The Effect of Rotor Roughness on Flow and Heat Transfer in Rotor–stator Cavities with Different Axial Gap

There are no absolutely smooth surface conditions in mechanical engineering. Nevertheless, most studies on rotor-stator cavities assume smooth walls. To accurately reflect the effect of rotor surface roughness on disk cavity flow and heat transfer within a certain parameter range. In this study, we numerically investigate the rotor-stator cavity with rotor surface roughness at different axial gap ratios. The numerical simulation is verifled by experiments to ensure its high accuracy. It is worth mentioning that the investigated axial gap ratio ranges from 0.05 to 0.2. This covers the vast majority of rotor-stator cavities, so our results have a high degree of applicability. Furthermore, our investigation of the effects of roughness includes not only the basic flow characteristics of the disk cavity (velocity, pressure, and temperature) but also a speciflc reflnement of some important parameters of the cavity. In particular, for the core swirl ratio and the average Nusselt number, we flt the prediction equation with a roughness term, which makes our predictions more realistic. The results show that the effect of the surface roughness of the rotor is drastic for the flow in disk cavities with small axial gap ratios. The speciflc effects can be summarized as a reduction in the radial extent of the central core at high radius and the degree of perturbation of the flow at low radius. To this end, we quantify the effect of roughness on the velocity and pressure in the disk cavity. It turns out that the roughness of the rotor leads to an overall increase in pressure and velocity in the disk cavity, and the smaller gap ratio, the greater the increase in pressure. For axial gap ratio is 0.05 and equivalent roughness is 192.03 mu m, the average total pressure increase in the disk cavity reaches 17.97 %. For the core swirl ratio, the most important aerodynamic parameter in the disk cavity, we flt the prediction equation with a roughness term so that the deviation from the calculated results is within 8 %. The surface temperatures of the rotor and stator increase and then decrease overall along the flow direction. The roughness causes a temperature drop on the rotor surface and a temperature rise on the stator surface. In addition, the roughness of the rotor surface improves the local heat transfer and causes the area with low heat transfer to be shifted upwards. A roughness term is added to the average Nusselt number prediction equation to achieve better agreement with the calculated results. Based on the results of our study, more accurate predictions are made for the unavoidable wall roughness of disk cavities in actual operation. These results can serve as a reference for the designers of machines with rotor-stator cavity structure.