RESUMEN
We present an alternative perspective on nonharmonic mode coexistence, commonly found in the shear layer spectrum of open-cavity flows. Modes obtained by a local linear stability analysis of perturbations to a two-dimensional, incompressible, and inviscid sheared flow over a cavity of finite length and depth were conditioned by a so-called coincidence condition first proposed by Kulikowskii [J. Appl. Math. Mech. 30, 180 (1966)] which takes into account instability wave reflection within the cavity. The analysis yields a set of discrete, nonharmonic frequencies, which compare well with experimental results [Phys. Fluids 20, 114101 (2008); Exp. Fluids 50, 905 (2010)].
RESUMEN
We applied to an open flow a proper orthogonal decomposition (POD) technique, on two-dimensional (2D) snapshots of the instantaneous velocity field, to reveal the spatial coherent structures responsible for the self-sustained oscillations observed in the spectral distribution of time series. We applied the technique to 2D planes out of three-dimensional (3D) direct numerical simulations on an open cavity flow. The process can easily be implemented on usual personal computers, and might bring deep insights regarding the relation between spatial events and temporal signature in (both numerical or experimental) open flows.
RESUMEN
The role of the heart and its working conditions on the shape of aortic pressure curves was studied by analysis of pressure signals produced at the input of an artificial ejection circuit by 25 isolated working hearts of rats aged 4-22 months. The hearts were paced at five successive heart rates and three levels were imposed for the left auricular perfusion pressure (LAPP). With ageing of the myocardium, increased LAPP and low heart rates, there was an alteration of the pressure wave visual aspect towards a tele-systolic maximum. This modification was regularly associated with significant differences in the harmonic content of the pressure signal. More precisely, there was a bigger increase in the first harmonic amplitude than in the second and third harmonic amplitudes. Because of the physical linearity of the artificial ejection circuit and the controlled working conditions for the heart, it is possible to explain these changes in the pressure wave shape. Lowering of the heart rate is associated with an involvement of a more left part of the circuit impedance curve. Ageing of the myocardium and increased LAPP change the pressure wave shape because they were associated with an increase in left ventricular ejection time.
Asunto(s)
Envejecimiento , Corazón/fisiología , Animales , Presión Sanguínea , Gasto Cardíaco , Electrofisiología , Frecuencia Cardíaca , Técnicas In Vitro , Ratas , Función VentricularRESUMEN
The effects of age, pre-load and heart rate on the juxta-aortic pressure wave form in an artificial ejection circuit were studied in 25 isolated perfused rat hearts beating at a controlled rate. The hearts were taken from male Wistar rats aged 4, 8, 12, 16 and 22 months. Each heart was submitted to 3 pre-loads by adjusting the level of left atrium perfusion to 15, 20, 25 cm H2O. Five different heart rates (300, 240, 198, 174 and 150/min) were imposed at each level of pre-load by pacing the interatrial septum after destroying the sinoatrial node. Age, increasing pre-load and bradycardia produced similar changes in the systolic part of the wave characterised by a delayed peak. The effects of these three factors were significant and independent and corresponded to significant changes of the harmonic composition of the pressure wave. In these three conditions, the amplitude of the first harmonic of the pressure increased significantly compared with the second, third and fourth harmonics. The predominance of the amplitude of the first harmonic is characteristic of pressure waves with delayed systolic summits . The linear character of the physical properties of the circuit was tested experimentally. A change in the wave form at a fixed rate is explained by a modification of ventricular ejection which is therefore necessarily present when pre-load is increased and the age of the heart varies. On the other hand, the effect of rate changes on the wave form are explained essentially by the interplay of different zones of the impedence curve of the circuit.(ABSTRACT TRUNCATED AT 250 WORDS)