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Abstract

The paper presents the effect of convergent-divergent nozzles profile across specified inlet pressures values from (1.5 bar-4 bar), with constant back pressure of (1 bar). The flow of air through three convergent-divergent nozzles was studied theoretically. The flow was assumed to be one-dimensional, adiabatic and reversible (isentropic). The flow parameters like static pressure ratio and Mach number were analyzed. The flow parameters were obtained in term of area ratio along the nozzle. MATLAB code was built in order to find the Mach number along the nozzles, by using Newton-Raphson method. The shockwave position inside the nozzles was determined, using "analytic method". ANSYS fluent 18 was used to simulate the flow through the three nozzles. Two- dimensional, turbulent and viscous models were utilized to solve the governing equations. K-ε model was used to model the turbulent effect. The results concluded that, reduction in inlet pressure can not affect the flow upstream the throat. Also the shockwave appearance can be noticed by a sudden rise in static pressure associated with a sharp decrease in Mach number. Shockwave moves toward the throat by reduction the inlet total pressure .By comparison the static pressure distribution along the three nozzles where can be deduced that the profile has an effect on the flow character i.e. (static pressure Mach no).The best performance among the nozzles is the performance of nozzle (N1), which (75%) of its length work as nozzle at the lowest inlet pressure of (1.5bar) while (44% and 60%) of the nozzles length for (N2 and N3) respectively work as the nozzle.

Accurate and efficient modeling of convective heat transfer coefficient (CHTC) by considering the detailed room geometry and heat flux density in building is demanding for economy, environmental amiability, and user satisfaction. We report the three-dimensional finite-volume numerical simulation of internal room flow field characteristics with heated walls. Two different room geometries are chosen to determine the CHTC and temperature distribution. The conservation equations (elliptic partial differential) for the incompressible fluid flows are numerically solved using iterative method with no-slip boundary conditions to compute velocity components, pressure, temperature, turbulent kinetic energy, and dissipation rate. A line-by-line solution technique combined with a tri-diagonal matrix algorithm (TDMA) is used. The temperature field is simulated for various combinations of air-change per hour and geometrical parameters. The values of HTCs are found to enhance with increasing wall temperatures.

The general configuration of a turboshaft gas turbine control systems model is presented. The control systems included the relationships between the engine and its limitations such as a compressor surge line limit, exhaust gases temperature, the speed of the engines spools. The control system is of Multi Input Single Output (MISO) type, where the inputs to the controller are the limitation signals and the demand whither the only single output is the fuel valve new setting. The main parameter that the system controls by is that the fuel mass flow rate and the device which is doing this job is the fuel controller. The control system changes the fuel flow according to the engine demands by changing the fuel valve angle (θ) .The time responses of each effective parameter was predicted for a different fuel valve angle and introduce the most effective specifications of the time response of the system (delay time, rise time, settling time and maximum overshoot). The behavior of the maximum overshoot value (if founded) is increasing with the fuel valve increasing. The value of delay, rising, and settling times decreases with the fuel valve angle increases. The present results show a good agreement with the previous works.