Numerical simulation of the internal flow field for the straight pipeline after a sonic nozzle and its influence on the discharge coefficient
By establishing the model, a nozzle outlet and its internal flow field for the straight pipeline after the sonic nozzle is simulated by the CFD software. The simulation results are compared with theoretical data and experimental tests respectively. According to the simulation results, pressure changes strongly from the nozzle outlet, and gradually rises to the back pressure after a distance of 3D (D is pipe diameter) from the nozzle outlet. With the 5D length of the straight pipeline after a sonic nozzle, the nozzle throat will keep critical flow when the back pressure ratio is less than or equal to 0.849, and the straight pipeline after a sonic nozzle has little influence on the discharge coefficient. But when the back pressure ratio is less than 0.507, the pressure in the pipeline appears fluctuations.
A new correlation to determine the discharge coefficient of a critical Venturi nozzle with turbulent boundary layer
Abstract A toroidal Venturi nozzle, operating mainly at critical conditions and shaped according to the recommendation of the ISO Standard 9300, was selected for the present study. The focus of this paper is to provide a new theoretical and numerical correlation for the calculus of the discharge coefficient on turbulent boundary layer conditions for gases at Pr = 0.7 . This study was performed to investigate the effects of the viscous stresses in the boundary layer, dimensionless wall temperature in the throat nozzle, and the flow field curvature at the nucleus of the nozzle on the discharge coefficient. The determination of this coefficient was based on the turbulent boundary layer theory and a numerical simulation for a two-dimensional flow. The numerical simulation of the flow was carried out by means of the commercial CFD code. The correlation obtained was validated by means of a direct comparison between the experimental correlations of the discharge coefficient of ISO-9300 and the correlations obtained by the Korea Research Institute of Standards and Science (KRISS) with turbulent boundary layer. This validation was performed for throat Reynolds numbers from 1.4 to 2.6×106. The agreement of the theoretical and measured discharge coefficients by these correlations was better than 0.2%.
Cooling and Roughness Effects on Transition on Nozzle Throats and Blunt Bodies
Observations of boundary-laye r transition in a supersonic wind-tunnel nozzle throat were made in the region where the local Mach number increased from 0.4 to 2. The wall temperature ranged from adiabatic to 0.66 times the stagnation temperature, and its surface was roughened with random sand-grain, weave-type, and wire-screen roughness. It was found that wall cooling accelerates transition markedly regardless of surface conditions and that for a given height the random sand-type roughness is generally the most effective transition trigger. Transition location was much less sensitive to weave-type roughness and its orientation, although a drastic transition Reynolds number decrease was noted when the weave wavelength increased. With the roughness small or absent, phenomena involving boundary-layer relaminarization were observed. A substantial portion of these data cannot be accounted for by existing blunt-body boundary-layer transition correlations.