nighthawk2174 Posted July 9 Posted July 9 (edited) 49 minutes ago, MA_VMF said: 3D Gotcha did you run the CFD you posted, if so you have the numeric results? Also tbh i'm suspicous of those numbers as that is rather quite high and doesn't line up with the graphs you posted or the wind tunnel results I posted. Edited July 9 by nighthawk2174
MA_VMF Posted July 9 Posted July 9 2 часа назад, nighthawk2174 сказал: Gotcha did you run the CFD you posted, if so you have the numeric results? Also tbh i'm suspicous of those numbers as that is rather quite high and doesn't line up with the graphs you posted or the wind tunnel results I posted. L- near 2kN D-near 420-430N Only half of the steering wheel was used
nighthawk2174 Posted July 9 Posted July 9 52 minutes ago, MA_VMF said: L- near 2kN D-near 420-430N Only half of the steering wheel was used This data your presenting is not lining up, not even with data you posted earlier. Do you have a screenshot of the numerical readouts or is this just what was told to you? You said that this data was for M2.5 5deg aoa I can't imagine that the fins halfway deflection point is only 5deg. Looking at the shocks if this is at M2.5 the angle the shocks are at would indicate a deflection of closer to 20deg not 5deg. null We also have the CD and CY values you posted earlier for the M2.5 case: null L/D at 5deg is 2.2 and at 20deg is 2. From the original study I posted at 5deg its Cy=0.25 and Cx=0.12 for a L/D of ~2.1. I don't have ref area used in the numbers you posted but assuming that the 2Kn of lift is right - sea level + STP - then drag using the coeficents provided would be 906N of drag not 420|430N.
MA_VMF Posted July 9 Posted July 9 1 час назад, nighthawk2174 сказал: This data your presenting is not lining up, not even with data you posted earlier. Do you have a screenshot of the numerical readouts or is this just what was told to you? You said that this data was for M2.5 5deg aoa I can't imagine that the fins halfway deflection point is only 5deg. Looking at the shocks if this is at M2.5 the angle the shocks are at would indicate a deflection of closer to 20deg not 5deg. I don't care what you've made up for yourself here. Once again, the conditions 2.5M and 5 AoA were set in the program. The fact that something doesn't match is your problem.
nighthawk2174 Posted July 9 Posted July 9 10 minutes ago, MA_VMF said: I don't care what you've made up for yourself here. Once again, the conditions 2.5M and 5 AoA were set in the program. The fact that something doesn't match is your problem. I haven’t made anything up; it is up to you to disprove what I’ve presented. You’ve provided no definitive proof to back the numeric results you listed. Said results don’t align with a substantial amount of wind tunnel and CFD data from NATO, US Army, and academic sources, including your own Russian sources that you posted earlier. I’ve studied lattices at a high level in university and have conducted my own CFD research on them. The numeric results you presented earlier simply don’t align with well-known data points from multiple reputable sources. The static pressure profile you posted matches nearly the pressure profile from the below report which is at M2.5 and 20deg of aoa. The expansion fan on the leward side of the lattice and the shock on the windward side match the above. Indicating to me the CFD results you posted are almost ceratinly from a higher angle of attack then claimed. CFD_analysis_of_grid_fins_for_maneuverin.pdf 1
MA_VMF Posted July 10 Posted July 10 (edited) 8 часов назад, nighthawk2174 сказал: я не сделал что-либо вверх; это является вверх к ты к опровергнуть что я представлено. Вы предоставил нет окончательный доказательство к Назад числовое результаты ты в списке. сказал результаты не выровнять с А существенный количество из ветер туннель и CFD данные От НАТО, нас Армия, и академический Источники, включая твой собственный Русский Источники что ты Опубликовано ранее. я изучал решетки в А Высокий уровень в университет и иметь проведенный мой собственный CFD Исследовать на их. числовое результаты ты представлено ранее Просто не выровнять с хорошо известный данные точки От несколько уважаемый Источники. Профиль статического давления, который вы разместили, совпадает почти с профилем давления из приведенного ниже отчета, который составляет M2.5 и 20Deg AOA. Вентилятор расширения на стороне Leward решетки и шок на стороне наветренной стороны соответствует вышеуказанному. Указывая мне, что результаты CFD, которые вы опубликовали, практически церально из более высокого угла атаки, а затем заявлены. Cfd_analysis_of_grid_fins_for_maneuverin.pdf Do you even understand what grids exist? Different t_bar, H_bar , n grid in my calculations t_bar=1, H_bar=0.5 nulldespite the fact that there is already a mutual influence of plans in your drawing, although according to the schedule. At a speed of 2.5M, this should not be the case. Edited July 10 by MA_VMF
nighthawk2174 Posted July 10 Posted July 10 9 hours ago, MA_VMF said: Do you even understand what grids exist? Different t_bar, H_bar , n grid in my calculations t_bar=1, H_bar=0.5 nulldespite the fact that there is already a mutual influence of plans in your drawing, although according to the schedule. At a speed of 2.5M, this should not be the case. Yes I do the tradeoffs are that by increasing tbar you decrease drag but also decrease lift and dynamic stability. Essentially larger boxes makes it have lower L/D with worse stability, but the sooner you stop getting shock reflections interfering with each other. The chart you posted will be the point where the shock angle is such that you stop getting shock reflections for various tbar's and aoas. The shocks will still interact inside the lattice at least until a much higher mach usally M4+. The pressure coeficent drawings fin outline is making it difficult to tell but the shocks in that example are not interacting with the other plate of the lattice just with the other sock/expansion fan which is to be expected for that mach and angle. null Also from your images tbar appears to be closer to 1.4, scaled such that chord = 1". Doc I linked with the pressure coeficent iso's is ~1.48 inner to inner surface.
MA_VMF Posted July 10 Posted July 10 3 минуты назад, nighthawk2174 сказал: The chart you posted will be the point where the shock angle is such that you stop getting shock reflections for various tbar's and aoas. The shocks will still interact inside the lattice at least until a much higher mach usally M4+. This is a diagram showing the relative pitch of the grating and the angle of attack. The plans will not interact with each other 5 минут назад, nighthawk2174 сказал: Also from your images tbar appears to be closer to 1.4, scaled such that chord = 1". Doc I linked with the pressure coeficent iso's is ~1.48 inner to inner surface. nullThis is the plane of symmetry
nighthawk2174 Posted July 10 Posted July 10 (edited) 12 minutes ago, MA_VMF said: This is a diagram showing the relative pitch of the grating and the angle of attack. The plans will not interact with each other Probably being lost in translation what i'm saying is that the chart you posted lines up with what i'd expect to be the points where you get direct interaction, shock reflections directly off the opposite fin. However this does not preclude the main shocks hitting and reflection off each other (which will still chock flow) while still within a chord length of the tip of the lattice. Shocks off the lattice will nearly follow the oblique shock tables for thin plates. The angle at which the shocks will only interact with each other (as in shock off shock reflection) more then a chord length from the lattice tip can be calculated. This is why flow is still chocked even up to M2.5 not as bad as with all the shock reflections at a lower mach such as M1.5 but it is why the L/D still remains poor except at very high machs 4.0+. 12 minutes ago, MA_VMF said: nullThis is the plane of symmetry Ok Edited July 10 by nighthawk2174
nighthawk2174 Posted July 10 Posted July 10 30 minutes ago, MA_VMF said: nullMach 2 AoA=5 Drag=345.34N Lift=1822.59N Is this plot for those condtions you listed?
MA_VMF Posted July 10 Posted July 10 2 минуты назад, nighthawk2174 сказал: Is this plot for those condtions you listed? I didn't understand the question
nighthawk2174 Posted July 10 Posted July 10 9 minutes ago, MA_VMF said: I didn't understand the question The plot has mach number listed with associated plot colors. M2.0 would be a light green to green'ish teal color. While upstream appears to be a light-medium blue instead. If upstream is M2.0 based on the expansion fans angular width i'd expect a much higher post fan mach. M2.5 - M 2.8 depending on how you measure out the fan angular width. But it itself appears to also be awfully close to M2?
MA_VMF Posted July 11 Posted July 11 (edited) Применена другая под программа и другой метод условия М=2.5 АоА=5.Отсутствует сгущение сетки на ударных волнах nullnull Edited July 11 by MA_VMF
nighthawk2174 Posted July 11 Posted July 11 2 hours ago, MA_VMF said: Применена другая под программа и другой метод условия М=2.5 АоА=5.Отсутствует сгущение сетки на ударных волнах nullnull L/D of ~2.4 which is reasonable and the shock angles are reasonable close for M2.5 at 5deg. The original paper I posted was at ~2.15 L/D and Russian document was ~2.2. Also are these body axis force coefficients or wind referenced?
MA_VMF Posted July 11 Posted July 11 (edited) 2 часа назад, nighthawk2174 сказал: Also are these body axis force coefficients or wind referenced? Body 2 часа назад, nighthawk2174 сказал: L/D of ~2.4 which is reasonable and the shock angles are reasonable close for M2.5 at 5deg. The original paper I posted was at ~2.15 L/D and Russian document was ~2.2. There was no reduction of the mesh on shock waves, which gives worse results Edited July 11 by MA_VMF
tavarish palkovnik Posted July 11 Posted July 11 c=относительная толщина профиля крыла=отношение наибольшей толщины крыла к хорде When fins are in classic form I understand and know how to calculate base pressure drag...but how to calculate it when having grid fins !? What should be used for thickness, thickness of just one layer in grid ?
okopanja Posted July 11 Posted July 11 (edited) 1 hour ago, tavarish palkovnik said: c=относительная толщина профиля крыла=отношение наибольшей толщины крыла к хорде When fins are in classic form I understand and know how to calculate base pressure drag...but how to calculate it when having grid fins !? What should be used for thickness, thickness of just one layer in grid ? I think you can not always calculate the drag as separate components giving a sum. Maybe for some simpler shapes this would work. The USA study used complete body, but different configuration than R-77. Edited July 11 by okopanja
nighthawk2174 Posted July 11 Posted July 11 2 hours ago, tavarish palkovnik said: C=Relative Wing Profile Thickness=Ratio of Greatest Wing Thickness to Chord When fins are in classic form I understand and know how to calculate base pressure drag... but how to calculate it when having grid fins !? What should be used for thickness, thickness of just one layer in grid ? I don't think there is a simple method by wich you could calculate it except at very low machs. Shock interactions basically make it so that you need CFD or wind tunnels to do this. You could probably estimate with a drag build up method but it'd have large error margins on it.
tavarish palkovnik Posted July 11 Posted July 11 (edited) I kind of disagree, manual calculations of individual components of total drag and making sum of them can be quite precise. Of course wind tunnels or live firing of telemetric missiles give real and true values, but if you read old documents (when manual work was only method available) differences are not so big, actually in most cases calculations could be accepted as quite accurate. CFD is nice piece of technology, but CFD is nothing more than program where all theoretical principles are combined in one helpful tool. Nose pressure, base pressure, wings pressure, body friction and wings friction and there it is. Some of components like base pressure are with including interface of other elements, wings and boattail configuration and shape, and all that is part of calculations. Actually I think that main reason why missile with grid fins has something higher drag compared to missile with classical fins is not so much because of pressure on fins but because of higher base pressure Edited July 11 by tavarish palkovnik
Recommended Posts