based investigations might result in too optimistic conclusions on gas turbine diagnosis reliability. To understand error features, deviations of real measurements are analyzed in the present paper. To make error presentation more realistic, it is proposed to extract an error component from real deviations and to integrate it in fault description. Finally, the effect of the new noise representation mode on diagnostic reliability is estimated. It is shown that the reliability change due to inexact error simulation can be significant.

A study of flow unsteadiness in a high pressure first stage turbine is presented. The study is based on numerical simulations of nozzle wake using a relative reference frame sliding mesh. Pressure and loads on first stage blades needed for stage efficiency calculation in turbine design are discussed. Excessive wear occurring at engine operating conditions affects the distance between rotating and non-rotating elements by varying throat size and axial clearance. Consequently, force unsteadiness produces changes on cyclic loads amplitude, which modifies the work produced by first stage. Compared against design, increments of throat minimum area lead to maximum total force, while throat area reductions increased pressure unsteadiness across the axial clearance. Also, the amplitude of load on blade increases as axial clearance length reduces. Harmonics of force on blade were used to calibrate a useful life prediction tool for turbine components through FFT analysis.

Mixing characteristics of under-expanded supersonic jets emerging from plane and notched rectangular nozzles are computationally studied using nozzle exit boundary layer swirl as a mean of passive flow control. The coupling of the rectangular jet instability modes, such as flapping, and the swirl is investigated. A three-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) code with shock adaptive grids is utilized. For plane rectangular nozzle with boundary layer swirl, the flapping and spanwise oscillations are captured in the jet’s small and large dimensions at twice the frequencies of the nozzles without swirl. A symmetrical oscillatory mode is also observed in the jet with double the frequency of spanwise oscillation mode. For the notched rectangular nozzle with boundary layer swirl, the flapping oscillation in the small jet dimension and the spanwise oscillation in the large jet dimension are observed at the same frequency as those without boundary layer swirl. The mass flow rates in jets at 11 and 8 nozzle heights downstream of the nozzles increased by nearly 25% and 41% for the plane and notched rectangular nozzles respectively, due to swirl. The axial gross thrust penalty due to induced swirl was 5.1% for the plane and 4.9% for the notched rectangular nozzle.