Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines

Burning hydrogen in conventional internal combustion (IC) engines is associated with zero carbon-based tailpipe exhaust emissions. In order to obtain high volumetric efficiency and eliminate abnormal combustion modes such as preignition and backfire, in-cylinder direct injection (DI) of hydrogen is considered preferable for a future generation of hydrogen IC engines. However, hydrogen's low density requires high injection pressures for fast hydrogen penetration and sufficient in-cylinder mixing. Such pressures lead to chocked flow conditions during the injection process which result in the formation of turbulent under-expanded hydrogen jets. In this context, fundamental understanding of the under-expansion process and turbulent mixing just after the nozzle exit is necessary for the successful design of an efficient hydrogen injection system and associated injection strategies. The current study used large eddy simulation (LES) to investigate the characteristics of hydrogen under-expanded jets with different nozzle pressure ratios (NPR), namely 8.5, 10, 30 and 70. A test case of methane injection with NPR = 8.5 was also simulated for direct comparison with the hydrogen jetting under the same NPR. The near-nozzle shock structure, the geometry of the Mach disk and reflected shock angle, as well as the turbulent shear layer were all captured in very good agreement with data available in the literature. Direct comparison between hydrogen and methane fuelling showed that the ratio of the specific heats had a noticeable effect on the near-nozzle shock structure and dimensions of the Mach disk. It was observed that with methane, mixing did not occur before the Mach disk, whereas with hydrogen high levels of momentum exchange and mixing appeared at the boundary of the intercepting shock. This was believed to be the effect of the high turbulence fluctuations at the nozzle exit of the hydrogen jet which triggered Gortler vortices. Generally, the primary mixing was observed to occur after the location of the Mach disk and particularly close to the jet boundaries where large-scale turbulence played a dominant role. It was also found that NPR had significant effect on the mixture's local fuel richness. Finally, it was noted that applying higher injection pressure did not essentially increase the penetration length of the hydrogen jets and that there could be an optimum NPR that would introduce more enhanced mixing whilst delivering sufficient fuel in less time. Such an optimum NPR could be in the region of 100 based on the geometry and observations of the current study

Spectral Attenuation Characteristics of Strong Ground Motions in East-Central Iran Using Theoretical Data

Ground-motion prediction equations are an essential element of PSHA. In seismic hazard analysis, attenuation calculations determine how quickly ground motions decrease as the distance from a seismic event increases. The estimation of ground motion for future earthquakes as a function of magnitude and distance is an important problem from earthquake engineering point of view. This article presents spectral equations for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes with magnitude range of Mw 5.0 to 7.4 and distance to the surface projection of the fault less than 100 km for theoretical (simulated) records. The reason for development of ground motion in this region is that strong ground motion data are too sparse to allow ground motion relations to be derived directly from sufficient observed data. By considering the modeling parameters, we have used the stochastic finite fault modeling to generate a large suite of acceleration time histories for this region. The attenuation characteristics of horizontal spectral accelerations of strong motion in near-field are studied in this paper and the attenuation relations for horizontal acceleration response spectrum in the period range of 0.1–5 s for rock classification in the East-Central Iran are established. These equations were derived by two-stage regression analysis, on a set of 1200 theoretical strong-motion records generated in this area. The present results will be useful in estimating strong ground motion parameters and in the earthquake resistant design in the East-Central Iran region

Large Eddy Simulation of Near-Nozzle Shock Structure and Mixing Characteristics of Hydrogen Jets for Direct-Injection Spark-Ignition Engines

Due to the ever increasing prices of conventional fossil fuels, as well as climate change and sustainability issues, several liquids and gases have been proposed as alternative fuels for internal combustion engines. Hydrogen has been investigated by several researchers as a promising alternative gaseous fuel. In general gaseous fuels are injected either in the intake port of an internal combustion engine or directly into the cylinder. Direct injection of hydrogen offers higher volumetric efficiency and eliminates abnormal combustion phenomena like pre-ignition and backfire. However, due to hydrogen’s low density, direct injection requires high injection pressures to achieve suitable mass flow rates for fast incylinder fuel delivery and mixing. Such pressures typically lead to chocked conditions at the nozzle exit, followed by a turbulent under-expanded jet. Therefore, fundamental understanding of the expansion process and turbulent mixing just after the nozzle exit is necessary in order to design an efficient hydrogen injection system and injection strategies for optimised combustion. In the current study large-eddy simulations were performed to study the effect of different nozzle pressure ratios, namely 10, 30 and 70, on the nearnozzle shock structure and turbulent mixing of underexpanded hydrogen jets. The computational tool was validated against an experimental test case available in the literature. It was found that the simulation methodology captured the nearnozzle shock structure, Mach disk, reflected shocks and turbulent shear layers in good agreement with the experiments. The height and width of the Mach disk and the position of the mixing shear layer were greatly affected by the injection pressure. It was also found that for hydrogen the near-nozzle shock structure and Mach disk need considerably more time to reach an almost steady-state condition in comparison to the time claimed for heavier gases in the literature. It was also seen that during the transient period the dimensions of the Mach disk temporarily reached higher values than the final steady ones. It was also found that not all of the hydrogen jet passed through the Mach disk; hydrogen-air mixing started immediately after the nozzle exit at the boundaries of the jet but the main mixing process started after the Mach disk

Deskripsi Keberadaan Sdn 3 Segalamider

This is a descriptive research that aims to assess the existence of SD Negeri 3 Segalamider. The informants of this research were the head master, teachers of SDN 3 Segalamider, parents of SDN 3 Segalamider and the leader of LK I AND II in gunung agung district. Collecting data through observation, structured interviews, and documentation.The results of this research indicates that (1) the accessibility to SD Negeri 3 Segalamider is easy categorized because from 66 informants, there were 52 people (78,78%) showed easy category. (2) the distance of SD Negeri Segalamider from nearby residential areas is close categorized. This is because the distance of the school from the residential areas is less than 3 km. (3) total number of children in the age of elementary school on the nearby residential with to SD Negeri 3 Segalamider that is the children at the age 7 until 12 years old on the environment of II (LKII), gunung agung district was in great quantities that are 755 people. (4) the capacity of SD Negeri 3 Segalamider was less for each class only reach ±30 students because the classroom of SD Negeri 3 Segalamider is not in ideal size, elementary school classrooms in 3 Segalamider measuring 6m x 8m and 5m x 8m

Direct numerical simulation of compressible turbulence in a counter-flow channel configuration

Counter-flow configurations, whereby two streams of fluid are brought together from opposite directions, are highly efficient mixers due to the high turbulence intensities that can be maintained. In this paper, a simplified version of the problem is introduced that is amenable to direct numerical simulation. The resulting turbulent flow problem is confined between two walls, with one non-zero mean velocity component varying in the space direction normal to the wall, corresponding to a simple shear flow. Compared to conventional channel flows, the mean flow is inflectional and the maximum turbulence intensity relative to the maximum mean velocity is nearly an order of magnitude higher. The numerical requirements and turbulence properties of this configuration are first determined. The Reynolds shear stress is required to vary linearly by the imposed forcing, with a peak at the channel centreline. A similar behaviour is observed for the streamwise Reynolds stress, the budget of which shows an approximately uniform distribution of dissipation, with large contributions from production, pressure-strain and turbulent diffusion. A viscous sublayer is obtained near the walls and with increasing Reynolds number small-scale streaks in the streamwise momentum are observed, superimposed on the large-scale structures that buffet this region. When the peak local mean Mach number reaches 0.55, turbulent Mach numbers of 0.6 are obtained, indicating that this flow configuration can be useful to study compressibility effects on turbulence

The effect of high intensity interval training on CTGF and RXFP1 genes expression of heart tissue and SGPT liver enzyme in rats with fatty liver

This study investigated the effect of high intensity interval training on CTGF and RXFP1 genes expression of heart tissue and SGPT liver enzyme in rats with fatty liver. 48 male Wistar rats (200-250 g) were divided randomly into the following 6 groups: Healthy base group (BH), base Steatosis group (BS), Healthy HIIT group (HIIT), Steatosis HIIT group (SHIIT), Healthy control group (CH), control Steatosis group (CS). Rats in the fatty liver group received oral tetracycline daily for two weeks. Rats in the training groups were also trained for 5 weeks / five days. Both BS and BH groups sacrificed at the end of the 2nd week. CS and training groups sacrificed at the end of 5th week and heart tissue samples were taken to examine CTGF, RXFP1, and SGPT genes expression. The results of the study showed that he amounts of SGPT in BS and CS groups were meaningfully higher than those in the other 4 groups. The level of this enzyme in SHIIT and HIIT groups was significantly lower than that in the fatty liver groups. The RXFP1 gene expression in CS, BS and SHIIT groups were significantly higher than those in the other 3 groups. Thus, it can be claimed that fatty liver increased cardiac fibrosis factors but by reducing these factors HIIT was able to prevent the process of cardiac fibrosis from liver Steatosis; therefore, HITT can be used as a new method to Cardiac rehabilitation of patients

On the performance of WENO/TENO schemes to resolve turbulence in DNS/LES of high-speed compressible flows

High‐speed compressible turbulent flows typically contain discontinuities and have been widely modelled using Weighted Essentially Non‐Oscillatory (WENO) schemes due to their high‐order accuracy and sharp shock capturing capability. However, such schemes may damp the small scales of turbulence, and result in inaccurate solutions in the context of turbulence‐resolving simulations. In this connection, the recently‐developed Targeted Essentially Non‐Oscillatory (TENO) schemes, including adaptive variants, may offer significant improvements. The present study aims to quantify the potential of these new schemes for a fully‐turbulent supersonic flow. Specifically, DNS of a compressible turbulent channel flow with M = 1: 5 and Re τ = 222 is conducted using OpenSBLI, a high‐order finite difference CFD framework. This flow configuration is chosen to decouple the effect of flow discontinuities and turbulence and focus on the capability of the aforementioned high‐order schemes to resolve turbulent structures. The effect of the spatial resolution in different directions and coarse grid implicit LES are also evaluated against theWALE LES model. The TENO schemes are found to exhibit significant performance improvements over the WENO schemes in terms of the accuracy of the statistics and the resolution of the three‐dimensional vortical structures. The 6th order adaptive TENO scheme is found to produce comparable results to those obtained with non‐dissipative 4th and 6th order central schemes and reference data obtained with spectral methods. Although the most computationally expensive scheme, it is shown that this adaptive scheme can produce satisfactory results if used as an implicit LES model

Simulation of the 2009, Mw = 4 Tehran earthquake using a hybrid method of modal summation and finite difference

The Greater Tehran Area is the most important city of Iran and hosts about 20% of the country?s population. Despite the presence of major faults and the occurrence of historical earthquakes, the seismicity is relatively low at present. Thus, it is important to estimate the ground motion for preventive, reliable seismic hazard assessment. An earthquake with magnitude Mw = 4, which occurred close to Tehran, 17 October 2009, is the first local earthquake that has been recorded by the local strong ground motion network in Tehran. To simulate the ground motion caused by the earthquake a hybrid technique is used. It combines two methods: the analytical modal summation and the numerical finite difference, taking advantage of the merits of both. The modal summation is applied to simulate wave propagation from the source to the sedimentary basin and finite difference to propagate the incoming wavefield in the laterally heterogeneous part of the structural model that contains the sedimentary basin. Synthetic signals are simulated along two East?West and Southeast?Northwest profiles. Frequency, response spectra, and time domain, waveforms and peak values, parameters are computed synthetically and compared with observed records. Results show agreement between observed and simulated signals. The simulation shows local site amplification as high as 6 in the southern part of Tehran