Transient growth in Taylor-Couette flow

Transient growth due to non-normality is investigated for the Taylor-Couette problem with counter-rotating cylinders as a function of aspect ratio eta and Reynolds number Re. For all Re < 500, transient growth is enhanced by curvature, i.e. is greater for eta < 1 than for eta = 1, the plane Couette limit. For fixed Re < 130 it is found that the greatest transient growth is achieved for eta between the Taylor-Couette linear stability boundary, if it exists, and one, while for Re > 130 the greatest transient growth is achieved for eta on the linear stability boundary. Transient growth is shown to be approximately 20% higher near the linear stability boundary at Re = 310, eta = 0.986 than at Re = 310, eta = 1, near the threshold observed for transition in plane Couette flow. The energy in the optimal inputs is primarily meridional; that in the optimal outputs is primarily azimuthal. Pseudospectra are calculated for two contrasting cases. For large curvature, eta = 0.5, the pseudospectra adhere more closely to the spectrum than in a narrow gap case, eta = 0.99

Pressure activated stability-bypass-control valves to increase the stable airflow range of a Mach 2.5 inlet with 40 percent internal contraction

The throat of a Mach 2.5 inlet with a coldpipe termination was fitted with a stability-bypass system. The inlet stable airflow range provided by various stability-bypass entrance configurations in alternate combination with several stability-bypass exit controls was determined for both steady-state conditions and internal transient pulses. Transient results were also obtained for the inlet with a choke point at the diffuser exit. Instart angles of attack were determined for the various stability-bypass entrance configurations. The response of the inlet-coldpipe system to internal and external oscillating disturbances was determined. Poppet valves at the stability-bypass exit provided an inlet stable airflow range of 28 percent or greater at all static and transient conditions

Transient Stability Assessment of Hybrid Distributed Generation and its Impact on Critical Clearing Time and Oscillation Duration Considering its Complementary Nature

Presently, the grid accommodates several mixed energies so as to improve power generation and cater for demand which is ever increasing. These energy sources interact with each other and with the existing grid. Due to the complementary nature of most renewable energy and the mixed dynamics associated with them coupled with the bi directional power flow, transient stability based on single source will not give the overall assessment of the network. This paper presents the impact of hybrid Solar PV-Wind and Small Hydro distributed generation on transient stability of power system so as to take advantages of their complementary roles. To investigate this impact, a detail modeling of grid connected wind / solar PV and small hydropower system with single machine infinite system is carried out. The configuration of the proposed typical grid connected hybrid distributed generation (HDG) consists of hybrid Doubly fed induction generator (DFIG), solar PV and small hydropower system. DFIG is integrated through PWM converter into the existing grid while the solar PV consisting of DC sources is integrated through PWM inverter and the hydro power is directly connected through a synchronous generator. The simulation was done in DIgSILENT power factory softwar