Thermal Environment and Aeroheating Mechanism of Protuberances on Mars Entry Capsule

Mars has only thin atmosphere composed mainly of carbon dioxide that differs significantly from the atmosphere of Earth in terms of characteristics of reentry flows. To connect with the orbiter, the Mars entry capsule is provided with titanium pipes and other units installed on the heat-shield. These units will create significant local interaction flow on the surface of the capsule and cause additional heating on the surface of the shield during the entry of the capsule. With a view to interaction thermal environment issues for the surface of the shield, in this paper, the characteristics of protrusion interaction flow on different location of the shield were studied by means of numerical simulation. Heating mechanisms of protuberances on different location were derived by analyzing characteristic parameters such as local flow velocity, pressure, and Mach number. The results show that the interaction thermal environment of protuberances in the windward area is smaller than that of protuberances in the leeward area, mainly because subsonic flow dominates in the windward area, and the interaction is weak, while in the leeward area, the direction of flow intersects with protuberances to form a boundary layer shear flow, which results in a stronger interaction before the protuberances.

Effect of Mesh Type on Numerical Computation of Aerodynamic Coefficients of NACA 0012 Airfoil

Mesh type and quality play a significant role in the accuracy and stability of the numerical computation. A computational method for two-dimensional subsonic flow over NACA 0012 airfoil at angles of attack from 0o to 10o and operating Reynolds number of 6×106 is presented with structured and unstructured meshes. Steady-state governing equations of continuity and momentum conservation are solved and combined with k-v shear stress transport (SST-omega) turbulence model to obtain the flow. The effect of structured and unstructured mesh types on lift and drag coefficients are illustrated. Calculations are done for constant velocity and a range of angles of attack using Ansys Fluent CFD software. The results are validated through a comparison of the predictions and experimental measurements for the selected airfoil. The calculations showed that the structured mesh results are closer to experimental data for this airfoil and under studied operating conditions.

Investigation of a Passive Flow Control Device in an S-Duct Inlet at High Subsonic Flow

This paper reports the investigation of a flow control strategy for an S-duct diffusers. The method incorporates stream-wise tubercles, and aims to enhance the performance of S-duct inlets by reducing the size and intensity of separated flow. These devices, bioinspired from humpback whale flippers’ leading edge protuberances, have been shown to be effective in increasing post-stall coefficients of lift of airfoils. In S-duct diffusers, the presence of convex curvature next to the separated region provides an ideal location for the installation of a tubercle-like device. The flow control effectiveness was evaluated by test-rig measurements and computational fluid dynamics (CFD) simulations of the flow in an S-duct at high subsonic flow conditions (Ma = 0.80). The S-ducts were rapid prototyped in plastic using 3D printing. Static surface pressure along the length and total pressure at the exit revealed pressure recovery, total pressure loss, swirl, and the nature of flow distortion at the S-duct exit. CFD simulations used ANSYS FLUENT with a RANS solver closed with the RKE turbulence model. The CFD simulation compared well with the test-rig data and provided useful information on flow mechanism and for understanding flow features. The performance of the baseline and variant with the flow control device was compared and flow control strategy was evaluated.