Setupĭownload the Mesh file required for setting up the simulation and associated Case and Data files here. Finally, you will compare the results from the simulations with the analytical results obtained using the shock-expansion theory. You will also learn how to implement grid adaption to increase mesh density in the vicinity of the shockwave in order to improve the accuracy of shock-capturing, and consequently, of the computed solution. In this homework, you will learn how to set up and solve a supersonic flow over a diamond-shaped airfoil using the density-based solver in Ansys Fluent. This homework gives you a hands-on feel for setting up this simulation and comparing the results with theoretical estimates. Though the flow-field is quite complicated, the shock-expansion theory is able to correctly estimate the flow variables such as pressure, Mach number, etc., in different regions of the flow. As the supersonic flow moves over the airfoil, it encounters both oblique shock waves and expansion waves. Garzon and J.R.Supersonic flow over a diamond-shaped airfoil is one of the classic canonical cases for demonstrating the application of shock-expansion theory. “Flight Tests of a Supersonic Natural Laminar Flow Airfoil” – Michael A.”The Flow and Force Characteristics of Supersonic Airfoils at High Subsonic Speeds”, W.F.Fundamentals of Aerodynamics – John D.The very thin airfoil edge around the entire fuselage of the SR-71 Blackbird which could fly over 3 times the speed of sound! A very thin airfoil cross-section seen on this YF-23, a supersonic aircraft. Most modern fighter aircraft employ similar airfoil designs and that combined with extra control surfaces, a thinner fuselage area near the wings and a high sweep angle allow high manoeuvrability while minimising additional drag at supersonic speeds. Thin, Diamond shaped Airfoil Cross section Bow shocks typically create more drag than oblique shock waves and an example where this phenomenon is used is the high amount of drag the Apollo capsule is designed to experience during re-entry to slow down from orbital speeds. The thin leading edge creates an attached (or Oblique) shock wave instead of the detached shock waves (bow shock wave) that would occur if a rounded airfoil leading edge would be used. The thin airfoil shape, resembling a diamond shape, combined with sharp leading and trailing edges is very effective at directing the flow of shock waves and reducing their strength to reduce their impact on lift generation. To counter this, Supersonic airfoils generally have a geometry as shown in the figure that has been found to be highly effective at minimizing the detrimental effects of shock waves at the wing surfaces near the edges. Prandtl-Meyer Expansion Fan made up of near infinite Shock waves The intensity of wave drag increases proportionally with a change in the Mach number and the angle of attack. This difference in pressures due to the velocity variations creates a drag force component opposing flow which is wave drag. The expansion waves are created on the top surface near the leading edge and at the bottom surface near the trailing edge. The consecutive expansion waves, thus created, exhibit a pressure drop below the free stream pressure as the flow progresses due to sharp increase in velocity with every turn of the shock along the edge. This leads to the creation of a Prandtl-Meyer Expansion fan, which consists of an infinite number of shock waves, each inclined by a very small angle to the airfoil surface. Wave drag is an inherent component of drag induced at supersonic and transonic flows due to the creation of expansion waves when supersonic air flow hits the inclined airfoil leading edge. The Concorde: the first supersonic passenger aircraft Wave drag causes an abrupt pressure drop over the wing surfaces, resulting in instantaneous loss of lift and hence, is very dangerous. It should also be noted that a new type of drag apart from skin friction and pressure drag known as the wave drag appears, due to the compressibility of the air and the presence of the high energy shock waves around the aircraft. Today I’ll be writing about the theory behind airfoil design for aircraft operation in the supersonic flow regime.Īircraft design and analysis of wings in the flow regimes over Mach 1 are complicated for several reasons: as the speed of the aircraft increases, shock waves appear, along with additional stresses on the wing and the tail and high temperature of the airflow around the airfoil.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |