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ME 441 Quiz 1
| Question | Answer |
|---|---|
| turbulence can help ___________ drag | reduce |
| for blunt bodies most of the drag is ___________ drag | pressure |
| for streamlined bodies most of the drag is ________ _________ drag | skin friction |
| what are Mach numbers? | dimensionless ratio that compares the speed of a flow to the local speed of sound |
| Mach number regimes: M < 0.3 | incompressible |
| Mach number regimes: 0.3 <= M < 0.8 | subsonic |
| Mach number regimes: 0.8 <= M <= 1.2 | transonic |
| Mach number regimes: 1.2 < M < 5 | supersonic |
| Mach number regimes: M >= 5 | hypersonic |
| what is the Reynolds number? | a dimensionless parameter that compares inertial forces to viscous forces in a flow |
| why is the Reynolds number important? what does it affect? | it affects: - boundary layer behavior - flow separation - drag (skin friction & pressure drag) - lift characteristics |
| low Re --> ________ flow --> early _________ --> higher ________ drag | laminar flow early separation higher pressure drag |
| what is skin friction drag? | drag caused by viscous shear stress b/w fluid and surface of a body as fluid flows along it |
| what cause skin friction drag? | fluid viscosity, velocity gradients in the B.L., no-slip condition at the wall |
| what is form drag? (pressure drag) | drag caused by a pressure difference b/w the front and back of a body due to flow separation |
| what causes pressure drag? | flow separation, large wake behind the body, adverse pressure gradient |
| what is steady level flight? | aircraft flies at constant velocity and constant altitude w/ no acceleration |
| what forces act on an aircraft in steady level flight? | lift (L), weight (W), thrust (T), drag (D) |
| what forces are vertically balanced in steady level flight? | L = W |
| what forces are balanced horizontally in steady level flight? | T = D |
| the net force on the aircraft in steady level flight is what? | 0 |
| how do we get the stall velocity for steady level flight? | start from the lift equation and apply the steady level flight condition at stall |
| what condition defines stall in S.L.F.? | lift equals weight & the lift coefficient is at its max value |
| how do flaps affect stall speed? | flaps increase C(L max) which reduces stall speed |
| what is meant by the Lagrangian viewpoint in describing a flow field? | it follows an individual fluid particle as it moves through space and time, tracking its properties along its path |
| what quantities are tracked in the Lagrangian viewpoint? | position of the fluid particle velocity pressure temperature density |
| What is meant by the Eulerian viewpoint in describing a flow field? | The Eulerian viewpoint observes fixed points in space and describes how fluid properties change at those locations as fluid flows past. |
| what quantities are described in the Eulerian viewpoint? | velocity field, pressure field, density field, temperature field |
| Which viewpoint is more intuitive for particle motion? | The Lagrangian viewpoint, because it directly follows individual fluid elements. |
| What does it mean when a system or process is adiabatic? | no heat transfer occurs between the system and its surroundings: Q=0 |
| What does adiabatic NOT mean? | does not mean no temperature change — temperature can change due to work. |
| What does it mean when a system or process is reversible? | idealized process that can be reversed with no net change to the system and surroundings. |
| What conditions are required for a process to be reversible? | No friction No viscosity No turbulence No shock waves Infinitesimal gradients |
| What does it mean when a system or process is isentropic? | entropy remains constant |
| A process is isentropic if and only if it is: | Adiabatic & Reversible |
| Can a process be adiabatic but NOT isentropic? | Yes. If a process is adiabatic but irreversible (e.g., shocks, friction), entropy increases, so it is not isentropic. |
| What equations result if viscous effects are neglected? | Euler equations. |
| What is the difference between integral and differential conservation equations? | Integral form: applies to a finite control volume Differential form: applies at a point in the flow field |
| What is the substantial derivative? | The substantial (material) derivative is the time rate of change of a property following a fluid particle as it moves through the flow. |
| When does the local derivative term vanish? | In steady flow |
Created by:
mccurdyo