Quasi-1D analysis and performance estimation of a sub-scale RBCC engine with chemical equilibrium

Kim, H.S.,Oh, S.,Choi, J.Y. ELSEVIER PARIS 2017 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

In this study, quasi-1D analysis with chemical equilibrium was applied at a sub-scale rocket-based combined cycle (RBCC) engine for a hypersonic flight test using a sounding rocket. A mission profile of the engine was designed in a previous study, and its off-design performance was examined in test-mission research for the flight test. The operational conditions are Mach 3 to 7 at altitudes of 10 to 30 km. A bleed duct and a pre-burner are applied in the engine. The analysis method was validated by comparison with HyShot II flight test data to ensure reliability. The thrust and the specific impulse at each design point are 595 N and 646 s in scramjet mode, while they are 9.07 kN and 1,543 s in ramjet mode.

Numerical evaluation of transient flow characteristics in a transonic centrifugal compressor with vaned diffuser

Zamiri, A.,Lee, B.J.,Taek Chung, J. ELSEVIER PARIS 2017 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

Three-dimensional, compressible, unsteady Navier-Stokes equations are solved to investigate the flow field of a transonic centrifugal compressor with high compression ratio. The computational domain is consisted of an inlet bell mouth and an impeller with splitter blades, followed by a two-dimensional wedge vaned diffuser. The numerical method was validated by comparing the results with those of experiments in terms of aerodynamic compressor performance and flow field within the compressor passages. A detailed analysis of instantaneous and time-averaged flow field was conducted in the impeller and diffuser passages. The present study focuses on the pressure fluctuations and entropy production within the impeller and diffuser passages at the compressor design point. It is shown that the interaction between the impeller and diffuser blades leads to unsteadiness at the interface region and a pulsating behavior within the diffuser passages. Pressure waves with different convective velocities, generated by the impeller-diffuser interaction and pseudo-periodic unsteady separation bubbles, are captured in the time/space domain along the diffuser blade surfaces. The pressure fluctuation spectra were evaluated to analyze the noise characteristics of the centrifugal compressor as the main source of blade passing frequency noise. It is expected that the current unsteady Reynolds-Averaged Navier-Stokes (URANS) approach can be used as a tool for the prediction of unsteady flow and compressor noise characteristics with a proper turbulence model and well-resolved grids.

Performance characteristics of a pintle nozzle using the conformal sliding mesh technique

Sung, Hong-Gye,Jeong, Kiyeon,Heo, Junyoung ELSEVIER PARIS 2017 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

<P><B>Abstract</B></P> <P>Numerical and non-linear internal ballistics analyses are conducted to investigate the performance characteristics of a pintle reciprocating in a nozzle. A conformal sliding mesh is successfully implemented to maintain smooth and continuous flow properties at the boundary of a moving pintle block. The proper mesh size is determined via a grid dependency test. The pintle nozzle operates under over-expansion conditions so that flow separation occurs at the nozzle wall at certain pintle stroke positions. Both the chamber pressure and thrust have hysteresis loci to allow for the reciprocation of the pintle's insertion and extraction motions, which have different trace-to-pintle speeds. The hysteresis loci reduce as the pintle speed increases. The thrust coefficient (rather than the thrust itself) is able to precisely determine the effects of the nozzle flow separation on overall performance.</P>

A coupled dynamic loads analysis of satellites with an enhanced Craig-Bampton approach

Lim, J.H.,Hwang, D.S.,Kim, K.W.,Lee, G.H.,Kim, J.G. ELSEVIER PARIS 2017 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

In this work, we conducted a coupled dynamic loads analysis (CDLA) of satellites with an enhanced Craig-Bampton (ECB) approach to predict maximum response (acceleration, displacement, and stress). The satellite was subjected to a relatively high frequency launch vehicle (LV) interface load (20-50 Hz) when it was launched by multiple satellite launcher or experienced the combustion instability caused by LV instead of a typical low frequency LV interface load (0-10 Hz). To minimize the error caused by mode truncation, ECB-like formulation, which considers the effect of residual modes, is employed and computes the maximum response of the given dynamic system. By using this method, we found that the response by the ECB model is more accurate and efficient over the classical Craig-Bampton (CB) model due to the enhanced transformation matrix from being subjected to an unexpected high frequency LV load. To demonstrate this performance, we solved several benchmark problems associated with CDLA.

Formation flight of unmanned aerial vehicles using track guidance

Lee, Dongwoo,Kim, Seungkeun,Suk, Jinyoung ELSEVIER PARIS 2018 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

<P><B>Abstract</B></P> <P>Precise flight path tracking capability is generally required for high performance unmanned aerial vehicles (UAVs) to conduct complex missions. Accurate waypoint navigation is a key feature that these UAVs usually possess. This study presents a track guidance algorithm for path-following guidance and modifies it based on the leader-follower scheme for formation flight. The suggested guidance algorithm is a spatial version of the first order dynamic characteristics for a time-dependent system. Hence, invariant tracking performance is guaranteed in the spatial domain such that a constant flight trajectory pattern can be obtained without considering the speed of the vehicle or the disturbance. In this algorithm, the heading or yaw rate of the vehicle is guided to direct the flight path a certain distance ahead of the UAV to minimize the track error between the pre-assigned flight path and the position of a single vehicle. The modified track-guidance algorithm is designed using the separated forward and lateral guidance law. A crucial design parameter is the spatial constant that controls the shape of the convergence to an assigned flight path. Reference flight trajectories are designed on a two-dimensional surface, and the proposed algorithms are verified by numerical simulation through multiple scenarios compared with other guidance schemes and disturbance effects.</P>

Near time-optimal feedback instantaneous impact point (IIP) guidance law for rocket

Jo, Byeong-Un,Ahn, Jaemyung ELSEVIER PARIS 2018 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

<P><B>Abstract</B></P> <P>This paper proposes a feedback guidance law to move the instantaneous impact point (IIP) of a rocket to a desired location. Analytic expressions relating the time derivatives of an IIP with the external acceleration of the rocket are introduced. A near time-optimal feedback-form guidance law to determine the direction of the acceleration for guiding the IIP is developed using the derivative expressions. The effectiveness of the proposed guidance law, in comparison with the results of open-loop trajectory optimization, was demonstrated through IIP pointing case studies.</P>

Dynamic optimal output feedback control of satellite formation reconfiguration based on an LMI approach

Wei, Changzhu,Park, Sang-Young ELSEVIER PARIS 2017 AEROSPACE SCIENCE AND TECHNOLOGY Vol. No.

<P><B>Abstract</B></P> <P>This study presents a dynamic quadratic-optimal (DQO) output feedback controller for satellite formation reconfiguration based on a linear matrix inequality (LMI) approach. A relative motion model involving communication topology of formation flying on a circular reference orbit is established through graph theory. As the design of a static quadratic-optimal (SQO) output feedback controller was determined to be infeasible, emphasis is placed on designing a DQO output feedback controller. Introducing an impulse function enables us to transform the original DQO output feedback control (DQO-OFC) problem into an optimal L<SUB>2</SUB>-norm problem, which can be solved in the standard frame of an LMI approach. It is infeasible to employ a conventional substitution method to treat a nonlinear term with a quadratic form. Thus, an elimination method is adopted in order to address nonlinear terms in the matrix inequalities to obtain a set of equivalent LMIs. Additional control quantities are developed in order to retain the formation configuration in a non-zero state. Simulation results demonstrate validity and functionality of the proposed DQO output feedback controller.</P>