Platinum Thin Film Sensors Research Articles

Experimental investigation of blunt cone model at hypersonic Mach number 7.25

Experiments were carried out in hypersonic shock tunnel in Defence Research and Directorate Laboratory at hypersonic Mach number of 7.25 using an 11.37° apex-angle blunt cone model. Heat flux measurement was carried out on cone model at different angles of attack with angle of rotation ϕ = 0° to 360° in steps of 45° with vacuum sputtered platinum thin film sensors. The measured experimental value of heat transfer data at stagnation point was compared with theoretical value estimated Fay and Riddell correlation. As angle of rotation was increased from ϕ = 0° to ϕ = 180°, the shock wave became closer to model surface due to high density ratio across the shock wave and consequently heat transfer rate became higher.

Attenuation of pulsation and oscillation using a disk at mid-section of spiked blunt body

The two most important modes of flow instability are observed on a flat-faced cylinder fitted with a spike, namely, pulsation and oscillation. A new technique is proposed in this article to attenuate both pressure and aerothermal fluctuations over the cylinder by using a circular disk at the mid-length of the sharp-tipped spike, which splits the separation region in front of the cylinder. Shock tunnel experiments are carried out at a free stream Mach number of M∞ = 5.7 and a Reynolds number of RD = 0.5 × 106 (based on the cylinder diameter, D). Aeroheating is measured using platinum thin film sensors painted over the front face of the cylinder. It is shown that the flow pulsation can be totally mitigated for the ratio of spike length to diameter (L/D = 1.0) by using a disk of diameter d/D = 28% at the mid-section of the spike, and the oscillation flow is suppressed using the same disk diameter with L/D = 1.5. This phenomenon is well evident from the measured heat transfer and schlieren data. Besides, a similar analysis showed that the flow fluctuation over an aerospike mounted on a hemispherical blunt body can be diminished with the use of double-aerospike, which, in turn, decreases the heat flux peak in the proximity of the reattachment. This is an effective means of flow fluctuation mitigation and presents to be a good thermal protection for the fore body.

Transient heat transfer measurements on pulsating and oscillating flows in a shock tunnel

Flow field over high-speed vehicles can be changed drastically with the addition of a spike. These spiked bodies are associated with pulsation and oscillation unsteady flow phenomena on a spiked-body configuration. The flow separation leads to fluctuations in pressure and heat transfer of high amplitude and frequency. An investigation is made in this study, to measure the heat flux using platinum thin film sensors for these two unsteady flow characteristics, which would provide additional insights and may lead to better understanding of such type of flows. Experiments are carried out on a sharp-tipped spike attached to a flat face cylinder in a shock tunnel operating at Mach 5.7. Provisions are made to vary the spike length to diameter ratio (L/D), ranging from L/D = 0.75, 1, 1.25 and 1.5 for current investigation. The measured heat transfer varied from 100 W/cm2 to 10 W/cm2 for a pulsation case (L/D = 0.75) and whereas for the oscillation case (except for the corner gauges) the sensors indicate a heat transfer variation between 50 W/cm2 to 5 W/cm2. In additions, the corner gauge shows a heat transfer of around 120 W/cm2 to 10 W/cm2. This indicates the region of shock-shock interaction. The results from schlieren technique, used for visualization of the flow field is compliments the quantitative results.

Effects of Angle of Attack and Bluntness on Heating Rate Distribution of Blunt Models at Hypersonic Speeds

The effects of nose radius on stagnation and surface heat transfer rate along the surface are addressed in this research paper. Experiments are carried out in hypersonic shock tunnel, at hypersonic Mach number of 6.56 for 11.38° apex angle blunt cone with nose radius of 0.2R, base radius of R. Similarly, experiments are carried out at Mach 7.32 for 13.87° apex angle blunt cone models with nose radius of 0.18R′, base radius of R′. Test is performed at stagnation enthalpy of 1.4 and 2 MJ/kg with effective test time of 3.5 ms. Convective heat transfer measurements have been carried out on the test model at two different angles of attack, namely 0° and 5° with angle of rotation of 0°, 90°,180° with platinum thin film sensors. ANSYS-Fluent used to simulate the flow over the blunt models at different Mach numbers. The measured shock standoff distance from Schlieren visualization images compared with theory and computational fluid dynamic study for both configurations. The measured stagnation heating value is compared with theoretical value estimated using Fay-Riddell expression and numerical simulation. The measured heat transfer rate is higher for configuration 1 than configuration 2. The increases in heat transfer rate is due higher density ratio across the shock wave and the reduced shock layer thickness. The measured shock layer thickness is 2.06 mm for Mach 6.56 and 3.45 mm for Mach 7.32. The heat transfer rate is higher for Mach 6.56 as compared to Mach 7.32.

Experimental study of forward-facing cavity with energy deposition in hypersonic flow conditions

Controlling nose surface peak heat fluxes is crucial to the design of hypersonic vehicles. In this study, we report a novel technique of convective heat flux reduction on the nose surface of a spherically blunted cone by employing a forward-facing cavity combined with heat energy deposition inside the cavity. The heat deposition is achieved by the exothermic reaction of a chromium film coated on the cavity surface. The experiments are performed in hypersonic shock tunnels using air as the test gas at free stream stagnation enthalpy conditions of 2.2 ± 0.08 MJ/kg (H1), 3.2 ± 0.018 MJ/kg (H2), and 5.4 ± 0.02 MJ/kg (H3), for a geometry of cavity length to diameter ratio of 1. Schlieren images of the flow are captured using a high-speed camera and a high-power pulsed diode laser light source. The surface heat flux measurements were performed using calibrated platinum thin film sensors. We observed that the heat deposition altered the cavity flow field significantly by lowering the flow oscillation frequency and increasing the shock standoff distances with higher oscillation amplitudes. The overall surface mean heat flux reduction is increased from ≈13% to ≈49% compared to the blunt body geometry, whose nose radius is 30 mm and enhanced with reference to the cavity without heat deposition from ≈15% to ≈35%. Chromium film surface reactions are studied using X-ray Photoelectron spectroscopy, and the results confirm that the exothermic surface reactions of the Cr thin film are attributed to the formation of oxides and nitrides of Cr.

Investigation of the separated region ahead of three-dimensional protuberances on plates and cones in hypersonic flows with laminar boundary layers

Heat transfer rate and pressure measurements were made upstream of surface protuberances on a flat plate and a sharp cone subjected to hypersonic flow in a conventional shock tunnel. Heat flux was measured using platinum thin-film sensors deposited on macor substrate and the pressure measurements were made using fast acting piezoelectric sensors. A distinctive hot spot with highest heat flux was obtained near the foot of the protuberance due to heavy vortex activity in the recirculating region. Schlieren flow visualization was used to capture the shock structures and the separation distance ahead of the protrusions was quantitatively measured for varying protuberance heights. A computational analysis was conducted on the flat plate model using commercial computational fluid dynamics software and the obtained trends of heat flux and pressure were compared with the experimental observation. Experiments were also conducted by physically disturbing the laminar boundary layer to check its effect on the magnitude of the hot spot heat flux. In addition to air, argon was also used as test gas so that the Reynolds number can be varied.

Hypersonic interference heating on cones with short three-dimensional protuberances

Heat fluxes around short, three-dimensional protuberances on sharp and blunt cones in hypersonic flow were experimentally measured using platinum thin-film sensors deposited on macor inserts. A parametric study of different protrusion geometries and flow conditions were conducted. Excessive heating was observed at locations near the protrusion where increased vorticity is expected, with the hottest spot being presented at the foot of the protuberance immediately upstream of it. If left unchecked, these hot spots could prove detrimental to hypersonic flight vehicles. Z-type schlieren technique was used to visualize the flow features qualitatively. New correlations to predict the heat flux at the hot spot have been proposed.

Modelling of Temperature Coefficient of Resistance of a Thin Film RTD Towards Exhaust Gas Measurement Applications

Abstract Current research in the automotive industry sector focuses on the application of platinum thin film sensors for exhaust temperature measurement. The prime intention of this paper is to pioneer the design and development of Platinum/Rhodium (Pt/Rh) sensors for exhaust gas temperature measurement. The developed sensors were able to endure harsh temperature environments (up to 950° C). In addition, the Pt/Rh sensors resistivity response to temperature increase was described by a second order polynomial characteristic equation. This equation can be stored in the electronics incorporated in the engine management system. Therefore, the resistance reading of the Pt/Rh sensor in the exhaust system can be decoded as a temperature measurement.

Experimental Investigation of the Effects of Aerospike Geometry on Aerodynamic Drag and Heat Transfer Rates for a Blunt Body Configuration at Hypersonic Mach Numbers

The effects of aerospike geometry on the drag reduction and heat transfer rates for a large-angle blunt cone flying at hypersonic Mach numbers are investigated in a hypersonic shock tunnel. Two spike geometries are considered. The first is a plain spike with a conical tip and the second is a telescopic aerospike fitted with discs of decreasing diameter in the direction opposite to the flow direction. These aerospikes are fitted to a 120° apex-angle blunt cone and results are investigated at free stream Mach numbers of 5.75 and 7.9 for different angles of attack. The aerodynamic forces are measured using an accelerometer-based force balance system and the heat transfer rates are measured using platinum thin film sensors. It is found that the telescopic aerospike has better drag reduction performance at angles of attack beyond 2° while the performance of the plain aerospike is better for angles of attack closer to zero degrees.

Platinum resistive film CO sensor without selective layer

Response in resistance of platinum thin film sensors were studied in the presence of carbon monoxide under constant operating current. Both oscillatory and non-oscillatory changes in resistance were examined. Oscillations in resistances were found in the CO concentration range from 50 to 1000 ppm at operating temperatures between 80 and 150 °C. Both the amplitude and period increased with the increasing CO concentration. In non-oscillatory region, two different responses were observed, one of which the resistance of the sensor increased with increasing CO concentration and the other, resistance slightly decreased. It is believed that oscillations occurred between two branches of a Langmuir–Hinshelwood reaction mechanism. Above the upper branch of the oscillatory region, the resistance of the Pt films increases quasi linearly with the increase of CO concentration. Conversely, it decreases slightly below the lower branch.

Heraeus Sensor Technology launched as new name for platinum thin-film sensors business

Heraeus Sensor Technology launched as new name for platinum thin-film sensors business

衝撃波管を用いた円錐上での正常反射からマッハ反射への遷移(J12-1 流体情報学1(実験と計算の融合研究),J12 流体情報学と融合研究)

Shock wave reflections over large apex angle cones have been investigated in a diaphragm-less shock tube with an intention of studying the phenomenon of transition from regular to Mach reflection over the cone surface. It is believed that over large angle cones with semi-apex angles ranging from 43 to 48 degrees, the reflection of an incident shock wave at a moderate Mach number of 2.38 may undergo a transition from regular to Mach over the cone surface due to viscous effects. The experiments are carried out with two test gases, nitrogen and argon. Flow visualization experiments are planned to study this phenomenon in detail over cones of different apex angles in the above range. Measurement of surface heat flux using platinum thin film sensors has also be carried out in order to analyze the heat transfer history over the cone surface during these reflection phenomena. The experimental results have been compared with the numerical results obtained from a commercial N-S solver Fluent (Version 6.1, Fluent Inc.). The experimental results obtained in this study are expected to be useful in validating CFD codes.

Studies on the Effects of Test Gas on the Flow Field around Large Angle Blunt Cone Flying at Hypersonic Mach Number.

The effect of the test gas on the flow field around a 120degrees apex angle blunt cone has been investigated in a shock tunnel at a nominal Mach number of 5.75. The shock standoff distance around the blunt cone was measured by an electrical discharge technique using both carbon dioxide and air as test gases. The forebody laminar convective heat transfer to the blunt cone was measured with platinum thin-film sensors in both air and carbon dioxide environments. An increase of 10 to 15% in the measured heat transfer values was observed with carbon dioxide as the test gas in comparison to air. The measured thickness of the shock layer along the stagnation streamline was 3.57 +/- 0.17 mm in air and 3.29 +/- 0.26 mm in carbon dioxide. The computed thickness of the shock layer for air and carbon dioxide were 3.98 mm and 3.02 mm, respectively. The observed increase in the measured heat transfer rates in carbon dioxide compared to air was due to the higher density ratio across the bow shock wave and the reduced shock layer thickness.

State News

Flow field over high-speed vehicles can be changed drastically with the addition of a spike. These spiked bodies are associated with pulsation and oscillation unsteady flow phenomena on a spiked-body configuration. The flow separation leads to fluctuations in pressure and heat transfer of high amplitude and frequency. An investigation is made in this study, to measure the heat flux using platinum thin film sensors for these two unsteady flow characteristics, which would provide additional insights and may lead to better understanding of such type of flows. Experiments are carried out on a sharp-tipped spike attached to a flat face cylinder in a shock tunnel operating at Mach 5.7. Provisions are made to vary the spike length to diameter ratio (L/D), ranging from L/D = 0.75, 1, 1.25 and 1.5 for current investigation. The measured heat transfer varied from 100 W/cm2 to 10 W/cm2 for a pulsation case (L/D = 0.75) and whereas for the oscillation case (except for the corner gauges) the sensors indicate a heat transfer variation between 50 W/cm2 to 5 W/cm2. In additions, the corner gauge shows a heat transfer of around 120 W/cm2 to 10 W/cm2. This indicates the region of shock-shock interaction. The results from schlieren technique, used for visualization of the flow field is compliments the quantitative results.