सार /ABSTRACT : Geometries with sudden symmetric expansion can be seen in devices ranging from household refrigerators to supersonic combustors of spacecraft. The flow inside such channels remains symmetric until a critical Reynolds number is reached [1]. After this threshold value of Reynolds number, it is known that the flow loses its stability to two stable asymmetric states called super-critical pitchfork bifurcation. This pitchfork bifurcation is attributed to the fluctuations in pressure and velocity emanating from the separated shear layer [1]. But from previous literature, it is clear that the bifurcation characteristics in plane sudden expansion and axi-symmetric sudden expansion are different [2]. The critical Reynolds number involving bifurcation in the axi-symmetric sudden expansion remains controversial. The experiments and the stability calculations for the critical Reynolds number in an axi-symmetric sudden expansion are not in general agreement with each other, whereas that in the sudden planar expansion does match with experiments and numerics. But the studies concerning the difference in the bifurcation characteristics of flow in geometrically similar planar and 3D sudden expansion geometries are scarce. The self-induced intermittent jet precession found in higher expansion ratio axi-symmetric sudden expansion without inlet swirl [3] and its absence in lower expansion ratio ducts is not well understood and studied. And most of the previous works focused mainly on low-speed characteristics of such bifurcating flow and concluded that this same asymmetric state extends to high-speed flow. But it is found that the asymmetric flow evolves to symmetric again at another critical Reynolds number, changing the nature of pitchfork bifurcation. The current work takes a holistic approach by investigating the evolution of this flow bifurcation from low speed to high speed using flow visualization, LDV, PIV, and computational techniques in both planar and 3D sudden expansion with both lower and higher expansion ratio. This will help in finding a proper theory for the difference in the symmetry-breaking bifurcation of flow in symmetric sudden expansion channels of different dimensions. This knowledge will be used in designing a novel and cost-effective mixing enhancement nozzle for Gas-turbine engines and related fields.