ME 311 Mechanical Measurements Page 1 of 6 Wind Tunnel Laboratory. Name: Group: Campus Mail:

Transcription

1 ME Mechnicl Mesrements Pge o 6 Wind Tnnel Lbortory Nme: Grop: Cmps Mil: NOTE: I my be 0-5 mintes lte becse I will be working with the vibrtion nd reqency lb grop to get them strted. Plese go over this lb hndot while yo re witing. Overview Objectives: Find the velocity in wind tnnel by mesring the dierence between the totl pressre nd sttic pressre o the ; Estimte the ncertinty in this velocity mesrement or the entire rnge o velocities ond; Identiy the cses o ncertinty nd wys to redce them. Instrmenttion: Pitot-sttic tbe Dierentil pressre gges (ll-scle rnges o nd in H O) Brometer Thermocople Schemtic o Pitot-sttic tbe: low direction to mnometer to mnometer

2 ME Mechnicl Mesrements Pge o 6 Wind Tnnel Lbortory Smple Clcltion: Recll the Bernolli s eqtion yo lerned in ES 0, p totl p sttic V ind the velocity o the moving (in t/sec) i the totl pressre is 60 inches H O nd the sttic pressre is 59 inches H O, nd the density o is slg/t. Ction with nit conversion: Yo will need to mke etensive se o nit conversions nd mke sre the nits o every term in this eqtion re consistent with one nother. Feel ree to se the inormtion on the net pge.

3 ME Mechnicl Mesrements Pge o 6 Wind Tnnel Lbortory Conversion o pressre rom inches o wter or inches o mercry to lb/t Hydrosttic eqtion: reltes the height o lid colmn to pressre dierence p lid g h lb t slg t t s Units conversion: ( t) wter slg.94 t nd Hg wter sg Hg.6 Compting density rom pressre nd tempertre nder tmospheric conditions Idel gs eqtion: reltes pressre, tempertre, nd density o n idel gs (when is the idel gs model pproprite?) R 8. 4 kj kmol K M kg kmol R R kj t lb 0.87 or 76 M kg K o slg R pv nr T R ( nm ) T m R T p R T M lb slg t lb o Units conversion: ( R) Compting Velocity t t slg o R p V t recll lb slg s Unit conversion: lb t t s slg t slg t s t slg t

4 ME Mechnicl Mesrements Pge 4 o 6 Wind Tnnel Lbortory Dt Sheet P tm in Hg T o F Reding Uncertinty o gge in H O Reding Uncertinty o gge in H O Trget Fn Speed (RPM) Actl Fn Speed (RPM) P (in H O) [sing gge nless noted] ( gge) 00 Above XXXXXXXXX XXXXXXXXX ( gge) Below XXXXXXXXX XXXXXXXXX ( gge) 00 Above XXXXXXXXX XXXXXXXXX ( gge)

5 ME Mechnicl Mesrements Pge 5 o 6 Wind Tnnel Lbortory Dt Redction Averge mesrements or the ctl n speed nd corresponding pressre dierences or ech nominl n speed sing only the dt rom the " gge. Do the sme or the " gge t 000 RPM. Compte the velocities or these verge pressre dierences. Uncertinty Anlysis Compte the ncertinty in pressre dierence by root-sm-sqring the two sorces o ncertinty in pressre: instrment ccrcy nd redbility. The instrment ccrcy is qoted s 0.5% o the ll-scle reding. The redbility is p to yor decision, typiclly / or /4 o scle division on n nlog gge. Note tht the ncertinty will be dierent or the two gges (why?) Compte the corresponding ncertinty in velocity (U v ) or this ncertinty in pressre dierence. This will involve tking prtil derivtive to get the sensitivity coeicient (the ctor tht determines how mch the velocity chnges de to chnge in pressre.) Plot V, VU v, nd V-U v ginst RPM on the sme grph or the dt rom the " gge only. Use mrkers nd solid line or the V verss RPM dt, bt only dshed line (i.e., no mrkers) or the ncertinty lines. Trn In This lb hndot with qestions nswered below nd dt sheet illed ot. Ech person mst trn in his/her own lb, bt I epect yo to work together. Plot o V verss RPM with ncertinty bnds Spredsheet with rw dt nd clcltions Smple clcltion o ncertinties Qestions To Answer. Compre the velocities nd ncertinties ond with the " gge nd the " gge t 000 RPM. Do their ncertinty intervls overlp? Wht does this imply?. Wht does the instrment ccrcy (0.5% o ll scle) imply bot the selection o gge or pressre mesrement?. Wht hppens to the ncertinty in velocity s velocity increses? Why?

6 ME Mechnicl Mesrements Pge 6 o 6 Wind Tnnel Lbortory Notes on the Uncertinty Anlysis When yo hve clclted qntity (,,..., n ) where clclted reslt bsed pon nmber o independent prmeters. i mesred vles o the independent prmeters (i.e. the nominl vles o the prmeters) i ncertinty in i net ncertinty in the clclted reslt de to the combined eects o i To determine how the vritions in i inlence the ncertinty o, we se n n L I the clcltion is prodct o terms, the clcltion cn be simpliied considerbly. For emple: then the percent ncertinty in is where i the eponent o i in the eqtion i i i vrible % ncertinty o