# wake survey - Drag estimation by wake survey Partha Ajit...

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1 of 7 Aerodynamics Lab Report, IIST Drag estimation by wake survey Partha Ajit Surve 1 Indian Institute of Space Science and Technology, Trivandrum, Kerala, 695547 Penumala Hemanth Chandra Indian Institute of Space Science and Technology, Trivandrum, Kerala, 695547 Peyyala Suguna Bhaskara Pratyush 2 Indian Institute of Space Science and Technology, Trivandrum, Kerala, 695547 Pallempati Sravani 3 Indian Institute of Space Science and Technology, Trivandrum, Kerala, 695547 Drag estimation by wake survey method is an experimental technique specially used for measuring the drag of airfoils at low angles of attack. In the experiment at aerodynamics lab, IIST, we used a circular cross-sectional aerofoil. This method is based on the momentum balance in the free-stream direction performed over a control volume that encircles the airfoil, and is developed essentially for two-dimensional flows.[1] Nomenclature D Drag force C d Coefficient of drag c Chord length P a Flow static pressure, Pa v flow velocity, m/s Re Reynolds Number ρ Flow density ρ Hg Density of Mercury, 13600 kgm 3 R Gas Constant T Ambient Temperature P stag Stagnation Pressure P stat Static Pressure ν Kinematic Viscocity of that fluid with that surface I. Introduction The profile drag of a two-dimensional airfoil is the sum of the form drag due to boundary layer separation (pressure drag), and the skin friction drag. Usually the profile drag is determined from force measurements made using a mechanical balance attached to the model. In the two-dimensional case, the profile drag may also be determined from momentum considerations by comparing the velocity ahead of the model with that in its wake; this method is used here and presupposes the flow is incompressible. Momentum changes can be derived from velocities obtained from a pressure rake across the wake. [4] 1 Student, Aerospace Department, IIST Student, Aerospace Department, IIST 2 Student, Aerospace Department, IIST 3 Student, Aerospace Department, IIST

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2 of 7 Aerodynamics Lab Report, IIST This experiment involves study of flow past a circular cylinder in a uniform stream. Different objects are cylindrically shaped since its volume is much higher than any other structures. On a typical airplane, cylindrical fuselage is a significant source of drag, even though it generates no lift. [5] II. Theory The wake survey measures static pressures and the decrease in total pressure within the wake and compares those values to the free stream total pressure. This pressure deficit, or essentially the momentum loss of the flow, can then be directly related to the profile drag. Figure shows a pictorial representation of the velocities before, station 0, and aft of the airfoil, stations 2 and 1. The shaded area represents the total moment
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