Propulsion
Nematollah Fouladi; Alireza Mohammadi
Abstract
The purpose of this research is to evaluate a ground test bed of an orbital transmission engine with pre-evacuation of the engine's internal space. In the usual tests on the ground, the initial pressure of the engine is atmospheric pressure. While during the orbital mission, the internal space of the ...
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The purpose of this research is to evaluate a ground test bed of an orbital transmission engine with pre-evacuation of the engine's internal space. In the usual tests on the ground, the initial pressure of the engine is atmospheric pressure. While during the orbital mission, the internal space of the engine may be in the vacuum pressure. Therefore, to ensure the proper performance of internal ballistics, it is necessary to test the performance by pre-evacuating its internal space. In this research, first, the suitability of an exhaust diffuser for this type of test is investigated numerically. Then, the unsteady numerical simulations have been done by applying the pressure-time profiles of the engine as the boundary condition of the inlet pressure. Investigations show that the two phenomena of flow being supersonic in the diffuser at very low engine pressures and the discharge of the return flow to the vacuum chamber prevent the significant influence of environmental conditions on the flow inside the nozzle. So, from the initial moment to the stable working of the diffuser, the flow in the first half of the nozzle is in the supersonic state. Therefore, the internal ballistics of the engine is evaluated independently of the conditions of the outside environment
Heat control
Nematollah Fouladi; Mohammad Farahani; Milad Mahdian Dowlatabadi
Abstract
The aim of this study is to evaluate the performance of water-jacket cooling system for thermal protection of exhaust large dimension diffuser at high heat fluxes in a wide range of coolant pressure. For this purpose, using the developed calculation code, the parameters of the water-jacket cooling system ...
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The aim of this study is to evaluate the performance of water-jacket cooling system for thermal protection of exhaust large dimension diffuser at high heat fluxes in a wide range of coolant pressure. For this purpose, using the developed calculation code, the parameters of the water-jacket cooling system are determined so that in addition to satisfying the temperature conditions of the metal body, the total pressure drop has remained in the desired range. In the following, the capability of numerical code to design and performance analysis of the cooling system has been evaluated in coolant pressure of 3 to 50 bar and high heat fluxes up to 3.5 MW/m2. The present studies show that the proper selection of coolant pressure is very important in the design of the cooling system with optimal mass flow rate and minimum coolant dimensions, especially at high heat fluxes, so that increasing the coolant pressure from 3 to 10 bar, in addition to significantly reducing the dimensions of the cooling system, reduces the mass flow rate by 75%.
Propulsion
Nematollah Fouladi; sina afkhami; Mahmood PasandidehFard
Abstract
In the present study, the effect of pre- evacuation on starting process of a second throat exhaust diffuser has been investigated experimentally by examining a thrust optimized parabolic nozzle. An experimental setup called high- altitude test facility has been used with compressed air as operating fluid. ...
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In the present study, the effect of pre- evacuation on starting process of a second throat exhaust diffuser has been investigated experimentally by examining a thrust optimized parabolic nozzle. An experimental setup called high- altitude test facility has been used with compressed air as operating fluid. According to the importance of area ratio parameter (Ad/Ast) of a second throat diffuser, the effect of this parameter variation has been examined on the start- up performance of the nozzle and diffuser. In each of the diffuser geometries, in order to evaluate the instantaneous performances, the pressure in the nozzle chamber has charged instantly in two modes; with and without pre- evacuation. Then, the vacuum chamber pressure and static pressure distribution along the diffuser were measured by a data acquisition system. The results show that pre- evacuation in the test chamber reduces the start- up time of the diffuser by 50 to 60%. In addition, pre- evacuating the test chamber eliminates the destructive transition phenomenon from the flow separation pattern during start- up of the nozzle and diffuser. Also, It has been observed that with the narrowing of the diffuser’s second throat duct, the minimum starting pressure of the diffuser increases and eventually flow chocks at the second throat in a certain area ratio.
