Diebold B, Delouche A, Abergel E, Delouche P, Dumée P, Péronneau P
Unité INSERM 256, Hopital Broussais, Paris, France.
Biorheology. 1991;28(3-4):287-99. doi: 10.3233/bir-1991-283-418.
So far, it has been hypothesized that numerical data obtained in steady flow conditions apply to pulsatile flows. In order to study the modifications of the velocity fields due to pulsatility, jets were produced by 8 orifices (with a diameter "D" of 4.4 to 11.3 mm) included in a chamber of 50 mm. The velocity was measured using laser Doppler anemometry with a pulsatile flow ("pf") and compared to the values obtained in steady ("sf"): at maximum velocity, the longitudinal velocity profile is qualitatively similar to this observed in steady flow: it is made of a plateau followed by an hyperbolic velocity decay in the turbulent area. The length of the core ("Lpf") is strongly related to "D" (Lpf = 3.72 D + 5.49, r = .99) and the velocity decay depends on the ratio between the distance "x" from the orifice and "D" (V/Vo = 2.83D/x + 3.46, r = .85, where V is the velocity at "x" and Vo the initial velocity). During the acceleration and the deceleration, the laminar core is disturbed by turbulences. The comparison of "pf" data with "sf" data demonstrated similar diameters at the origin of the jets (Dpf = 0.96 Dsf + .12, r = .99), but significant (p less than .0001) differences both for "L" and "V/Vo": Lpf = .91Lsf + 6.58, r = .97, V/Vopf = .63 V/Vosf + .34, r = .76. Thus, pulsatility modifies velocity fields and the results obtained in steady flow conditions do not apply to pulsatile jets.
到目前为止，人们一直假设在稳定流动条件下获得的数值数据适用于脉动流。为了研究脉动性对速度场的影响，通过包含在一个50毫米腔室中的8个孔口（直径“D”为4.4至11.3毫米）产生射流。使用激光多普勒测速仪测量脉动流（“pf”）下的速度，并与稳定流（“sf”）下获得的值进行比较：在最大速度时，纵向速度剖面在定性上与稳定流中观察到的相似：它由一个平台组成，随后在湍流区域中速度呈双曲线衰减。核心长度（“Lpf”）与“D”密切相关（Lpf = 3.72D + 5.49，r = 0.99），速度衰减取决于距孔口的距离“x”与“D”的比值（V/Vo = 2.83D/x + 3.46，r = 0.85，其中V是“x”处的速度，Vo是初始速度）。在加速和减速过程中，层流核心会受到湍流的干扰。“pf”数据与“sf”数据的比较表明，射流起点处的直径相似（Dpf = 0.96Dsf + 0.12，r = 0.99），但“L”和“V/Vo”均存在显著差异（p小于0.0001）：Lpf = 0.91Lsf + 6.58，r = 0.97，V/Vopf = 0.63V/Vosf + 0.34，r = 0.76。因此，脉动性会改变速度场，在稳定流动条件下获得的结果不适用于脉动射流。
