Flow visualisation of plane jets in the Reynolds number (Re) range of 90 to 750 is carried out experimentally, considering water as fluid. A conventional rectangular nozzle with the exit dimensions of 20 mm × 2 mm is used. Various visualisation experiments are carried out using a colour dye mixed or injected with the jet flow. Images are processed using image processing software to estimate the characteristics of the jets. Besides, to assess the growth of the shear layer in free jets, a nozzle with an extension of its base wall by 5 mm is considered. The resulting images indicate that the mean spread rate of a turbulent plane jet is around 0.152. In the case of laminar jets, a vortex street with large size vortices is observed at lower Reynolds numbers. The Strouhal number of the vortices formed in the laminar jet is observed to increase with an increase in the Reynolds number. The amplitude of the oscillations of a laminar jet column at Re ≈ 90 is observed to increase with an increase in the axial distance. The dissipation and spread rates are lower for smaller Reynolds number laminar jet. The flow emerging from a nozzle with an extended base-wall is found to be asymmetric along its nozzle centreline, attributed to the delay in the shear layer formation at the wall side.

雷诺数（Re）以水为流体，通过实验在90到750的范围内进行。使用出口尺寸为20 mm×2 mm的常规矩形喷嘴。使用与喷射流混合或注入的彩色染料进行各种可视化实验。使用图像处理软件对图像进行处理，以估计喷嘴的特征。此外，为了评估自由射流中剪切层的生长，考虑使用喷嘴的底壁延长5 mm的喷嘴。所得图像表明，湍流平面射流的平均扩散速率约为0.152。在层流射流的情况下，在较低的雷诺数下观察到具有大涡旋的涡街。观察到层流射流中形成的旋涡的斯特劳哈尔数随雷诺数的增加而增加。再≈90被观察到，以增加与增加的轴向距离。对于较小的雷诺数层流射流，耗散率和扩散率较低。发现从具有延伸的底壁的喷嘴流出的流动沿着其喷嘴中心线是不对称的，这归因于在壁侧的剪切层形成的延迟。