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.
Influence of diffuser angle on discharge coefficient of sonic nozzles for flow-rate measurements
Abstract A series of numerical simulations were conducted to investigate the influence of diffuser angle on discharge coefficient of sonic nozzles for gas flow-rate measurements satisfied with the regulation of ISO-9300 and operated at atmospheric condition with throat diameter from 0.15 to 5 mm and 2.0 × 10 3 ≤ R e d ≤ 6.6 × 10 4 . When throat diameters are larger than 1 mm, the discharge coefficients are almost the same for nozzles with different diffuser angles, while they increase with increasing diffuser angle for smaller nozzles. A concept or effective critical flow was introduced to explore the effect of diffuser angle on discharge coefficient. Using a new parameter, effective throat diameter or deviation of effective throat diameter from the minimum effective diameter δ , a very good description is derived to discuss the effect of diffuser angle on the discharge coefficient.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.