Aerospace Science and Technology
Mohammadreza Varshavi; Sahar Noori
Abstract
Air-breathing hypersonic flight is presumed by many of the savants in the field of aeronautical engineering as the last boundary of aerial vehicle design to be pushed back. An auspicious design configuration for the prospective hypersonic transport vehicles of the future is a “Waverider,” ...
Read More
Air-breathing hypersonic flight is presumed by many of the savants in the field of aeronautical engineering as the last boundary of aerial vehicle design to be pushed back. An auspicious design configuration for the prospective hypersonic transport vehicles of the future is a “Waverider,” using the Scramjet engine cycle as its propulsive system. Two-dimensional CFD Analysis and case-to-case study of three pre-defined waverider configurations with 2-ramp, 3-ramp, and 4-ramp inlet geometries are carried out in the hypersonic flight regime of Mach numbers 5, 6, and 7. This is done in an attempt to study the single-oriented and also correlative-oriented impacts of increasing/decreasing the number of inlet ramps and increasing/decreasing the flight Mach number upon the behavior of final aerodynamic coefficients and ratios. The paramount outcome of the present work is the generation of some tables which can be utilized as primary guidelines for aeronautical design engineers who are designing waverider configurations on a preliminary basis.
Aerospace Science and Technology
Hamzeh Eshraghi
Abstract
In the current article, using results of previous researches, a guideline has been developed to select a proper value for solidity of a tandem blade row in an axial flow compressor stage. Next, using this guideline, a highly loaded tandem compressor stage has been designed. To verify the selected solidity ...
Read More
In the current article, using results of previous researches, a guideline has been developed to select a proper value for solidity of a tandem blade row in an axial flow compressor stage. Next, using this guideline, a highly loaded tandem compressor stage has been designed. To verify the selected solidity value, some other cases have been designed with different solidity values. Other geometrical parameters have been selected similarly in all cases. At the next stage, a three dimensional numerical model is developed to predict the characteristic performance of each tandem stage. The model is validated with the experimental results of NASA Stage and Rotor 37, and the level of the accuracy of the model is presented. Using a similar model, the performance of all cases has been derived and the effect of solidity variation on the overall performance of machine has been discussed. Lastly, the effect of solidity variation on the tip leakage flow structure near peak efficiency point is discussed for all cases.
Aerospace Science and Technology
Ali Cheraghi; Reza Ebrahimi
Abstract
Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, ...
Read More
Feed pumps play a crucial role in the dynamics of hydraulic systems. The surge phenomenon is a common type of instability in pumps and compressors. This phenomenon is a systematic instability and is influenced by the dynamics of all components of a hydraulic system, including tank, valves, suction pipes, impeller and the turbomachine itself. Surge emerges when a pump is operating with a positive slope of head and flow curve. The coincidence of the surge phenomenon with cavitation results in a damaging phenomenon called "auto-oscillation." Thus, predicting a pump's behavior outside the design points is of great importance particularly in low flow rates. In this paper, the characteristic curve of a high-speed centrifugal pump is extracted using CFD analysis to determine the stable operating range of the pump. The studied pump consists of an inducer, impeller and volute. The simulation in the pump was carried out three-dimensionally due to the asymmetry of geometry. The simulations are performed over a wide range of flow rates and the characteristic curve of the pump (head coefficient in terms of mass flow rate coefficient) is extracted. Finally, the range of stable operation of the pump is determined using its characteristic curve.
Aerospace Science and Technology
Alireza Akbari; Sahar Noori; Payman Spahvand
Abstract
The main application of dynamic coefficients is in the flight path simulation and autopilot design of flying objects. This paper reveals a general process for calculating the roll damping coefficient of a typical airship. The process presented in this article has a step-by-step path that can be used ...
Read More
The main application of dynamic coefficients is in the flight path simulation and autopilot design of flying objects. This paper reveals a general process for calculating the roll damping coefficient of a typical airship. The process presented in this article has a step-by-step path that can be used to calculate the roll dumping coefficient of all projectiles and flying objects. The method applied in this paper is fully numerical and the dynamic coefficient will be extracted from the Fluent software using the moving reference frame (MRF) techniques. In this process, first, the roll moment coefficient is extracted from the fluent using the moving reference frame technique, and then the roll damping coefficient will be calculated using some relations presented in this paper. At the beginning of the present work, the general process of calculating dynamic coefficients is discussed. This process is then used to calculate the dynamic coefficient of a typical geometry. The results of the present work and the process of calculating this coefficient, which is fully discussed in this article, can be used to calculate this coefficient in other flying objects with similar geometry. In order to validate the present article, the results of the present work are validated with the results of another article. Acceptable agreement of the results of the present work with references, proves the correctness of the process presented in this paper for calculating this dynamic coefficient.
Aerospace Science and Technology
Ali Cheraqi; Reza Ebrahimi
Abstract
This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation ...
Read More
This paper aims to present an investigation on determining the critical cavitation number of a high-speed centrifugal pump by computational fluid dynamics. In doing so, characteristic curves of the pump used in this study were obtained in the presence and absence of cavitation. The critical cavitation number was calculated based on the cavitation breakdown characteristic curve. Two-phase flow inside the pump was simulated using the homogenous mixture method and the Rayleigh-Plesset model. The SST turbulence model and MRF rotating model were used to simulate turbulence and rotation of the flow throgh the pump, respecively. The critical cavitation number that was the outcome of numerical analysis results was compared to the experimental data. This comparison implied the necessity of considering the safety factor for determining the critical cavitation number and inlet pressure required to uninterrupted operation of the pump cavitation, using the results of numerical analysis.
Davoud Hassanzadeh
Volume 9, Issue 1 , March 2012
Abstract
An implicit unsteady upwind solver including a mesh motion approach was applied to simulate a helicopter including body, main rotor and tail rotor in hover flight. The discretization was based on a second order finite volume approach with fluxes given by the Roeand#39;s scheme. Discretization of Geometric ...
Read More
An implicit unsteady upwind solver including a mesh motion approach was applied to simulate a helicopter including body, main rotor and tail rotor in hover flight. The discretization was based on a second order finite volume approach with fluxes given by the Roeand#39;s scheme. Discretization of Geometric Conservation Laws (GCL) was devised in such a way that the three-dimensional flows on arbitrary moving grids could be solved. The accurate geometric representation together with the flexibility required for grid displacement was achieved by using a tetrahedral grid. First, the numerical methodology was validated through experimental test data; then, our supposed helicopter configuration was utilized. At the same time, the main rotor loading measurements were done through flight tests. Two methods of moving reference frame (MRF) and viscous/inviscid Dynamic Mesh were compared resulting in robustness of Dynamic Mesh approach. Ultimately, our calculationsyieldedvalid solutions to the blade loading and wake structure.
