Osney Lab History

History of the Group

The group started from research in hypersonics...

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(Gas expanding from a shock tunnel at Mach 10 and 16,000K)
In the 1960's under the guidance of Professor Douglas Holder and Professor Donald Schultz, there was significant hypersonic research undertaken at Oxford. These studies related to re-entry and consequently very high temperatures were necessary due to the extremely high vehicle velocities, of several kilometres per second. Such conditions can only be produced for very short times of order milliseconds and special short duration wind tunnels were developed for this purpose. The gun tunnel runs for 30 milliseconds and operates by increasing the reservoir pressure to 200 bar to burst a diaphragm

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(A typical re-entry model with Thin Film Gauges)
This propels a piston down the tube supersonically creating a shock wave which reflects off the end of the tube and causes the gas in the tube to rise to very high pressures and temperatures. This gas is then expanded in a hypersonic nozzle to Mach 7 or 8 where the models of the re-entry vehicles were tested. The gas is so hot 16 000 K (1½ times the surface temperature of the sun) that it radiates strongly. The flow can be seen impinging on a cone which is mounted on a flat plate normal to the flow.

The attached, inclined shock waves radiate red light as the flow temperature rises on passing through the shock wave. The flow then passes through a normal shock and the flow radiates bright white light. It was a challenge to measure heat transfer in this situation and Thin Film Heat Transfer Gauges were employed.

The electrical resistance of the platinum films varies as the temperature changes, and by measuring this the surface temperature history of the model may be found. The heat transfer rate to the surface was then calculated by analysing the unsteady, heat conduction process within the model material.

In 1969 the turbine entry temperature in gas turbines was rising sharply as more thrust and efficiency were sought. It was suggested that our techniques could be used to measure this heat transfer and film cooling was the first topic investigated.

From shock tunnel to ILPT...

Film cooling is a means of protecting turbine blades and vanes from the hot combustion gases by blowing a film of cool air over the blade surface through rows of small holes.

With a commission from Rolls-Royce plc the first tests were performed in a Shock Tunnel. The test time was 10 milliseconds and the coolant was started by bursting a second diaphragm as the shock wave in the facility was moving down the tube. The hot tunnel flow entering from the tube and the coolant coming from the small chamber above. Thin Film Gauges were utilised.

It became obvious to Prof Jones and his research team that shock tunnels were not the ideal facility to test turbines as they were really designed for very high temperatures as already explained. Whereas, in turbine testing it was not necessary to create such high gas temperatures in order to simulate the physics of the heat transfer process.

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(A typical film cooled nozzle guide vane)
Reynolds number and Mach number were readily satisfied but as the wall temperatures in our short duration wind tunnels were always close to ambient; then a gas temperature of only 500 K was necessary. Thus the author devised a new form of wind tunnel, the Isentropic Light Piston Tunnel (ILPT), which employed relatively slow piston compression and heating rather than shock wave heating.

The piston was driven by compressed air and the hot compressed gas in the tube was allowed to pass through the test section by a fast acting valve after compression by the piston. The flow lasted for 300 milliseconds and gave a steady flow if the inflow and outflow from the tube were carefully matched. Professor T.V. Jones and colleagues have built many such tunnels over the years. The tunnels were commissioned by Rolls-Royce plc and the research undertaken with the company grew.

Image: (The Shock Tunnel used in the first film cooling tests at Oxford)

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Image: The film cooling test section & The Oxford Rotor ILPT

Image: The DERA Pyestock ILPT & The ILPT Test Section

The largest ILPT tunnel at Oxford shown above is capable of testing a rotor. The rotor is spun up to speed in vacuum prior to the run which lasts for several hundred milliseconds. Currently a 1½ stage, i.e. an HP stage plus IP vane, is under test.

Image: The DERA Rotor

A tunnel with five times this capacity has been built by Oxford for the UK government research organisation DERA (now QinetiQ), at Pyestock, Farnborough, which is only 60 miles from Oxford.  The Oxford team also performs research for Rolls-Royce plc in this facility.

The UTC is formed and Thin Films are developed...

In 1980, a University Technology Centre primarily supported by  Rolls-Royce plc was established in the group, located in the Osney Laboratory/Southwell Building, which is a converted power station on the River Thames.

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Osney Lab/Southwell Building, River Thames

Data measurement and collection techniques are critical to successful research undertaken in engine operating-like conditions.  One type of instrument, the Thin Film Heat Transfer Gauge, is used exclusively in shock tunnels and ILPT.  At present, platinum films are sputtered on to plastic sheets which are then bonded to blades with adhesive. A recent success has been the measurement of heat transfer on the blade tip and casing of a rotor. This is the first time such measurements have been taken and it is worthwhile pointing out that the Thin Film Gauges were subjected to over 30 000 g acceleration while rotating at 10 000 rpm. The casing instrumentation was an array of such gauges and showed the peak in heat transfer as the rotor tip passes by. Such measurements are of great importance to the engine designer in this extremely high temperature environment.

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 Image: A nozzle guide vane instrumented with Thin Film Gauges

Image: Thin Film Gauges mounted on the tip of a rotor blade

Thin Film Gauges were also used in flight trails of a Rolls-Royce plc Laminar Flow Nacelle. The test aircraft is shown below and the Oxford instrumentation can be seen in as the dark rectangles on the side of the nacelle. The aim of the measurement was to determine the state of the boundary layer and to examine where the transition from laminar to turbulent flow occurred. The Oxford UTC team flew on all the flight trials.

History13Image: The laminar flow nacelle flight tests Laboratory

History15Liquid crystal section on the nacelle 

                                                                          Image: The thin film array and liquid crystal section on the nacelle

These tests were extremely successful and demonstrated that laminar flow was possible despite engine vibration and acoustic effects. Sophisticated boundary layer suction and insect removal systems were developed.

Development of liquid crystals technique and CHTT...

Liquid Crystals produce a coating which changes colour with temperature. This allows the temperature of complete surfaces to be monitored and The group has developed this technique to enable detailed heat transfer to be measured over the surface. This has been applied to the measurement of the heat transfer within cooling passages and an example for an impingement cooling system is shown in a figure on the right hand side where it can be seen that the effects of cross flow are apparent. Many geometries have been tested with the technique and this is now used in routine testing of cooling systems within Rolls-Royce plc. Again these measurements are usually of short duration whereby the hot flow is suddenly passed through the model and the transient thermal response observed.

History16Image: Liquid crystal results for impingement cooling

Another large short duration test facility is the Blowdown, Cold Heat Transfer Tunnel (CHTT). Again all the instrumentation techniques described above are employed. The tunnel runs for approximately five seconds and employs an annular cascade at 1.5 times engine scale. All engine flow parameters are simulated except for the temperature of the gas flow which is unheated. The power requirement for the latter to be accomplished is prohibitive and this is avoided by heating or cooling the test nozzle guide vane before the experiment.

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Image: The Blowdown Cold Heat Transfer Tunnel CHTT

The work in hypersonics led to the development in instrumentation which was applied to the research needed in gas turbines. This activity led to the establishment of the UTC supported by Rolls-Royce plc, and the further extension of measurement techniques and testing methods. Interestingly, the process has turned full circle in that these methods are now aiding recent tests on hypersonic propulsion. In the Hyshot programme (supported by QinetiQ [formerly DERA], UK; NASA, USA; and the Universities of Queensland, Gottingen, and Oxford) a Terrior-Orion, two stage, rocket was launched to ~350 km altitude to conduct Scramjet tests as it re-entered the earth's atmosphere between 30 and 20 km altitude.

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Film cooling on the pressure surface of a NGV & A nozzle guide vane with film cooling instrumented with Thin Film Gauges

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The Orion rocket with Scramjet intake being tested in the Oxford Gun Tunnel