DESIGN OF LOW-DRAG AUTONOMOUS UNDERWATER VEHICLES AND FLOW CONTROL

Design of autonomous underwater vehicles (AUV) met the opposite challenges. Their achievable route can be enhanced with drag reduction due to an increase of AUV slenderness. However, blunt short AUV have others operational advantages. The possibility to design low-drag bodies for Reynolds numbers employed by contemporary AUV (2×106<Re<107) is based on a combination of known facts. First, blunt bodies experience a drag crisis associated with laminar-turbulent transition in their boundary layers and some boundary layer suction additionally reduces their drag. Second, the transition can be delayed till much higher Re for bodies without adverse pressure gradients over their forward and medium parts. Suction on sterns of such bodies allows for the very substantial drag reduction. Several body shapes with distributed suction with extremely low slenderness (L/B<1.5) are presented. Their drag coefficients are between 0.007 and 0.02, whereas for ellipsoid of the same slenderness it exceeds 0.08.

An Effective Simulation Scheme for Predicting the Aerodynamic Heat of a Scramjet-Propelled Vehicle

Currently, aerothermal research into scramjet-propelled vehicles characterized by a wedge-shaped section is relatively sparse. Based on the Mach number, grid strategy, and numerical method, an effective simulation scheme for predicting the aerodynamic heat of a scramjet-propelled vehicle during flight is proposed in this paper. At different Mach numbers, the appropriate grid strategy and numerical method were determined by validation tests. Two-dimensional external flow field models based on wedge sections were established and, unlike in blunt bodies, the tests showed that at the high supersonic stage, the ideal cell Reynolds number should be no larger than 16. At the hypersonic stage, the ideal cell Reynolds number and aspect ratio of wall cells near the shock should be no larger than 40, and the AUSM+ flux type performs better than Roe’s FDS flux type at the above stages. The aerothermal prediction indicates that during a flight time of about 34 s, the temperature change reaches about 1913.35 °C, and the maximum average temperature change rate reaches 115 °C/s.

La historia del viento en las ciudades = The history of the wind in the cities

ResumenLa relación entre el viento y las ciudades se desarrolla a lo largo de la historia de manera accidentada, discontinua y en varias disciplinas. En sus orígenes, el conocimiento del viento era más de carácter intuitivo y se basaba en la observación de sus manifestaciones visibles, ya sea en la lluvia, los remolinos o los elementos que arrastra. Estas observaciones permitieron, en diversa épocas, generar ciertos criterios para diseñar ciudades con principios eólicos genéricos. Con el paso del tiempo, los avances científicos y las nuevas tecnologías, fue posible ir avanzado en el conocimiento del viento. Así, diversas disciplinas como la geografía, la meteorología, la arquitectura y el urbanismo avanzaron por caminos separados, cada una buscando sus propios objetivos en relación al viento. A medida que nos acercamos al siglo XX empiezan a aparecer ramas de estas mismas disciplinas, como la climatología o la bioclimatología, sumándose también nuevas áreas del conocimiento como la ingeniería aeroespacial, la que se desprende la ingeniería aerodinámica para cuerpos romos no fuselados y cuerpos estáticos como los edificios, los puentes, etc. Todas estas ramas del conocimiento desarrollan caminos paralelos, pero al final del siglo XX y comienzos del XXI se empiezan a mezclar, compartiendo sus propios descubrimientos. Hoy, la necesidad de reunir estos conocimientos se torna fundamental para lograr un avance interdisciplinario que permita comprender la importancia del viento para la planificación urbana en un mundo que necesita cada vez más conciencia ambiental.AbstractThe relationship between the wind and the cities has developed throughout history in an uneven, discontinuous way and in various disciplines. In its origins, the knowledge of the wind was more intuitive in nature and was based on the observation of its visible manifestations, whether in the rain, the eddies or the elements that it drags. These observations allowed, at different times, to generate certain criteria to design cities with generic wind principles. With the passage of time, scientific advances and new technologies, it was possible to advance in the knowledge of the wind. Thus, various disciplines such as geography, meteorology, architecture and urban planning advanced in their separate ways, each seeking its own objectives in relation to the wind. As we approach the 20th century, branches of these same disciplines begin to appear, such as climatology or bioclimatology, also adding new areas of knowledge such as aerospace engineering, which is derived from aerodynamic engineering for non-fuselated blunt bodies and static bodies. like buildings, bridges, etc. All these branches of knowledge develop parallel paths, but at the end of the 20th century and the beginning of the 21st they begin to mix, sharing their own discoveries. Today, the need to gather this knowledge becomes fundamental to achieve an interdisciplinary advance that allows understanding the importance of the wind for urban planning in a world that increasingly needs environmental awareness.

Aerothermal prediction of hypersonic flow around spherical capsule model using IDDES approach

The prediction of heat transfer for blunt bodies in hypersonic flows remains a great challenge. In particular, the uncertainties are larger in the leeside due to the complexity of the wake flow. Generally, the heat transfer is over-predicted using the Reynolds-averaged Navier–Stokes (RANS) models. In this paper, the improved delayed detached eddy simulation (IDDES) method is used to simulate the Mach 6 flow around a scaled spherical capsule model. In addition, a low dissipative WENO scheme is used for inviscid fluxes and dual-time stepping method is applied for time advancement. Results are compared to experimental data for mean and instantaneous heat transfer in the leeside of the aftbody. It is shown that the integrated error is 75.49% for RANS while 35.69% for IDDES method. Moreover, the multi-scale structures in the separation region are also resolved well by the IDDES method.

A Numerical Study of Shock and Heating With Rarefaction for Hypersonic Flow Over a Cylinder

The numerical computation of hypersonic flows over blunt bodies is challenging due to the difficulty in robust and accurate wall heat flux prediction and proper capturing of shock waves free from the “carbuncle” phenomenon and other shock anomalies. It is important to understand how this behavior is affected due to rarefaction, which in turn will help to improve the study of aerospace vehicles flowing in rarefied and hypersonic regime. Recently, the SLAU2 convective scheme was shown to suppress the shock anomalies found in capturing strong shocks, however, it still showed a wavy pattern of heating. We have proposed a modification to the SLAU2 convective scheme to improve the accuracy of flow predictions in the presence of strong shocks. We then perform the numerical simulation of hypersonic viscous flow over a cylinder at Mach 8 and 16.34 at different Knudsen numbers. We carry out the study using the modified SLAU2 and the classical Roe schemes. We study how the shock anomalies found in the continuum hypersonic flows behave with the degree of rarefaction. It is found that the modified SLAU2 captures the shock free from the shock anomalies at all Kn, while the Roe scheme lacks robustness for Kn≲10−3. The variation of different flow properties such as heat flux, wall shear stress, and the Mach number is investigated. The peak heating value was observed to decrease with the degree of rarefaction.