Supersonic-swirling-separation technology is an innovative gasconditioning technology that separates heavy hydrocarbon and water vapor from natural gas. The Laval nozzle, where the condensation occurs, is used to generate supersonic flow and achieve a high degree of supersaturation in this natural-gas dehydration unit. Therefore, the nozzle shape has a strong impact on the nonequilibrium phase transition and plays a decisive role in distribution of nucleation and growth rate. To optimize the structure of the Laval nozzle and achieve higher separation efficiency, numerical simulation plays an important role in accelerating development cycles and cutting down the cost of experiment.To avoid the complexity of using the multiphase model and real-gas model, a quick and efficienct method is validated and used to determine the location of the nucleation zone and the dropletgrowth zone in this paper.On the basis of the Fluent software, this paper presents a numerical-simulation method for condensing flow using userdefined function (UDF). This method itself is an extension of Fluent software for simulating condensing flow by adding a condensation model. The corrected internally-consistent-classicaltheory (ICCT) model and Gyarmathy model (gya82) are employed to prescribe this phase transition. Actually, this problem is solved by coupling the Navier-Stokes (N-S) equation and condensate mass equation.Condensing flow in a Laval nozzle is simulated at different nozzle-pressure ratios (NPRs) and initial supersaturations. The results show that high cooling rate results in a high value of supersaturation and nucleation rate in a supersonic expansion Laval-nozzle flow. When condensation occurs, the flow is affected by the latent heat released and the total temperature is increased. This method can accurately predict the distribution of the condensing flow parameters, find an optimized flow state to obtain larger droplets, and ensure that the latent heat released is moderate to maintain a steady flow. Finally, this method is applied to the numerical simulation of a full-scale supersonic-swirling-separator flow field under different work conditions.
The traditional squealer tip of turbine blade performs good property in decreasing the leakage mass flow rate. The improvement of the aerodynamic performance for turbine blade tip is always continuing associated with the understanding of the leakage flow characteristic. Thus, a novel turbine blade tip, which is derived from the conventional squealer tip, is investigated numerically in this paper. The characteristic of the tip region flow field, the tip blade loading distribution and the tip leakage mass flow is analyzed in detail. The results show that, first some part of the tip region flows are forced to flow downstream along the guided groove formed by the recessed pressure side rim, which contributes to the preventing of the leakage mass flow and the descending of leakage loss as well. Besides, the blade loading of the novel geometry is raised than the traditional squealer tip, which reveals that the mass flow rate of the working fluid is increased. Third, the leakage mass flow is reduced so that the efficiency is increased. The CFD analysis predicts that, the novel squealer tip case shows 30% less leakage mass flow and a 0.11% total isentropic efficiency increase for a single rotor compared to the baseline squealer tip case.
The aerodynamic performance of a winglet baffle cavity tip is investigated at different inlet incidences from -12.5° to +12.5°. This blade tip shows geometry feature with a pressure side winglet and a baffle within the tip cavity. The experimental studies were carried out in a large scale linear cascade, and the numerical methods were also used to obtain the detail physics. The baffle on the tip divides the cavity vortex into two main parts, which increases the flow mixing over the tip. As the flow within the vortex exits the tip near the baffle and cavity corner, flow separation occurs over the suction side and reduces local tip leakage mass flow rate significantly. The additional pressure side winglet reduces the contraction coefficient on the pressure side squealer. It is found that the winglet baffle cavity tip can reduce the tip leakage mass flow by 12.1%, and the near tip loss by 4.2%, compared with the squealer tip. As the incidence of incoming flow decreases, the loss near the tip reduces mainly due to a reduction of the passage vortex, which develops from the casing endwall. At the same incidence, the aerodynamic performance of the winglet baffle cavity tip is better than the squealer tip.
Leakage flow losses are an important factor affecting turbine aerodynamic efficiency. In this paper, experimental and numerical computational studies are used to target three different tips of highly loaded turbine rotor. The single cavity tip formed by squealers is considered as the original cavity tip structure, and based on this, two structures were improved, cavity winglet tip and double cavity combined winglet tip. Five-hole probe and oil flow visualization are used for experimental studies; numerical calculations are used to analyze vortex system structure and loss development. It was found that the double cavity combined winglet tip structure can effectively change the vortex structure inside the cavity and reduce the leakage flow rate. At the same time, the aerodynamic performance has been optimized by 4%.
Experimental and numerical studies of a linear high-loaded turbine cascade with a dual−cavity tip structure are presented in this paper. The experimental conditions contained an increase in the outlet Mach number from 0.42 to 0.92, a change in the incidence angle from −15° to 15° and an increase in the relative clearance size from 0.36% to 1.4%. The ability of the dual−cavity tip to control leakage losses and vortices is assessed using the total pressure coefficient and the Q-criterion. This research indicates that the leakage vortex interacts strongly with the passage vortex, and the change in working conditions affects the balance between the two vortices and thus the flow field structure. The experimental and numerical results prove that the dual−cavity tip can reduce losses in all operating conditions, with the best control effect reduced by 0.025 in a large clearance size condition. In addition, the leakage control effect of the blade tip structure is more influenced by the incoming flow angle and clearance size than the Mach number.
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