Purpose -The purpose of this paper is to present an engineering inviscid-boundary layer method for the calculation of convective heating rates on three-dimensional non-axisymmetric geometries at angle of attack. Design/methodology/approach -Based on the axisymmetric analog, convective heating rates are calculated along the surface streamlines which are determined using the inviscid properties calculated on an unstructured grid. Findings -Since the method is capable of using inviscid properties calculated on an unstructured grid, it is applicable to a variety of configurations and it requires much less computational effort than a Navier-Stokes code. The results of the present method are evaluated on different wing body configurations in laminar and turbulent hypersonic equilibrium flows. In comparison to experimental data, the present results are found to be fairly accurate in the windward and leeward regions. Practical implications -With this approach, heating rates can be predicted on general threedimensional configurations at hypersonic speeds in an accurate and fast scheme. Originality/value -In order to calculate the heating rates at any specific point on the surface, a technique is developed to calculate the inviscid surface streamlines in a backward manner using the inviscid velocity components. The metric coefficients are also calculated using a new simple technique.
In this study, the heaving and pitching motions of a biologically inspired airfoil (Bio airfoil) and a NACA 0015 airfoil in power extraction ( Po ) and propulsion ( Pr ) operating regimes are numerically simulated considering the ground effect. The effect of the mean distance of the flapping airfoil to the ground surface on the aerodynamic coefficients, Po and Pr efficiency, is investigated. The simulation is done at Reynolds number of 1100, using overset mesh capability of OpenFOAM. Mean distance from airfoil center of rotation to the ground surface varies from 1.25 to 4 times of airfoil's chord length, c. Motion parameters such as heaving and pitching amplitudes and their phase difference are kept constant at 1c, ∕4 , and ∕2 , respectively. The reduced frequency of the motion is selected 0.1 or 0.2. The obtained results show that the change in the distance to the ground does not change the nature of the operating regimes. In the Po regime, the Po efficiency of the Bio airfoil decreases with an increase in mean distance to the ground; however, it slightly changes for NACA 0015 airfoil. In the Po regime, the Bio airfoil has a higher efficiency than NACA 0015 airfoil. Due to the ground help, the leading edge vortex increases Po efficiency only on Bio airfoil. In the Pr regime, the Pr efficiency of both airfoils decreases with an increase in the distance to the ground, and NACA 0015 airfoil has a higher efficiency than Bio airfoil.
In the present study, a direct simulation Monte Carlo solver is utilized to simulate the effects of heater plates on the performance parameters of microelectromechanical propulsion devices. The simulation is two dimensional. Proper cell dimensions, number of particles per cell, and grid study are used to guarantee the accuracy of simulations. Three types of microthrusters including cold gas as type 1, a propulsion device with heaters in the walls as type 2, and a microthruster with heater plates inside the domain as type 3 are studied. Type 1 is considered as a reference case and two other types are compared with type 1. It is observed that heater plates inside the microelectromechanical thruster enhance the downstream temperature due to conversion of pressure drop occurred by plates into temperature. In type 3, the specific impulse is enhanced but the thrust force is decreased in comparison with type 1. Heating the walls in type 2 accelerates the flow while there is no considerable pressure reduction. Moreover, all performance parameters are increased in this type. It is also demonstrated that increasing of wall temperature increases thrust and specific impulse and decreases the sensitivity of thruster due to rarefaction effects.
A simple approach is proposed to incorporate the effect of viscous interaction in the calculation of aerodynamic heating of three-dimensional geometries by Euler/boundary-layer methods. In the present study, aerodynamic heating is calculated from the solution of a set of approximate convective-heating equations along the streamlines. These heating equations are derived using axisymmetric analogue. To determine streamline paths and flow properties along them, Euler equations are solved around the three-dimensional body. The effect of viscous interaction on the aerodynamic heating can be significant, especially if the Reynolds number is low. To incorporate this effect, the whole process should be repeated having considered the boundarylayer thickness all around the body. However, this approach causes different difficulties, and is not cost efficient as well. In the present work, the effect of boundary-layer thickness on the aerodynamic heating is incorporated through the correction of pressure distribution on the surface of the body. This approach of correcting pressure distribution is applied to spherical and elliptical blunted cones in laminar hypersonic flows. It is shown that the heating rates are improved in low Reynolds numbers, where viscous-interaction effect is significant. The present approach can result in a reduction of computational cost, when viscous interaction is significant in calculation of aerodynamic heating.
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