Impingement Distance Research Articles

Characteristics of Flat-Wall Impinging Spray Flame and Its Heat Transfer under Diesel Engine-Like Condition: Effects of Injection Pressure, Nozzle Hole Diameter and Impingement Distance

<div class="section abstract"><div class="htmlview paragraph">Substantial amount of fuel energy input is lost by heat transfer through combustion chamber walls in the internal combustion engines. Thus, these heat losses account for reduced thermal efficiency, in that spray-wall impingement plays a crucial role in Direct Injection diesel engines. The objective of this study is to investigate the mechanism of the heat transfer from the spray/flame to the impinging wall under small diesel engine-like condition and how the spray characteristics are affected with regards to effect of injection pressure, nozzle hole diameter and impingement distance. The experiment results showed that injection pressure was predominant factor on spray-wall heat transfer.</div></div>

Influence of moving plate velocity on conjugate heat transfer due to the impingement of an inclined slot jet

In this paper, a dimensionless numerical study of the flow-field and heat transfer characteristics of an incompressible turbulent slot jet impinging obliquely over a moving surface of finite thickness is presented. Simulations were performed using [Formula: see text] eddy viscosity turbulence model. The temperature field was solved simultaneously in the solid and the fluid domain. For a fixed impingement distance and a fixed Reynolds number, the impingement angle ([Formula: see text]) and plate velocity ([Formula: see text]) were varied in the range of 30–75∘ and 0–0.3, respectively. In the results, the length of the potential core depends on the jet inclination, which increases with increase in jet angle. The jet angle and plate velocity have more influence on the uphill side compared to the downhill side. The location of stagnation displaces toward the uphill side as the inclination angle decreases, and the drifting of stagnation point is noted with the variation in plate velocity. The average skin-friction coefficient increases with increase in [Formula: see text] and [Formula: see text], and the influence of [Formula: see text] on the skin-friction coefficient is reduced as [Formula: see text] increases. The maximum Nusselt number ([Formula: see text]) increases with increase in [Formula: see text], and the drifting of [Formula: see text] is observed with increase in plate velocity. It is found that the average Nusselt number increases quickly with increase in plate velocity for lower angles of impingement. The distribution of local heat flux follows the same trend as the local Nusselt number.

Fluid Flow and Heat Transfer Characteristics of Multiple Swirling Impinging Jets at Various Impingement Distances

This research investigates the fluid flow and heat transfer characteristics for the effect of multiple swirling jets impinging on a heated plate. In this regard, numerical simulations were performed for the inline-type jet arrangement using ANSYS v16.2. Governing equations for turbulent swirl flows were solved by coupled algorithm whereby turbulences are described by SST k-ω model. The analysis is studied for Reynolds number Re = 11600 and swirl number 0.74 at impingement distances equal to 1, 2, 3 and 4 times nozzle diameter. The numerical results showed that impinging distance has a significant effect on both heat transfer and fluid flow characteristics. In case of low impinging distance (H=1D) swirling effect was dominant and the strong recirculation zones resulted in a higher heat transfer from the heated surface. With the increase of impingement distance, the turbulent kinetic energy reduced significantly near the heated surface. It was evident that for higher impingement distance (H=4D) the effect of swirl was greatly reduced resulting in a lower heat transfer from the heated surface

The use of pelvic radiographs as a predictor for gluteal tendinopathy and bursitis.

To evaluate the relationship between radiographic measurements of the hip and sonographic evidence of gluteal tendinopathy and bursitis in patients with lateral hip pain. Patients with lateral hip pain referred for ultrasound of the hip in our institution over a 5-year period were identified. Findings of gluteal tendinopathy and subgluteal or trochanteric bursitis on ultrasound were recorded. Radiographs of the hip were also evaluated and femoral offset (FO), global offset (GO), abductor lever arm (ALA) and trochanteric impingement distance (TID) were recorded. The mean of each measurement was compared between patients with gluteal tendinopathy and subgluteal or trochanteric bursitis. 273 patients were included in the study. 107 patients (39.2%) had a THA. In the asymptomatic hip, a range of normal measurements were obtained: FO 22.4-76.5 mm, GO 40.1-116.1 mm, ALA 45.0-98.4 mm and TID 13.8-63.1 mm. In the native hip and post THA, there was no statistically significant relationship between FO, GO, ALA and TID in patients with gluteal tendinopathy or trochanteric or subgluteal bursitis. Lateral hip pain is a common presenting complaint in patients with hip pain and is reported in a small proportion of patients post THA. No statistically significant relationship was found between radiographic measurements and ultrasound findings in our patient cohort. However, we describe the range of measurements obtained from the normal asymptomatic hip in this large cohort of patients, which may aid in the evaluation and management of patients with lateral hip pain.

Experimental study of single-row chevron-jet impingement heat transfer on concave surfaces with different curvatures

To address the curvature effect on single-row chevron-nozzle jet impingement heat transfer on concave surface, a series of experiments are conducted in the present investigation. Four concave surfaces including one semi-cylindrical concave surface and three parabolic concave surfaces with different width-to-depth ratios are tested under three typical Reynolds numbers (Re = 5000, 10000 and 15000) and several dimensionless nozzle-to-surface distances ranging from 1 to 8. The results show that the concave curvature has a clear impact on chevron-nozzle jet impingement heat transfer, tightly dependent on jet Reynolds number and impinging distance. In general, the semi-cylindrical concave surface produces the highest longitudinally-averaged Nusselt number at the leading line of concave surface. Under a low jet Reynolds number, the parabolic concave surface with a highly curved curvature produces higher longitudinally-averaged Nusselt number at the leading line and more uniform longitudinally-averaged Nusselt number distribution along the curvilinear direction. However, the longitudinally-averaged Nusselt number at the leading line of concave surface is the lowest for the highly curved surface under a high jet Reynolds number and large impinging distance. In comparison with the round-nozzle, chevron nozzle plays a more significant role on improving jet impingement heat transfer at small impinging distances.

Nozzle exit conditions and the heat transfer in non-swirling and weakly swirling turbulent impinging jets

Investigations have been conducted into turbulent impinging jets but the exact flow dynamics and mechanisms leading to the observed heat transfer distributions at the impingement plane remain outstanding. In particular, use of different swirl generators (vanes, twisted inserts) means the role of varying inflow conditions (at the nozzle exit plane x/D = 0) should be studied to resolve its role on the observed convective heat transfer trends. The present paper studies axisymmetric turbulent weakly swirling (S = 0.31) jets (D = 40 mm) impinging onto a heated plate. Parameters varied include inflow conditions and the effects of impingement distance (H/D = 2, 4, and 6). The Reynolds Averaged Navier Stokes (RANS) equations are used to model the jets using the k-kl-ω turbulence model, which is benchmarked against other models. Three azimuthal ( ) velocity profiles at a Reynolds (Re) number of 24,600 are used at the nozzle exit plane: Uniform (UP), Solid Body Rotation (SBR), and Parabolic Profiles (PP). The start of the wall jet region, designated through elevated levels of turbulent kinetic energy correlates well with the widely observed first peak in Nu distribution. This is however extremely sensitive to the imposition of any swirl, with the application of even weak swirl (S = 0.31) minimally modifying flow dynamics (in the upstream jet region) and leading to recirculation zones stabilized at the impingement plane. This occurs in near-field impingement (H/D) for some inflow conditions (S031-UP), but not others thereby highlighting the significance varied nozzle and swirl generation methods on trends observed in the literature. The imposition of elevated levels of turbulence at the nozzle inflow (x/D = 0) appreciably modifies the heat transfer distribution, particularly in far-field impingement (H/D = 6).

Effects of flame-plane wall impingement on diesel combustion and soot processes

This work aims to assess the effects of flame-wall impingement on the combustion and soot processes of diesel flames. For this work, experimental measurements were performed in a constant-volume combustion chamber (CVCC) at ambient conditions that are representative of compression-ignition engines. The characteristics of impinging and free flames were compared at two identical ambient and injector conditions (20.8 kg/m3 ambient density, 6 MPa ambient pressure, 1000 K bulk temperature, 15 and 10 vol% ambient O2 concentration, and 100 MPa injection pressure). To simulate flame-wall impingement, a flat plane steel wall, normal to the injector axis, was initially placed at 53 mm from nozzle, but was varied from 53 to 35 mm during the experiments. Under the test conditions of this work, it was found that wall impingement resulted in lower soot temperature and soot content, in addition to a loss of momentum for the wall jet. The results also revealed that decreasing impingement distance from the nozzle resulted in reduced soot temperature and soot level for the wall jet. The reduced soot content observed for the wall jet appeared to be mainly driven by enhanced mixing. Flame transparency modeling was also performed to assess the uncertainties of two-color measurements for flame-plane wall impingement. The analysis indicated that the derived soot temperature and concentration values would be affected by the actual temperature profiles, rendering the technique useful to reveal trends, but not reliable for absolute soot concentration measurements.

Effects of injection pressure and impingement distance on flat-wall impinging spray flame and its heat flux under diesel engine-like condition

Heat loss is one of the main causes of energy losses in modern direct injection diesel engines. This heat loss of the engine occurs during combustion, mainly due to the heat transfer between the impinging spray flame and the piston cavity wall. It is of more critical in small size engines. In order to decrease heat transfer, we need to examine the phenomenon of heat transfer through the combustion chamber walls more fully. To achieve this, we investigated the effects of flame impingement on transient heat flux to the wall. By using a constant volume vessel with a fixed impingement wall, the surface heat flux of the wall at the locations of spray flame impingement was measured with three thin film thermocouple heat flux sensors. The combined effect of impingement distance and injection pressure on the heat transfer was investigated parametrically. The results showed that an increase of injection pressure with longer impinging distance led to an increase in the heat transfer coefficient, which had a dominant effect on local heat flux compared with local temperature distribution. Moreover, we confirmed that the relation between Nusselt number and Reynolds number is a useful measure for describing the heat transfer phenomena in diesel combustion.

A comprehensive experimental investigation on the PFI spray impingement: Effect of impingement geometry, cross-flow and wall temperature

In this work, an experimental study on the effects of the impingement geometry, the cross-flow intensity and the wall temperature on the characteristics of an impinging port fuel injection (PFI) spray was conducted. The transient development of the impinging spray was recorded by a high-speed camera with Mie scattering. Based on the high-speed images, the spray tip penetration (S) and the impinged spray height (Hw) were obtained. The results show that with the increase of the impingement distance (Lw), S increases and Hw decreases at the same time after the impingement. As the impingement angle (θw) increases, S decreases while Hw first increases and then decreases. With the increase of the cross-flow velocity (Uc), less part of the spray impinges onto the wall, and S significantly increases. As the wall temperature (Tw) rises, S does not show much variation. However, Hw increases gently for Tw lower than 420 K, and it increases sharply for Tw higher than 420 K due to the Leidenfrost mechanism. The effects of the above factors (Lw, θw, Uc, Tw) on S and Hw were finally evaluated and compared through the introduction of a contribution index.

Impingement of propeller jet on a vertical quay wall

This study experimentally investigates the mean and turbulent flow fields of a propeller jet impinging on a vertical quay wall. Four impingement distances, namely, wall clearances (= longitudinal distance between the propeller and vertical wall), were used to examine their influence on the flow behaviors. In order to investigate the characteristics of the three-dimensional impinging jet, both the streamwise (jet central plane) and transverse (impingement plane) flow fields were measured for each impingement distance using the particle image velocimetry (PIV) technique. Based on the wall clearance, three regions are identified, namely free, impingement and wall jet regions. Additionally, the results show that the evolution of the impinging jet is governed by two mechanisms: jet diffusion and wall obstruction. Their relative importance under varying wall clearances was interpreted in terms of the mean flow patterns and energy dissipation. Moreover, the proper orthogonal decomposition (POD) method is employed to identify the dominant flow structures associated with these two mechanisms in terms of the POD modes and their corresponding dominant frequency, which in turn provides a quantitative means to single out the individual flow mechanism.

Numerical study of a fully confined supersonic slot impinging jet from bleed system

A supersonic slot jet issuing from a bleed system and impinging into a plenum is numerically investigated to deepen our understanding of the flow field and heat transfer of a fully confined impinging jet. The air of the slot jet is forced to exhaust from a plenum in unidirection, resulting in a fully confined configuration. It is of significant practical interest because of its presence in the bleed systems of a scramjet or other related applications. Three primary factors are surveyed, i.e., impingement angle, impingement distance, and back pressure at the plenum exit. The results show that the supersonic slot jet spontaneously generates a plate shock standing on the impingement wall and a strong jet shock on the right side of the jet core. On the left side, the jet shear layer can directly impinge the wall because of the pressure self-adaption effect of a recirculation region. The jet shock and jet shear layer result in two peaks of Stanton number. As the impingement angle increases, the jet shock weakens gradually and moves toward the impingement region of the shear layer until the shock disappears. And thus a single heat peak occurs in place of the previous two peaks. When the downstream flow of the plenum is choked, a wall jet pattern is exhibited because of the formation of a large scale recirculation region. The walls suffer severe aerodynamic heating as the plenum back pressure increases. In particular, the impingement wall endures the maximum thermal load at a certain back pressure at which the jet reduces to the sound speed. The plenum should be controlled to keep the back pressure below this threshold so that the slot walls Stanton number won't increase further. And the plenum should be designed as high as possible to relieve its thermal load.

Instability modes of millimeter-scale supersonic jets

The appearance of instability modes on subsonic and supersonic impinging jets is a phenomenon of great interest that has been observed in jets produced by nozzles of different sizes. The present study describes these instabilities in millimeter-sized supersonic jets produced by convergent and convergent–divergent nozzles ( $$D_\mathrm{throat} = 2 \hbox { mm}$$ ). The smaller nozzle sizes allowed for a comprehensive parametric study involving 378 impingement distance values between $$H{/}D=0.5$$ and $$H{/}D=9.9$$ , as well as 30 nozzle pressure ratio values for both nozzles, totaling a set of more than 22,000 experiments. The detailed resolution on the impingement distance parameter allowed for the observation of acoustic resonant tones that alternate between two or three distinct frequency bands. It was observed that very small changes in the impingement distance ( $$\Delta H{/}D \le 0.5$$ ) are sufficient for resonant mode switching, which is related to the instability mode switching phenomenon. The complementary high-speed schlieren images, captured for a set of 36 cases, allowed for the effective observation and classification of the jet resonant modes via feature tracking. A correlation between the resonant mode shape (helical or axisymmetric) and the resonant tone was clearly observed and quantified. Further experiments with high-resolution schlieren images showed the shape of the acoustic waves produced, connecting the acoustic wave packets with the production of shear layer instabilities. In the helical instability mode, it was possible to observe what appears to be a helix-shaped acoustic wave.

Impingement heat transfer of quadruple synthetic jets

In this work, the heat transfer performance of impinging quadruple synthetic jets is experimentally investigated by means of infrared thermography and the heated thin foil technique. Four configurations (monopole-like, dipole-like, quadrupole-like and 90-degrees-circularly-shifted-jets), obtained by introducing different phase shifts between the single synthetic jets, are comparatively studied at constant values of the Reynolds and Strouhal numbers, equal to 4000 and 0.2, respectively. It is shown that the heat transfer behavior is strictly related to the dynamics of the coherent vortex structures that form after the interaction of the vortex rings inherent to the single jets. The signature of these vortical structures on the heat transfer distributions is evident at short impingement distances, where the most significant differences between the investigated configurations are indeed found. In the comparison, the 90-degrees-circularly-shifted-jets configuration is observed to offer the highest heat transfer rates, although with the lowest degree of uniformity, while the monopole-like jet is characterized by the lowest Nusselt number values and the highest uniformity. As the impingement distance increases, these differences are progressively smeared out and the four configurations exhibit equivalent performance from the viewpoints of both magnitude and uniformity of the heat transfer rate.

Cone angle effects on noise characteristics of jets impinging on conical obstacles

This paper presents an acoustic measurement experiment to investigate noise characteristics of jets impinging on conical obstacles of different cone angles. Besides cone angle, effects of impinging velocity and impinging distance are also studied. Overall sound pressure level (OASPL) and noise spectrum are analyzed. The results suggest that effects of cone angle on noise characteristics of the impinging jet are mainly related to the impinging distance. The main spectrum characteristic for impinging jet cases is of broadband characteristic in the middle and high frequency bands. Further, compared to the free jet case, main acoustic sources of the impinging jet for three cone angle cases are discussed under different impinging distances, combined with flow field analysis and spectrum analysis. Finally, a detailed noise directivity study is carried out. The OASPL of impinging jet for different cone angle cases is presented under various impinging distances and monitoring point positions.

Effect of changing femoral head diameter on bony and prosthetic jumping angles.

In THA, using a larger femoral head can increase the oscillation angle and jumping distance. However, there have been no reports which indicate precisely how increasing the jumping distance leads to an increase in the angle from impingement to dislocation (jumping angle). In this study, we clarified the jumping angle of various head diameters and its relationship with pelvic morphology. Using a three-dimensional templating system, virtual THA and ROM simulations were performed in 82 patients. We investigated the distance between bony and prosthetic impingement points and the head centre and calculated the jumping angle for various head diameters. We measured various pelvic shapes and length to clarify the relationship between pelvic morphology and impingement distance. Jumping angles were 7.7° ± 3.2°, 12.1° ± 1.6°, 15.4° ± 2.5° and 10.0° ± 3.0° with flexion, internal rotation with 90° flexion (IR), extension and external rotation (ER), respectively, when we used a 22-mm head diameter. Bony jumping angle increased about 0.5°, 0.8°, 1.0° and 0.7° per 2-mm increase in head diameter with flexion, IR, extension and ER. On the other hand, prosthetic jumping angle remained almost stable at about 31°. Impingement distance was related to pelvic morphology in all directions. Bony jumping angles differed with ROM; the biggest was seen with extension, followed by IR, ER and flexion. On the other hand, bony jumping angle was less than prosthetic jumping angle in all cases. Bony jumping angles differed with ROM; the biggest was seen with extension, followed by IR, ER and flexion. Prosthetic impingement angles were stable. In addition, the bony jumping angle was less than the prosthetic jumping angle in all cases.

The fluctuating velocity field of a forced planar impinging gas jet

ABSTRACTThe fluctuating velocity field of a planar impinging gas jet is studied using particle image velocimetry, while anti-symmetrically forcing the jet column at the nozzle exit using planar synthetic jets. The jet exit velocity is set to = 11 m/s providing a jet Reynolds number of , and the impingement distance is held constant at eight times the nozzle width W. Under forcing conditions near unstable frequencies, both the stream-wise and cross-stream fluctuating velocity fields of the jet have very different characteristics than that of the unforced jet. The fluctuating velocity fields reported here were also found to have qualitatively similar features to that of a high-speed self-excited impinging jet. For the highly periodic flow conditions tested, a triple decomposition, and a low order reconstruction of the fluctuating velocity field using proper orthogonal decomposition is employed. These methods allow for the extraction of the coherent velocity and turbulence fields from the forced planar impinging gas jet.

Performance analysis of multiple microjet impingement cooler

A kind of multiple microjet impingement cooler with return channels was designed. Thermal performances of the cooler have been studied by experimental and numerical methods. Under steady-state conditions the distribution of temperature, velocity and pressure were obtained at different running parameters and structure parameters of the cooler, respectively. The results show that impingement distance has a great effect on the thermal performance of the cooler. Average Nusselt number increases with the impingement distance increasing. Average temperature of the target surface decreases with the impingement distance decreasing and have a more uniformed temperature distribution on the target surface. Temperature of target surface decreases with decreasing of air volume flow rate. Pressure drop increases with Reynolds number increasing, and it will rapid increases when Reynolds number is higher than 5000. Average heat transfer performance is inversely proportional to air volume flow rate, it will be improved when air volume flow rate increases.

Experimental study on flat-wall impinging spray flame and its heat flux on wall under diesel engine–like condition: First report—effect of impingement distance

Reducing heat loss is one of the most important development concerns for improving the thermal efficiency of the diesel engine. In order to know heat transfer through the combustion chamber wall mo...

Numerical and experimental study of spray impingement and liquid film separation during the spray/wall interaction at expanding corners

The liquid film separation at expanding corners during the spray/wall interaction is usually encountered in internal combustion engines, which has significant influence on the fuel/air mixing and combustion processes, and consequently the engine-out emissions. However, fundamental investigations on the film separation during the spray/wall interaction at expanding corners are very limited, especially under the relevant operating conditions of engines. In the present study, a new film separation and atomization model was proposed, including the sub-models of film separation criterion, film separation mass ratio, and the film atomization model derived from the Rayleigh-Taylor instability theory. By implementing the proposed model into a computational fluid dynamics (CFD) code, the reliability of the new model was validated by the experimental measurements conducted in this study. The results indicate that the effects of the injection pressure, impingement distance, and corner angle of the expanding corner on the evolution of the impinging spray and the wall film dynamics after the corners are satisfactorily reproduced by the present model. Moreover, the predicted size distribution of the detached droplets formed by the film separation is in good agreement with the measurement. It is also found that the expanding corner angle remarkably affects the impinging spray structure and the film separation characteristics, and the predictions of the new film separation model agrees better with the measurements than the previous model.

Effect of spray impingement distance on piston top fuel adhesion in direct injection gasoline engines

Direct injection is an attractive technology for improving fuel economy and engine performance in gasoline engines. However, the adhered fuel formed on the piston surface has significant influence on the combustion efficiency and emissions. To obtain a better understanding of fuel adhesion, this work involved investigation of the spray and impingement on a flat wall through a mini-sac injector with a single hole. Different impingement distances and injection pressures were investigated. The evolution of the impinging spray was obtained by the Mie scattering method. The refractive index matching method was applied to measure fuel adhesion. The mass, area, and thickness of adhesion under different conditions were compared. The experimental results show that the fuel adhesion on the wall increases significantly with a large impingement distance. Moreover, the maximum thickness increases and the thickness uniformity of the fuel adhesion declines under a large impingement distance condition.