Endwall Heat Transfer and Cooling Performance of a Transonic Turbine Vane with Upstream Injection Flow

Detailed experimental and numerical studies on endwall heat transfer and cooling performance with coolant injection flow through upstream discrete holes is presented in this paper. High resolution heat transfer coefficient (HTC) and adiabatic film cooling effectiveness values were measured using a transient infrared thermography technique on an axisymmetric contoured endwall. The tests were performed in a transonic linear cascade blow-down wind tunnel facility. Conditions were representative of a land-based power generation turbine with exit Mach number of 0.85 corresponding to exit Reynolds number of 1.5 × 106, based on exit condition and axial chord length. A high turbulence level of 16% with an integral length scale of 3.6%P was generated using inlet turbulence grid to reproduce the typical turbulence conditions in real turbine. Low temperature air was used to simulate the typical coolant-to-mainstream condition by controlling two parameters of the upstream coolant injection flow: mass flow rate to determine the coolant-to-mainstream blowing ratio (BR = 2.5, 3.5), and gas temperature to determine the density ratio (DR = 1.2). To highlight the interactions between the upstream coolant flow and the passage secondary flow combined with the influence on the endwall heat transfer and cooling performance, a comparison of CFD predictions to experimental results was performed by solving steady-state Reynolds-Averaged Navier-Stokes (RANS) using the commercial CFD solver ANSYS Fluent V.15.

Analisa kinerja cooling tower tipe counter flow induced draft

Paper ini bertujuan untuk memberikan wawasan tentang kinerja menara pendingin. Menara pendingin yang diamati adalah menara pendingin tipe counterflow induced draft. Analisa dilakukan untuk mengetahui pengaruh temperatur lingkungan terhadap kinerja menara pendingin, kerugian energi dan alternatif perbaikan. Metode yang digunakan adalah pengumpulan data operasional, pengolahan data dan selanjutnya menganalisa hasil pengolahan data. Parameter kinerja menara pendingin yang dicari meliputi range, approach, efektifitas, kapasitas pendinginan. Kerugian yang terjadi selama operasional menara pendingin seperti kerugian penguapan, blow down dan drift juga dihitung. Hasil analisa kinerja menara pendingin menyatakan bahwa efektivitas menara pendingin tinggi karena laju penguapan yang tinggi dan lebih sedikit kehilangan karena penguapan, blowdown, dan drift. Laju penguapan yang tinggi dapat terjadi karena jumlah uap air yang rendah di udara dan menunjukkan kelembaban relatif yang rendah, sehingga penurunan temperatur wet bulb akan besar.

Optimal Design of Electrically Fed Hybrid Mars Ascent Vehicle

The optimal design of the propulsion system for a potential Mars Ascent Vehicle is analyzed, in the context of the Mars Sample Return Mission. The Mars Ascent Vehicle has to perform an initial ascent phase from the surface and then circularize into a 170 km orbit. A two-stage launcher is taken into account: the same hybrid rocket engine is considered for both stages in order to limit the development costs. A cluster of two, three or four engines is employed in the first stage, whereas a single engine is always used in the second stage. Concerning the feeding system, three alternatives are taken into consideration, namely a blow down, a regulated and an electric turbo-pump feed system. The latter employs an electric motor to drive the oxidizer turbopump, whereas the power is supplied to the motor by lithium batteries. All the design options resulted in viable Mars Ascent Vehicle configurations (payloads are in the range of 70–100 kg), making the hybrid alternative worth considering for the sample return mission. The use of an electric turbo-pump feed system determines the highest vehicle performance with an estimated 10–25% payload gain with respect to gas-pressure feed systems.

Birational geometry of moduli spaces of perverse coherent sheaves on blow-ups

In order to study the wall-crossing formula of Donaldson type invariants on the blown-up plane, Nakajima–Yoshioka constructed a sequence of blow-up/blow-down diagrams connecting the moduli space of torsion free framed sheaves on projective plane, and that on its blow-up. In this paper, we prove that Nakajima–Yoshioka’s diagram realizes the minimal model program. Furthermore, we obtain a fully-faithful embedding between the derived categories of these moduli spaces.

THERMAL AND OVERPRESSURE HAZARDS MODELLING AND SIMULATION: A CASE STUDY OF REFINERY FIRED HEATER

Crude oil-fired heaters are associated with considerable fire and explosion hazards. The heaters present higher risks at later operational life due to ageing, wear and obsolescence. It is therefore important to re-evaluate such heaters to determine the adequacy or otherwise of the existing safeguards. This paper presents results of studies on hazard levels in aged fired heaters through quantitative consequence modeling method. A number of credible failure scenarios were considered. In particular, characteristics of potential jet fires due to Liquefied Petroleum Gas (LPG) leaks from hole sizes: 15, 30, 50 and 100 mm were investigated. For the 100 mm hole size, it was found that thermal radiation level of up to 37.5 kW/m2 could be experienced within 25 m radius of the heater, which is enough to affect nearby operators severely and could also adversely affect critical pieces of equipment around. Fireball potential with peak thermal density of about 12.5 kW/m2 was also observed within 2 m radius. For the 100 mm hole size, lower flammability limit of the fuel could be attained within 16 m downwind which poses flash fire risks. Overpressures of 1.02, 1.14 and 1.21 bar could be experienced at 30, 6 and 4 m respectively away from the fired heater which could result in partial demolition of structures that are within the radius.Overall, the results indicate that the risk profile is very sensitive to leak sizes, operating and atmospheric conditions as well as the fuel quantity being held, among others. For the chosen case study, higher integrity protection layers, in form of safety instrumented systems, relief, blow down and alarm systems, are recommended. Keywords: Downwind distance; Consequence modeling; Radiation intensity; Flame length; Overpressure; Toxicity; Liquefied Petroleum Gas.

Upstream Film Cooling on the Contoured Endwall of a Transonic Turbine Vane in an Annular Cascade

The effects of mainstream flow velocity, density ratio (DR), and coolant-to-mainstream mass flow ratio (MFR) on a vane endwall in a transonic, annular cascade were investigated. A blow down facility consisting of five vanes was used. The film cooling effectiveness was measured using binary pressure-sensitive paint (BPSP). The mainstream flow was set using isentropic exit Mach numbers of 0.7 and 0.9. The coolant-to-mainstream density ratio varied from 1.0 to 2.0. The coolant-to- mainstream MFR varied from 0.75% to 1.25%. The endwall was cooled by 18 discrete holes located upstream of the vane passage to provide cooling to the upstream half of the endwall. Due to the curvature of the vane endwall, the upstream holes provided uniform coverage entering the endwall passage. The coverage was effective leading to the throat of the passage, where the downstream holes could provide additional protection. Increasing the coolant flowrate increased the effectiveness provided by the film cooling holes. Increasing the density of the coolant increases the effectiveness on the endwall while enhancing the lateral spread of the coolant. Finally, increasing the velocity of the mainstream while holding the MFR constant also yields increased protection on the endwall. Over the range of flow conditions considered in this study, the binary pressure-sensitive paint proved to be a valuable tool for obtaining detailed pressure and film effectiveness distributions.