THERMAL EFFECTS OF HYPERSONIC FLIGHT

B. RAHUL (11UQ1A2102)B. PRUDHVI RAJ (11UQ1A2107)S. LALITH KUMAR (11UQ1A2138)

• Three vechiles classes are in background - non- winged reentry vechiles(RV-NW)- winged reentry vechiles(RV-W)- airbreathing cruise and accelaration/ ascent and reentry vechile(CAV/ARV)

• Generally flight in the earth atmosphere and in the continuum regime

• Attached viscous flow is consider to be of boundary layer type.

• Hypersonic flow can be approximately separated into a number of regimes.

INTRODUCTION

Thermal effects in hypersonic flight • The classical heat flux concept is

extended in to the concept of thermal state of surface.

• Thermal state of surface(q,T) includes both the thermal loads and thermal surface effects

• Thermal surface effects are the effects of q,T on wall and wall near viscous flow and thermo chemical phenomena

• Especially air breathing hypersonic flights vechiles are viscous effects dominated.

• Necessary and permissible surface properties are atmost important for hypersonic flight vechiles.

Alleviation of thermal effects in structures

• There exist a variety of methods of alleviating thermal stresses in aircraft subjected to kinetic energy

• The Method of alleviating thermal stresses in aircraft structures are discussed under two headings

1. preventing of structure or allowing heating but evening out the

temperature difference (cooling and external insulation)

2. structural design against thermal stresses

Structural design against thermal stresses

• We shell consider here the design of certain structural components to alleviate particular types of thermal stress.

- corrugated and jointed webswhen is subjected to kinetic heating the skin heats up more rapidly than the webs, causing compressive stress in skin

and tensile stress in webs.

both stress may be considerably reduced if straight webs are replaced by conjugated webs.

flexibility and thermal stress in corrugated

webs

• leading edge stresses

Due to thermal stresses there is a chord wise variation in skin temperature, because the adiabatic wall temperature and the

heat transfer both reduce.

Wings have been proposed, made of two materials, one with good low temperature properties and other with good high temperature properties.

(a & b) are thermal stress in heated wing

• Leading edge slats– Slats in leading edge allow the leading edge to expand

independently of the rest of the wing thus reducing the thermal stress in the rest of wing.

– The effective leading edge slats depends upon spacing and skin thickness presents of webs or fillets and temperature distribution particular configuration.

• Stresses in honeycomb sandwich

– If honeycomb is used in an aircraft subjected to kinetic heating, the temperature of the outer face of the sandwich rises faster than that of inner face.

• Stresses in fuel tank boundaries

– The temperature difference cause stresses near the fuel tank boundaries- compressive in the skin not covering fuel tanks and tensile in that covering the tanks

– Fuel tanks in the fuselage, bending stresses may be produced near the bulkheads, therefore radical expansion outside the tanks accommodate changes in the skin thickness which aggravate the situation

(a-c) Heating at fuel tank boundaries

• The basic property required for cooling liquid must be high heat capacity between the temperature of the aircraft on the ground and the maximum allowable temperature of the structure.

• This high heat capacities can be obtained by using two methods of cooling 1. transpiration cooling2. circulation cooling

External insulation :

• In the external insulation, the exposed part of the vehicle will be covered with metallic shields.

• These shields will with stand the exposure of the atmosphere at any applied temperature.

Preventing of structure or allowing heating but evening out the temperature difference :

Combination of coolant and external insulation

• If cooling and insulation are used combination in total weight thermal protection required may be less than that required using either on it’s own .

• The presence of a layer of insulation reduces the quantity of heat entering the structure and consequently the quantity of coolant required, and also the weight of piping and other other equipment .

• An optimum combination of coolant and insulation which provides the required thermal protection to a structure for a minimum weight penalty

How to overcome• Most critical challenges in design and development of a large vehicle

are– Determination and verification of laminar- turbulent transition location, viscous

inlet- onset flow, control- surface effectiveness, thermal loads.– Airframe propulsion integration

• Design of the structure to minimize, the thermal stresses for a given temperature distribution, tends to cause loss of strength and stiffness, loss which has to be rectified by addition of extra material.

• Reduction of thermal stresses by choice of structural material is possible only to limited extent.

• Thermal stress depends upon the coefficient of thermal expansion and of young’s modulus

• Thermal stress will lead to the buckling of the materials.

Conclusion• Technology development for hypersonic flight proceeds since decades.• Much and important system and technology knowledge has been

gained, but only capsules and the space shuttle are operational, not airbrathing hypersonic flight vechile.

• Important lessons have been learned from past technology programmes.

• No future single extraordinary technology break through can be expected, but major steps are made, e.g. in materials, vehile shapes, propulsion.

• Airbreating hypersonic flight still poses major challenges.• Numerical disciplinary and multidisciplinary simulation and optimization

has very large potential.• Needed are adequate flow- physics, thermodynamics, and structure-

physics models.• The overall challenges are very large.• Long and continuous technology development effort and experimental

vehicles are still needed to arrive at highly efficient flight vehicle and transportation systems.

• Hypersonic has a bright future.

Thank you