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This research was conducted to determine the number of companies listed on the IDX that had been carried out and the effects presented in the application of tax avoidance. From the study results, there are variables of board gender diversity, board diligence, and board size that have no significant effect, and variables of financial distress and tax risk management bring significant influences between the dependent and independent variables, which are supported by moderating variables. So, the result suggests that companies implementing tax risk management can affect tax avoidance. ABSTRAK Penelitian bertujuan untuk mengetahui dan menganalisis dampak yang ditimbulkan oleh penerapan penghindaran pajak. Dari hasil penelitian, terdapat variabel board gender diversity, board diligence, dan board size yang tidak berpengaruh signifikan, serta variabel financial distress dan tax risk management berpengaruh signifikan antara variabel dependen dan independen yang didukung oleh variabel moderasi. Hasil penelitian menunjukkan bahwa perusahaan yang menerapkan manajemen risiko pajak dapat mempengaruhi penghindaran pajak.

Era digital disruption mengimbas kepada ketidakstabilan bisnis di berbagai macam sektor termasuk sektor industri baja. Banyak perusahan-perusahaan yang memikirkan ide yang out of the box agar selamat dari dampak digital disruption, bahkan beberapa perusahaan lebih sukses dalam memajukan bisnisnya. Bisnis industri baja menghadapi tantangan yang berat untuk melakukan transformasi digital antara lain di area supply chain, penjualan, produksi, inventory, delivery dan transaksi keuangan. Suatu hal tidak mustahil bila bisnis industri baja dapat terintegrasi melalui online marketplace, dengan bobot material yang berton-ton dan melibatkan transaksi yang milliaran. Pada penelitian ini perancangan model bisnis digambarkan dengan menggunakan Bisnis Model Canvas (BMC) dan elemen-elemen yang terlibat diintegrasikan menggunakan Archimet Model Tools. Hasil permodelan dengan mengintegrasikan elemen bisnis, elemen aplikasi, elemen data dan teknologi diharapkan perusahaan bisa membangun marketplace yang efektif, efisien dan menciptakan customer experience yang baik sebagai value proposition. Berdasarkan wawancara dengan ahli yang berpengalaman pada industri baja dan bisnis marketplace, studi ini menitikberatkan kepada sedikitnya 4 (empat) sumber pendapatan yaitu: penjualan produk baja, biaya berlangganan seller member, sharing revenue logistic tracking, sharing revenue payment gateway.

Location and geometry optimisations of Straight Plate Upstream Deflector (SPUD) for performance enhancement of a three-straightbladed Vertical Axis Wind Turbine (VAWT) are carried out at three regimes of tip speed ratios (TSRs). Results analysis reveals that SPUD location has significant effect on the power coefficient ( Cp) increment of VAWT. Placing two SPUDs both upward and downward in upstream of VAWT can achieve the highest Cp improvement at all regimes of TSRs. Overall, placing SPUD in upstream of VAWT can improve the Cp value at all regimes of TSRs, but the percentage of improvement can vary. The largest Cp improvement of 126.7% is achieved at low regime of TSRs, while at the medium and high regimes of TSRs, Cp improvements decrease to 52.7% and 52.5%, respectively. Increasing the width of SPUD can increase the average VAWT Cp improvement by 2.83% at all regimes of TSRs.

Penelitian ini bertujuan untuk meneliti pengaruh fraud diamond terhadap financial statement fraud dan peran dari innovation strategy dalam memoderasi pengaruh fraud diamond terhadap financial statement fraud. Penelitian dilakukan pada perusahaan yang terdaftar dalam Bursa Efek Indonesia menggunakan teknik purposive sampling, adapun alat analisis yang digunakan adalah analisis regresi logistik dan analisis regresi moderasi. Sampel didapatkan dari 89 perusahaan yang terdaftar pada tahun 2017-2021. Hasil penelitian menunjukkan bahwa komponen dari fraud diamond yang berpengaruh signifikan hanya pada variabel DER, adapun hasil penelitian terbukti bahwa innovation strategy memoderasi pengaruh antara fraud diamond terhadap financial statement fraud., This study aims to examine the effect of fraud diamond on financial statement fraud and the role of innovation strategy in moderating the effect of fraud diamond on financial statement fraud. The research was conducted on companies listed on the Indonesia Stock Exchange using purposive sampling technique, while the analytical tools used were logistic regression analysis and moderating regression analysis. Samples were obtained from 89 companies registered from 2017-2021. The results showed that the component of the fraud diamond had a significant effect only on the DER variable, while the results of the study proved that the innovation strategy moderated the effect of the fraud diamond on the financial statement fraud.

Bisnis keluarga berkembang pesat dan menjadi bisnis yang dominan di Indonesia. Semakin penting bisnis keluarga pada perekonomian Indonesia menjadikan bisnis keluarga menjadi sorotan di dunia ekonomi. Pada perusahaan keluarga terdapat keunikan dimana mayoritas kepemilikan saham dimiliki oleh anggota keluarga, sehingga dapat menyebabkan konflik keagenan yang mengurangi transparansi dalam pengungkapan informasi. Penelitian ini bertujuan meneliti pengaruh tata kelola perusahaan terhadap pengungkapan sukarela pada perusahaan keluarga. Variabel tata kelola perusahaan yang digunakan dalam penelitian adalah kepemilikan institusional, kepemilikan asing, kepemilikan manajerial, ukuran dewan, komisaris independen, dan audit komite. Sampel dari penelitian ini menggunakan 125 perusahaan keluarga yang terdaftar di Bursa Efek Indonesia pada periode 2010- 2014 yang dipilih dengan menggunakan metode purposive sampling. Penelitian ini diolah menggunakan program Eviews 7 serta Statistical Package for the Social Sciences (SPSS) 21. Data yang digunakan dalam penelitian ini adalah laporan tahunan dari setiap perusahaan yang dipublikasikan (www.idx.co.id). Data yang telah diperoleh akan diuji dengan pengujian regresi panel. Dari hasil penelitian ditemukan bahwa pada perusahaan keluarga, kepemilikan selain keluarga seperti kepemilikan institusional, kepemilikan asing dan kepemilikan manajerial tidak berpengaruh signifikan terhadap pengungkapan sukarela. Ukuran dewan, komite audit, ukuran perusahaan, dan profitabilitas memiliki pengaruh signifikan positif terhadap pengungkapan sukarela. Komisaris independent dan leverage tidak memiliki pengaruh signifikan terhadap pengungkapan sukarela. Kesimpulan dapat ditarik bahwa dalam perusahaan keluarga, kepemilikan selain kepemilikan keluarga tidak memiliki pengaruh signifikan terhadap pengungkapan informasi secara sukarela

Tujuan penelitian ini untuk menguji independensi komite audit, rapat komite audit, ukuran komite audit, keahlian komite audit, leverage, jumlah anak perusahaan, persentase anak perusahaan asing, persentase direktur non eksekutif, keahlian dewan direksi, board size, dan growth terhadap penyajian kembali laporan keuangan, dengan memanfaatkan data perusahaan yang terdaftar di Bursa Efek Indonesia (BEI). Penelitian ini memakai metode purposive sampling yang memiliki beberapa kriteria dalam menggumpulkan data yang terdaftar pada BEI dari tahun 2014-2018. Data sekunder yang digunakan berasal dari laporan keuangan perusahaan yang sudah dipublikasikan di BEI dengan pengujian metode uji regresi logistik. Hasil penelitian yang diperoleh dapat disimpulkan adanya pengaruh antara ukuran komite audit, jumlah anak perusahaan, persentase direktur non eksekutif dengan penyajian kembali laporan keuangan. Sedangkan pada variabel independensi komite audit, rapat komite audit, keahlian komite audit, leverage, persentase anak perusahaan asing, keahlian dewan direksi, board size, dan growth tidak memiliki pengaruh pada penyajian kembali laporan keuangan. ********************************************************************** The purpose of this study is to examine the independence of the audit committee, audit committee meetings, audit committee size, audit committee expertise, leverage, number of subsidiaries, percentage of foreign subsidiaries, percentage of non-executive directors, board of director expertise, board size, and growth on the restatement of financial statements by utilizing company data listed on the Indonesia Stock Exchange (IDX). A purposive sampling method that has several criteria for gathering data registered on the Indonesia Stock Exchange from 2014-2018 was used in this study. The secondary data used came from the companyaamp;amp;amp;amp;amp;amp;#039;s financial statements that have been published on the IDX by testing the logistic regression test method. The concluded results are; there is an influence between the size of the audit committee, the number of subsidiaries, and the percentage of non-executive directors with the restatement of financial statements. While the audit committeeaamp;amp;amp;amp;amp;amp;#039;s independence variables, audit committee meetings, audit committee expertise, leverage, percentage of foreign subsidiaries, board of director expertise, the board size, and growth do not affect the restatement of financial statements.

Penelitian ini menafsirkan hubungan karakteristik komite audit terhadap keterlambatan audit pada perusahaan-perusahaan yang terdaftar di Bursa Efek Indonesia tahun 2014-2018 dengan penggunaan variabel independen yakni keahlian keuangan komite audit, independensi komite audit, ukuran komite audit, pertemuan komite audit, piagam komite audit, profitabilitas, ukuran perusahaan, konsentrasi kepemilikan, pergantian auditor, opini audit, koneksi politik, dan auditor spesialis industri. Sampel penelitian ini mencakup 446 dari 649 perusahaan dengan jumlah akhir 1.720 data observasi yang diperoleh. Teknik pengumpulan sampel berdasarkan metode penetapan sejumlah kriteria yang telah ditentukan. Data penelitian selanjutnya diuji melalui bantuan program SPSS 22 dan Eviews 10. Hasil dari penelitian menyimpulkan ukuran komite audit, ukuran perusahaan dan profitabilitas berpengaruh signifikan negatif, sedangkan opini audit memiliki pengaruh signifikan positif terhadap keterlambatan audit. Variabel keahlian keuangan komite audit, independensi komite audit, pertemuan komite audit, piagam komite audit, konsentrasi kepemilikan, pergantian auditor, koneksi politik, dan auditor spesialis industri tidak memiliki pengaruh signifikan terhadap keterlambatan audit.

Studi ini bertujuan untuk mengkaji pengaruh dari karakteristik audit dan karakteristik perusahaan terhadap pergantian Kantor Akuntan Publik di Indonesia. Karakteristik audit terdiri atas opini audit, keterlambatan audit, dan reputasi KAP. Karakteristik perusahaan terdiri atas ukuran perusahaan, kesulitan keuangan, pergantian manajemen, pertumbuhan perusahaan, dan kompleksitas perusahaan. Data yang dikaji dalam studi ini terdiri atas laporan tahunan perusahaan yang tercatat pada Bursa Efek Indonesia pada tahun 2014 sampai dengan 2018. Sampel diambil dengan memanfaatkan metode purposive sampling dan yang terpilih sebanyak 439 perusahaan (2.131 data).

This article provides a comprehensive review about passive flow control devices (PFCDs) implemented in lift-type vertical axis wind turbine (LVAWT), focusing on the underlying flow physics mechanisms and to what extents they can improve the LVAWT performance. In addition, some novel concepts that can be potentially implemented in future are also presented. Based on literature review, it is observed that PFCDs can enhance the power generation of LVAWT up to 172.73% compared with a clean LVAWT. However, this significant improvement still needs to be evaluated carefully by considering the economic feasibility aspect, because PCFDs can increase the design complexity, weight penalty and manufacturing cost of LVAWT. Furthermore, it is essential to design and evaluate the effectiveness of PFCDs using a full VAWT configuration by considering the blade rotating effects and blade-to-blade interactions. Finally, evaluation of PFCDs needs to be performed at all ranges of tip speed ratios (TSRs) operation conditions, as there are clear evidences on the correlation between LVAWT performance and different range of TSRs.

This study aims to determine the effect of corporate governance and finance on mergers and acquisitions and to use human capital efficiency as a moderating variable. This research theoretically uses the theory of corporate control. The research sample is companies that carry out merger and acquisition activities and have been listed on the IDX in 2017-2021. The analytical method used was logistic regression and moderated regression analysis (MRA). The results showed that the size of the board of directors, institutional shareholders, and foreign ownership had a significant positive effect on mergers and acquisitions. Human capital efficiency is able to moderate the relationship between institutional shareholders and cash dividends on mergers and acquisitions. Keywords: Merger and Acquisition; Corporate Governance; Human Capital Efficiency

Comparison study of unsteady Reynolds-averaged Navier-Stokes (URANS) and hybrid RANS-LES models is carried out for predicting the performance of three-straight-bladed vertical axis wind turbine operating within tip speed ratios (TSRs) ranges of (1.44–3.3). The evaluation is focused on power coefficient, moment coefficient and vortex structure generation, growth and transportation predictions. It was found that URANS turbulence modelling is sufficient for averaged power coefficient prediction and specific range of TSR evaluation, and it also benefits from short simulation run time. To further evaluate flow field details and to understand the underlying flow physics such as dynamic stall behaviour, hybrid RANS-LES turbulence modelling is necessary. Comparing between hybrid models adopted, stress-blended eddy simulation based on transition shear-stress transport (TSST) model has achieved an overall better performance, such as a reduction of simulation discrepancy by 50% in low TSRs range compared to TSST turbulence model. In both medium and high TSRs ranges, the modelling discrepancies are less than 3% compared to TSST turbulence models at about 25% extra computational time. Furthermore, in high TSRs range, hybrid RANS-LES models are able to predict the appearance of vortex shedding at high azimuthal angles (θ ≥ 180°) for which URANS models failed to capture.

Purpose The aim of this paper is to assess the ability of a stress-blended eddy simulation (SBES) turbulence model to predict the performance of a three-straight-bladed vertical axis wind turbine (VAWT). The grid sensitivity study is conducted to evaluate the simulation accuracy. Design/methodology/approach The unsteady Reynolds-averaged Navier–Stokes equations are solved using the computational fluid dynamics (CFD) technique. Two types of grid topology around the blades, namely, O-grid (OG) and C-grid (CG) types, are considered for grid sensitivity studies. Findings With regard to the power coefficient (Cp), simulation results have shown significant improvements of predictions using compared to other turbulence models such as the k-e model. The Cp distributions predicted by applying the CG mesh are in good agreement with the experimental data than that by the OG mesh. Research limitations/implications The current study provides some new insights of the use of SBES turbulence model in VAWT CFD simulations. Practical implications The SBES turbulence model can significantly improve the numerical accuracy on predicting the VAWT performance at a lower tip speed ratio (TSR), which other turbulence models cannot achieve. Furthermore, it has less computational demand for the finer grid resolution used in the RANS-Large Eddy Simulation (LES) “transition” zone compared to other hybrid RANS-LES models. Originality/value To authors’ knowledge, this is the first attempt to apply SBES turbulence model to predict VAWT performance resulting for accurate CFD results. The better prediction can increase the credibility of computational evaluation of a new or an improved configuration of VAWT.

Oil scavenge flow in aero-engine bearing chamber remains largely a challenging problem for many engine designers. Research campaign on scavenge flow has been conducted by G2TRC – Gas Turbine and Transmissions Research Centre (previously Rolls Royce University Technology Centre in Gas Turbine Transmission Systems) at the University of Nottingham. It was recognized that a deep sump performs better than shallower one due to its ability to “shield” the collected oil in the sump from the shaft windage thus reducing the amount of oil being picked up by the bulk air rotation. However, such a deep sump design cannot be employed in some engines and especially at certain locations where space is limited. A parametric study combined with phenomenological approach on shallow sump geometry has been conducted and presented in the previous publication where a certain optimized shallow sump variant was proposed depending on whether the flow in the chamber is wall film dominated or airborne droplets dominated. The parametric phenomenological approach was employed since it can be done relatively quicker than typical data gathering through an experiment. However the approach relies on qualitative interpretation of the flow features, and its application in bearing chamber flow research has never been validated before. This paper presents the results of quantitative measurements of residence volumes of an optimized shallow sump variant identified in the parametric phenomenological study. Comparison was then made with the residence volumes of some existing engine sumps. It was found that the optimized shallow sump for wall film dominated flow has lower residence volumes compared to some existing engine sumps. In some cases, the residence volume can be reduced by up to 75%. An optimized shallow sump variant for airborne droplets dominated was also identified in the previous parametric phenomenological study, although the residence volume measurement is yet to be conducted. The optimized shallow sump for wall film dominated flow was also identified as a good sump regardless of the flow regime. However when it was tested in airborne droplets dominated flow, its residence volumes are higher than some of the existing engine sumps. This highlights the importance of considering the flow regime in the bearing chamber in any attempt to optimize a sump geometry.

Implementation of corporate governance is expected to provide prosperity and welfare for shareholders. This study intended to analyze the impact of board size and audit quality proxies from corporate governance on firm value. This study also uses managerial ownership which is proxies from ownership structure and also cash holdings to analyze deeper its impact on firm value. There were also three control variables: leverage, firm size and firm age. Companies listed in the Indonesia Stock Exchange in 2014 to 2018 were objects that supporting this research. Data collection utilizes purposive sampling method and selected according to the criteria of 448 companies. Companies that met the criteria were further tested using the panel regression method to analyze the existing influence between the independent variable and dependent variable. The findings obtained in this study indicate that there is no significant relationship between board size and audit quality on firm value. Meanwhile, managerial ownership and cash holdings prove that there is a significant positive correlation to firm value. Then for the control variable, leverage does not affect the value of the company, but the size and age of the company both have a significant positive effect on firm value.

Optimisation of Gurney flap (GF) geometries mounted on a three-straight-bladed vertical axis wind turbine (VAWT) is evaluated with computational fluid dynamics (CFD) solution and Taguchi method, considering the blade rotating effect at three tip speed ratios (TSRs) of low, medium and high ranges. A hybrid RANS-LES model applying stress-blended eddy simulation with transition shear-stress transport turbulence model is adopted. Results analysis confirms that GF geometry optimisation needs to consider multiple rotational blades rather than a single stationary one, owing to different optimum GF geometries and their performances at a different range of TSRs. It is found that VAWT with GF can significantly improve the power coefficient at low range TSRs (up to 233.19%), but it decreases with the increase of TSRs ranges (up to 69.94% and 41.36% at medium and high ranges of TSRs, respectively).

Penelitian ini dilatarbelakangi oleh program literasi di SDN Sendangmulyo 04 yang sudah mendapatkan prestasi nasional dalam mutu pendidikan. Sub fokus penelitian ini adalah: (a) bagaimana perencanaan; (b) bagaimana pengorganisasian; (c) bagaimana pelaksanaan; (d) bagaimana pengendalian sekolah dalam program literasi sekolah di SDN Sendangmulyo 04?, (e) bagaimana dengan minat baca di SDN Sendangmulyo 04?Objek penelitian ini adalah SDN Sendangmulyo 04 Semarang, dengan tujuan untuk mengetahui, mendiskripsikan, dan menganalisis manajemen pengelolaan literasi sekolah di SDN sendangmulyo 04. Metode pengumpulan data dilaksanakan dengan cara wawancara, observasi langsung, dan dokumentasi melalui metode studi kasus. Analisis dilakukan dengan melalui tiga alur kegiatan yaitu reduksi data, penyajian data, verivikasi data selanjutnya manarik kesimpulan.Hasil penelitian dapat disimpulkan bahwa manajemen literasi sekolah di SDN Sendangmulyo 04 dalam meningkatkan minat baca telah sesuai teori manajemen dan berjalan dengan baik: (a) perencanaan berjalan secara baik dengan menetapkan tujuan, menentukan sasaran program literasi, identifikasi potensi, dan merancang program, (b) pengorganisasian dengan menyusun tim yang melibatkan organisasi di sekolah dan sekaligus menyusun program-program kegiatan literasi, (c) pergerakkan telah berjalan dengan adanya bentuk-bentuk program kegiatan dan memberikan penghargaan kepada warga sekolah, (d) pengawasan dilakukan dengan baik dengan adanya monitoring langsung di masing-masing kegiatan literasi, menyusun program pengawasan literasi, dan tindak lanjut, dan (e) minat baca para siswa sudah baik dengan di dukung dengan sudut baca di kelas dan kunjungan di perpustakaan.

Recently, the Gurney Flap (GF) has been used to improve the performance of Horizontal Axis Wind Turbine (HAWT) by enhancing its lift coefficient. Compared to HAWT, research on GF application for Vertical Axis Wind Turbine (VAWT) is very limited. Moreover, most works studied a GF geometry attached to the trailing edge of a stationary airfoil, without considering the rotating effect experienced by VAWT. For this reason, a three-straight-bladed VAWT rotating blade with GF is studied by transient RANS simulation together with a stress-blended eddy simulation (SBES) turbulence model to investigate the GF height effect and the flow characteristics near the blade trailing edge. Results have shown that by introducing the blade rotating, an optimum GF height is found to be 3% of the blade chord, slightly higher than 2% chord in a stationary airfoil case. In addition, the presence of GF can delay deep stall of VAWT blades, thus eliminating negative instantaneous moment coefficient and improving the turbine performance.

In an aeroengine oil is supplied to the bearings for lubrication and cooling. Subsequently, it creates a two phase flow environment in the bearing chamber that may contain droplets, mist, wall film, ligaments, froth or foam and liquid pools. After the oil has served its purpose, it is scavenged out of the chamber and recycled. Effective oil removal is essential as unnecessary working of the oil can lead to excessive heat generation in the chamber, increased risk of seal leakage, and reduced overall efficiency. However the task of oil removal is not trivial as it is entrained in a highly rotating environment induced by the rotating shafts. Shallow sump variants were investigated using a design of experiments approach. A previous publication discussed the performance of the sump variants using categorization of visualization data relating to the extent of hydraulic uplift in the sump region. Hydraulic uplift was found to be directly related to residence volume in the gravity dominated wall film flow regime. Furthermore, it was found that the flow condition factors such as flow regime and shaft speed are the dominating factors affecting the hydraulic uplift severity. In terms of the geometrical factors, a deeper sump can reduce the hydraulic uplift severity. This reinforces the importance of sump depth, as a deeper sump tends to have lower residence volume but is often not implemented due to space constraint. This paper presents further results from the experimental study on the shallow sump variants in terms of some important flow characteristics such as upstream flow detachment, upstream flow dry-out, and secondary flow. In addition to the geometrical factors, the flow condition factors such as the flow regime defined by how oil enters the chamber, flow rate, shaft speed, and scavenge ratio were investigated. Upstream flow detachment was observed only for cases where airborne droplets were present and at higher shaft speeds, also known as the windage dominated airborne droplets flow regime. It was noted that the geometrical factors are less important than the flow condition factors for upstream flow detachment as well as upstream flow dry-out and secondary flow.

Gas turbine aero-engines employ fast rotating shafts that are supported by bearings at several axial locations along the engine. Due to extreme load and heat, oil is injected to the bearings to aid lubrication and cooling. The oil is then shed to the bearing chamber before it is extracted out by a scavenge pump. Scavenging oil from the bearing chamber is challenging due to high windage induced by the fast rotating shafts as well as the two-phase nature of the flow. A deep sump has been found to increase scavenge performance due to its ability to shelter the pooled oil from the bulk rotating air flow thus minimizing two-phase mixing. However, in many cases, a deep sump is not an option due to conflicting space requirements. The space limitation becomes more stringent with higher bypass ratio engines as the core becomes smaller. Therefore, it is imperative to have a high performing shallow sump. However, shape modification of a shallow sump is too constrained due to limited space and, therefore, has minimal impact on the scavenge performance. This research presents several alternative concepts to improve scavenge performance of a generic baseline shallow sump by augmenting it with attachments or inserts. These augmentations attempt to exploit two known mechanisms for reducing the residence volume: momentum reduction and sheltering. The experimental results show that some augmentations are able to reduce the residence volume of a shallow sump by up to 50% or more in some cases.

The original sump design of Rolls-Royce AE3007 central sump is a tangential sump. An experimental program at Purdue University was conducted to investigate the characteristics of a tangential sump design. The research employed a bespoke experimental rig consisting of modular transparent chamber to allow unprecedented view of the two-phase flow inside the bearing chamber. It was found that a persistent liquid pooling near the drain entrance of a tangential sump obstructs the outflow to the scavenge off-take. While space requirement is minimal, the scavenge performance of a tangential sump is poor. A prototype advanced sump was proposed and built with features to address various issues found in the tangential sump. In this paper, further experimental work on the refinements of the advanced sump is presented. This includes experimental study on the effect of a fence and splitter plate, off-take hole diameter and its location, the effect of gravity by tilting, upstream wall fairing, as well as the depth of the sump itself. The experiments showed that the faired upstream wall modification can reduce residence volume significantly across different operating conditions, indicating improvement in scavenge performance. The other modifications help to reduce residence volume only in certain operating conditions. The results of this study helped towards the birth of an optimized sump design, known as Indy sump. The Indy sump has been accepted as a superior sump design and has been used as a benchmark in many sump design studies.

An aero-engine bearing chamber is a structure that is used to contain and collect oil used in lubricating and cooling the bearings supporting the high-speed engine shafts. There are various bearings in an aero-engine. Within the bearing chambers, there are typically the bearings, rotating shafts, seals and gears (in some designs). The walls of the bearing chamber are stationary and there are vents and sumps to take out the oil, via an offtake pipe, and the sealing air. The oil collected via the sump and vents is recycled and used again in the loop. To prevent oil degradation and reduce chance of coking in the chamber, it is desired that all of the oil goes through the recycling loop, with no oil staying longer than necessary in the chamber. The sealing air is used to maintain a positive pressure to keep the oil within the chamber. The flow inside a bearing chamber is highly turbulent and consists of a rotating mixture of oil and air. A smaller amount of the oil, mostly as oil-droplets, exits at the vents and is separated from the air using de-aerators [1]. It is expected that by gravity, most of the oil collects at the sump and can be easily scavenged. This is provided the sump can be large enough. The geometry of a bearing chamber is, however, complex largely because of space limitations. It is very important that oil is not resident longer than necessary to prevent over-heating and therefore deterioration or coking. Experimental observations by Chandra & Simmons [2], have shown that bearing chambers with deep sumps perform better that those with shallow sumps. Since shallow sumps are inevitable, a number of innovative studies have been done to improve bearing chamber designs. The presence of air in the oil (e.g. as bubbles) reduces the efficiency of the scavenging pump. Other factors such as oil momentum and windage can take oil away from the off-take pipe potentially increasing oil residence volume. Chandra & Simmons [2] placed inserts such as grille cover, perforated plate, etc, on a side of the bearing wall and improvements in the residence volume were seen. In this work, we are looking at a detailed computational fluid dynamics (CFD) simulation of one of the inserts that performed well. This will aid understanding of the flow characteristics of using an insert to improve oil residence in a bearing chamber.

Aero-engines incorporate various bearing chambers and these typically contain bearings, seals, rotating shafts, stationary walls and struts, and sometimes gears. Oil is supplied for lubrication and cooling and is removed (scavenged) from the sump region of the chamber (note that in some parts of the world the entire bearing chamber is referred to as the sump). Depending on the location and function of the bearing chamber, the sump region may be deep or shallow. Effective oil removal is essential as unnecessary working of the oil can lead to excessive heat generation and reduced overall efficiency. Therefore the design of the scavenge region in a bearing chamber, as well as the ability to assess its performance is very important. Previous work, much of which was conducted at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems (UTC) suggests that oil often does not flow cleanly into the off-take due to a combination of several factors: oil momentum, windage, three-dimensional air flow that blocks the off-take flow or transports oil away from the off-take, and pooling because of separated air flow that acts on the oil once oil momentum is dissipated. Experimental research at the UTC found that scavenge performance is highly affected by the sump geometry, especially its depth. Variations of shallow sumps, although some are better than the others, cannot offer the same level of performance as a deep one. However space limitation in an engine often only allows for a shallow sump. This paper presents some experimental exploration on new design ideas. They are in the form of various inserts and attachments that were designed to improve scavenge performance of a shallow sump. These “custom” sumps were tested on the UTC’s scavenge test facility at various flow settings (wall film/flying droplets, liquid flow rates, scavenge ratios, shaft speeds). The residence volumes were measured and compared to a baseline configuration with reduction in residence volume desirable. The inserts tested were a Grille Cover, a Stepped Spillway, a Perforated Plate and a Porous Insert. Both the Porous Insert and the Perforated Plate showed reduced residence volumes in the demanding droplet/windage dominated flow condition with the Perforated Plate offering the best improvement over baseline.

Aeroengine bearing chambers typically contain bearings, seals, shafts and static parts. Oil is introduced for lubrication and cooling and this creates a two phase flow environment that may contain droplets, mist, film, ligaments, froth or foam and liquid pools. Efficient and effective liquid removal from a bearing chamber is a functional requirement and in recent years the University of Nottingham Technology Centre in Gas Turbine Transmission Systems has been conducting an experimental and computational research program one strand of which is investigating bearing chamber off-take flows. Initial investigations focussed on a chamber where there was a relatively deep pocket for oil collection below the chamber [1, 2]. In more recent studies Chandra et al have investigated a shallower geometry [3]. In both sets of studies, chamber residence volume and wall film thickness data have been obtained for a range of shaft speeds, scavenge ratios and liquid supply rates. Two methods of introducing liquid to the chamber have been used: a film generator that puts liquid directly onto the chamber wall and a droplet inlet system that distributes droplets from the rotating shaft. During some of the previous investigations, visual data relating to the two phase flow in the outlet pipe immediately below the chamber was gathered together with data from pressure transducers one located in this pipe and one on the chamber itself. It has been observed that for some parameter combinations the chamber flow is gravity dominated whereas for others (typically at higher shaft speeds) the flow is shear dominated. During transition between regimes a pressure spike on the pipe pressure transducer is observed and this may be linked to a change in two phase flow regime within the outlet pipe. A study by Baker et al [4] on transient effects in gas-liquid separation has shown pressure spikes during transitions to new equilibrium conditions for two-phase pipe flow where the gas flow rate is suddenly increased. In this paper outlet visualisation, chamber visualisation and pressure data are combined and conclusions are drawn relating to the parameters controlling whether shear or gravity dominate. The effect of the chamber flow regime on the outlet flow regime is assessed and presented. An implication of the analysis is that during transitional conditions a bearing chamber may contain a different quantity of liquid than in steady state conditions.

Oil removal (scavenge) from aeroengine bearing chambers is an ongoing challenge for aeroengine designers. Effective scavenging of oil is necessary to avoid excessive heat generation, degradation of oil properties and deterioration in heat transfer functionality. However the task of oil removal is not trivial. Oil is entrained in a highly rotating environment induced by the rotating shafts. Simply removing a larger volume of fluid from the chamber with the scavenge pump can create higher air flowrates but lead to oil becoming trapped in the chamber and so no reduction in residence volume (the amount of oil present in the chamber during operation). The University of Nottingham Technology Centre in Gas Turbine Transmissions Systems has been conducting experiments investigating two phase behaviour within a simplified aeroengine bearing chamber operating at ambient pressures with water as the working liquid. The rig is constructed from polycarbonate enabling good visual access. In the chamber offtake region a number of behaviours can be observed relating to the hydraulic uplift and general flow behaviour as gas and liquid exit the chamber. Chandra et al [1] reports a parametric study using a design of experiments approach into geometrical variants of a shallow offtake region defined by curved approaches and a small offtake volume. Phenomenlogical factors were quantified and used to identify the best performing geometry. Previous work at the UTC [2, 3] has used residence volume as the primary comparative performance parameter. In this paper residence volume data is obtained for two sumps for which phenomenological data exists. The paper compares performance on the basis of these visual factors with performance on the basis of residence volume and concludes that although both frameworks have value, they do not lead to identical conclusions for all operating conditions. In film dominated cases significant hydraulic uplift usually corresponds to larger residence volume but for droplet dominated cases this is not necessarily so.

Oil removal from aeroengine bearing chambers presents a challenge for aeroengine designers. Effective scavenging of oil is necessary to avoid excessive heat in the bearing chamber as this may lead to degradation of oil properties and deterioration in heat transfer functionality. However the task of oil removal is not trivial. Oil is entrained in a highly rotating environment induced by rotating shafts. An aeroengine scavenge pump must remove both air and oil from the chamber and the ratio of the two fluids depends on pump operating point as well as the geometry of the exit region. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems is conducting an on-going experimental programme investigating liquid and gas flow behaviour in a relevant highly rotating environment. Previously reported work [2, 4] in combination with work conducted by Purdue University [3, 5] suggests that a deeper sump may help to reduce residence volume. More recently a study has been conducted that investigates geometries incorporating features sometimes included in aeroengine scavenge. Three very different exit geometries were investigated experimentally using chamber residence volume as a parameter of comparison. Data for one of these, the so called Curved Wall Deep Sump (CWDS), has already been reported in [4]. This paper presents residence volume data for all three sumps over a range of shaft speeds, inlet flow rates and scavenge ratios. Trends are analysed and presented and areas for future work identified.

Aeroengine bearing chambers typically contain bearings, seals, shafts and static parts. Oil is introduced for lubrication and cooling and this creates a two phase flow environment that may contain droplets, mist, film, ligaments, froth or foam and liquid pools. Some regions of the chamber contain a highly rotating air flow such that there are zones where the flow is gravity dominated and zones where it is rotation dominated. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems, is conducting an ongoing experimental program investigating liquid and gas flow behavior in a relevant highly rotating environment. Previously reported work by the UTC has investigated film thickness and residence volume within a simplified chamber consisting of outer cylindrical chamber, inner rotating shaft and cuboid off-take geometry (termed the generic deep sump). Recently, a more aeroengine relevant bearing chamber offtake geometry has been studied. This geometry is similar to one investigated at Purdue University and consists of a “sub-sump” region approached by curved surfaces linked to the bearing chamber. The test chamber consists of an outer, stationary cylinder with an inner rotating shaft. The rig runs at ambient pressure and the working fluid (water) is introduced either via a film generator on the chamber wall or through holes in the shaft. In addition to visual data (high speed and normal video), liquid residence volume within the chamber and film thickness were the two numerical comparators chosen. Data was obtained for a number of liquid supply rates, scavenge ratios and shaft rotation speeds. The data from the current model is compared to that from the earlier studies. The data shows that in contrast to the previously reported generic deep sump study, the residence volume of the curved wall deep sump (CWDS) designs is far less sensitive to shaft speed, liquid supply rate and scavenge ratio. The method of liquid supply only makes a significant difference at the lowest scavenge ratios. Residence volume data for the Nottingham CWDS is comparable, when appropriately scaled, to that for the Purdue design. The film thickness data shows that at the lower shaft speeds investigated the flow is gravity dominated whereas at higher shaft speeds shear dominates.

A tangential sump design is employed in several aero-engines mainly due to its simplicity and compactness. However various problems have prompted investigations of the sump design. An experimental program at Purdue University (Chandra, 2006, “Flows in Turbine Engine Oil Sumps,” Ph.D. thesis, School of Aeronautics and Astronautics, Purdue University and Radocaj, 2001, “Experimental Characterization of a Simple Gas Turbine Engine Sump Geometry,” M.S. thesis, School of Aeronautics and Astronautics, Purdue University) was conducted to investigate the characteristics of a tangential sump design like one used in the AE3007 aero-engine. The research employed a transparent chamber to allow unprecedented view of the flow inside the bearing chamber. It was quickly found that a persistent liquid pooling near the drain entrance of a tangential sump obstructs the outflow to the scavenge pump. The air flow near the drain entrance has been shown to have strong reverse flow, even with, or perhaps due to, substantial over-scavenging. Various modifications were tested with varying degrees of success. The work highlights limitations of a tangential sump design. Based on the lessons learned, a new sump design was proposed. Preliminary test of the new sump design has shown positive results.

Aeroengine bearing chambers typically contain bearings, seals, shafts and static parts. Oil is introduced for lubrication and cooling and this creates a two phase flow environment that may contain droplets, mist, film, ligaments, froth or foam and liquid pools. Some regions of the chamber contain a highly rotating air flow such that there are zones where the flow is gravity dominated and zones where it is rotation dominated. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems, is conducting an ongoing experimental program investigating liquid and gas flow behavior in a relevant highly rotating environment. Previously reported work by Chandra et al [1, 2] has investigated film thickness and residence volume within a simplified chamber consisting of outer cylindrical chamber, inner rotating shaft and cuboid off-take geometry (termed the generic deep sump). Recently a more aeroengine relevant bearing chamber offtake geometry has been studied. This geometry is similar to one investigated by Chandra [3] at Purdue University and consists of a “sub-sump” region approached by curved surfaces linked to the bearing chamber. The test chamber consists of an outer, stationary cylinder with an inner rotating shaft. The rig runs at ambient pressure and the working fluid (water) is introduced either via a film generator on the chamber wall or through holes in the shaft. In addition to visual data (high speed and normal video), liquid residence volume within the chamber and film thickness were the two numerical comparators chosen. Data was obtained for a number of liquid supply rates, scavenge ratios and shaft rotation speeds. The data from the current model is compared to that from the earlier studies [1, 2, & 3]. The data shows that in contrast to the previously reported generic deep sump study, the residence volume of the curved wall deep sump (CWDS) designs is far less sensitive to shaft speed, liquid supply rate and scavenge ratio. The method of liquid supply only makes a significant difference at the lowest scavenge ratios. Residence volume data for the Nottingham CWDS is comparable, when appropriately scaled, to that for the Purdue design. The film thickness data shows that at the lower shaft speeds investigated the flow is gravity dominated whereas at higher shaft speeds shear dominates.

In a typical aero engine bearing chamber, oil is introduced to lubricate and cool the bearings as well as the bearing chamber wall. The flow of the oil in the bearing chamber is very complex due to the presence of various forces: gravity, windage, capillary, etc. These pose a great challenge for designers, in particular on how to effectively and efficiently scavenge the hot oil out of the bearing chamber. The University of Nottingham Technology Centre in Gas Turbine Transmission Systems is conducting an ongoing experimental program on liquid and gas flow behavior in the highly rotating environment typically found in a bearing chamber. This paper presents results from a study of the thin film on the wall of a generic bearing chamber consisting of an inner rotating shaft and outer stationary cylindrical wall. Thin liquid film behavior in a cylindrical chamber, subject to only gravity or together with the presence of shearing air flow is of interest in many industrial applications and processes. Measurements of film thickness were taken at various axial and angular locations, at various representative inlet flow rates, scavenge ratios and shaft rotational speeds. The experimental data provides insight on the behavior of thin liquid film as it travels down the inner chamber wall subject to both gravity and shearing air flow and provides a data set eminently suitable for CFD validation. The film thickness measurements are discussed in relation to previously published chamber residence volume data [1].Copyright © 2011 by Rolls-Royce plc

Aeroengines incorporate various bearing chambers that house the shaft bearings and the oil used to cool and lubricate these bearings must subsequently be recovered from these chambers. Effective oil removal (scavenge) is essential to avoid heat generation through unnecessary working of the oil which can lead to excessive heat generation and reduced overall efficiency. Therefore the design of the scavenge region (sump) in a bearing chamber, as well as the ability to assess its performance is very important. An ongoing research program into bearing chamber scavenge comprising experimental and computational components is being conducted at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems. This program is enhancing understanding of sump performance and design. In this paper an experimental study into a simplified but representative scavenge is reported. This experimental work helps to further understanding of the complex two-phase flow physics in a bearing chamber, particularly in the scavenge region, by means of various measurements and flow visualization. For the study a bespoke test rig has been built. It consists of a simplified, generic bearing chamber with simple sump geometry constructed entirely of Perspex to allow visualization. A shaft in the centre of the chamber capable of rotating up to 15,000 rpm is employed to introduce a windage flow in the chamber. Water (the working fluid) is fed to the chamber via an inlet pump and an outlet pump removes liquid from the chamber, closing the circuit. Several pneumatic pinch valves are installed in the flow circuit to allow residence volume measurement. A completely air-tight reservoir with internal baffle functions as a simple liquid-gas separator, allowing measurement of gas volumetric flow rate in the off-take pipe; hence the scavenge ratio (ratio of total exit volume to liquid volume) can be obtained. Residence volume measurements highlight the importance of sump geometry as an ill-designed sump can lead to an undesirable increase in residence volume.Copyright © 2010 by Rolls-Royce plc

In many aero-engines, the power to drive accessories is transmitted through high speed bevel gears in a chamber in the center of the engine. The windage power loss (WPL) associated with these gears makes a significant contribution to the overall heat generation within the chamber. Shrouding the gears provides an effective method of reducing this WPL and managing the flow of lubricating oil. Experimental and computational programs at the University of Nottingham Technology Centre in Gas Turbine Transmission Systems are providing an improved understanding of shroud performance and design. This paper presents the results from a pair of shrouded meshing gears run at representative speeds and oil flow in a rig with speed and torque measurement. A previously published study of a single bevel gear operating in air (Johnson et al., 2007, “Experimental Investigation Into Windage Power Loss From a Shrouded Spiral Bevel Gear” ASME Paper No. GT2007-27885) found a reduction in torque of up to 70% from shrouding. In this work, the addition of oil and the pinion gear did not lead to high torque due to the buildup of oil under the shrouds, but the reduction in torque due to fitting the shrouds is significantly less than was found for the same gear in air alone. In order to isolate the various parameters, further testing with a single gear was carried out. A fully (360 deg) shrouded gear shows a big improvement over an unshrouded gear when running in air alone, but much of this benefit disappears as soon as a very small amount of oil is introduced under the shroud. This implies that the oil is recirculating under the shroud. Increasing the oil flow beyond this initial level increases the torque by the amount required to accelerate the oil mass flow up to the peripheral speed of the gear. Providing a full width slot in the shroud downstream of the oil jet allows the oil to escape without any recirculation and restores much of the benefit of the shroud. Further insight into the oil behavior is obtained from torque measurements and observations through a transparent shroud and with various slot configurations. Video observation shows evidence of a vortex flow under the shroud that carries some of the oil toward the inner diameter of the gear. The three main windage contributors, air alone, recirculation of oil under the shroud, and acceleration of the feed oil, are quantified and methods for achieving the optimum design are discussed.

Experimental research was conducted into a scooped rotor system that captures oil from a stationary jet and directs it through passages within the shaft to another axial location. Such a system has benefits for delivering oil via under-race feed to aeroengine bearings where direct access is limited. Oil capture efficiency was calculated for three jet configurations, a range of geometric variations relative to a baseline and a range of operating conditions. Flow visualization techniques yielded high-speed imaging in the vicinity of the scoop leading edge. Overall capture efficiency depends on the amount of oil initially captured by the scoop that is retained. Observation shows that when the jet hits the tip of a scoop element, it is sliced and deflected upward in a “plume.” Ligaments and drops formed from this plume are not captured. In addition, some oil initially captured is flung outward as a consequence of centrifugal force. Although in principle capture of the entire supply is possible over most of the shaft speed range, as demonstrated by a simplified geometric model, in practice 60–70% is typical. Significant improvement in capture efficiency was obtained with a lower jet angle (more radial) compared to baseline. Higher capture efficiencies were found where the ratio of jet to scoop tip speed was lower. This research confirms the capability of a scoop system to capture and retain delivered oil. Additional numerical and experimental work is recommended to further optimize the geometry and increase the investigated temperature and pressure ranges.