Giuseppe Franchini

The Effect of an Upstream Ramp on Cylindrical and Fan-Shaped Hole Film Cooling: Part II — Adiabatic Effectiveness Results

The present companion papers report the results of an experimental investigation on possible beneficial effects of an upstream ramp on discrete hole film cooling. This analysis was carried out on a flat plate model. Two hole geometries have been considered: cylindrical and fan-shaped with conical expanded exit. To compare different cooling schemes, a combined aero-thermal analysis was performed. Tests have been carried out at low speed and low inlet turbulence intensity level, with blowing ratios varied in the range 0.3–1.0. Part I was focused on the aerodynamic analysis: it has been shown that the introduction of a ramp is always detrimental, as it gives a strong loss increase (+5%). Fan-shaped hole was instead the best solution, as it gives losses comparable with the cylindrical one, reduced turbulence mixing and jet dilution. Part II of this paper faces the thermal analysis. The thermal behaviour of the cooled surface has been analysed using the wide banded TLC’s technique, so to obtain adiabatic effectiveness distributions. Additional air temperature measurements have been carried out by traversing a thermocouple downstream of injection holes. The upstream ramp was found to provide a thermal protection improvement (+40%) only at low blowing rate in the case of cylindrical hole. The application of a ramp upstream of a fanshaped hole was instead detrimental for all blowing conditions. The fan shaped hole geometry with no ramp resulted to be the best solution also in terms of adiabatic effectiveness (50% higher than the cylindrical one at BR = 0.5).Copyright

The Effect of an Upstream Ramp on Cylindrical and Fan-Shaped Hole Film Cooling: Part I — Aerodynamic Results

The present companion papers report the results of an experimental investigation on possible beneficial effects of an upstream ramp on discrete hole film cooling. This analysis was carried out on a flat plate model. Two hole geometries have been considered: cylindrical and fan-shaped with conical expanded exit. To compare different cooling schemes, a combined aero-thermal analysis was performed. Tests have been carried out at low speed and low inlet turbulence intensity level, with blowing ratios varied in the range 0.3–1.0. The aerodynamic investigation has been performed through the measurements of discharge coefficients and detailed flow field measurements. Surveys were carried out by traversing a flattened Pitot tube. Additional turbulence measurements have been carried out by means of hot wire traverses. All this information, together with the adiabatic effectiveness results presented in Part II of this paper, allowed drawing a comprehensive picture of the complex aero-thermal flow field in the injection region. The upstream ramp provided a moderate improvement in the case of cylindrical holes, as it allows the coolant to diffuse someway, before interacting with the mainflow, but it produced also a significant increase of aerodynamic losses. The fan shaped hole geometry without the ramp resulted to be the best solution, as it provides a coolant injection with a good lateral spreading and a low turbulence level.Copyright

Endwall Film Cooling Through Fan-Shaped Holes With Different Area Ratios

The present paper reports on the aero-thermal performance of a nozzle vane cascade, with film cooled endwalls. The coolant is injected through four rows of cylindrical holes with conical expanded exits. Two endwall geometries with different area ratios have been compared. Tests have been carried out at low speed (M = 0.2), with coolant to mainstream mass flow ratio varied in the range 0.5–2.5%. Secondary flow assessment has been performed through 3D aerodynamic measurements, by means of a miniaturized 5-hole probe. Adiabatic effectiveness distributions have been determined by using the wide banded thermochromic liquid crystals (TLC) technique. For both configurations and for all the blowing conditions, the coolant share among the four rows has been determined. The aerothermal performance of the cooled vane have been analyzed on the basis of secondary flow effects and laterally averaged effectiveness distributions; this analysis was carried out for different coolant mass flow ratios. It was found that the smaller area ratio provides better results in terms of 3D losses and secondary flow effects; the reason is that the higher momentum of the coolant flow is going to better reduce the secondary flow development. The increase of the fan-shaped hole area ratio gives rise to a better coolant lateral spreading, but appreciable improvements of the adiabatic effectiveness were detected only in some regions and for large injection rates.Copyright

Fan-Shaped Hole Effects on the Aero-Thermal Performance of a Film Cooled Endwall

The present paper investigates the effects of a fan-shaped hole endwall cooling geometry on the aero-thermal performance of a nozzle vane cascade. Two endwall cooling geometries with four rows of holes were tested, for different mass flow rate ratios: the first configuration is made of cylindrical holes, whereas the second one features conical expanded exits and a reduced number of holes. The experimental analysis is mainly focused on the variations of secondary flow phenomena related to different injection rates, as they have a strong relationship with the film cooling effectiveness. Secondary flow assessment was performed through downstream 3D aerodynamic measurements, by means of a miniaturized 5-hole probe. The results show that at high injection rates, the passage vortex and the 3D effects tend to become weaker, leading to a strong reduction of the endwall cross flow and to a more uniform flow in spanwise direction. This is of course obtained at the expense of a significant increase of losses. The thermal behavior was then investigated through the analysis of adiabatic effectiveness distributions on the two endwall configurations. The wide banded TLC’s technique was used to determine the adiabatic wall temperature. Using the measured distributions of film cooling adiabatic effectiveness, the interaction between the secondary flow vortices and the cooling jets can be followed in good detail all over the endwall surface. Fan-shaped holes have been shown to perform better than cylindrical ones: at low injection rates, the cooling performance is increased only in the front part of the vane passage. A larger improvement of cooling coverage all over the endwall is attained with a larger mass flow rate, about 1.5% of core flow, without a substantial increase of the aerodynamic losses.Copyright

Aero-Thermal Performance of a Rotor Blade Cascade With Stator-Rotor Seal Purge Flow

The present paper investigates the effects of purge flow from a stator-rotor seal gap on the aerodynamic and thermal performance of a rotor blade cascade. Particular attention is paid to thermal results in the leading edge area that is typically difficult to protect. Experimental tests have been performed on a seven-blade cascade of a high-pressure rotor stage of a real gas turbine at low Mach number (Ma2is = 0.3). To simulate the rotational effect in a linear cascade environment, a number of inclined fins have been installed inside the stator-rotor gap, making the coolant flow to exit with the right tangential velocity component. Tests have been carried out at different blowing conditions, with mass flow rate ratios up to 2.0%. Aerodynamic effects of purge flow on secondary flow structures were surveyed by traversing a 5-hole miniaturized pressure probe in a plane 0.08cax downstream of the trailing edge. Film cooling effectiveness distributions on the end wall platform were obtained by using Thermochromic Liquid Crystals technique. Results allowed to investigate the effect of purge flow injection from the upstream gap on the secondary flows development and on the thermal protection capability. Purge flow injection of 1.0% reduced secondary flow losses and was found to effectively protect the front end wall region, up to about 0.5cax downstream of the leading edge. Increasing the purge flow up to 1.5%–2.0% provided a better thermal protection not only stream wise, but also in the region close to the leading edge because of the weakened washing activity of the horseshoe vortex.Copyright

Modeling, construction and monitoring of a Plus-Energy building in Dubai

This work presents the performance analysis of the very first Energy+ building in Dubai certified by the German Passive House Institute. The analysis is presented as comparison between numerical predictions and the first available monitored data. Trnsys is the software used to create the energy model, including both thermal envelope and HVAC system. The use of highly insulating materials, together with a design aimed to reduce the solar heat gains, allows for minimizing cooling loads. A 40 kW PV field, coupled to a 25 kWh battery storage and to a high-efficiency air-cooled electric chiller, fulfills the electric and cooling demand, making the building energy-autonomous. The study demonstrates the high accuracy of the energy model, able to predict precisely the building cooling loads, the energy production and the cooling system performance. The Energy+ building, inaugurated in November 2016, is a pioneering pilot-project and it represents an advance in the field of sustainable construction for all Arabic area.

Influence of Coolant Flow Rate on Aero-Thermal Performance of a Rotor Blade Cascade With Endwall Film Cooling

This paper investigates the influence of coolant injection on the aerodynamic and thermal performance of a rotor blade cascade with endwall film cooling. A 7 blade cascade of a high-pressure-rotor stage of a real gas turbine has been tested in a low speed wind tunnel for linear cascades. Coolant is injected through ten cylindrical holes distributed along the blade pressure side. Tests have been preliminarily carried out at low Mach number (Ma2is=0.3). Coolant-to-mainstream mass flow ratio has been varied in a range of values corresponding to inlet blowing ratios M1 = 0 – 4.0. Secondary flows have been surveyed by traversing a 5-hole miniaturized aerodynamic probe in two downstream planes. Local and overall mixed-out secondary loss coefficient and vorticity distributions have been calculated from measured data. The thermal behaviour has been also analysed by using Thermochromic Liquid Crystals technique, so to obtain film cooling effectiveness distributions. All this information, including overall loss production for variable injection conditions, allow to draw a comprehensive picture of the aero-thermal flow field in the endwall region of a high pressure rotor blade cascade.

Effects of Trenched Holes on Film Cooling of a Contoured Endwall Nozzle Vane

The present paper investigates the effects of the application of trenched holes in the front part of a contoured film cooled endwall. Two trench configurations were tested, changing the trench depth. Tests have been carried out at low speed (M2is = 0.2) and low inlet turbulence intensity level, with coolant mass flow rate ratio varied within the 0.5–2.5% range. Pressure probe traverses were performed downstream of the vane trailing edge to show the secondary flow field modifications and to evaluate trench additional losses. Endwall distributions of film cooling effectiveness have been obtained by TLC technique. For each injection condition energy loss coefficient and film cooling effectiveness distributions were analyzed and compared to the ones obtained from rows of cylindrical holes. Laterally and area averaged effectiveness as well as pitch and mass averaged kinetic energy loss coefficient were computed to enlighten any change induced by the introduction of trenched holes. A uniform and high thermal coverage was obtained in the region just downstream of the trench, but it quickly decayed, because of enforced mixing of coolant with main-flow. Compared to the cylindrical hole configuration, trenches are able to provide a higher global cooling effectiveness, but a larger amount of coolant injection is required. The introduction of both trenches is responsible for a secondary thermodynamic loss increase of about 0.7%, at low coolant injection rates. Increasing blowing rates, the additional loss is going to vanish.Copyright

Endwall Film Cooling Effects on Secondary Flows in a Contoured Endwall Nozzle Vane

The present paper investigates the effects of endwall injection of cooling flow on the aerodynamic performance of a nozzle vane cascade with endwall contouring. Tests have been performed on a 7 vane cascade with a geometry typical of a real gas turbine nozzle vane. The cooling scheme consists of four rows of cylindrical holes. The same cooling scheme, applied to a flat endwall, was already investigated by the authors. Tests have been carried out at low speed (M2is = 0.2) with a low inlet turbulence intensity level (1.0%) and with a coolant to mainstream mass flow ratio varied in the range from zero (solid endwall) to 2.5%. Energy loss coefficient, secondary vorticity and outlet angle distributions were computed from 5-hole probe measured data. Contoured endwall results, with and without film cooling, were compared to planar endwall data. Endwall contouring was responsible for a significant overall loss decrease, thanks to the reduction of both profile and planar side secondary flows losses; a loss increase on the contoured side was instead observed. Like as for the planar endwall, even for contoured endwall coolant injection modifies secondary flows, reducing their intensity, but the relevance of the changes is reduced. Nevertheless for all the tested injection conditions, secondary losses on the contoured side are always higher than in the planar case, while contoured cascade overall losses are lower. A unique minimum overall loss injection condition was found for both tested geometries, corresponding to an injected mass flow rate of about 1.0%.Copyright