Correct Answer : Convergent-Divergent
Explanation : In order to achieve supersonic speed from rest we use a convergent divergent nozzle. This is because in the convergent section the flow is subsonic and is accelerated with decreasing cross-sectional area of the nozzle. The flow reaches sonic speed at the throat after which it is further accelerated in the divergent section as the supersonic flow increases with the increasing cross-sectional area of the nozzle.
Correct Answer : Downstream of the limiting characteristic
Explanation : For solving method of characteristic, it is important to choose an initial point where the flow field properties are known. The method os characteristic can thus be used to find the flow downstream point by point. For nozzle flor or internal flow, the initial point is taken downstream of the limiting characteristic which is approximately slightly downstream of the sonic line.
Correct Answer : Unit process
Explanation : In order to design a supersonic nozzle, it is important to apply methods of characteristics which helps us in determining the flow properties. Solving the compatibility equation point by point along the characteristic line based on whether the internal or wall point is known as unit process.
Correct Answer : Neglect the internal points
Explanation : The method of characteristic is a three step procedure. The first step is to determine the characteristic lines. After this, we determine the compatibility equations based on whether the point is an internal or wall point, and finally, we solve for these equations point by point along the characteristic line.
Correct Answer : 2
Explanation : For a point in a streamline, there exists two characteristic liens according to this formula :Where, θ is the angle made between the tangent to the point P and horizontalμ is local Mach angle = sin-1(1/M)Thus the two characteristic lines have slope tan?(θ + μ) and tan?(θ – μ). The one which is inclined above the streamline is labelled as C+ and the characteristic line inclined below the streamline is C–.
Correct Answer : Straightening section
Explanation : When we see the nozzle contour, there are two sections. One where the angle θ which is the angle formed between the tangent to the wall and horizontal increases until it reaches a maximum point. After this, θ reduces until it is equal to zero at the nozzle exit. This section is known as straightening section.
Correct Answer : No information on wall contours of nozzle
Explanation : Flow properties at any section of the nozzle can be predicted by the quasi-one-dimensional analysis. It represents the average flow quantities. There are two major shortcomings of using this analysis. First being that it does not predict the three-dimensional flow in convergent-divergent nozzle and secondly, it does not provide us with the information of wall contours in the nozzle.
Correct Answer : Get pressure distribution over hypersonic body
Explanation : We use Newtonian theory for the purposes of Hypersonic flow problems. It gives us the pressure distribution over the surface of the hypersonic body for both straight and curved surfaces. Newtonian theory gives an approximate estimate rather than an exact result.
Correct Answer : False
Explanation : One of the conclusions derived from Newtonian theory is that the result of coefficient of pressure is more accurate for three – dimensional bodies such as the cone compared to the two – dimensional bodies such as a wedge.
Correct Answer : Parallel to the surface
Explanation : In a hypersonic flow, there is a formation of a thin shock layer over a wedge surface. The streamline pattern follows the trend such as upstream of the shock wave, the flow moves in a straight – line. On moving downstream of the shock wave, the flow is parallel to the wedge – surface inclined at the wedge – angle.
Correct Answer : 0
Explanation : For each body, the freestream particle impacts the surface in the frontal region. The rear side remains un – impacted by this flow. This portion is known as the ‘shadow’ where no impact pressure is felt. The coefficient of pressure in this region is zero (0).For example for a flat plate that is kept at 90 degrees to the incoming freestream flow, the frontal region feels the impact, whereas the back surface is in shadow and the coefficient of pressure in this region is thus zero.
Correct Answer : Stream of particles in rectilinear motion
Explanation : Newton formulated the Newtonian theory by modeling the fluid flow as a stream of particles that move in a rectilinear motion. The individual particles of the flow stream do not move in a random direction. The particles lose the momentum normal to the surface once it strikes. Its tangential momentum is retained without any loss.
Correct Answer : Force on inclined plane in moving fluid
Explanation : Isaac Newton worked on a fluid – dynamics theory which would address the force on an inclined plane in a moving fluid applicable to low – speed flow which was later applied to hypersonic flow. According to the law, the force varies as square of sine of the deflection angle.
Correct Answer : Cp = Cp max sin2 θ
Explaination : Lester Lees proposed modified Newtonian pressure law for blunt surfaces at hypersonic flow. According to the modified formula, coefficient 2 in Newtonian theory is replaced with Cp max. The maximum pressure over a blunt body arises at the stagnation point.
Correct Answer : M∞ → ∞, γ → 1
Explaination : Newtonian theory is applicable only under certain limitations. The first being the Mach number tends to infinity as we are talking about hypersonic flows and γ tends to 1. Only under these conditions are the results accurate.
Correct Answer : θ = π/2
Explaination : For a blunt body, the coefficient of pressure is maximum at π/2. This result is derived from Newtonian theory according to which the coefficient of pressure is related to θ by:Cp = 2sin2 θFor sin π/2, which is the stagnation point, we get maximum value of coefficient of pressure.
Correct Answer : Lack of experimental facility
Explanation : The hypersonic bodies which fly at very high Mach numbers exist today which are tough to analyse experimentally because it is hard to replicate such high Mach numbers in a wind tunnel. The hyperonic flow has very high Reynolds number and tempertaure which is not easy to replicate. For these reasons, engineers resort to the use of computational fluid dynamics to design vehicle flying in hypersonic regime. The results are accurate enough.
Correct Answer : Pitching moment coefficient
Explanation : Chemically reactive flow affects the pitching moment over the space shuttle in hypersonic flow. Usually, for a chemically reactive gas, the pressure on the forward part of the shuttle body is higher and it is lower in the rearward part. This leads to a positive pitching moment of the shuttle.
Correct Answer : Complex use
Explanation : Hypersonic flow makes use of computational fluid dynamics to get accurate results because it is very inexpensive, is fast and gives straighforward results. The practical engineering problems are approximated by making some assumptions to find pressure distribution, lift drag etc. The hypersonic flow usually varies from subsonic and supersonic flow because of the presence of a thick boundary layer between the surface and thin shock wave. This cannot be solved by the conventional boundary layer methods. Hence CFD plays an important role in finding the results.
Correct Answer : Boundary-layer solution
Explanation : In analyzing the hypersonic flow, it is assumed that the flow is viscous throughout. There are three main approaches taken which are-Viscous shock-layer solutions, parabolized Navier-Stokes solution and full Navier-Stokes equation. These three equations are much more accurate than the boundary-layer equations in order to solve the fully viscous shock layer present over the blunt body in a hypersonic flow.
Correct Answer : No slip condition between two plates
Explanation : In analyzing Coutte flow, we have two flat plates kept parallel to each other with viscous fluid contained between the two. One major assumption made is that there is a no slip condition thus resulting in no relative motion between the fluid and the plate.
Correct Answer : Kinetic energy transformed into internal energy
Explanation : The flow has kinetic energy which is partially dissipated in the form of internal energy due to the presence of skin friction drag that exists between the fluid and the flat plate. The change in internal energy leads to change in dissipation. These particular phenomena are known as viscous dissipation.
Correct Answer : Heat flowing from fluid to wall
Explanation : The two flat plates in case of a Couette flow is kept at different temperatures thus creating a temperature gradient. This results to heat transfer through the fluid at both upper and lower surfaces of the plate. When the heat flows from fluid to the wall it is known as cold wall case, and when the heat flows from the wall to the fluid, it is known as hot wall case.
Correct Answer : Midpoint between the two plates
Correct Answer : Shear stress law
Explanation : Newtonian fluids are characterized by those fluids that obey the shear stress law. Aeronautics domain makes use of newtonian fluids only (air, other gases). Those fluids that don’t obey shear stress law are known as non – newtonian fluids (blood).
Correct Answer : Decreases
Correct Answer : Fourier law
Explanation : Fourier law which is also known as the law of heat conduction is used to find out the heat flux at any point in the fluid. It is given by the formula:Where, heat flux is in the y – directionMinus sign indicates that the heat flows from high temperature to low temperature and thus q?y is in opposite direction to the temperature gradient.
